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HomeMy WebLinkAboutElectric Power Supply And Distribution 1984CcCNaQ Grid *TM 5-811-1/AFM 88-9, Chapter | This manual contains copyright material. TECHNICAL MANUAL DEPARTMENTS OF THE ARMY No. 5-811-1 AND THE AIR FORCE AIR FORCE MANUAL NO. 88-9, CHAPTER 1 WASHINGTON, DC, 12 September 1984 ELECTRIC POWER SUPPLY AND DISTRIBUTION The proponent agency of this publication is the Office of the Chief of Engineers, United States Army. Users are invited to send comments and suggested improvements on DA Form 2028 (Recommended Changes to Publications and Blank Forms) or 2028-2 located in the back of this manual direct to: HQDA (DAEN-ECE-E), WASHINGTON, DC, 20314. A reply will be furnished direct to you. Paragraph Page CHAPTER 1. GENERAL OPI oc Sore he Ss hg icu tore s 5 wien & aie earn FEN 858 5 LOE eas FOG E46 8h EOBAE ER EE a et pe 1-1 yi Economic considerations . 1-2 1-1 Standards and codes .... 1-3 1-1 Design procedures........ 1-4 1-1 DORIA PAO EATIAIENOING 050, ecinyinrer ss» aie) vielen epee une aisid Siale & wie'ecld # Gye) s Sig) empl atee SMa TRON Stee 1-5 1-2 2. ELECTRIC POWER REQUIREMENTS Gemnee beita hse cys mierd gis nas sade as co ed Caleb Es EME ST OMIOT AE Ea gus opigidens «batt 5 Ae 2-1 2-1 Terminology ... 2-2 2-1 Load estimates. . . na 2-3 2-1 RSME MIMUMAOOR 55:5 5i., 55:01 0. «ora snicididined Haie'd woh d bse fis SOLAR Lured a clas vince ace <eiae ee anny era 2-4 2-4 3. SELECTION OF THE ELECTRIC ENERGY SOURCE AND THE PRIMARY DISTRIBUTION VOLTAGE MRL ora SS Vib aw Vid ora ip ey tia Glas od un: 09s ead ee Fore Ps ae bs 2 as is Se ee 3-1 3-1 Types of electric energy systems ...... 3-2 3-1 Station or plant equipment terminology 3-3 3-1 Selection of electric energy source—new installations... . 3-4 3-1 Selection of electric energy sources—existing installations F, 3-5 3-1 MEUM 2 yousace coun. ford v0 LEE Fars 9 Seed FR LFS TE 4G CG ME TORO ChE LOM EER IG AIG aed 3-6 3-2 Selection of primary distribution voltage—new installations ............ 00. c cece cece e cece ee eeeee 3-7 3-3 Selection of primary distribution voltage—existing installations .........0...00 0. cece eee eee eee eee 3-8 3-3 4. MAIN ELECTRIC SUPPLY STATION I CS dare a Birt a Knit Wi « Fall" Sioee:ejeini o wei dye lmre wend sienelgne began tips svi Aamiciee eine EIN (0s che ty SE vain olility sing pibkeipindia accwnvolky civmy ave summdeph sed Gn ais usenet uae Station designation and elements . Main electric supply station...... oy IML 6S Sicllvcs shia arate, ge pve his 0 9.9: 9 SWW-9 8 dade oleh d o-sinejarel Clete OES Line switching and protective apparatus . . Substation equipment .............. oy INTE EMU SAPOIIETS CPTECT Nias ois aes icles wis a arere od sierae aici o sis Siew sclea bik pre meee Ne 5. ELECTRICAL DISTRIBUTION LINES 1 1 ALLA LQ LP we ' Ohawnnyee hee ee BABAR ONH Beers Fe ss 4 5s 5-1 5-1 Types of underground lines . . 5-2 5-1 Types of aerial lines 5-3 5-2 Voltage drop ........ 5-4 5-2 Power factor correction 5-5 5-2 Perey CMONNEEN Gaicck cl Flais yh cis oer vise, + 4s A ERG 0015 Hee MASE Sais SEV TOMS EC cate Fees ek EE ee atwa 5-6 5-3 6. AERIAL DISTRIBUTION LINES (Cle RRs sare sub ts fc si sisted lhe Giapk S t50 Ss doe, one poe bene tacue Raat We > ade oan ae pee Sara 6-1 6-1 Ep PRPRRES CURMMUCEINANNDS 65000: 5co:n, 5,0, + jpi.e dioiaione: oleie Hip saloresive, gilin esha in ore qetah ad pualasiet awe o eam oh 6-2 6-1 Conductors 6-3 6-1 UE ere ee 6-4 6-3 Circuit configurations 6-5 6-5 OO ri tes Ga 995 8.016 Gia CRRA ina das ABLE SINT LS Vaaslh Se See RR OR ee a ee en ea 6-6 6-9 CO 6-7 6-12 Miscellaneous items 6-8 6-13 7. UNDERGROUND DISTRIBUTION LINES Br SSP ORLA cts Best eiered Gxt Tate Sere aiguvec sis) bua eoae «BR OB e Me Pegs fae ele ae ee eS OE 7-1 7-1 Co errr reer rT eer ree i VOR TPA TE NESEY eee Uae ae aaa cee 7-2 7-1 *This manual supersedes TM 5-811-1/AFM 88-9, Chapter 1, 27 July 1965. TM 5-811-1/AFM 88-9 Chapter 1 Paragraph Page MURR las see igs Fe aio alls Gastar stra 0) e wengge tan gmiere Saat esi tee cee viene pees es et 7-3 7-6 Manholes, handholes, and pullboxes i 7-4 7-11 Divectaniwan Canaan NA COMB oo bin ass 91s 5 arid vin 6 wiersrg ied erie Chinn 49.4 3 Wels any amie ade gine ¢ qeerclamtas © 7-5 7-14 Cuapter 8. TRANSFORMER INSTALLATIONS Definitions ~ - Installation of distribution-to-utilization voltage transformers... ........... 00.0 cece eee eee Provision of transmission-to-distribution voltage transformers ; : a Insulation for transformers having windings rated 1,000 voltsor more ..............00e cece e eee eees vanetormoencharacperisiaes <2 a0 <2). 52i,": ape bay sain é suis Saweneg is dine Das Seales Sein cies e's us = — 9. SURGE PROTECTION AND GROUNDING Voliapoeuiesman NORMAL RACINE 2... caunnass 19cgoinasg ti has cate nese ts A aag eew sd a8 9-1 9-1 Methods of controlling voltage surges and potential gradients 9-2 9-1 Ground electrodes : ‘ ee 9-3 9-5 Grounding deteiie arid requirements: 6 2c ois. sic's inc bos cates ole bale cde ima cew tect Snes ees menage s 9-4 9-5 10. ROADWAY AND AREA LIGHTING PRIN cs ioen itor: aGsa Pee te casa Fp Rss Sed nds ow Lows ORES RAM Ca Aw serie ioR Thee ERM eG EERO S aie 10-1 10-1 Roadway lighting design 10-2 10-1 Area lighting design ... 10-3 10-4 Walkway and bikeway lighting design 10-4 10-5 Light Sources ss ass ate a0 5 oe v0) 10-5 10-5 Lighting control and wiring system....... 10-6 10-6 11. PROTECTIVE LIGHTING MINE ee AG anes gase 4 ida hg) yt Bish yb 4:84 sd a ow boots Scape RNR e| Moe SRD OLEAN Sua See ee alate 11-1 11-1 Authorization . : 11-2 11-1 Use of protective lighting systems 11-3 11-1 Types of areas to be lighted... . . . 3 a 11-4 11-1 Mapa PUNE AR Re TNR 6 sod snes spe anus Gwe <4 B19 Sidbal ie’. discs vm Waceed a ou gig p dale 4a CoS PROREMES 11-5 11-2 Despre gc Si aay div old Uiassly hss Aa VSL crs erste gotiiggile © ole les tie Mia deeje Shoei ota win 11-6 11-3 Electric power sources . : , : we 11-7 11-3 pre eee en et Orr On oe er ene ne er Pe eer ors Or a 11-8 11-5 PATERNITY i555 sie « ais!’ obs «dus «ota 0g seas Sone LOA Lae Copeate nals w epee Sime eee 11-9 11-6 12. DESIGN ANALYSIS General requirements 12-1 12-1 Rh na a 5 iets = aE aoe he's Sts e stetiamvig sg wets 394s es OEY canada wie eae gO RG eee Oo 12-2 12-1 Basis for design . . ‘ : . 3 at 12-3 12-1 Dae CLGELIIND yo io ocho hin Tain 6 ans: ¢ wins SaaS TGA GSE The ICR AN Saal tein rs his guide ee Somme 12-4 12-2 13. UNINTERRUPTIBLE POWER SUPPLY SYSTEMS Co AOC ere te Cpr eee Sree conc coer Tee ee eer Mart dkd Rice isla. 5 Gil LA hha 5 Bak SE ONS SOLAS BISA ans Cates asad Rtas wo rage ied ee ee Definitions Installation . ‘ ‘ . a BUpponting Sy scene ic g tin sae Saas rs sed sind wae a wR Blew ode esis ee oe ied Sl ows Ow Oke TUPI IO BY OCONIS os i. 5 sic. ois 3 sia, s Ges ates bas PEO RMA TLS DOCH owe Hye bela vi eSis vale US ER APPENDIX A SIZING OF DISTRIBUTION TYPE TRANSFORMERS FOR FAMILY HOUSING UNITS . IED Ra MRED Ss apy ant secs eronsen.s ies oes» GSegg N Bedal EI hofene ops lone) = toned Ae eam C BIBLIOGRAPHY LIST OF FIGURES Illustration of diversity factor application 2-2 Monthly electric cost computation 100,000 square-foot office building calculated demand Converting utility company short circuit MVA to current Example of sizing substation transformer capacity Single line of a primary unit substation with two transformers Circuit breaker interrupting rating approximation Main electric supply substation, 46 kV minimum Main electric supply switching station, 35 kV maximum Normal allocation of voltage drop Average energy savings example Primary distribution arrangements commonly used Symbols for aerial electric distribution Tangent construction configurations Armless primary configurations Crossarm primary configurations Figure PRRPBAAAE A Spe Hw DAMN HALORPKEPAIAIAA RE Ne 7 i 7 7 PRPAPAATA AAA Sw DD hRONHFWNHFATNARWNHWNE ii TM 5-811-1/AFM 88-9 Chapter 1 Figure 6-5 Neutral-supported secondary cable configurations 6-10 6-6 Ranges of insulator dimensions 6-11 6-7 Expanding anchor details 6-14 6-8 Types of guy installations 6-15 6-9 Guy details 6-10 In-line guy strength requirements 7-1 Symbols for underground electric distribution Conventional taped or resin system cable joints Medium-voltage taped termination Medium-voltage preformed slip-on termination and stress cone Fireproofing of insulated cables Concrete encased duct details Duct line drainage Factors influencing manhole design Ascale example of a cable installed in manhole Typical double manhole Manhole appurtenances Electric or communication handhole Pullbox installation Underground system marker Cluster-mounted transformer bank installation Crossarm-mounted transformer bank installation Load center transformer installation Pad-mounted compartmental transformer installation Zones of protection for masts and shield wires Grounding of a main electric supply station Grounding of a load center transformer station Provision of surge arresters at a medium-voltage riser pole pee Ia 1 rFoeonmnrane PPV? Beene BIAIBRARWNES i 1 I ARNARWONHOOBIAT AONE RPE Eee 1 1 1 WN ATARHONH ONE AWNHPARWNHPRWNHERONHPOOBDIAMAWOND rr SSSSLOGCOPMMHANAVAAIAIAIAIAIAIAGD 8. 8 8 8 9. 9. 9, 9 10- Typical roadway lighting installation 10-: 10- Lateral lighting distributions 10- 10-' Intersection lighting placement 10- 10- Key to standard HID lamp designations 10- 11- Boundary lighting beam directions 11- 11-! Application of required lighting intensities 11- 11- HPS outage time for normal to emergency source transfer 11- 12- An example of a voltage drop calculation 12-3 12- Examples of short circuit calculations 12-4 12- An example of protective device coordination 12-5 12-. An example of an aerial conductor strength analysis 12-7 12- An example of a pole strength analysis 12-8 13- Single-line diagram of a nonredundant configuration 13-2 13-: Single-line diagram of a redundant configuration 13-3 13- Simplified diagram of a rotary UPS unit 13-4 LIST OF TABLES Page Table 2-1 Demand Factors 2-1 2-2 Diversity Factors 2-2 2-3 Typical Maximum Demands and Usages 2-3 2-4 Typical Unit Connected Loads for Lighting 2-3 3-1 System Use and Voltage Range Relationship to Equipment Rating 3-2 3-2 Nominal Voltage Classes and System Voltages 3-3 4-1 Minimum Relaying for Transformers 4-8 4-2 Minimum Metering for Metal-Clad Switchgear 4-9 4-3 Minimum Relaying for Metal-Clad Switchgear 4-9 5-1 Three-Phase Primary Circuit Loading Check Values 5-5 5-2 Primary Distribution System Statistical Reliability Constants 5-5 6-1 Conductor Materials—Physical Properties 6-3 6-2 Initial Stringing Sags for 200-Foot Spans 6-4 6-3 Final Loaded Tensions and Sags for 200-Foot Spans 6-5 6-4 Minimum Primary Wood Pole Lengths and Classes 6-5 6-5 Relation of Crossarm Configuration to Conductor Size 6-9 6-6 Anchors Suitable for Various Soils 6-13 7-1 Insulation Conductor Temperatures 7-3 7-2 Quick Check of Allowable Ampacities of Medium-Voltage Cables 7-3 7-3 Low-Voltage Cables Suitable for Below Grade Installation 1-4 TM 5-811-1/AFM 88-9 Chapter 1 Table Standard kVA Capacities Daily Allowable Peak Loads for Normal Life Expectancy Loading on the Basis of Ambient Temperatures Basic Impulse Insulation Levels Standard Load Center Percent Impedances Aerial-Mounted Oil-Immersed Transformer Surge Protective Margins Resistance of One 5/8-Inch by 8-Foot Ground Rod in Various Soils Illumination Versus Spacing Sports Lighting Characteristics of Light Sources Protective Lighting Requirements Floodlight Beam Descriptions Floodlight Class Descriptions Demand Factors PeeEeeH Prem ODSOOD DH HM T PONE WONHENE AR WN iv > oR « 1 1 BPeeEHEeEH PeREERSOSDOHOOMMDMDMMH i FPAMwSARHEANOBIAD TM 5-811-1/AFM 88-9 Chapter 1 CHAPTER 1 GENERAL 1-1. Scope. This manual is a general guide for the design of elec- tric power supply and distribution systems for Depart- ment of the Army and the United States Air Force in- stallations, consisting of bases, camps, forts, sites, sta- tions, etc. Criteria should achieve economical, durable, efficient, and dependable electric supply and distribu- tion systems to support Army and Air Force installa- tions. Where special conditions and problems are not specifically covered in this manual, acceptable indus- try standards will be followed. Modifications or addi- tions to existing systems solely for the purpose of meeting criteria in this manual are not authorized. The guidance and criteria herein are not intended to be retroactively mandatory. Clarification of the basic guidelines and standards for a particular application, and supplementary standards which may be required for special applications, may be obtained through normal Army or Air Force channels, from HQDA (DAEN-ECE) WASH, DC 20314 or, HQ USAF (LEEEU), WASH, DC 20330. 1-2. Economic considerations. The selection of one particular type of design for a given application, when two or more types of design are known to be feasible, will be based on the results of an economic study in accordance with the require- ments of DOD 4270.1-M. Standards for economic - studies are contained in AR 11-28 and AFR 178-1, re- spectively. Subject to guidance resulting from imple- mentation of Executive Order 12003 and related guid- ance from the Department of Defense (DOD), the cited economic analysis techniques are to remain valid. The basic underlying principles and the most commonly used techniques of economic analyses are described in some detail in standard textbooks on engineering economy such as “Principles of Engineering Economy” by Grant, Ireson, and Leavenworth; guides published by professional organizations such as the American In- stitute of Architects’ “Life Cycle Cost Analysis—A Guide for Architects;” and handbooks prepared by gov- ernment agencies such as NAVFAC P-442. (See ap- pendix B for references) 1-3. Standards and codes. Applicable electrical industry codes, standards, or pub- lications referenced will apply to equipment, mate- rials, and construction covered by this manual. The minimum requirements of the National Electrical Code, NFPA 70 (NEC) and the National Electrical Safety Code, ANSI C2 (NESC) must be met, and ex- ceeded when more stringent requirements are speci- fied. 1-4. Design procedures. Design procedures for the planning of new electrical utility features or systems should be performed con- currently with the planning of new installations or new projects at existing installations, as applicable. Determinations should be made as soon as practical following award of the design contract as the deter- minations relate to the selection and consequent de- sign of applicable electric power supply and distribu- tion systems, sub-systems, or features required by the contract provisions. Factors related to the availability, capacity, maintainability, reliability, and stability of existing and new electric power supply and distribu- tion systems should be determined prior to proposing new electrical designs for electrical utilities required to serve new or modified facilities. a. New installations. Assistance from local electric utility companies and cooperatives may be sought dur- ing preliminary design, but no commitment should be made to obligate the Government to procure electrical power or engage in contract negotiations. DOD pro- curement procedures requires that competition be sought wherever it exists. Contact with the local sup- plier should be limited to obtaining information on sources of electricity, their connection point location in regard to the site, conditions of service, and general rate information. The contemplated design of electric supply and distribution systems should utilize equip- ment arrangements which conform to prevailing prac- tices of the utility service area insofar as they do not conflict with criteria in this manual. The environ- mental criteria of chapter 4 will also apply to design of main electric supply stations. b. Existing installations. Planning for electric util- ities to serve an extension or expansion of an existing system on an installation should be accomplished with the assistance and cooperation of the Facilities Engi- neer or Base Civil Engineer, and with other users of electrical utilities on the installation. An early deter- mination should be made that an adequate and stable source of electricity of proper reliability and availabil- ity can be obtained, and that existing equipment is TM 5-811-1/AFM 88-9 Chapter 1 adequate in capacity and condition to serve the planned extension or expansion. Compatibility with the master plan for the installation is necessary, even for those installations for which no specific electrical master plan exists. Construction methods will be gen- erally compatible with the existing system, but methods need not be necessarily identical, especially if the extension is a large one. Use of antiquated, in- ferior, or expensive methods merely to match existing construction is not justified. 1-5. Unusual service conditions. Temperature, humidity, and other climatological factors as well as altitude may require special design techniques at some installations. a. Arctic conditions. Basic engineering practices governing design and construction of electric power systems in temperate areas are applicable to arctic and subarctic zones. Modifications, as necessary, will be made to combat snow and ice above ground and perma- frost conditions in underlying subsoils. Such design conditions are covered in TM 5-349, TM 5-852-5, and NAVFAC DM-9. Methods used in temperate zones for installing electrical distribution poles are adequate in most cases; occasionally, special pole construction techniques, using cribs and tripods or blasting or drill- ing into the permafrost, may be required. Utilidors, which are usually rigid, insulated, and heated conduits with either crawl- or walk-through space for servicing and which are usually installed underground, may also be used. b. Tropic conditions. Excessive corrosion, moisture, and fungus are conditions generally encountered in tropical zones; otherwise, design and construction of power systems in temperate and tropical zones are similar. TM 5-809-11/AFM 88-3, Chapter 14, recom- mend engineering solutions based on actual experience in meeting special tropical conditions. Observation of proven local practice is also of value in understanding the nature of the problem and its solution. Potential problems which may result from corrosion and termite infestation, as well as the feasibility of using local ma- terials, should be investigated in order to select the most suitable elements for the system. Outdoor switchgear will be enclosed and have space heaters with automatic controls. In typhoon areas, design will provide sufficient strength for the extreme wind load- ing conditions applying. Electric equipment which is not inherently fungus-resistant will be treated as necessary. c. Corrosive or contaminated atmospheres. Atmos- pheres where corrosion occurs, because of excessive humidity or from industry contamination which may be intensified by fog, may require more than normal protection. Generally, such upgrading should only be provided when local practice indicates the additional cost is necessary. (1) Finishes. Standard finishes are not always ade- quate for areas where corrosion is a problem. (a) Transformers. American National Standards Institute (ANSI) C57.12.00 requires a minimal tank finish consisting only of a pigment paint. (b) Switchgear. ANSI C37.20 requires a better finish for switchgear in that a phosphatizing treat- ment or equivalent is necessary before application of corrosion-resistant paint. External surfaces of outdoor units need an additional coat over the single one re- quired for internal surfaces. Undersurfacing for out- door switchgear is also necessary. (c) Upgrading corrosion resistance. Where a bet- ter than standard coating is required, a salt spray test can be specified for the finish. Length of the testing period should be in accordance with standard practice for the area. Also for aerial transformers, stainless steel cases are available. (2) Insulating devices. Over insulation is often necessary in contaminated areas. Chapter 6 discusses criteria for insulators. In contaminated areas, bush- ings are often specified for the next higher basic im- puse level (BIL) than required for that device insula- tion class. Some localities have problems from salt de- posits on bushings which can cause tracking leading to corrosion at the bushing base and may require special treatment. d. Altitude and other usual service conditions. In- dustry standards generally list altitudes at which equipment can function without a derating factor. Most apparatus can function without derating up to an altitude of 3,300 feet (1 kilometer). Other service con- ditions covered are acceptable ambient temperature ranges and deratings applying to frequencies other than 60 Hz. Where unusual service conditions occur, such as exposure to abnormal atmospheres or vibra- tion or unusual space limitations, applicable standards should be consulted and design adjusted accordingly. Unusual conditions should be brought to the attention of those responsible for application, manufacture, and operation of the equipment. TM 5-811-1/AFM 88-9 Chapter 1 CHAPTER 2 ELECTRIC POWER REQUIREMENTS 2-1. General. Before the most feasible method of supplying and dis- tributing electric power can be selected, a maximum demand for the installation must be estimated. In the early design stages, this demand may be based on area or population; while in later design stages, summation of individual building connected loads modified by suitable demand and diversity factors will be used. For early stages, use of kW, kVA, and hp interchangeably on a one to one basis is sufficiently precise. During final design, hp can be converted to kVA; and kVA can be multiplied by the estimated power factor to obtain kW. Power factors will usually be in the 0.85 to 0.95 range. 2-2. Terminology. Analysis of load characteristics will take into account the demand factor relationship between connected loads and the actual demand imposed on a system. Just as the maximum demand for the various types of connected loads within a building will be less than the sum of the individual loads, so the maximum demand for a group of buildings is less than the sum of in- dividual building maximum demands, since loads do not generally peak concurrently. a. Demand factor. The demand factor is the ratio of the maximum demand on a system to the total con- nected load of the system or Maximum demand ——* Total connected load oii The range of demand factors for industrial buildings, offices, and residences are listed in Table 2-1. Demand factors are also noted in the National Electrical Code. Demand factors reflect the number, the type, the duty rating (continuous, intermittent, periodic, short time, and varying), and the wattage or voltampere rating of equipment supplied by a common source of power, and the diversity of operation of equipment served by the common source. Demand factors are indicative of a load density between about 3 and 12 voltamperes per square foot for enclosed facilities. The lower densities pertain to residences and the higher densities pertain to the industrial types of facilities. Demand factors are used to determine the ampacity of conductors, the capacity of transformers, and the ampacity or capacity of other items of materials or equipment required to distribute electrical power to utilization equipment. Realistic demand and diversity factors must be as- signed to reduce costs while insuring that items of equipment and materials are adequate to serve exist- ing, new, and future load demands. No more than ten percent spare capacity should be considered during de- sign unless more space capacity is warranted by future facilities approved for construction in later years. Table 2-1. Demand Factors “ Usage Demand Factors Industrial buildings 0.50 to 0.90 Offi6es isa. oi. diss sake 0.50 to 0.90 Residences 0.45 to 0.80 ® From “Standard Handhook for Electrical Engineers” by Fink and Beaty, Copyright 1978 by McGraw-Hill, Inc. Used with permis- sion of McGraw-Hill Book Company. b. Diversity factor. The diversity factor is the ratio of the sum of the maximum individual demands of a subdivision of a system to the maximum demand of a system, or Sum of individual Diversity factor = ee demas. (2-2) Maximum system demand Typical diversity factors are given in table 2-2 and an illustration of their use is shown in a demand flow re- lationship in figure 2-1. This illustration indicates the load at substation “X” would be 0.45 (1/2.24) times the summation of the demands based on the given data. Since utilities calculate loads on a less conservative basis, diversity factors for main electric supply sta- tions on military installations will usually be higher than the 2.24 shown in figure 2-1 (lower than 0.45 de- mand). 2-3. Load estimates. Loads are estimated in various ways dependent upon the design stage of the installation. a. Preliminary area or site loads. By using the repre- sentative load data given in table 2-3, preliminary estimates of the expected maximum demands and elec- tric energy usage can be computed. These values are based on existing installations and have been extrapo- lated to allow computations to be made based on either population or building area. Per capita loads are for an average daytime population. 2-1 TM 5-811-1/AFM 88-9 Chapter 1 Table 2-2. Diversity Factors * Diversity factors Lighting General Large Relationship Item Residence Commercial power users Individual users.............. 1.45. - Siena Utilization transformers ....... 1.35 . 1.05 Distribution feeders........... 1.15. 1.05 GSnbstutions ®t 8 sass was 1.10. 1.10 Haan Utilization transformers ....... 1.45 - ree Distribution feeder 1.95 1.15 re Substation >........ sede 2.24. 1.32 Utility generating plant........ 2.46 1.45 @ From “Standard Handbook for Electrical Engineers” by Fink and Beaty, copyright 1978 by McGraw-Hill, Inc. Used with permission of McGraw-Hill Book Company. » Main electric supply station. 8B Users 1 , ei |4.—_______ Demand flow indication 2. Transformers Generating plant Feeder 1 ee i Substations ELECTRIC DEMAND FLOW DIAGRAM | ELECTRIC DEMAND FLOW RELATIONSHIPS” 1. Transformer I demand = (User A + B demands) + (User diversity factor or item ®) = ((A + B) + 1.45] = User loads + (1.45 or item ®) 2. Feeder 1 demand = (Transformer I + II demands) + (Transformer diversity factor or item @®) = ({(A +B) + 1.45) + [(C + D) + 1.45]) + 1.35 = User loads + (1.95 or item @) 3. Substation X demand = (Feeder 1 + 2 demands) + (Feeder diversity factor or item ®) = ({(User loads) + 1.95] # 1.15) = User loads + (2.24 or item ©) 4. Generating plant demand = (Substation X + Y demands) + (Substation diversity factor or item ®) = ({(User loads) + 2.24] + 1.10) = User loads + (2.46 or item ®) Figures used are from general power column of table 2-2. US Army Corps of Engineers Figure 2-1. Illustration of diversity factor application 2-2 TM 5-811-1/AFM 88-9 Chapter 1 Table 2-3. Typical Demands and Usages Per capita Per 1,000 square feet Maximum demand Usage per year Maximum demand Usage per year Service Installation kW kWh kW kWh Development & Readiness ........... LOEROrs aciatin, 7,500-25,000 Ob Qin ae eras 5,000-20,000 Army RGAE os pce sige res cee sos Foes ees OBST pray aes 3,000- 6,000 LB is se 563 snes 5,000-25,000 Command Training:& Doctrine « suis.x so: i ess sca OGRN2 <crcisai 2,500- 7,500 Nes rs cans ces 5,000-20,000 Logistics Command ................ Tac 7,000- 10,000 7 ee 10,000-20,000 Air Force Military Airlift Command ........... POPZIB 5 is 5,000-10,000 ae eek 5,000-15,000 Base Tactical AirCommand.............. 0.5-2.0 ar, aes 3,000- 6,000 Dota rues 10,000-20,000 PRGAIMUAE, ccs sect isos ih sas at os L0=E6 5. ses sce 4,000- 6,000 BHO sci ess 10,000-20,000 US Army Corps of Engineers (1) Energy costs. An order of magnitude for ener- gy costs can be computed as shown on figure 2-2 using population values from table 2-3. Cost comparisons have been simplified for clarity and do not include such items as fuel and power factor adjustment charges, “off-peak” or “on-peak” demands, or other bill- ing practices used by utilities. (2) Load factor. Load factor is a load relationship over a designated period of time and is expressed as the ratio of the average load to the peak load occurring in the same time period or Average load Peak load If the daily average load on a transformer is 500 kVA and the daily peak load is 1,000 kVA, the daily load factor would be 0.50. Load factors will vary with lower values encountered on one-shift operations and higher values on multiple-shift operations. Higher values will also apply if the area includes housing and community facilities. Load factors are usually in the 45 to 65 per- cent range. b. Preliminary building loads. The estimated de- mand for a building is usually based on totaling vari- ous types of loads, applying a demand factor to each load and a diversity factor to the sum of the demands. Preliminary estimates can be made on a volt-amperes (VA) per square-foot basis using unit loads appropriate to the building requirements. As design proceeds, con- nected loads will be more precisely defined and will be based on the branch circuit loads indicated on the proj- ect drawings. Building loads are generally subdivided into various types of loads to permit a better judge- ment as to the applicable demand factor. (1) Lighting loads. Lighting loads can be approxi- mated from the data given in table 2-4 prior to accom- plishment of the lighting design. Estimates of con- nected lighting loads should never be less than the minimum requirements of the National Electrical Code regardless of the computation method used. De- mand factors for lighting loads generally range from 0.90 to 1.00, but more rigorous energy conservation may make lower values applicable in the future. Load factor = (2-3) Table 2-4. Typical Unit Connected Loads for Lighting ¢ Unit connected load VA per square foot » Illumination-footcandles 10 20 30 50 70 Light sources Tntandestene sis id. ie) sae Varese. a 10 PURO oe ee Gti s noe 065 6420,.2.1.5 .. 2:5 is Mercury vapor............... OG... 8255, 18-,. 30... 2 DISCAU Cn. 0 vtec wie sso ew one Oa. Oe 012.25 2,0"... 2 High-pressure sodium ......... O38) 016 ...,/0:9 °. 10... 25 * Courtesy of Keller & Gannon » Based on an assumption of: average (4) room cavity ratio, light color surfaces, medium dirt atmosphere, and cleaning every 12 months. (2) Convenience outlet loads. Convenience outlets are those outlets which provide electric service to busi- ness machines, cleaning equipment, and other portable devices. Facilities such as laboratories or dining facili- ties have been found to have demands as low as 0.1 VA per square foot; however, normally the demand for convenience outlets will be approximately 0.5 VA per square foot. Demand factors have been found to range from 0.2 to 0.5. (3) Occupancy loads. Occupancy equipment is that equipment necessary to the Using Agency’s operation such as industrial, communication, computer, labora- tory, and kitchen equipment. Often the designer may receive only fragmentary load data and must base re- quirements on unit load data acceptable to the user. Demands can vary from 12 VA per square foot or more for communication or computer type installations to as low as 1.5 VA per square foot for nontechnical training classrooms. The actual values used in the ear- ly design stages will normally be based on very pre- liminary estimates from the Using Agency and the de- signer’s judgement. Demand factors have been found to range from 0.2 to 0.9. (4) Building system loads. Building system equip- ment is that equipment necessary to provide the re- quired environmental conditions, such as cooling and heating equipment. Loads are usually furnished by the mechanical designer; however, in the absence of pre- liminary loads, an approximation may be made by as- 2-3 TM 5-811-1/AFM 88-9 Chapter 1 Air Force Training base Assume: Population = 9,000 Demand charge = Energy charge = $0.025 per kWh 1. Maximum demand per month = $3.00 per kW of billing (maximum) demand 9,000 people x 1.3 kW per capita = 11,700 kW 2. Energy used per month = (9,000 people x 4,000 kWh per year) + 12 months = 3,000,000 kWn 3. Energy costs a. Demand b. Energy = US Army Corps of Engineers 11,700 kW x $3.00 per kW 3,000,000 kWh x $0.025 per kWh Total monthly energy cost = $ 35,100. $ 75,000. $110,100. Figure 2-2. Monthly electric cost computation Preliminary design cal Type of load culations Project design calculations Connected Demand ene loads# factor Wnt Lighting, fluorescent with 80 percent of 80,000 ft2 x 2.5 va/ft2 + the area at 50 fc and 20,000 ft2 x 1.0 VA/ft2 = 220 kVA 0.9 198 kVA 220 kVA x 0.9 demand fact 20 percent of the area at 20 fc or = 198 kVA Convenience outlets 100,000 ft2 x 0.2 VA/ft2 = 20 kVA 100 kVA 0.2 20 kVA Occupancy 100,000 ft2 x 1.5 VA/ft? = 150 kVA 250 kVA 0.6 150 kVA Building system 100,000 ft2 x 3.0 VA/ft2 = 300 kVA 375 kVA 0.8 300 kVA Subtotal Summation of demands = 669 kVA 945 kVA 0.7 668 kVA Design demand = (668 kVA : 1.2 diversity fact or) x 1.25 load growth factor = 700 kVA 4Based on branch circuit loads indicated on project dr US Army Corps of Engineers awings. Figure 2-3. 100,000 square-foot office building calculated demand suming a cooling unit demand of 2 VA per square foot for office buildings in mild temperate areas up to more than 8 VA per square foot for communication or com- puter type buildings where high ambient temperatures are encountered. Demand factors have been found to range normally from 0.6 to 0.8. The values listed above include allowances for chillers, fans, pumps, and other ancillary equipment. 2-4. Load calculations. Demands based on preliminary building loads can now 2-4 be calculated as shown on figure 2-3. This preliminary estimate can be refined as indicated when the building design has been finalized. The demand factor of 0.70 agrees with the range of 0.50 to 0.90 given in table 2-1. The diversity factor used is more conservative than the 1.45 given in the general power column of ta- ble 2-2 for utilization transformers, since military de- sign margins are generally more conservative than those of utilities. TM 5-811-1/AFM 88-9 Chapter 1 CHAPTER 3 SELECTION OF THE ELECTRIC ENERGY SOURCE AND THE PRIMARY DISTRIBUTION VOLTAGE 3-1. General. The design of electric supply and distribution systems can proceed only after a source of electric energy and a distribution voltage have been determined. The electri- cal impact of the installation or facility as well as its location will influence the selection. A new service may be necessary or extension of an existing service may be acceptable. Before discussing selection of the electric energy source, types of electric energy systems and station or plant terminology need to be defined. Voltage system terminology must be also presented to clarify the primary distribution voltage selection dis- cussion. Normally, this material applies only to instal- lations having electric loads greater than 1,000 kVA and primary distribution feeder lengths greater than 1,000 feet. 3-2. Types of electric energy systems. Electric energy systems generally used are either the conventional or the cogeneration type. Cogeneration can be by either total energy or selective energy sys- tems. a. Conventional. A conventional energy system sup- plies electric energy which is not generated by the user and over which the user normally has only local con- trol. Usually conventional energy systems are pro- vided and supplied by a utility; unless that electric source has been clearly demonstrated to be inadequate or unreliable, or another energy source has been proven to be more economical. b. Total. A total energy system supplies energy re- quirements for electricity, heating, air conditioning, and other uses from a single source making maximum use of available waste heat. Usually such a system is independent of other energy sources and is generated and controlled by the user. c. Selective. A selective energy system uses all the electric energy that the installations system can gener- ate plus additional electric energy obtained from con- ventional sources. Selective energy systems often in- corporate waste heat recovery systems. 3-3. Station or nology. Equipment provided is dependent upon whether the installation requires control of an outside energy source, and whether local generation is necessary. a. Purchased electricity. When electricity is gener- plant equipment termi- ated by others, a main electric supply station provides for revenue metering of the supplier’s electric power at the electric interconnection point between the supplier and the consumer. At this point the user takes control of the system providing protective switching and, de- pendent upon the system, transformers and voltage regulating equipment. b. On-site generation. Diesel engines, gas turbines, or steam turbines may be used to provide energy gen- erated on the installation. Generating plants are classi- fied as prime (class “A”) or auxiliary (class “B” or “C”) plants, dependent upon the period of time for which electric energy must be generated. 3-4. Selection of electric energy source— new installations. The most economical system normally will be selected. a. Feasibility study. It may be necessary to deter- mine whether the most economical supply system is a conventional energy source or a generator plant, or a combination of the two. A source document which should be studied is the criteria in TM 5-810-1. The conventional or off-site source supplies energy to the main electric supply station. The total or selective energy on-site generation requires a class “A” generat- ing plant. b. Potential energy sources. In such feasibility studies, the energy sources usually compared include coal, oil, and purchased electricity. Where applicable, refuse-derived or biomass-derived fuel may also be considered. Normally natural gas will not be used as a fuel source. c. Relevant factors. Factors affecting the choice of energy sources are availability, reliability, land right- of-way requirements, station or plant site needs, first costs for the installation including any pollution abate- ment requirements, and annual costs for energy and operating personnel wages. 3-5. Selection of electric sources—existing installations. energy In general, a selection of an electric energy source is necessary only when the existing source is inadequate to supply the requirements for the facility being added. If the facility is incorporated as a part of the overall installation master planning program, then the energy needs should have been forecast in the electri- cal systems master planning, and determination al- 3-1 TM 5-811-1/AFM 88-9 Chapter 1 ready made as to whether the existing electric energy source should be expanded or whether some other alternative would be more economical. When the mas- ter plan does not provide the contemplated electric re- quirements, an engineering study may be necessary. a. Engineering studies. The basic considerations for evaluating outside energy supplies are knowledge of the following: (1) Reliability of the source. (2) Cost of energy to the installation, based on projected demand and usage requirements. (3) The suppliers ability to serve the present and the expected load for the next 5 years. (4) System outages over the last 5 years, if avail- able. Where outage information for at least 1 year is not available, or where it is meaningless because it ap- plies to a system since changed, the system being con- sidered will be evaluated on the basis of the utilities reliability projections. b. Electrical master planning. When an electrical master plan is not available, it is necessary to evaluate existing facilities by making a physical inspection of the existing facilities and accumulating the following data: (1) Condition and characteristics of the existing off-site electric energy sources including data previ- ously listed. (2) Number, condition, and characteristics of prime and auxiliary generating plants. (3) Load information. 3-6. System voltage terminology. Voltage systems are classified generally either by the system use or the voltage range. More specific meth- ods include using the voltage rating of equipment, the nominal voltage class, or the nominal system voltage. a. System use. The requirement for electric power transfer will cause certain voltage levels to be more economical than others. A transmission system trans- fers energy in bulk between the source of supply (the utility) and the center for local distribution (the main electric supply station). A primary distribution system delivers energy from a main electric supply station to utilization transformers. A secondary distribution sys- tem delivers energy from a utilization transformer to points of utilization. b. Voltage ranges. Voltage ranges are classified as low-voltage (1 kV or less); medium-voltage (above 1 kV to 72.5 kV); high-voltage (above 72.5 kV to 242 kV); and extra-high-voltage (above 242 kV to 800 kV). c. Voltage rating of equipment. Voltage rating of equipment is based on nominal voltage classes which} in conjunction with the maximum voltage rating for that class, provides a simple method for rating equip- ment. Table 3-1 indicates the nominal voltage class designation (also known as the insulation class) used in this manual, along with the maximum voltage rating that may be handled by the equipment, and the normal basic insulation level (BIL) applying, and relates these characteristics to system use and voltage range. d. Nominal systems voltage. The nominal system voltage is the nominal value assigned to designate a system of a given voltage class. Nominal system volt- ages are classified by IEEE 141 as standard and non- standard voltages. In addition, some of the standard voltages are designated as preferred to provide a long- range plan for reducing the multiplicity of system voltages. In table 3-2, nominal system voltages are shown and related to a nominal voltage class. Stand- ard voltages without parentheses are the preferred standard voltages. 3-7. Selection of primary distribution volt- age—new installations. A preferred nominal system voltage such as 12 kV, 12.5 kV, 13.2 kV or 13.8 kV, should usually be se- lected for the primary distribution system. On sizable installations where distances to loads are considerable Table 3-1. System Use and Voltage Range Relationship to Equipment Rating Equipment rating Nominal Rated maximum System Voltage voltage class BIL use range kV kV PMN SRE SES etiea ck fo 900 High 161 750 Transmission 138 650 115 550 69 350 46 250 35 200 Medium 25 150 Primary 16 «3 110 distribution HD 3% 95 Bi a uss Soest station coat eae 95 US Army Corps of Engineers 3-2 Table 3-2. Nominal Voltage Classes and System Voltages * Nominal voltage class Standard Associated nonstandard kV nominal system voltage nominal system voltage (2,400) 2,200 or 2,300 (4,160Y/2,400) 5 and 7.5 4,160 4,000 (4,800) 4,600 (6,900) 6,600 or 7,200 (8,320Y/4,800) 11,000 or 11,500 12,000Y/6,930 15 12,470Y/7,200 13,200Y/7,620 (13,800Y/7,970) 13,800 14,400 (20,780Y/12,000) (22,860Y/13,200) 25 (23,000) 24,940Y/14,400 34,500Y/19,920 35 (34,500) 33,000 (46,000) 69,000 66,000 69 to 230 115,000 110,000 or 120,000 138,000 132,000 (161,000) 154,000 230,000 220,000 8 From table 2 of IEEE 141-1976 and reprinted by permission of the Institute of Electrical and Electronics Engineers, Inc. or loads are large, the use of 34.5 kV or 24.9 kV pri- mary distribution systems may be more economical. Where on-site generation is provided, generation volt- ages should normally be that of the primary distribu- tion system. Primary distribution voltages of the TM 5-811-1/AFM 88-9 Chapter 1 nominal 7.5 kV class and under should not be used, un- less an off-site supply of a higher voltage is not avail- able. Seldom is the lower voltage advantageous. For such cases, the size of the installation and the dis- tances involved must make the use of voltages below 7.5 kV more economical in order to justify the selec- tion. 3-8. Selection of primary distribution voltage—existing installations. Normally, when small facilities are added to an instal- lation, the primary distribution system voltage within the addition will match the existing system. However, if the addition is substantial and large voltage drops or line losses can occur when existing voltages are re- tained, or if the main electric supply station is inade- quate, then the economics of a higher voltage for the primary distribution system must be taken into ac- count. Generally the electrical master plan will have already provided for such deficiencies. When a master plan indicates a contemplated voltage increase, trans- formers for use in ongoing construction should be spe- cified to have dual primary voltages, when economic and transformer delivery time considerations permit such a requirement. If the facility to be added is not in- cluded in the master plan, an engineering study may be necessary to determine the most feasible method of providing service. Acquisition or preparation of maps of transmission and distribution systems with dis- tances between principal points and single line dia- grams of the systems will be required. Then a determi- nation of the extent to which the existing system volt- age can satisfy installation requirements, or the economics of a higher voltage level and benefits of such a system will be evaluated. TM 5-811-1/AFM 88-9 Chapter 1 CHAPTER 4 MAIN ELECTRIC SUPPLY STATION 4-1. Provisions. New stations shall be provided for new installations as required. New stations should be provided at existing installations only when it is not possible to modify any existing station to serve new projects and existing fa- cilities or when it is impractical to do so. Determina- tion of the feasibility for modifying existing stations or constructing a new station will be made at the ear- liest practicable stage of project planning. Existing stations shall be modified when permitted by the util- ity company or other owners, operators, and users of the station and when the station is otherwise suitable for modification at a cost less than the estimated life cycle cost of a new, smaller capacity station. Consider- ation shall be given to the surplus capacity in existing lines and the station and the availability for use of the surplus capacity. Space available for station modifica- tions and rights-of-way for any new transmission and distribution lines require, adequacy of transmission and distribution voltages and mVA interrupting rat- ing of station and line equipment. Age or condition of lines and station equipment and modifications re- quired to supply total installation power demands with sufficient reliability, availability, and maintain- ability to fulfill the requirements of the using agen- cies. Other factors to be considered include the loca- tion of the existing station in relation to the location and size of the new projects, the quantity, sizes, lengths and voltage ratings of new lines, the need for any voltage regulation and reclosing features, proper coordination between devices required to protect new existing lines and station equipment, rate schedules and any other site peculiar features that affect design, construction, operation and maintenance costs of new or modified stations. When a new station is contem- plated at an existing installation served by a main sup- ply station, the total life cycle cost of station modifica- tions and new distribution facilities shall be compared against the cost of a smaller capacity station located in closer proximity to the new project, with less extensive distribution facilities. Generally, any new station should be located as near as practicable to the bound- ary of the installation and be served by a single three- phase utility line originating at the existing station when the present source is adequate to serve new proj- ects and existing facilities. New utility lines shall be considered only when the existing source or sources are inadequate, when required to comply with the reli- ability, availability, or maintainability requirements of the using agency or agencies, when a new line is more cost effective than alternate methods or for other justifiable causes. Otherwise, multiple power sources and two or more metering points should be avoided. Location of a new station remote to the boundary of the installation and the need for more than one new main supply station requires a waiver from HQDA (DAEN-ECE-E) for Army projects and HQUSAFILEEEU for Air Force projects. The request for such a waiver, and the justification therefore, shall be furnished to that office by the field operating agency responsible for the design of new projects. Jus- tifications shall be based on greater cost effectiveness or other factors discussed above. Justifications may also include a discussion of the importance of new proj- ects to national interests, probable consequences and expenses for lost production or manufacturing efforts more common to less reliable systems over the project life, or other reasonable causes that fully substantiate the preferred and more costly design addressed in the waiver request. The following should be considered in relation to the design of new stations or the modifica- tions of existing stations. a. Rates. Based on the estimated demand and usage, all electric service rate schedules applicable to the proj- ect should be carefully evaluated to ensure an ade- quate supply of electrical power at the lowest available cost. Care should be taken to see that the chosen sched- ule compares favorably with that of any other utility serving the area, and that the rates are no higher than those paid by other customers for similar service. The possibility of recovering any connection charges, by deducting a certain percentage of each monthly bill or by a fixed annual or monthly refund, should be investi- gated. b. Right-of-ways. The Government grants all right- of-ways needed within their property limits and the utility procures all others. Utility-owned facilities should be located to avoid any interference with instal- lation activities and planned functions. c. Coordination. Selection of utility rate schedules and right-of-ways over Government property should be coordinated with, and approved by authorized per- sonnel. 4-2. Ownership. When electricity is supplied by a utility, equipment on 4-1 TM 5-811-1/AFM 88-9 Chapter 1 the line side of the station transformers and the sta- tion transformers are normally provided by the utility. Government ownership of line equipment and power transformers should be considered when permitted by the utility and when Government ownership would be more economical, based on an estimated life of 25 years for the transformers and line equipment. In making that determination, the cost of Government ownership must be compared against the correspond- ing cost for utility ownership, based on the same ener- gy demands and usage and the different construction costs and applicable rate schedules. 4-3. Station designation and elements. Station elements generally consist of apparatus asso- ciated with incoming and outgoing electrical power transmission, sub-transmission and distribution cir- cuits, and the equipment required for the instrumenta- tion and control of the apparatus and circuits. The sta- tion elements may include power transformers with or without automatic load tap changing provisions. Sep- arate voltage regulators may be provided to regulate station voltage when power transformers are not pro- vided, or to regulate station voltage when non-auto- matic load tap changing transformers are provided. The latter may be preferred to prevent outage of pow- er transformers because of outage of automatic load tap changing mechanisms, or to circumvent the prob- lems associated with the parallel operation of trans- formers with dissimilar features or characteristics. The station is to be designated a “Main Electric Supply Station” when there is no power transformation fea- tures, and a “Main Electric Supply Substation” when power transformers constitute a station element. 4-4. Main electric supply station. The main electric supply station is usually the installa- tion/utility interface point where further transmis- sion, distribution and utilization of electrical power, the monitoring and control of such power or equip- ment and the protection of electrical equipment or sys- tems becomes the sole responsibility of the Govern- ment. Electrical power is normally supplied by the same utility over one or more incoming power lines that are metered by the use of items of equipment pro- vided and maintained by the utility. The design of new stations, or modifications to existing stations, usually must be coordinated with the supplying utility and with any other suppliers or users of power supplied through the station. Such coordination should be ac- complished by the responsible field operating agency, or a designer employed to accomplish the coordination and design of new electrical facilities. Complete coor- dination should be performed to insure proper protec- tion for electrical equipment and systems, to obtain the required degree of availability, reliability and 4-2 maintainability and to achieve the most cost effective billing, construction, operation and maintenance costs during a station life of 25 years or less. a. Revenue (energy) billing. Billing costs usually in- clude several charges. Energy charges relate to kilo- watt-hours metered during a given billing period; us- ually a calendar month. Demand charges are based on the kilowatts or kilovoltamperes that represent the maximum demand for a given month and that occurs during the peak demand metering period; usually 30 minutes or less on the maximum load day. Demands may be the maximum demand or, when time metering is used, demands may be broken down into charges for on-peak demand (daily period when greatest electric usage occurs), partial-peak demand (medium usage) and off-peak demand (lowest usage). A fuel adjustment charge may be added to the billing statement, as well as a power factor penalty charge which increases bill- ing charges for power factors lower than 0.90 or a less- er value. Rate schedules vary between utilities. There- fore, billing costs may be computed differently than just described for the more common rate schedule or tariff. (1) Revenue metering. A utility usually provides a totalizing watthour meter equipped with a demand register that is supplied by highly accurate instrument transformers. A demand type of varhour meter will normally be provided by the utility when the rate schedule includes a poor power factor penalty charge. In general, a utilities meters cannot be used for any other purpose without prior approval by the utility. Revenue metering equipment will be provided by the Government only when required by the utility, and shall comply with the utility requirements when so provided. (2) Energy conservation requirements. Reduction in energy usage is a national goal. Several programs have been implemented to effect energy reduction, and include energy monitoring and control systems (EMCS). EMCS design is described in TM 5-815-2/ AFM 88-36. Provisions for future EMCS applications should be provided when the installation is con- structed, and consist of raceways installed to accom- modate future EMCS equipment and associated wir- ing. (3) Power factor correction. Provisions for future installation of shunt capacitor equipment will not be initially provided in the main electric supply station. Normally, power factor correction capacitors should be provided at or near the terminals of inductive devices to minimize energy losses in the electrical supply sys- tems. 6. Protection. The time-current characteristics or settings of power fuses or protective relays will be se- lected to afford optimum protection to the electrical equipment and systems. Utilities may have other re- quirements when any electric power generating units on the site are to be paralleled. Some utilities have car- rier current relaying schemes, and may require the Government to provide line relays, or companion type of relays, power supplies and housing for carrier cur- rent relaying equipment. Auxiliary equipment such as batteries and chargers, annunciator panels, and super- visory or tele-metering equipment may need to be pro- vided or housed or supplied. Written utility require- ments and approval of the system proposed should be obtained in the criteria development or early design stages of a project. c. Short circuit capacity. The available short circuit capacity of the electrical power sources influences the design of circuit-controlling and protective devices lo- cated in the station, and those provided in distribution system. The future planned short circuit current should be considered in the design as well as the short circuit current available at the time of design. 4-5. Environmental aspects. The main electric supply station should be as pleasing as possible without a significant increase in costs. The environmental impact will be evaluated for compli- ance with Public Law 91-190. a. Noise mitigation. The impact of transformer noise must be considered, particularly in developed or future areas of planned development where noise abatement is or will be mandatory. In warehouse and industrial areas, noise impact should be evaluated and provided for, except where economic and technical rea- sons warrant otherwise. Transformers with 115 kV primaries, that comply with NEMA standards for noise levels, will transmit only about 50 to 55 decibels to a point 100 feet from the transformer. The most economical way of obtaining acceptable noise levels is to locate the station at least 100 feet from the nearest facility. b. Appearance. The following requirements not only assure that the physical appearance of the station will be acceptable, but should decrease maintenance prob- lems. (1) Structure-mounted equipment. The use of me- tal structures with tubular or H-beam supports is con- sidered the most desirable design. The conventional lattice structure is unattractive in appearance and more difficult to maintain. Except for incoming line structures which require the extra height, low-profile structures will be installed. (2) Transformers. Unit substations require less land space, are less visually objectionable and, because of the integrated transformer and secondary connec- tions, are more reliable than transformers located sep- arate to the associated switchgear. (3) Connection to aerial distribution lines. Under- ground connections from a new or modified station to TM 5-811-1/AFM 88-9 Chapter 1 feeders or incoming lines will be provided when phase- to-phase voltage is less than 35kV. Underground in- stallation of cabling reduces the risk of outages, be- cause of lightning, and enhances the appearance of the station installation. 4-6. Line switching and protective appara- tus. Apparatus required for the switching of incoming lines, and for the protection of primary station ele- ments when required, may be provided by the supply- ing utility or by the Government to meet any require- ments of the utility and the needs of the Using Agen- cy. The following applies to the instances where such apparatus are provided by the Government, with the concurrence of the utility. The exact type, ratings and the consequent cost of apparatus will depend on the protective coordination required, the voltage rating of the incoming lines or feeders, the full-load current and the fault current availability at the station. Figure 4-1 includes an example of converting fault mVA to sym- metrical fault current and the multiplication by a factor of 1.6 to convert symmetrical current to an asymmetrical value. a. Circuit breakers. Circuit breakers are usually more costly than other apparatus, used singly or in combination, to accomplish line switching and to pro- tect station elements. However, circuit breakers will be used for all switching stations, when stations are served by more than one incoming line or contain transformers rated 10 mVA or above, when econom- ically justified, when required to obtain the required degree of reliability, or when their use is required for coordinated circuit protection or switching to limit the duration and frequency of outages to the installation. Circuit breakers will be of the oil type when the incom- ing line voltage is greater than 35 kV. The design of the station will include provisions to isolate oil circuit breakers and to bypass them with power fuse discon- necting units when required to ensure continued pro- tection of station buses and equipment when circuit breakers are out-of-service. The bypass feature is not required if other circuit equipment can protect station elements when circuit breakers are inoperative, or if the utility line breakers afford the required degree of protection. b. Power fuse disconnecting units. This type of unit may be used in conjunction with the group-operated, load-break type of air switches when circuit breakers or the more expensive load or fault-interrupting switches cannot be justified. Generally, the use of pow- er fuse disconnecting units should be limited to sta- tions with an incoming line voltage of 35 kV or less and to stations with a capacity of less than 5 mVA, be- cause such units are less reliable, have limited selectiv- ity, afford less protection against high resistance 4-3 TM 5-811-1/AFM 88-9 Chapter 1 USING VALUES BELOW MVA = Utility company short circuit contribution in MVA kV = Utility company transmission voltage in kV kA_ = Utility company short circuit contribution in symmetrical kiloamperes (rms) kA_ = Utility company short circuit contribution in asymmetrical kiloamperes (rms) IN FORMULAS BELOW EXAMPLE FOR DEVICE SIZING Utility company transmission voltage = 69 kV Utility company short circuit contribution = 1,200 MVA ica oj 22200 © 169 inxi v3) kA, = 1.6 x 10 = 16 ka. Minimum device withstand ratings: 10 kA symmetrical 16 kA asymmetrical US Army Corps of Engineers a Tiger tee CL) Figure 4-1. Converting utility company short circuit mVA to current faults, prolong the extent of outages and are prone to single-phasing. c. Metal-enclosed interrupter switchgear. Metal-en- closed interrupter switchgear is more economical than circuit breakers and may be used when more expensive switching and protective equipment cannot be justi- fied. The use of such switchgear is to be limited to sta- tions supplied by incoming lines rated 35 kV or below. d. Fault-interrupter switches. Fault-interrupter switches may be used for line switching and fault pro- tection of station elements as a less costly substitute for circuit breakers. The interrupting ability of the switches is limited and the operation of them must be blocked if fault currents exceed the interrupting rat- ing of the switches. This requires that a circuit breaker on the line side of the switch operate to clear the fault. Therefore, permission of the utility company must be obtained for the use of fault-interrupter switches when the circuit breaker or protective element ahead of the switches is under the exclusive control of the supply- ing utility, and the available fault current exceeds the interrupting rating of the fault-interrupter switches. These types of switches should not be used when the station is supplied by only one incoming line when the switches are to be used for the opening and closing of the line, as opposed to the protection of transformers 4-4 and separate line switching apparatus. The interrupt- ing element of the switches is an SF, unit that are con- nected in series for higher voltage ratings, which makes them less reliable at voltages greater than 46kV. Therefore, fault-interrupter switches are not recommended for use when the incoming line voltage exceeds 46kV. e. Motor operated disconnect switches. Motor-driv- en, group-operated disconnect switches may be used for line switching, as well as isolation of station ele- ments, under no-load conditions. This requires the use of such switches in conjunction with other circuit pro- tective and switching apparatus. Motor operated dis- connect switches must be interlocked with other ap- paratus to ensure their operation under no-load, in- cluding possible interlocking with main transformer secondary circuit breakers. 4-7. Substation equipment. a. Power transformers. Power transformers will be the outdoor, oil-immersed type. A more detailed dis- cussion on transformers is presented in chapter 8. (1) Quantity of substation transformers. The quantity of substation transformers to be installed in an existing substation will depend on the present con- figuration and features of the substation, and on any ASSUME LOADING Estimated peak load... . Estimated peak load duration Estimated constant load. . . Estimated constant load duration Estimated load growth... -. ss ee Estimated life of substation. .. TM 5-811-1/AFM 88-9 Chapter 1 15 MVA 8 hours 7.5 MVA 16 hours + « « « 2.5 percent per year « « « 25 years PweNne ASSUME INITIAL PROVISIONS OF Two 7.5 MVA transformers (55° C temperature rise and 25 year life), which when provided with forced-air-cooling will raise capacity to 9.375 MVA, plus space for installation of a similar third unit. AVAILABLE EXTRA CAPACITY AT 30°C AMBIENT Running transformers at 65° C rather than 55° C tempereture’ rise . . cs <p ot «© dade tek 2% Using ANSI C57.92 peak load factors for normer rive: Cepectancy , v3. sk ke pe ee 18% CALCULATE TIME WHEN EACH CAPACITY INCREASE IS REQUIRED Length of time original capacity is acceptable: Total peak load capacity = 15 MVA X 1.12 X 1.08 = 18.1 MVA Load growth = 15 MVA X 102.5% per year X 8 years = 18.3 MVA Add forced-air-cooling in eighth year Length of time fan cooling capacity is acceptable: Total peak load capacity = 9.375 X 2 X 1.12 X 1.08 = 22.7 MVA Load growth = 18.3 MVA X 102.5% per year X 9 years = 22.9 MVA Add additional forced-air-cooled unit in seventeenth year Ability of three units to handle capacity for 25-year life: Total peak load capacity = 9.375 X 3 X 1.12 X 1.08 = 28.1 MVA Load growth = 22.9 MVA X 102.5 X 8 years = 27.9 MVA TO PROVIDE FOR ASSUMED LOADING Tnitial design 213i ss 0s i220 st Install two 7.5 MVA units SAME Fear sos 6 6 5 wo 6 6 6 is Add forced-air-cooling Seventeenth year. . 2... « + + « « « Add third 9.375 MVA units At end of life (25 years) .... . . Units 99 percent loaded US Army Corps of Engineers Figure 4-2. Example of sizing substation transformer capacity requirements of the utility and the Using Agency. The number of transformers to be installed in new substa- tions will normally be two of like design and ratings when the substation capacity is 40 mVA or less. A larger quantity may be required for substations with a greater capacity to comply with reliability, availability or maintainability criteria of the Using Agency. The exact number of power transformers may be deter- mined by the utility if transformers are to be supplied by the utility. Coordination with the utility and the Using Agency will be required when requirements im- posed by the utility or the Using Agency dictate the design of new or modified substations. In any instance, a new substation should be constructed with not less than two transformers of ample capacity to prevent the outage of one transformer from causing a complete loss of power to an installation. (2) Capacity of substation transformers. The ca- pacity of a new or modified substation will be adequate to supply all installation or project demands deter- mined during design. The capacity of substations will otherwise be sufficient to accommodate expected load growth in later years. Load growth should be based on increases of 1 to 5 percent of the estimated peak load per year, when more exact load growth information is not available. The base capacity or rating of new trans- formers will be the self-cooled rating for a 55 degrees Celsius unit. Increased capacity of individual trans- formers will be obtained by specifying a dual thermal rating and forced-cooling provisions when available and necessary to accommodate load growth, and to al- low for overloading of transformers without sacrific- ing transformer life. (a) Dual thermal rating. Transformers with a 4-5 TM 5-811-1/AFM 88-9 Chapter 1 dual thermal rating of 55/65 degrees Celsius will per- mit operation of the transformers at 112 percent load- ing in a daily average ambient temperature of 30 de- grees Celsius. (b) Forced-air-cooling. Only single-stage fan cooling is available for the smaller sizes of power transformers. Single-stage air-cooling will provide an additional 15 percent capacity to units rated 1,667 kVA and below and 25 percent for units rated 2.5 to 10 mVA. Either single- or dual-stage forced-air-cooling can be obtained for units rated more than 10 mVA, and will provide a 33.3 percent increase in the trans- former capacity for each of the two stages of cooling. Single-stage cooling will be specified for all transform- ers when that option is available, and when the selec- tion of that option is more cost effective than increas- ing the self-cooled rating of transformers to accommo- date peak demands of limited duration. Provisions for future second-stage cooling will be specified for trans- formers when the option is available. Second-stage cooling may be specified to be provided initially when load demands are expected to increase substantially in early years following construction of the station, be- cause of planned expansion of facilities at the installa- tion. (3) Example of determining station capacity. Fig- ure 4-2 contains an example of determining the capac- ity of a new substation, based on the assumptions giv- en. The example and the preceding assumes that pow- er transformers will be installed in a daily average am- bient temperature of 30 degrees Celsius or less. The ca- pacity and features of power transformers will be de- termined and selected in accordance with industry practices and standards when transformers are to be installed in a higher ambient temperature region, or when other assumptions made do not suit actual site conditions or standard transformer designs. Unusual service conditions will be determined and compensa- tion made for them in specifying substation equip- ment. (4) Load-tap-changing (LTC) transformers. Trans- formers may be equipped with manual LTC mechan- isms, operated under no-load conditions, or automatic LTC mechanisms to compensate for voltage changes under varying load conditions. Automatic LTC trans- formers is a convenient method of compensating for voltage changes in the primary or secondary voltage systems. However, failure of such automatic LTC pro- visions may cause the outage of the associated power transformer during the period required to repair the automatic LTC mechanism. Separate voltage regula- tion equipment is, therefore, a preferred alternative when a substation is equipped with only two trans- formers or a larger number that are incapable of sup- plying daily power demands during the outage of an automatic LTC transformer. Manual no-load tap- 4-6 changing mechanisms should be specified for power transformers when separate and automatic load vol- tage regulators are specified, either for installation in the main electric supply station or in the distribution system. Specification of automatic LTC transformers, or manual LTC features in conjunction with separate three-phase voltage regulators, should consider the ef- fects of power factor corrective capacitors when in- stalled in the substation to improve the power factor. Capacitors do not regulate voltage unless they are automatically switched. However, they do increase the voltage level in accordance with the following formula. (Capacitor kvar) Approximate percent = (Substation % imped.) of voltage increase (Substation kVA)(4.1) (5) Transformer arrangement. Transformers will be arranged for connections as shown in “arrangement one” in figure 4-3. Such an arrangement will allow for the least expensive method of adding new transform- ers or switchgear in the future. b. Voltage regulators. Voltage regulation will be provided when required to obtain acceptable voltage levels at either new or existing stations. Step-voltage regulators will be required for switching stations and in substations that are not equipped with automatic load-tap-changing transformers. Step-voltage regula- tors provide a plus or minus 10 percent voltage correc- tion. Therefore, the regulator capacity need only be 10 percent of the load to be regulated. Three-phase regu- lators should be specified whenever feasible to mini- mize open wiring and space requirements. The use of an open-delta connection, to simplify the connections of single-phase regulators, is not permitted. The open- delta connection causes a voltage imbalance that, al- though small, can appreciably increase heating on fully loaded polyphase motors. c. Metal-clad switchgear. Metal-clad switchgear will be used exclusively in switching stations and in substa- tions to switch and protect distribution lines originat- ing at the stations. The interrupting duty of switch- gear installed in switching stations will be the same as for incoming lines, even though the interrupting switchgear installed in substations will be less because of transformer impedance. Figure 4-4 is an example of calculating the fault mVA and determining the inter- rupting rating of circuit breakers. The general method shown should only be used for approximation pur- poses. The utility should be requested to furnish a more accurate value of available fault mVA than can be delivered by incoming lines. Contributions to the fault mVA by on-site generators and motors rated at or above 50 horsepower must also be considered before selecting and specifying the interrupting rating of the switchgear. d. Design of stations. The initial design of new sta- TM 5-811-1/AFM 88-9 Chapter 1 = a a Sey ea se Ree: 7 ao tes ce Sentipest oh f Future Feeders Incoming lines Feeders Future ARRANGEMENT ONE Recommended as expansion is easy Transformer Transformer a 1 Sea Feeders Feeders ARRANGEMENT TWO Not recommended as expansion is difficult US Army Corps of Engineers Figure 4-3. Single line of primary unit substation with two transformers Transmission voltage = 69kV Distribution voltage = 13.8 kv Assumed utility short circuit capacity = Infinite Assumed transformer rating = 25 MVA Assumed transformer impedance = 6 percent 25 MVA + 0.06 percent = 416 MVA Use 500 MVA circuit breaker rating US Army Corps of Engineers Figure 4-4. Circuit breaker interrupting rating approximation AL Incoming line TM 5-811-1/AFM 88-9 Chapter 1 tions will include provisions to facilitate the addition of future lines, transformers and associated apparatus to minimize the expense for station expansion in later years. The area, fencing, grounding and station ar- rangement will be such as to permit the installation of an additional incoming line and at least one additional power transformer and related equipment or materials in the future with a minimum of modifications. Sta- tion access roads, vehicle and personnel access gates and other station elements should be initially located to avoid relocation if the station is expanded in the fu- ture. Switching stations or conventional substations should be similarly designed to allow for future modi- fications at a minimum of cost. The design of modifica- tions to existing stations should also allow for future expansion to the station with a minimum of expense whenever expansion is likely or possible. 4-8. Miscellaneous station design criteria. a. Metering and relaying. Meters and relays should be limited to the types and minimum number required to comply with any requirements of the utility or the Using Agency, or to afford adequate monitoring or protection of electrical power system conductors or equipment. The use of solid-state relays for the protec- tion of medium-to-high voltage conductors or equip- ment is not recommended, because they have proven to be less reliable than the electromechanical types. Further, solid-state relays have proven to be prone to misoperation during transient overvoltage conditions on the systems, which caused nuisance tripping and consequent outage of electrical service. (1) Oil circuit breakers. An ammeter and phase over-current relays will be used when oil circuit breakers are specified for installation. The meter and relays will be supplied by current transformers usually mounted in the bushing wells of the oil circuit breakers. ANSI C76.1 requires that potential taps be provided only on bushings having an insulation class of 115 kV or above. Therefore, separately mounted po- tential transformers will be specified when the incom- ing line voltage is less than 115 kV and when a poten- tial source is required for instruments or relays. Other- wise, potential taps on bushings are to be specified. (2) Buses. The metering of station buses is not usually required. Separate bus differential relaying provisions will be specified only when protection against bus faults is deemed to be sufficiently impor- tant to warrant the additional expense, and to risk nuisance tripping because of the mis-operation of bus differential relays. Instead, consideration should be given to the relaying of buses in conjunction with any transformer differential relaying scheme. IEEE sur- veys indicate an extremely low failure rate on buses, with most failures attributed to the lack of adequate maintenance. This is opposed to the usual causes of electrical faults, such as birds, ice, lightning, wind, etc. or their effects. (3) Transformers. The metering of transformer “mains” or conductors between the transformer sec- ondary terminals and the switchgear is described be-. low. The minimum relaying requirements are noted in table 4-1. Relays and meters or instruments are to be located in the metal-clad switchgear. (4) Metal-clad switchgear. Minimum metering re- quirements are indicated in table 4-2, and are in addi- tion to any revenue metering or others types of meter- ing required by the utility or the Using Agency. Mini- mum relaying requirements are similarly shown in ta- ble 4-3. Provisions will be made for monitoring energy demand and consumption for the purpose of demand limiting or energy reduction required for separately specified energy monitoring and control system equip- ment. Such provisions will usually be limited to empty raceways extended from beneath switchgear units, containing instrument transformers or instruments containing transmitting devices, to a point 2 feet ex- ternal to the switchgear foundation. (a) Automatic circuit technology relays. Auto- matic circuit reclosing relays should be specified for Table 4-1. Minimum Relaying for Transformers Transformer minimum ANSI unit capacity Device Relay function device number or other requirement actuation Winding or top oil 49 Only on units having forced-air-cooling Alarm reporting system or circuit breaker tripping temperature in accordance with installation policy Fault (sudden) 63 10 MVA and larger, or where justified, down to 5 pressure MVA Transformer 87 Only where a primary circuit breaker is provided Primary and secondary circuit breaker control differential and unit is 10 MVA or larger, except where justi- fied for smaller units US Army Corps of Engineers 4-8 TM 5-811-1/AFM 88-9 Chapter 1 Table 4-2. Minimum Metering for Metal-Clad Switchgear ANSI Type of meter abbreviation Circuit metered Ammeter AM On all mains. On feeders only when transformer unit capacity exceeds 2.5 MVA Voltmeter VM On all mains Wattmeter WM On all mains. On feeders only when transformer unit capacity exceeds 10 MVA Varmeter VARM On all mains Watthour demand WHDM On all mains meter US Army Corps of Engineers Table 4-3. Minimum Relaying for Metal-Clad Switchgear ANSI Relay function device number Circuit breaker function Nondirectional overcurrent, 50/51 and On all mains and feeders when short circuit current can flow only one direc- phase and ground 50N/51N tion. Directional overcurrent, 67 and On all mains and feeders when short circuit current can flow in both direc- phase and ground 67N tions. Automatic circuit 79 Feeders for long overhead lines, except relays may be installed on mains in- reclosing stead of feeders where transformer unit capacities are 2.5 MVA and below US Army Corps of Engineers use in conjunction with aerial lines that are essential to supply power to important facilities, such as hos- pitals, communication or emergency centers, produc- tion lines, or other facilities of prime importance to the installation. Reclosing relays should be considered jointly with sectionalizing switches which should be installed to minimize the duration of outages of power to other facilities served by the same aerial line, as a result of sustained faults. The use of sectionalizing switches should be considered in relation to the line length and frequency of lightning storms at the instal- lation as well as the nature of the loads. Studies indi- cate that between 75 and 90 percent of the faults on aerial lines are temporary and self-clearing, and are most commonly caused by lightning, “brushing” by tree limbs, “galloping” conductors, birds, and other ex- ternal causes of a momentary nature. Such external causes are not common to underground cable systems. Therefore, the use of automatic circuit reclosing relays or other devices cannot usually be justified for under- ground feeders. Reference is made to REA Bulletin 65-1 for further design guidance in these regards. (b) Directional overcurrent or power relays. Re- lays will be specified when required to protect against the reverse flow of current or power when onsite generation exists or is to be provided at the installa- tion. Similar protection is to be afforded when electri- cal power is to be provided over separate incoming lines owned by different utilities and relaying is re- quired to detect and correct abnormal conditions on the transmission, sub-transmission or distribution lines that serve the installation. (5) Protective coordination. A coordination study is necessary to determine settings of adjustable protec- tive devices and ratings of associated power fuses. This requires the following data: (a) System single-line diagram. (b) Short circuit analysis. (c) Special requirements including utility pro- tective devices. (d) Graphs of protective device coordination (see fig. 12-3 for an example). b. Other equipment and personnel protection. (1) Surge protection and grounding. Grounding, and surge protection against lightning and switching surges, are discussed in chapter 9. (2) Station enclosure. A station fence, with three strands of barbed wire above a seven-foot high fence fabric, is the minimum requirement. Other station en- closure materials, or heights, may be required to pro- vide equipment masking, sound attenuation, or protec- tion against sabotage. A minimum 10-foot wide ve- hicle gate, a 3-foot wide personnel gate, and a suffi- cient access space for removal and replacement of sta- tion elements is required to permit maintenance or modifications to the station without interruption to the electrical service. c. Control power. An alternating source of power will be provided to supply power to station equipment manufactured only for use on an alternating-current source of power. An alternating source of power will also be provided when the utility or Using Agency re- quires a capacitor-tripping scheme for circuit breakers or other power switching apparatus to permit tripping 4-9 TM 5-811-1/AFM 88-9 Chapter 1 following a power outage to the station. Otherwise, and because of greater reliability, a direct-current source of power will be provided for the close and trip operations of circuit switching equipment, and for other equipment rated for direct-current applications. The direct-current source of power will normally be a lead-calcium type of battery rated at 48 volts, or at 125 volts when the additional cost is warranted be- cause of the ampere-hour capacity required to supply station loads. A battery-charger will be provided to en- sure that the battery is fully-charged at all times. The battery and charger and a direct-current panelboard should be installed in the station switchgear assembly, to avoid the additional cost for a separate enclosure. The battery, charger and panelboard should be in- stalled in a separate enclosure only when the capacity, voltage rating and consequent size of the battery war- rants a separate housing, or when a separate control house is required to house the battery, charger, panel- board, annunciators, carrier current, supervisory, tele- metering, relaying or other instrumentation or control equipment. d. Station protection and structures. (1) Station structures. The standard design of the manufacturers of aluminum or galvanized steel struc- tures will normally be used to avoid the greater costs associated with specially designed structures. Struc- tures will be designed to withstand all dynamic or static forces that are likely to be imposed on structures during a 25-year life of the station, without damage or failure. A minimum of 1,000 pounds of tensile force will be assumed for stranded conductors to be termi- nated on station structures when conductors originate and terminate within the station, or when the station is supplied by incoming line conductors installed slack between the last pole or structure and the dead-end pole or structure within the station. Figure 4-5 is an 4-10 example of a substation with incoming line structures for incoming lines rated 46 kV or above. Generally, switching stations or substations with primary protec- tive devices, and underground connections to the utili- ty line, are all that is necessary for an incoming line voltage of 35 kV or less. Figure 4-6 is an example of a switching station that is suitable when the incoming line voltage is 35 kV or less. Relative to switching sta- tions, an economic analysis should be made to select the most economical choice between a fenced outdoor- type of switchgear and indoor switchgear to be in- stalled in a concrete-block structure without fencing. (2) Protection. The main electric supply stations will be protected against “lightning strikes” and the ef- fects of lightning on incoming aerial lines. Protection of stations against lightning strikes to the station ele- ments will be provided by grounded aerial terminals installed above and on poles or structures to provide the necessary “cone of protection.” Ground conductors will be grounded to the station ground grid and will be protected against physical damage and corrosion to terminations for ground conductors. (3) Foundations. Foundations will be designed to support static and dynamic loads of station elements. Normally, the designer will formulate foundations de- tails based on the maximum loading on foundations by the equipment specified. A maximum soil bearing pressure of 4,000 pounds per square foot will be used as a basis of design. However, since sandy or soft clay soils can have soil bearing pressure of as low as 2,000 pounds per square foot, a knowledge of the actual site conditions may be necessary. When necessary to deter- mine the actual soil type and bearing pressures, soil borings will be made and the resulting analysis will be used in the design. The guidelines contained in NEMA SG 6 will be used during designs, and will include a minimum safety factor of 1.5 for overturning loads. TM 5-811-1/AFM 88-9 Chapter 1 Overhead ground Aerial terminal wire . ‘ G Incoming fio overated at ee sconnecting switch Tubular column Suspension insulators Lightning arrester if not mtd. on transf Fused disconnect switch Concrete > foundation S&S ELEVATION A-A $49 #4 9 + 9 4+ 0 #0 94 Fence, grounded, with Batterv or personnel and vehicle gates control. house Tubular column tvne metal surport structure x Buried conduits with feeder con- 7 | i WWkuctors (new and dt! future) ¥ ? nd ' I ae Sub- : station |! if te Bus tie feeder con- " duit and conductors 1 . ay see figure 4-3 Tubular column type ', ' metal support Ve structure ‘il af ? ' ' pera u { ja x A|— er ! “ = Substation ae 2 Buried conduits with feeder conductors (new Luminaire for station and and future) switch illumination (typ.) k LL PLAN US Army Corps of Engineers Figure 4-5. Main electric supply substation, 46 kV minimum 4-11 TM 5-811-1/AFM 88-9 Chapter 1 oF oO —— “o> Battery Switchgear assembly 5, i. Buried conduit with incoming conductors fe— Battery charger Test rack t Fence, prounded, with % Sw. unit 2 a 33 personnel and vehicle 3 ~ gates 3 | 7. unit 4 : x Sw. uni >} 3 ; Ruried conduita with oS ee Q feeder conductors (new ee ee, eee ee a A and future) be. Br eal a ee ae 2 ~ ate eres 3 ¥ x ‘3 PLAN Concrete foundation Fence Switchrear assembly Gpana SECTION A-A US Army Corps of Engineers Figure 4-6. Main electric supply switching station, 35 kV maximum 4-12 TM 5-811-1/AFM 88-9 Chapter 1 CHAPTER 5 ELECTRIC DISTRIBUTION LINES 5-1. Selection. Criteria for electric distribution lines is based on the requirements of DOD 4270.1-M. a. Aerial line requirements. Aerial lines should be used in all areas, except in the following instances: (1) Where aerial lines would constitute hazards such as near flight lines (where poles must be outside of the glide path) or near munitions buildings (where poles can be no closer than the height of the pole carry- ing the line or 50 feet, whichever is greater). (2) Where aerial lines would obstruct operations (eg interfere with crane-type, materials-handling equipment). (3) Where aerial lines would interfere with high- frequency communication or electronic equipment (eg generally not within 250 feet of Communications-Elec- tronics-Meterological (CEM) Operation Buildings, not within 1,500 feet of receiving antennas, or not within 1,000 feet of other antennas). (4) Where aerial installations would conflict with current policy for Family Housing Areas. (5) Where areas have such high load densities that underground electric lines are economical, and under- ground installation is approved by HQDA (DAEN- ECE-E) for Army projects and HQUSAF/LEEEU for Air Force Projects. (6) Where aerial lines would be incompatible with the environment or architectural concept, and under- ground installation is approved by HQDA (DAEN- ECE-E) for Army projects and HQUSAF/LEEEU for Air Force projects. b. Underground line requirements. Underground distribution lines will be provided for the exceptions listed above, for minor extensions to existing areas served by underground distribution lines, and for medium-voltage or large low-voltage electric services to buildings. 5-2. Types of underground lines. There are two methods of installing underground lines. The first method consists of underground race- way systems (ducts) installed below grade in which ca- ble is pulled. Ducts may or may not be provided with concrete encasement, but where concrete encasement is specified, concrete should have a strength of not less than 2500 pounds per square inch when cured for 28 days, unless reinforced concrete is required. The sec- ond method consists of underground cable systems in- stalled directly in the ground. Cables may be integrally provided with extra protection such as coilable plastic duct or metallic armoring. Generally in this manual, the word duct will be used rather than conduit. a. Requirements for primary (medium-voltage) lines. Where underground systems are provided, the following standards will be followed: (1) In industrial and densely populated areas, ca- bles will be installed in underground duct lines with manholes. Ducts will be concrete encased. (2) In lightly populated areas, cable in noncon- crete-encased duct may be used. (3) The use of direct-burial cable should be lim- ited, especially the concentric-neutral type which has a history of corrosion problems. If the concentric-neu- tral type is selected, the cable should be specified to have an outer jacket to prevent corrosion whether di- rect buried or installed in duct lines. Other types of di- rect-burial cable may be installed only for long, un- tapped runs in lightly populated areas where the relia- bility requirements are low or the facilities served by the cables have a short-term life or for other reasons which would justify the use of the more economical di- rect-burial installations. b. Manhole and duct line systems. A manhole and duct line system provides the best available under- ground system. Such a system allows for growth and permits cost effective replacement of existing cables or cable terminations damaged by faults or made obso- lete by aging. Concrete encasement provides the cables with minimum susceptibility to damage and optimum safety to personnel. (1) Duct lines with concrete encasement. Medium- voltage power and communication cables should be in- stalled in concrete-encased ducts when justified. In- stallation of communication cables will usually be com- pleted by others. However, duct lines and power cabling will usually be installed under Government contract. (2) Duct lines without concrete encasement. Gen- erally low-voltage electric power and lighting system duct lines that cannot be installed in the same trench with medium-voltage or communication ducts should be installed without concrete encasement (direct-buri- al). However, concrete encasement for direct-burial ducts will be provided under paved areas, railroad tracks, and any other area where vehicular traffic war- 5-1 TM 5-811-1/AFM 88-9 Chapter 1 rants it. Direct-burial duct line systems may include handholes or concrete pullboxes. c. Cable systems. Cable systems consisting of cable suitable for direct-burial or integral cable in coilable plastic duct can be used where comparative costs make a cable system an economical acceptable alternative to an aerial system. Low-voltage direct-burial cable will be restricted to light loads, such as roadway and area lighting in areas where cable systems will be rarely dis- turbed. The use of direct-burial medium-voltage cable for primary feeders serving isolated installations is subject to the restrictions previously listed. Integral cable in coilable plastic duct is an alternative to direct burial when installation of direct-burial cable is consid- ered acceptable; however, such cable is available as a shelf item usually only for low-voltage insulations. The duct provides some mechanical protection and new ca- bles may be pulled in when necessary, but the cost is greater. 5-3. Types of aerial lines. Generally, bare conductors will be used for medium- voltage circuits and insulated conductors will be used for low-voltage circuit. a. Open wire medium-voltage construction. Bare wires will be installed on pole lines using either arm- less or crossarm construction. Armless construction, which is normally more economical, present a more pleasing appearance and therefore will be provided for new lines, except where prohibited by technical consid- erations. The use of crossarm construction for existing line extensions or pole replacements should be mini- mized. b. Insulated cable lines. Aerial insulated cables will be of the messenger-supported type. The use of self- supported insulated cable or of messenger-supported insulated cable with insulated spacers is not recom- mended. (1) Medium-voltage lines. Such construction is ad- visable where it is necessary to avoid exposure to open wire hazards, for example, high reliability service in heavy storm areas. Cable will be of the preassembled type, factory attached to the messenger. (2) Low-voltage lines. Normally low-voltage lines will be of the neutral-supported secondary and service drop type which uses a bare messenger as a neutral wire and as a support for insulated phase conductors. Weatherproof conductors (line wires), which are nor- mally supported on secondary racks, are less attractive and more expensive to install than neutral-supported cable. Use of secondary-rack construction should be limited to minor extensions of existing systems. 5-4. Voltage drop. Normal allocation of voltage drops will not exceed the values shown on figure 5-1. The maximum allowance 5-2 of 12.5 percent from the main electric supply station to the point of utilization is based on ANSI C84.1 re- quirements. The voltage drops shown for utilization transformers on figure 5-1 are extremely conserva- tive. Transformers having impedances of 5.75 percent and operating at 90 percent power factor will have a voltage drop of about 3 percent when fully loaded and less than 2.5 percent for a 75 percent loading. On mul- tiple lighting systems, maximum voltage drop from the transformer secondary to the approximate center of the load will not exceed 10 percent. 5-5. Power factor correction. System power factor is influenced mainly by the characteristics of the motors supplied. Such character- istics can vary widely and therefore the kvar capacity cannot be correctly estimated at the time of the distri- bution system design, but only after firm data is avail- able. Generally, a year’s operating history is needed be- fore the amount of fixed and switched capacitance can be selected to best meet actual operating conditions. Large motors are often provided with integral capaci- tors. a. Capacitor justification. In general, capacitors are justified when amortization of the installation can be made in accordance with DOD criteria. An example of computing the average energy savings per year is shown on figure 5-2. This yearly savings is then com- pared to the annualized costs of the capacitor installa- tion using current DOD amortization methods. Where a serving utility does not have a power factor clause, only line losses will apply. b. Capacitor equipment. Capacitors for overhead distribution systems can be pole-mounted in banks of 300 to 1,800 kvar for most medium-voltage systems up to 35 kV phase-to-phase. Pad-mounted capacitor equipment is available in the same range of sizes and voltage ratings for underground systems. Generally power capacitor equipment should have grounded wye connections so switch tanks and frames will be at ground potential for greater personnel safety. Grounded capacitors can bypass some line surges to ground, provide a low impedance path for harmonics, and group fusing need not be so precise. For maximum efficiencies, capacitor equipment will be located as close to the load controlled as is feasible. Surge ar- resters should be specified to limit the magnitude of voltage surges caused by capacitor switching. Applica- tions of surge arresters will be consistent with guidance contained in industry standards. c. Capacitor control. Switched capacitors should be provided only when differences between full-load and light-load power factors warrant such control. The load and power factor profile of the system will deter- mine the economics of switched control, and whether there is a necessity for more than one switching step. Percent voltage drop allowance 22.5 10 —— Industrial Residential (large loads) US Army Corps of Engineers (small loads) TM 5-811-1/AFM 88-9 Chapter 1 Main electric sunnlv station pover transformer E Primary feeder Nistribution transformer Secondary feeder Service entrance equinment Service conductors | aaa Mtilization transformer Branch circuits Point of utilization Figure 5-1. Normal allocation of voltage drop Time clock control is the least costly type of control, but can only be used where power factor and demand vary on a firm time basis. Voltage control is used where objectionable voltage changes occur with vary- ing voltages. Current control is used when loads change, but voltage is well regulated or load power fac- tor remains substantially constant. Current control is effective also when power factor varies in a predict- able manner with the load. Kilovar control is used when load voltage is regulated, but power factor varies in an unpredictable manner to corresponding load variations. More sophisticated current and voltage control than that covered by IEEE 18 can be provided, and manufacturers should be consulted for application and specification information. An expanded discussion on the application of shunt capacitors and their con- trol is contained in REA Bulletin 169-1. 5-6. Primary circuits. a. Number. The number of primary circuits should be determined on the basis that each circuit must be capable of serving the load over the required distance without exceeding the allowable voltage drop. Generally, copper or copper-equivalent conductor sizes will range from No. 2 AWG to No. 4/0 AWG for aerial circuits and No. 1/0 AWG to 500 kemil for under- ground circuits. (1) Quick check values. Table 5-1 has been pre- pared to allow a quick check of the capacities of three- phase primary circuits at 0.90 power factor by giving the approximate kilovolt-ampere-mile loading for a 3 percent voltage drop. For voltages not given, the use of a factor of the square of the ratio of the desired voltage divided by the known voltage times the megavolt-am- pere-miles will provide a sufficiently accurate determi- 5-3 TM 5-811-1/AFM 88-9 Chapter 1 Main electric supply station Load = 4,000 kW at 0.82 pf TN. Provide 900 kvar capacitor to raise nD pf to 0.90 5 miles No. 4/0 AWG copper 13.8 kV SINGLE LINE DIAGRAM ASSUMED UTILITY RATES Energy charge Losses = VR = $0.035 per kWh = 1.35 kW Power factor clause credit = 0.001 times value in percent that power factor (pf) is raised above a stipulated amount. = $110 a year = $2,690 a year Cos @ = 0.82 T1i7 _amps [2,792 kvar 204 amps 4,878 kVA! Without capacitor Cos @ = 0.90 167 amps 81 amps 1,937 kvar With capacitor VECTOR DIAGRAMS | CALCULATIONS = [(204 - 186) amperes] 2 x 5 miles x 3 conductors x 0.278 ohms per mile Line loss savings = 1.35 kW x 0.6 load factor x 4,000 hours x $0.035 Power factor savings (increase 82 percent to 90 percent) = 4,000 kW x 0.6 load factor x 4,000 hours x $0.035 x[ 0.001 x 8] Total Savings = $110 + $2,690 = $2,800 a year US Army Corps of Engineers Figure 5-2. Average energy savings example nation. For instance, taking the value for aerial No. 4/0 AWG copper at 25 kV or 29.2 megavolt-ampere- miles and multiplying by (35/25) ? gives a value of 57.2 megavolt-ampere-miles which is almost the value given in table 5-1. For underground circuits, where proximity effects apply, a greater variation will be en- countered, but estimated demand loads are probably within the same accuracy range. (2) New feeders. For new installations, with esti- mated demands based on requirements covered in chapter 2 and estimated feeder lengths based on the site plan, a determination of circuit requirements can be made. Normally, feeders should be large enough to allow a growth factor of 25 percent of the design maxi- mum demand. (3) Existing feeders. Circuit capability should be determined by measuring loads over a suitable period 5-4 of time. Where such information is unavailable, knowledge of the station maximum demand and over- all transformer capacity can permit determining an in- stallation’s demand factor on the basis of overall con- nected transformer capacity. Circuit capability can be roughly evaluated by totaling the transformers con- nected to the feeder and applying this factor; however, this method is too inaccurate as a basis for justifying new feeders or adding large loads. 6. Arrangements. There are many arrangements of distribution circuits, but only the radial, loop, and selective types shown on figure 5-3 are discussed here. These circuits are generally the most suitable for the type and distribution of loads encountered on military installations. The radial system costs the least to in- stall. The cost of a selective system can be equal to or somewhat more expensive than the cost of a loop sys- TM 5-811-1/AFM 88-9 Chapter 1 Table 5-1. Three-Phase Primary Circuit Loading Check Values * Wire Voltage size AWG 4.16kV 13.8kV 25kV 35kV or Maximum Megavolt-ampere-mile » Type of line Material kemil amperes (Maximum megawatt load) og Nn 0.8(3.1)....... 8.8(10.3).....29.2(18.7)..... 57.3 (26.2) PAOD «oss O68): et. C2-TDT..'.s Zee 14 0). es. 44,1 (19.6) oe |) ee 0.5 (2.0)... « DOB): « 6:4. 19-5024);.... 38.1 (16.9) Copper PO is: 0.5 (1.7). 6:1(.638); ; .=:; 16.5 (10.5)... .. 32.3 (14.7) BUG s sing 0.4 (1.5). 43(49)....:5 1410 8.8)...3.35 27.6 (12.5) oe ED ie 0.3 (1.2)... « SOC BS)... SBC UO. a. 19.2( 9.8) £80), . od 0.2 (0.8). 2.0( 2.8). GC B,1).. 20.» 13.1( 7.1) Aerial lines ° $805 5 3. 0.8 (3.4). 9:8 (ETA): «2% 30.4 (20.7)..... 59.8 (28.9) or. eee 0.5 (2.2)... « BOC %8).5 1ws IDA IBS). 5.0 «s 38.0 (18.5) ACSR oe 0.5 (1.9). 6:0 Gop =... LOCI): :.... = 32.7 (16.4) HO oie. 0.5 (1.8). 4.4( 5.8)..... 14.4 (10.5)..... 28.3 (14.7) oF 28095 6 <1 0.3 (1.5)... Bet 49); «ve LZB O90)... . 23.9 (12.5) 200 55 0.2 (1.2). 2.7( 3.9) 8:9 7:0). 2c; 17.5( 9.8) MBG os <2hs Ass ome su so 26.0(10.0)..... GELS): tines so ma ss ge ee Copper Pcs ale erie «oat DOC AO)... (ZAR DO). a. 030.055 tos wis o bce woe Underground lines 4 Bsa: cot saa MLA ene cg FA BCBG) oc sin BUDO) o.oo os tose wre wes Aluminum i 9:8( 4.9)... ..81.8@9.0)... WO... DAC BB)ias cag EEOC OM: os 56: aus + 3518 ore ae ® For balanced loads. > For loads having a 90 percent power factor this value represents a 3 percent voltage drop. The values given in parenthesis represent the megawatt capacity of the wire and values were computed using the method shown on figure 12-1. ¢ Based on values from Standard Handbook for Electrical Engineers (Eleventh Edition) for 60 Hz circuits approximately 75 percent loaded and operating at a temperature of 50°C and an equivalent spacing of 5 feet. 4 For conductors operating at 40°C. tem, dependent upon the physical layout. (1) Reliability and availability. The system pro- vided should be commensurate with the degree of re- liability or availability required by the mission or use of the facility. Reliability is defined as the ability of an item to perform a required function under stated conditions for a stated period of time. Availability is defined as the fraction of time that the system is actu- ally capable of performing its mission. IEEE 493 dis- cusses reliability and availability determination in greater detail. The failure factors shown in table 5-2 show the relative impact of a failure at various system components. (2) Economic justification. The additional cost re- quired to install loop or primary selective systems must be justified. Individual components such as loop or selective switches at transformers should be consid- ered where the project will need increased reliability in the future. Special cases, involving large demands or high reliability requirements, may make the installa- tion of two sources of supply advisable. Hospital pri- mary circuit arrangements will be in accordance with the requirements of TM 5-838-2 or AFR 88-50. c. Automatic circuit reclosers. Chapter 4 covers provision of reclosing relays on outgoing feeder circuit breakers at a main electric supply station. Where a re- closing relay on a station circuit breaker does not pro- vide a protective zone which covers an entire feeder be- cause of circuit length and impedance, automatic cir- cuit reclosers may be necessary remote from the sta- Table 5-2. Primary Distribution System Statistical Reliability Constants ¢ Mean time Mean time Failures between failures to repair Component Unit per year years hours IRISH Se REIDY F066 ses pie TVW Siacwcpo 6:0 o'nieae cesene serie Bae 08 .co.chs oivg Oe 5: dle imal Se 1.56 1.33 Aerial lines ....... i 0.0998 . on Ose 4.6 Underground cables . . 0.0326 BOM. 20.4 SUIHMIRMESMINEEB Oe da acs Siwo yy obs cscs ace genet afs cos 6 SCH sss cx as eats 0.0030 333-1/3, 382 or 74.3> ® This material is reproduced with the permission of the Institute of Electrical and Electronic Engineers from an IEEE Committee Report en- titled “Report on Reliability Survey of Industrial Plants, Part I: Reliability or Electrical Equipment” from the March/April 1974 issue of IEEE Transactions on Industry Applications. > First number is time to repair failed unit, a second number is time to use. replace with a spare transformer. Times are for industrial not utility 5-5 TM 5-811-1/AFM 88-9 Chapter 1 en "—~Main electric supply station bus anne ates _ a S5SSS . TTT TF e, Radial primary 2 feeder Fuse cutouts where required To other ) Load center g load centers POOREST AVAILABILITY - RADIAL SYSTEM Load center =f Mata electric supply station bus | Lee Seen of Ten poe 7° 99 J feeder pT poet pa eS INTERMEDIATE AVAILABILITY - LOOP SYSTEM Main electric supply station bus 4 He Load center € 5 > 9 ? ) Dual primary feeders Fuse cutouts where required @ To other load centers GREATEST AVAILABILITY - SELECTIVE SYSTEM US Army Corps of Engineers Figure 5-3. Primary distribution arrangements commonly used tion. This application of automatic circuit reclosers will be provided only to protect the aerial portions of the feeder, and only when reclosing is also provided on that feeder at the main electric supply station. d. Connections to transformers. Normal trans- former circuit design will eliminate most circuit ele- ments which produce the destructive voltages which can arise from ferroresonance. (1) Overvoltage. Ferroresonant overvoltages occur when the ratio of the distributed line-to-ground capacitance (Xc) in series with the transformer magne- tizing (no-load) impedance (Xm) is nearly equal and the effective resistance in the circuit is minimal (almost no load connected to the transformer). At such times the circuit may be near resonance resulting in a total cir- cuit impedance close to zero. Under these conditions, a high current will flow and cause correspondingly high voltages. (2) Overvoltage prevention. Destructive overvolt- ages do not occur when group-operated switching is provided. Pole-mounted transformers are normally switched so close to transformer terminals that there is not sufficient line capacitance for resonance. Blow- ing of one fuse in a line should not be a problem, be- cause the transformer is loaded at that time. Very rarely are aerial lines long enough to provide enough capacitance to cause ferroresonance. (3) Occurrence. Ferroresonance may occur on long underground circuits which are single-pole switched. TM 5-811-1/AFM 88-9 Chapter 1 Since the occurrence of ferroresonance cannot be relia- bly predicted, group-operated switches are required for ground-mounted transformers. e. Transition points. Normally transition points be- tween aerial and underground sections (riser poles) will be provided with primary fuse cutouts and surge arresters for protection of the underground cables and cable-supplied equipment. When the underground service supplies two or more transformers, some of which may be remotely located, fuse cutouts will be of the load-break type. When the underground feeder supplies only one transformer installation in the im- mediate vicinity of the riser pole, nonload-break fuse cutouts may be acceptable. Where the capacity of the line is more than the maximum ampere rating of fuse cutouts, power fuse units will be installed. Installation of lines having an ampere rating above that of power fuses will be avoided, since more expensive protection devices such as those covered in chapter 4, will be nec- essary. Group-operated load-break switches used for sectionalizing aerial-to-underground connections can be either integrally fused or nonfused devices. Over- current protection of some form is necessary to protect underground cable systems. Group-operated load- break switches at transition poles are not justifiable solely on the basis of preventing possible ferro- resonance, since such switches at ground-mounted transformers will probably eliminate most causes of transformer ferroresonance. 5-7 TM 5-811-1/AFM 88-9 Chapter 1 CHAPTER 6 AERIAL DISTRIBUTION LINES 6-1. General. Aerial lines will be provided in all areas as established in chapter 5. In order to use the same poles for both aerial distribution and roadway lighting and to avoid interference with possible future projects, pole lines normally will be installed adjacent to roadways. a. Symbols and codes. For uniformity, symbols shown on figure 6-1 will be used. Installation will comply with the requirements of the National Electri- cal Safety Code (NESC) for Grade “B” construction. The loading district will be that applying to the loca- tion of the installation. Where state safety rules are predominantly accepted, such rules may be used pro- vided they are essentially at least as stringent as those of the NESC. 6. Circuit configurations. Typical circuit configura- tions and details are provided later in this chapter as a general guide in the design. In addition, such publica- tions as the Rural Electrification Authority (REA) Bul- letin 160-2 or Fink and Beaty “Standard Handbook for Electrical Engineers” may be helpful. c. Other conditions. Unusual service conditions are covered in chapter 1. Special items such as overhead ground wires, grounding, and surge protection are covered in chapter 9. Other conditions should follow the guidelines established by the NESC, the Rural Electrification Authority (REA), or the local utility as applicable. 6-2. Installation considerations. Spans for aerial lines in built-up areas will be 150 to 200 feet. In sparsely settled areas, increased spans may be more economical. Normally not more than two medium-voltage circuits will be installed on one pole. Switches to facilitate the transfer of load should be provided where circuitry makes this provision econom- ically justifiable. 6-3. Conductors. a. Sizes. Because of physical loading problems (ice and wind) as well as maintenance considerations, con- ductor sizes will be limited generally to a maximum of No. 4/0 AWG copper or equivalent aluminum. The economical minimum conductor size for circuits serv- ing built-up areas is No. 2 AWG hard-drawn copper or equivalent aluminum. For small, isolated loads a mini- mum size of No. 6 AWG copper equivalent will be used. 6. Material. Aluminum-conductor-steel-reinforced (ACSR), aluminum alloys, and hard-drawn copper (CU) are used for medium-voltage lines. Low-voltage con- ductors normally will be of aluminum alloys with ACSR messengers or of copper. (1) Types of aluminum alloys. In their standards and data publication, the Aluminum Association recognizes three alloys of aluminum as suitable for electric conductors. All-aluminum-conductors, former- ly known as hard-drawn aluminum or EC grade are now designated as alloy 1350-H19 and the acronym to be used will be AAC. This alloy with a 61 percent cop- per conductivity is not a preferred type because of the alloy’s low inherent tensile strength. The intermediate strength (5005-H19), alloy will not be used since the conductivity is only 1 percent greater than the high- strength alloy. The high-strength 62011-T81 (acro- nym AAAC) alloy with a 52.5 percent copper conduc- tivity is often used as a substitute for ACSR where problems of corrosion have resulted because of the combination of both aluminum and steel in ACSR con- ductors. (2) Use of other conductors. Special conductors such as copper-clad steel may be used where the appli- cation warrants. Conductor selection, where corrosive or salt-laden atmospheres are encountered, may re- quire investigation. The determination of acceptable conductors for special atmospheres will be based on evaluations which will consider local utility practices. Table 6-1 indicates physical properties of conductors for commonly used materials. c. Conductor insulation. Most medium-voltage con- ductor installations use bare conductors. Where the use of insulated cable has been justified for medium- voltage lines, the insulation will conform to the re- quirements applying to underground conductors covered in chapter 7. Messenger wire composition and weatherproof covering, for low-voltage lines will be in accordance with applicable International Power Cable Engineering Association/National Electrical Manufac- turers Association (IPCEA/NEMA) requirements. d. Sags and tensions. The maximum tension in a span is limited by the strength of the wire and its sup- porting elements. ANSI C2 permits conductor sags, such that for ice and wind loadings applying, the ten- sion of the conductor must not exceed 60 percent of the conductor’s rated breaking strength. Also, the un- loaded tension at 60°F must not exceed 35 percent of TM 5-811-1/AFM 88-9 Chapter 1 Existing to be Existing removed to remain New iy ° ® ty a x a ee — ty A . 500 MY A & 342 246 SPA ————— mmm Pole, type (i.e. wood, metal, concrete) length and class as indicated Roadway light Down guy and anchor, strength in pounds as indicated Aerial mounted transformer(s), single phase unless otherwise indicated. Number and rating in KVA as shown phase unless otherwise indicated. Ground mounted transformer, three Rating in KVA as shown | __KV primary line, number and size of wires as indicated V secondary line, number and size ‘OF wires as indicated Where many aerial lines occur and space is limited or when a conflict with other symbols might result, the different combination symbols below can be used. —G,L,P,S,W— Aerial line "G" denotes overhead guy (span) "L" denotes lighting circuit "Pp" denotes primary circuit "Ss" denotes secondary circuit "w"' denotes overhead ground wire “this material fs reproduced with the permission of the American National Standards Institute from the ANSI Standard entitled "Graphic Symbols for Electrical Wiring and Layout Diagrams Used in Architecture and Building Construction," ANSI ¥32.9, copyright 1972. work status, Modifications have been made as necessary to indicate Figure 6-1. Symbols for aerial electric distribution the rated breaking strength before any load is applied and must not exceed 25 percent after full loading has been removed. Thus both under normal and maximum ice and wind conditions, any conductor will not be loaded beyond limits of safety. In some areas, it may be common practice to reduce the maximum loaded tension to 40 percent or less. 6-2 (1) Initial sags. Typical initial stringing sags are given in table 6-2 for various conductor materials, sizes, and loading districts for a 200-foot span, since this is a commonly used ruling span. For other ruling spans, manufacturers should be consulted. A ruling span is an assumed “design span” that assures average tension throughout a line of nonuniform span lengths TM 5-811-1/AFM 88-9 Chapter 1 Table 6-1. Conductors Materials—Physical Properties Size Rated Number Diameter Weight Area breaking Conductor ASTM of inches lb/ft in? strength Code material * standard kemil strands D. W. Ac lb word 26.2 se O02 0 280 Ob.7 yi: ..- 0.033 ... 1,940 cu Bl C64: 3:5 ... 0.052 ... 3,042 (copper, hard-drawn) or 838.7 «5% .-. 0.066 .. . 3,804 E=17x 108 B8 +2 106.6 sx. ... 0.083... 4,752 X=94x 10° RMA os ... 0.105 .. . 5,926 217.6) 544 .. 0.166... 9,154 AAC 66.4... ... 0.052 ... 1,850 Tris (all-aluminum- §- LOBE ev, . 0.083 ... 1,990 Poppy conductor, oc ABEL'S} ... 0.105... 2,510 Aster 1350-H19) B231 LOT aes -+- 0.132 ... 3,040 Phlox E=10x 108 S2Th6.-¢. . +. 0.160... 3,830 Oxlip X=128 x106 336.4 . . - 0.264 ... 6,150 Tulip AAAC Tt? ... 0.061... 2,800 Ames (all-aluminum- ABB O iad 5 ...0.097... 4,460 Azuza alloy-conductor, + 155.4... itis O822 1: 5,890 Anaheim 6001-T81) B399 Ree es, ...0,154... 6,790 Amherst E=10x10° - 246.9... -..0.194... 8,560 Alliance X= 128x104 394.5... . 0.310... 13,300 Canton ACSR ° Bit ave 66.4... ...0.061... 2,850 Sparrow (aluminum-conductor- me TO Oe eR ae set ...0.097... 4,380 Raven steel-reinforced) B232 ee te eM ices «SON ws 8s eras OME Ha 2 art's ...0.122... 5,300 Quail E=11.5 x106 f10TS ...”. nes ... 0.154... 6,620 Pigeon X= 105x104 9 UG iy OAs wis cays OF .. 0.194... 8,350 Penguin BAB AAS AEN | aisssccas 0.720 . 0.307 ... 14,100 Linnet *E = final modulus of elasticity in lb/in 2, X = final coefficient thermal expansion per degrees F. > Size of AAAC is approximately 15 percent larger than ACC to give equivalent current-carrying capacity. © Strength given for ACSR/GA. First number denotes number of aluminum strands, second number denotes number of steel strands. US Army Corps of Engineers between deadends and can be calculated exactly by the following equation: Si+Si+S3....... st % Ruli = —— is ors [é +S.+8;....... S, ro Use of the approximate formula, which is not given, can introduce errors of as much as 20 percent. The large variations in temperatures, wind, and ice condi- tions encountered at various military installations makes it extremely important that conductors be properly sagged. The copper-equivalent sizes, given in table 6-2, are based generally on assuming that alumi- num conductors two sizes larger than copper are equivalent in ampacity. (2) Final sags and tensions. The final loaded ten- sion data shown in table 6-3 indicates final loaded ten- sions and sags for conductors which were initially strung to the sags of table 6-2. Sags are a maximum at the indicated loading conditions. Tensions will be less at higher temperatures when wind and ice loads do not apply (final unloaded conditions). (3) Unusual loading conditions. The National Electrical Safety Code stipulates loading and installa- tion requirements for normal conditions, as shown in table 6-3; however, many areas will be subjected to cli- matic conditions much more severe than those listed, in respect to both wind and ice loads. In these in- stances, a complete analysis will be required to deter- mine acceptable sagging versus strength. An example of an aerial conductor strength analysis is given in chapter 12. 6-4. Poles. a. Types. Solid wood poles are ordinarily used for electric distribution lines, while concrete and steel poles are more often used for roadway or area lighting circuits carried underground or separately from distri- bution lines. Concrete or steel poles may be justified for medium-voltage distribution circuits where wood poles do not provide adequate strength, or where cli- matic conditions cause wood poles to deteriorate rapid- ly. Use of laminated wood poles is not recommended; however, in some instances the surrounding environ- ment may make their installation appropriate for roadway and area lighting applications. (1) Wood poles. Solid wood poles are covered by ANSI 05.1. Pole strengths are designated by classes 1 through 6 for normal strengths and H1 through H7 for 6-3 TM 5-811-1/AFM 88-9 Chapter 1 Table 6-2. Initial Stringing Sags for 200-Foot Spans Stringing temperature Conductors 30°F 60°F 90°F Loading districts AWG Light Medium Heavy Light Medium Heavy Light Medium Heavy Material copper (aluminum) Stringing sag feet ph aa etna 2.0 AO) sip kin 2B es acs 5 26 1G) es sai Ora 2.5 4/0(336.4) OT eens BID i srs 1.3 OFF cue cs TOs om se 14 BO isla. cd pbs eee 2.6 BB ag Genial A esvvet asta 2.7 2/0(4/0) Ul ie 5 be v9 OD se cere xe 1.3 OD ay acs is V2 ss aes 1.4 BO! ease BBs Puss: 26 e's eis Benn inse 3.3 1/0(3/0) OF sak ot Cais te 13 OD) 6 sass a 12) 14 2.0) Si.05 3 26). mists 2.6 bh lies dag 3.8 1(2/0) OM hes ODE sa 7% 1.3 OS i a. a2 ee 13 20) sie 28 sb inse 2.6 Li avtews QA i sidasn 48 2(1/0) Gr nase OS tna 1.1 Orcs es De ee ot SS wctoan Sei 3.8 BB cia sep DAs sais +n 6.7 4(2) 0:6 2.53.5 OB ss ass 1 Oo akan ee 1.0 BO) vert Shire sisrocts - he 28.533 5.0. 04s 10.2 6(4) 0.6) 52.358 OB ict ees 24 GO os ga OO janis 2.0 US Army Corps of Engineers higher strengths. These classes establish pole circum- ference limitations for each class and species of wood. (2) Concrete poles. Normal reinforced concrete poles are usually not strong enough for the wind and ice loads which prevail in some areas. Either cen- trifugally spun or cast, prestressed concrete poles are acceptable, but special pole design, based on calcula- tions of pole loads, will be necessary to assure ade- quate strength. Where strength requirements dictate excessive concrete pole diameters, steel poles should be used. (3) Tapered tubular metal poles. Galvanized steel poles are covered by NEMA TT 1, but no classes are given. Generally aluminum poles are not acceptable, since corrosion may be a problem and aluminum poles usually do not provide adequate strength. b. Lengths and strengths. Pole lengths will be se- lected conservatively, making allowance for the instal- lation of communication lines and the required pole 6-4 setting depth. Communication space will include al- lowance for telephone lines, and may include allow- ance for fire alarm, television, or other signal circuits as may be required. If at the time of design, exact re- quirements cannot be determined, a 2-foot space allo- cation is ample and will be provided on all poles even though present plans do not include telephone lines. Longer poles will be provided in areas where the fu- ture installation of additional electric circuits and equipment can be reasonably expected. Pole strengths will meet the NESC requirements for grade “B” con- struction for the applicable loading district. Since the normal maintenance activity does not have the finan- cial or personnel capabilities of a utility, it may be nec- essary to use pole strengths greater than code mini- mums. Table 6-4 indicates pole lengths and classes (strengths) which are considered the minimum for nor- mal use. Generally poles less than 45 feet in length will not be installed for primary (medium-voltage) TM 5-811-1/AFM 88-9 Chapter 1 Table 6-3. Final Loaded Tensions for 200-Foot Spans Loading districts Conductors Light Medium Heavy 9 lb/ft ? horizontal wind 4 lb/ft horizontal wind 4 lb/ft ? horizontal wind AWG no ice 1/4-inch radial ice 1/2-inch radial ice Material copper 30°F 15°F O°F (aluminum) Tension Sag Tension Sag Sag Ib ft Ib ft ft a a a 4/0(336.4) 1.9 2.2 2.8 1.0 1.4 2.0 1.0 14 1.9 a a a 2/0(4/0) 2.1 2.5 3.3 12 1.6 2.4 1.2 ea 2.4 a a a 1/0(3/0) 1.9 2.7 4.0 1.3 1.8 2.7 1.4 1.9 2.7 a a a 1(2/0) 2.3 29 4.5 14 2.1 3.0 1.5 2.1 2.9 a a a 2(1/0) 2.4 3.2 5.5 1.5 2.3 3.2 1.5 2.3 3.2 a a a 4(2) 2.7 4.1 15 1.8 2.9 4.0 1.8 2.8 3.8 a a a 6(4) 3.0 58 10.9 2.0 3.6 5.5 2.1 3.4 5.2 ® Sag for CU not available. US Army Corps of Engineers lines. The required pole embedment is dependent upon the loading district and upon soil conditions. A pole length and strength calculation is shown on figure 12-5. Table 6-4. Minimum Primary Wood Pole Lengths and Classes Type of pole MERI DOU NEL ahe'g dress tsgie fiyec ages wna & NR ee eae ore dent en ese po ee eee res US Army Corps of Engineers 6-5. Circuit configurations. Preferred and alternate configurations for tangent construction are shown on figure 6-2. Also shown on this figure are methods of mounting overhead ground wires and locations for primary neutrals when re- quired. Primary insulation shown on the figures in this chapter is for a nominal 15 kV class. a. Primary (medium-voltage) circuit configurations. Armless and crossarm mounting are both used for open wire lines. Armless mounting as shown on figure 6-3 is preferred for open wire circuits because of its more attractive appearance and lower maintenance cost. REA Bulletin 61-12 provides additional details on armless construction. Triangular tangent construc- tion requires the least pole space and is the most economical. Where such a configuration is not suit- able, because of special requirements such as the need for an overhead ground wire, vertical tangent con- struction will be provided. Requirements for overhead ground wires are covered in chapter 9. Crossarm con- struction as shown on figure 6-4 will be limited to equipment installations, or where use of armless con- struction would result in excessive pole heights. (1) Angles at which guying is required. Guying re- 6-5 TM 5-811-1/AFM 88-9 Chapter 1 -- Overheac ground wire on suspension clamp, where required Overhead ground wire on bayonet, where required Brackets where required to provide climbing space Primary neutral, where required Primary neutral, where required Secondary line cable, Neutral supported rack supported secondary cable ELEVATION ELEVATION PREFERRED CONFIGURATION ALTERNATE CONFIGURATION US Army Corps of Engineers Figure 6-2. Tangent construction configurations 6-6 TM 5-811-1/AFM 88-9 Chapter 1 Climbing Climbing Guy locati ) on 10°. to:15° inascations/4 TRIANGULAR VERTICAL a AND MINOR ANGLE TANGENT AND MINOR ANGLE INTERMEDIATE ANGLE @ Climbing | space Climbing space *x” CONNECTION @ "LE CORNER US Army Corps of Engineers Figure 6-3. Armless primary configurations TM 5-811-1/AFM 88-9 Chapter 1 Guy location / indication ~ MINOR ANGLE INTERMEDIATE ANGLE \ "LC ANGLE "T’ CORNER "x" CONNECTION @ US Army Corps of Engineers Figure 6-4. Crossarm primary configurations 6-8 quirements for other than in-line circuits are de- pendent upon the angle of deviation, the size of the conductor, and the loading district. REA pole details show guys for angles of deviation greater than 2° on their armless construction configurations, regardless of conductor size or loading. Local practice may permit larger angles for smaller conductors or vertical con- struction, but any pole where the angle of deviation of the line exceeds 5° will be guyed. This requirement ap- plies both to armless and crossarm construction. (2) Angles at which changes in configurations ap- ply. The degree to which the more rigid line-post or pin type insulator support can be used will also vary de- pendent upon the angle of deviation and the size of the conductor. Suspension insulators can be used for any angle, but are usually a more expensive installation; therefore, their use should normally be required only when the line-post or pin type is unsuitable. Normal angles for armless configurations are shown on figure 6-3 and are in line with REA pole details. Table 6-5 indicates normal angles for crossarm configurations related to conductor size. Table 6-5. Relationship of Crossarm Configuration to Conductor Size * Maximum Tangent Minor Intermediate conductor size angle “A” angle “B” angle “C” AWG degrees degrees degrees Os cokes 55) Se POR sig 3 rn ious» BES. ccna tn 5-45 Mess can cueeatl DPD nase sis tomes br Sis i stae.s si 9-45 » eer. rts aid 6 vd i aes CE aa ies cow 13-45 Gis i aces cae ee TOE... oct ie 25-45 “Credit: US Corps of Engineers. Angles “A”, “B”, and “C” are shown on figure 6-3. b. Secondary (low-voltage) circuit configurations. Secondary circuits are supported generally by clamp- ing the bare neutral wire of an neutral-supported secondary aerial cable to a spool/clevis insulator as- sembly as shown on figure 6-5 or by use of spool insu- lators on secondary racks supporting insulated line and neutral conductors. Because of both the space re- quirements and the unattractive appearance, line con- ductors supported on secondary racks will be limited to special circumstances. 6-6. Insulators. The operating performance of aerial lines is dependent upon the quality of the line insulators. Insulators will be of the wet process porcelain type; the only presently acceptable alternative in an appropriate situation is toughened glass, which is an industry standard only for suspension insulators. Glass is much more suscepti- ble to shattering than porcelain; so where vandalism is a problem, glass should not be permitted. Polymer in- sulators have some advantages such as light weight and resistance to vandalism; once industry standards TM 5-811-1/AFM 88-9 Chapter 1 are issued, use of polymer units should be considered. Insulators need to provide ample mechanical strength for the expected ice and wind loads and must be capa- ble of withstanding the stresses of lightning and switching surges without dropping the conductor. Operating stresses are increased under atmospheric conditions which causes pollutants to build up on the insulator surface. Various types of insulators are manufactured to meet requirements imposed by dif- ferent applications. Each type is industry rated by ANSI in classes which establish dimensions and mini- mum electrical and mechanical performance values. a. Types. Line-post or suspension insulators will be used for medium-voltage circuits; spool insulators for low-voltage circuits; and strain insulators for insulat- ing guy wires. In crossarm construction, pin insulators may be used as a designer’s option, but line-post insu- lators are superior in operation to corresponding pin types since line-post units are stronger, more resistant to vandalism, and inherently more radio-interference- free. b. Classes. Selection of the class used is dependent upon operating voltage and degree of atmospheric pol- lution. Long periods without rain to wash off insulator contamination tend to aggravate the pollutant build- up problem. Selection of suitable insulator ratings will be based on local practice. Where lines are to be con- structed on existing Government installations, that in- stallation’s experience or that of the serving utility should determine the insulation level used. c. Dimensions. Figure 6-6 indicates dimensional ranges of insulators used. ANSI suspension Classes 52-3 and 52-4 have the same electrical, mechanical, and overall dimensions; but Class 52-3 has a ball-and- socket connection Class 52-4 has a clevis eye connec- tion. Selection of the type of connection provided is generally a matter of individual preference. Line-post insulators shown are either tie-top or clamp-top. The only difference between Class 57-1 and Class 57-11 is that Class 57-1 denotes a tie-top and Class 57-11 de- notes a clamp-top. Generally tie-tops can be used for angles up to 2° and clamp-tops are necessary for an- gles greater than 15°. For angles of 3° to 15°, choice will be dependent upon mounting and loading require- ments. Tie-top units are less expensive in cost, but a clamp top eliminates both material and labor costs for the tire wire thus providing ease of installation. Where horizontal mounting is required there is, at present, no ANSI class; specifications therefore will indicate elec- trical, mechanical, and overall dimensions are the same as for the appropriate 57 subclass. Insulators with short studs (S) are used on armless configura- tions; those with long studs (L) are used on wood cross- arm configurations. d. Colors. Insulator colors generally available are brown and light gray. Normally light gray insulators 6-9 TM 5-811-1/AFM 88-9 Chapter 1 Quadruplex 4-Guy location neutral- indication supported aerial cable Tie wire Bare neutral | ‘Insulated phase wires | TANGENT MINOR ANGLE "L' CORNER | @ Climbing Quadraplex aerial cable Note: A maximum of two service drops connected at same point are permitted and drops shall be attached so they are in a straight line. "T CORNER x’ CONNECTION SERVICE DROP @ US Army Corps of Engineers ——= Figure 6-5. Neutral-supported secondary cable configurations 6-10 US Cle,is eye 6-1/2" max. dia. SUSPENSION, CLASS 52-2 Ball and socket (52-4 same except witn cleyis eye) a 10-3/4" max. dia. | SUSPENSION, CLASS 52-3 3-1/8" dia. SPOOL, CLASS 53-2 4" dia. SPOOL. CLASS 53-5 Army Corps of Engineers 3-1/2" GUY STRAIN, CLASS 54-1 6-3/4" 3-1/2" ao 4 SE GUY STRAIN, CLASS 54-4 4-3/4" dia. PIN, CLASS 55-3 \ 9-1/2" PIN, CLASS 56-4 Figure 6-6. Ranges of insulator dimensions 6-3/4" dia.+ TM 5-811-1/AFM 88-9 Chapter 1 5-1/2" dia. 3-3/4" + aids with short stud for offset bracket or direct armless mounting LINE POST, CLASS 57-1S 6" dia. —12" + Tie-top with long stud for wood crossarm mounting LINE POST, CLASS 57-2L ¢r16-1/2"+ Clamp-top for vertical mounting LINE POST, CLASS 57-13 7-1/4" dia. + Clamp-top for horizontal mounting LINE POST SIMILAR TO CLASS 57-14 6-11 TM 5-811-1/AFM 88-9 Chapter 1 will be used; however, in wooded areas or where lines are seen principally against hillside or tree-covered backgrounds, the brown glaze may provide a more ac- ceptable appearance. 6-7. Guying. Particular care will be taken to ensure that all points of strain in the pole lines are adequately guyed. Im- properly or inadequately guyed lines soon begin to sag, degrading the reliability of the line as well as creating an unsightly installation and increased maintenance. a. Components. A guy installation consists of vari- ous components as follows: (1) Guy wire (strand). The major component in each guy installation is the guy wire, whose rated breaking strength determines the requirements for all other components. Wire of either three or seven strands is commonly used. Each strand consists of a steel core having a protective coating of zinc, copper, or aluminum. Zinc coatings are available in standard ASTM coating weights. A Class A coating weight is half of a Class B coating weight and a third of a Class C coating weight. The coating weight used is de- pendent upon atmospheric corrosion with Class A used in dry or desert areas with little industrial contamina- tion, Class C used in salt-ladden or foggy areas or heavily contaminated locations, and Class B used else- where. Rated breaking strength used will be not less than 6,000 (6M) pounds. Normally not more than two strengths of guys should be used for any one project. (2) Grounded guys. Conductive poles such as steel or concrete, poles with overhead ground wires, and poles with guys connected to primary neutrals are con- sidered grounded, since insertion of guy strain insu- lators does not isolate any portion of the pole from the ground. (a) Connection to primary neutrals. For some in- stallations, connection of primary neutrals to guys can improve secondary equipment protection. A detailed discussion of why this improvement is effected is given in REA Bulletin 83-1 which also covers the in- fluence of such grounding on anchor rod corrosion. For other installations, such a connection may not meet lo- cal code requirements or will not be possible when the installation does not have a primary neutral system. (b) Anchor rod corrosion. Corrosion can be a problem in systems that have primary neutrals inter- connected with grounded guys when such systems are installed in areas having a low soil resistivity and a low ratio of buried steel to buried copper. In such cases, an- chor rods and grounding electrodes should be of the same composition, either both of galvanized steel or both of copper-clad steel. The first installation is less expensive, but also provides more resistance. Choice of the rod composition will be done in accordance with the installation’s usual practice. 6-12 (c) Ground and guy wires. Ground wires will al- ways be copper when grounding apparatus, regardless of the type of rods used. Guy wires should be of similar composition to rods. (3) Nongrounded guys. Where guy strain insula- tors are installed in a guy, to provide sectionalizing of grounded portions from nongrounded portions, that guy is considered ungrounded. Strain insulators should be provided in all guys on wood poles, except where grounded guys are required or where local code requirements such sectionalizing in higher voltage lines. (a) Strain insulator location. Insulators will be located at least 8 feet vertically above grade, so that in the event a guy wire is broken, the uninsulated upper portion of the guy wire cannot swing to any point less than 8 feet above the ground. Insulators will be located also at least 6 feet horizontally from the top of a pole, thus increasing the separation between a lineman and a grounded guy wire segment. Where guy wires pass through line conductors or can fall on line conductors, additional insulators may be required. (b) Strain insulator ratings. Ratings and strengths of insulators should be suitable for the cir- cuit insulated. Since the maximum available ANSI guy strain insulator strength is 20,000 pounds this re- quirement could limit nongrounded guy strengths to 20M and may require two or more downguys if more than a 20,000 pound pull is necessary. Stronger insula- tors, which are not ANSI listed, may be used also. (4) Anchors. The type of anchor used must pro- vide suitable resistance to uplift and therefore is dependent upon soil conditions. Table 6-6 indicates suitable anchor types based on a range of soils from hard to soft. While the soil descriptions are not an in- dustry standard, manufacturers are familiar with this or similar classifications. For the majority of cases, the most suitable anchor is an expanding type as shown on figure 6-7, because most lines are installed in ordinary soils. Strengths for available sizes of expanding an- chors are also shown on figure 6-7. Rock or swamp an- chors are described in manufacturer's catalogues. In the past log anchors, generally consisting of 8-inch to 12-inch diameter by 4-foot to 5-foot long creosoted logs, have been used in marshy soil. Since log anchors tend to rot, no matter how well creosoted or otherwise treated, their use is prohibited. Expanding anchors, with extra long anchor rods reaching firm underlying soil, may be acceptable in some cases. Multihelix screw anchors can also be installed in swampy soils when this type of anchor can provide the required holding power. Three-eye thimbles will be provided normally on all anchor rods. This permits use of individual down guys for primary, secondary, and communication cir- cuits and anchors must provide adequate strength to support all of these loads. TM 5-811-1/AFM 88-9 Chapter 1 Table 6-6. Anchors Suitable for Various Soils ¢ Soil Type of anchor General No. Classification description type 1 Solid bedrock Rock Hard 2 Dense clay; compact gravel; dense fine sand; laminated rock; slate; schist; sand- stone 3 Shale; broken bedrock; hardpan; compact clay-gravel mixtures 4 Gravel; compact gravel and sand; claypan Expanding Ordinary 5 Medium-firm clay; loose sand and gravel; compact coarse sand 6 Soft-plastic clay; loose coarse sand; clay silt; compact fine sand Swamp or Soft 7 Fill; loose fine sand; wet clays; silt esau 8 Swamp; marsh; saturated silt; humus ® Based on copyrighted data, courtesy of A. B. Chance Company, Centralia, Missouri and reprinted with its express written permission. (5) Rod assemblies. Rod assemblies must meet NEMA PH 2 tensile loading tests. A 5/8-inch diameter rod is rated at about 16,000 pounds breaking strength, a 3/4-inch diameter rod is rated at about 23,000 pounds and a 1-inch diameter rod is rated at about 36,000 pounds, but some manufacturers offer a 3/4- inch diameter rod rated at 25,000 pounds and a 1-inch diameter rod rated at 40,000 pounds. (6) Guy markers (guards or protectors). The purpose of guy markers is to provide a substantial and conspicuous indication to pedestrians that an impedi- ment to passage exists. AR 385-30 requires that markers be yellow to provide the greatest visibility, unless other finishes are approved for the installation. b. Installation. Guys are installed to balance line tensions and are therefore appropriate where lines be- gin, end, or where lines change direction. (1) Types. Most installations utilize down guys, wherein the guy wire is led away from the pole at a 45° angle down to an anchor. Since this configuration can interfere with traffic, span or sidewalk guys may be necessary to shorten guy leads. Head guys are pro- vided at heavily loaded corners to reduce tension in a corner span and strain on the corner pole. Dead-end guys should be provided in long straight lines at not less than every 2,500 feet to limit the effects from line breaks. Storm guys should be provided in long straight lines at not less than every 5,000 feet to reinforce lines against storm effects. Various types of guys are shown schematically on figure 6-8. Figure 6-9 shows down and span guy requirements in more detail. Although several guys are shown on the down guy detail, a sin- gle guy is permissible when adequate holding strength is provided. (2) Guy lead angle and strength requirements. A lead angle (lead) is the angle that a guy wire makes with the center line of the pole. As can be seen on fig- ure 6-10, the greater the lead angle the larger the horizontal component and thus the lower the mini- mum breaking strength needed to provide the neces- sary holding capacity to balance conductor tension. However, for down guys, the greater the lead angle the more the guy interferes with other use of the space. Typically, lead angles from 45° (optimum) to 15° (minimum to be used) can be used to balance conductor tensions of 70 to 25 percent of the guy wire minimum rated breaking strength. Where clearances over pedes- trian areas require sidewalk guys, the holding capacity will be greatly decreased because there is a bending moment on the pole at strut height; therefore, side- walk guys should be installed only when no other method is feasible or the conductor tension is minimal. A computation for in-line guy strength requirements is shown on figure 6-10. (3) Bisect angle guys versus in-line guys. The maximum permitted angle of line deviation for a sin- gle angle guy installation (one guy installed on the bi- sect of line angle) is 45°. For greater angles, a down guy installation in line with each direction of pull is re- quired. 6-8. Miscellaneous items. a. Pole line hardware. Hardware will be of a type specifically developed for pole line installation in ac- cordance with industry standards. All steel or wrought iron hardware will be hot-dip galvanized as specified in ANSI C135.1. b. Aerial line connector hardware. Copper line con- nector hardware will be of copper alloys and aluminum line connector hardware will be of aluminum or alumi- num-lined alloys. Since bolted line connectors ag- gravates the cold-flow tendencies of aluminum conduc- tors and cause maintenance problems, other types of connections such as compression type are preferred. c. Crossarms. Laminated wood, synthetic materials, 6-13 TM 5-811-1/AFM 88-9 Chapter 1 and channel iron brackets are occasionally used for equipment crossarm type supports; however, it is only for unusual installations that the use of anything other than solid wood crossarms can be justified. 6-14 Ratings® Holding power Se Minimum Minimum anchor in a rod rod ordinary square diameter length soil inches feet inches pounds C5000. 50s ja as BAS 7 63000 2. sg 100 ws 4.6 DIS 7 TO 000 ers tA 20) a Jee *s: OBIS 8 E2000 oe, ieee) se at oe 8 *From REA Bulletin 43-5. Approximate after strain is applied =\Thimble eye Anchor rod Normally 45° but must be in line with pull of the attached guy wire when under load Expanding anchor Size of hole to be same as unexpanded anchor Note: Projection of anchor rods above grade may be increased to a maximum of 12 inches in planting beds or other locations where necessary to prevent burying the eye. US Army Corps of Engineers Figure 6-7. Expanding anchor details TM 5-811-1/AFM 88-9 Chapter 1 Lead angle Sidewalk guy— --8'-6" minimum. Mount as low as is practicable Down guy — Ne penanding anchor uv / Storm guys - US Army Corps of Engineers Figure 6-8. Types of guy installations 6-15 TM 5-811-1/AFM 88-9 Chapter 1 .6 feet minimum Clamp Zone in which guy strain insulator may be installed, when required Clamp at eye Thimble-eye anchor rod 5 feet minimum Zone in which guy strain insulator may be installed. pe Insulator in center of a span as a minimum when pemnitted by the NESC ~ S Down guy x : iy, 18 feet minimum in most cases US Army Corps of Engineers Figure 6-9. Guy details 6-16 Guy hook or eye bolt Fececreene: pecceeeeet —— Provide one insulator as a minimum where required 8 feet minimum 6 feet minimum 8 feet minimum TM 5-811-1/AFM 88-9 Chapter 1 USING VALUES BELOW L = Guy lead Hy = Guy attachment height H, = Conductor attachment height © = Lead angle, T. = Individual conductor tension at point of pole connection Tg = Individual conductor tension at point of guy attachment T = Total of all conductor tensions at point of guy attachment P = Total pull on guy from all conductor tensions IN FORMULAS BELOW Tg = (Tc) x (He/Hg) (10-1) Me Tey? Segnt tag te (10-2) © = Arc tangent L/Hg (10-3) P = T/sin 0 (10-4) APPLY NESC FACTORS Required guy strength = (P) x (Overload) + (Safety) (10-5) EXAMPLE Given: Three No. 1 AWG copper-equivalent ACSR conductors installed in a light loading district in a vertical configuration with the guy connected at a lead angle of 45° and at the same height as the center conductor. Then: Ty = 1,480 pounds a given in table 6-3 (10-1) T = 3 x 1,480 pounds = 4,440 pounds (10-2) P = 4,440 pounds + 0.707 = 6,280 pounds (10-4) Required guy strength = (6,280 x 1.5) + 0.9 = 10,466 pounds (10-5) Use: 3/8 inch, 7 strand, utilities grade, zinc-coated, steel strand with a minimum breasing strength of 11,500 pounds (ASTM A 475) * Courtesy of Keller & Gannon Figure 6-10. In-line guy strength requirements 6-17 TM 5-811-1/AFM 88-9 Chapter 1 CHAPTER 7 UNDERGROUND DISTRIBUTION LINES 7-1. General. Underground lines will be provided only in those areas as established in chapter 5. Underground lines will be installed adjacent to roadways, wherever practicable, so as to avoid interference with future buildings. A careful study will be made of all underground utilities in order to ensure a minimum of interference between electrical lines and other underground utilities, wheth- er existing, being constructed, or proposed as a defi- nite future construction project. Electrical lines will be at least 6 feet from any steam or hot water lines, ex- cept at crossings where a 1-foot separation from such lines is adequate. a. Symbols and codes. For uniformity, symbols shown on figure 7-1 will be used. Installation will comply with the requirements of the National Elec- trical Safety Code (NESC) and the National Electrical Code (NEC). Where state safety rules are predomi- nantly accepted, such rules may be used provided they are essentially as stringent as those of the NESC. b. Construction and other conditions. Typical underground construction details are shown later in this chapter. Unusual service conditions are covered in chapter 1. Special items such as grounding and surge protection are covered in chapter 9. Other conditions should follow the guidelines established by the NESC, the Rural Electrification Authority (REA), or the local utility as applicable. 7-2. Cable. For most installations, the cable selection should allow all applicable options so as to encourage competitive bidding. Restricting extensions of existing systems to a specific conductor material and insulation type in or- der to match an existing cable type is permitted only when a need has been established. Neutral cables, where required, will be installed with 600-volt insula- tion. In duct lines, neutrals will be installed in the same circuit with associated phase cables. a. Conductor material. Since underground conduc- tors are continuously supported, soft-drawn copper or aluminum alloy 5005 provides adequate strength. The need for mechanical flexibility requires that conduc- tors should be stranded and the NEC makes this man- datory for cables larger than No. 8 AWG installed in raceways. Normally, installations of conductors larger than 500 kemil are not practical economically, and such large cables should be used only under exception- al circumstances. Large ampacities can generally be served by parallel or multiple circuits. Three 15 kV, single-conductor, nonmetallic-jacketed cables larger than No. 4/0 AWG may require use of ducts larger than the standard 4-inch size (i.e. three single-conduc- tor cables making up a three-phase circuit and each having individual overall diameters greater than 1.25 inches will need to be installed in a duct larger than 4 inches). One three-conductor cable is usually more costly than three single-conductor cables, and use of multiple-conductor cable should be restricted to spe- cial conditions. b. Insulation and jacket. The type of insulation used will be dependent upon the voltage level and type of service required. Factors affecting selection will be the effects of the surrounding environment, the impor- tance of the load in regard to operation of the installa- tion, and whether peak loading is continuous or inter- mittent. (1) Medium-voltage cable (601 to 35,000 volts). Cable will be specified as 133 percent insulation level (ungrounded) which allows greater margin for voltage surges, insulation deterioration, and fault clearing time than does the use of the 100 percent insulation level (grounded). Shielding is required by industry standards for electric power cables with nonmetallic jackets operating above 2 kV and for metallic-jacketed cable operating above 5 kV. (a) Nonmetallic-jacketed cable. Nonmetallic- jacketed cable will be used, except where circum- stances warrant other coverings. Insulation will be either crosslinked-polyethylene (XLP) or ethylene-pro- pylene-rubber (EPR) in accordance with the appropri- ate IPCEA/NEMA specifications (WC-7 and WC-8). These cables meet the NEC requirement for 90° C. op- eration and are classified by the NEC as medium-volt- age (type MV) cable. Comparisons of various cable in- sulations, as shown in table 7-1, indicate the advan- tages of these two insulations over other types. Nor- mally, coverings (jackets) will be any of the rubber or plastic options covered by IPCEA/NEMA specifica- tions. This option allows the use of cables which are available as stock items in small quantities. In some environments, selection may be necessary because properties of some jacket materials may not provide adequate cable protection. Special shielding or cover- ings will not be specified, unless the designer has checked that the footage installed for each different 7-1 TM 5-811-1/AFM 88-9 Chapter 1 Existing Existing to be to Removed Remain New O B My: ty 8 N u Za Hi = [ssa] xn A es *« &§ va SASS LALLKAAS LY Single manhole (for either power or communica- tion but not both) Double manhole (power with adjacent communica- tion) Handhole Pullbox Roadway light pole Ground-mounted trans- former station Direct burial cable Underground duct line Where many other underground utilities and aerial lines are shown or when a conflict with other symbols might result, the different line identification symbol below can be used. Underground duct line E denotes electric L denotes lighting T denotes communication First line denotes num- ber and type of duct and then size Succeeding lines denote circuits. For require- ments see appropriate schedule or diagram *This material is reproduced with the permission of the American National Standards Institute from the ANSI Standard entitled "Graphic Symbols for Electrical Wiring and Layout Diagrams Used in Architecture and Building Construction," ANSI Y32.9, copyright 1972. work status. Modifications have been made as necessary to indicate Figure 7-1. Symbols for underground electric distribution cable diameter is large enough for manufacturers to make the special runs required. (6) Metallic-armored cable. Armored cable is generally justified only when cable is installed under water (submarine cables) and sometimes when in- stalled in cable trays or trenches. Armored cable will 7-2 have XLP or EPR insulation covered with a thermo- plastic core covering and then provided with an inter- locked-metal tape armor. A nonmetallic jacket is re- quired for underground installations and, where corro- sion and moisture protection is desirable, might also be specified for installations in outdoor cable trays or TM 5-811-1/AFM 88-9 Chapter 1 Table 7-1. Insulation Conductor Temperatures * Insulation Maximum voltage Maximum temperatures degrees C kV Operating Overload Short-circuit Cepaslinked-pélvethyletioe (XLP). 566 hOB Si ei ce oes Ethylene-propylene-rubber (EPR) Prem 558. il inncat hens thls wll deer th yes PR RPMONOE ore gates, 5 att ots a cre ci bute: bse ela a ee ome FE NMR regs Cea i viele ese me ian mettle WEN TMEIROOINONUE 56's ccre visu oe Psat oayet sore noe bite sions fbr s ses « Natunsl polyethylene’... «igo s <a ttss ans nopsyed eats yous tose ee eves 250 250 200 200 200 200 200 200 200 150 ® From table 80 of IEEE 141-1976 and reprinted by permission of the Institute of Electrical and Electronics Engineers, Inc. > ICEA/NEMA requires that the insulation conductor temperatures not exceed the values given above if normal cable life is expected. Over- load conditions are limited to a maximum of 100 hours a year for not more than 500 hours during the lifetime of the cable. for submarine cables. Submarine cable may also re- quire a lead covering. Generally cable having a steel armor should be three-conductor type to avoid the high hysteresis and eddy current losses which can re- sult when single-conductor cable is used. (c) Lead-covered cable. Lead-covered cables should not be used, unless extenuating circumstances prevail. The lead covering is both more costly and more difficult to handle. The use of laminated insula- tion such as paper-insulated (PILC) or varnished-cam- bric (VCLC) instead of the solid or extruded dielectrics such as crosslinked-polyethylene (XLPL) or ethylene- propylene-rubber (EPRL) is not approved. In addition, these cables have lower temperature ratings. (d) Ampacity. The current carrying capacities of medium-voltage cable will be in accordance with ampacities given in the NEC, which are based on ICEA/NEMA values. There are many factors taken into account in determining these allowable ampaci- ties such as operating temperatures, soil effects, shielding losses, and conductor configurations, but the variables which cause the most concern are usually cir- cuit loading and location in a duct bank. Because of load diversity, peak demands for cables in a duct bank will not occur concurrently in most cases. This diver- sity factor should be taken into account when com- putating expected heat build-up in a duct bank. Heat dissipation from a cable is also influenced by the posi- tion occupied by the cable in a duct bank. Cables in duct bank corners dissipate heat more effectively than cables in interior ducts, because of the greater soil dissipating area and the smaller heat contribution from neighboring cables. Calculations of the position effect indicate that, to equalize operating tempera- tures, full-load ratings of cables appropriate for iso- lated (one-way) ducts should be decreased for multiple- duct banks. For example, in an eight-way-duct bank the recommended full-load percentage decrease for each corner duct is 95 percent and for each interior duct is 83 percent giving an average load percentage decrease of 89 percent. This derating still allows provi- sion for loads in excess of the normal feeder capacity usually found on military installations, as the summa- tion of feeder capacities is generally from three to eight times the overall capacity of a main electric sup- ply station. Table 7-2 has been prepared to allow a quick check of medium-voltage cable capacities when installed in duct. Actual capacities should be in accord- ance with the NEC. Table 7-2. Quick Check of Allowable Ampacities of Medium- Voltage Cables * Copper AWG or Aluminum Amperes kemil AWG or kemil 10 2/0 4/0 350 500 * Based on tables 310-47 and 310-48 of NFPA 70-1978 for one circuit, three single-conductor cables in underground ducts for operation up to 35 kV. (2) Low-voltage cable. Cables suitable for below grade installations are listed in table 7-3 by the NEC type designation. Insulation will be either XLP (NEMA WC 7) or EPR (NEMA WC 8) and jackets or other protection should be in accordance with the ap- plicable Underwriter’s Laboratories (UL) specification covering that NEC type. Use of metal-clad (MC) cable will be limited as previously discussed for metallic-ar- 7-3 TM 5-811-1/AFM 88-9 Chapter 1 mored cable. The use of the less expensive Moisture- and Heat-Resistance Thermoplastic (THWN) or Mois- ture-and Heat-Resistance Cross-Linked Synthetic Polymer (XHHW) is not recommended for under- ground work as their thinner insulation has been de- signed for interior usage. Moisture-and-Heat Resistant Thermoplastic (THW) wiring does have the same thickness of insulation as Heat-Resistant-Rubber (RHH)/Moisture-and Heat-Resistant Rubber (RHW)/Underground Service-Entrance (USE) wire, but polyvinyl-chloride insulation is considered to have only fair electrical and mechanical insulation proper- ties as compared to the excellent properties exhibited by XLP and EPR insulation. UF cable may have a greater insulation thickness, but some sizes have a low- er ampacity rating than does USE cable. Table 7-3. Low-Voltage Cables Suitable for Below Grade Installation @ NEC type RHH-RHW-USE....... Direct-burial or in duct . Direct-burial or in cable tray Approved application ® Approved for operation in both wet and dry locations at a maximum operating temperature of 75° C per NFPA 70-1978. US Army Corps of Engineers c. Power cable joints. A splice which connects cables rated 2.5 kV an above is known as a power cable joint. Cable joints are composed of connectors to join two or more cables for the purpose of providing a continuous electric path plus necessary components for maintain- ing symmetrical stress distribution, minimizing volt- age gradients, and maximizing environmental protec- tion. (1) Connectors. Normally connectors will be of the compression type or the plug-in type. Mechanical con- nectors of the bolted or screw type or thermal connec- tors of the soldered, brazed, or welded type will be used only in special cases where the application so war- rants. Compression connectors above 5 kV need to be of the tapered-end type, or have semiconducting (semi- con) tape or molded construction to give the same ef- fect and thus limit stresses. (2) Other necessary joint components. The other necessary components are contained with the connec- tors in kits to provide joints which range from the fully field-assembled type to those kits with mostly factory-formed parts which require less installation la- bor. (a) Conventional taped or resin system splice kits. These kits cost the least for materials and are used to make up a significant number of cable joints, but this type requires the most labor to install. Joints are longer and bulkier than other types. Quality is depend- ent upon the splicer’s skill level, so joint workmanship 7-4 can vary widely. Figure 7-2 shows acceptable field- formed joints suitable for up to 35 kV usage. Dimen- sions shown are for 133 percent insulation. Any kit selected must have splice tapes suitable for the cable insulation. (b) Heat-shrinkable splice kits. These kits in- clude factory preformed splices which are heat-treated in the field to fit the conductor. This type is simpler to install than the conventional taped or resin type and, in general, provides a less bulky splice than any of the other types. A kit will fit a range of cable sizes, but kits may not be available for other than solid dielectric single-conductor cables. (c) Separable insulated connectors. Such connec- tors are fully factory preformed into the minimum of parts necessary to adapt either the receptable and plug or the connector and splice body to the cable insula- tion, shielding, and jacket. Such joints cannot be used for laminated insulations, but provide a waterproof and totally submersible joint for solid or extruded di- electric insulations. These joints are the quickest to in- stall, but the labor savings may be outweighed by the highest initial cost. Greater reliability has been re- ported by utility and industry records for these joints. If used in manholes, the separable function is tempo- rarily lost after cables are fireproofed, but fireproofing can be easily removed and reapplied. Connections do provide disconnectability for future taps or for cable sectionalizing during fault testing. The preformed kit must be suitable for the cable insulation and correctly sized for the cable diameter. (3) Choice. Any of the cable joints discussed may be permitted as a contractor's option, whose selection is made by balancing labor savings against material costs. However, disconnectable load-break or nonload- break separable connectors, which are the most expen- sive type of cable joints, will be used only where the disconnect feature is necessary. Metallic-armored cable splices will be enclosed in compound-filled metal splice boxes. (4) Dissimilar material. Both aluminum-to-copper conductor and nonmetallic-jacketed to lead-covered cable connections are easily made when connectors and splicing materials are correctly utilized and in- stalled. While transitions from one material to another will not be permitted when installing new lines, such transitions between existing and new work are accept- able for extensions and additions. d. High-voltage cable terminations. A device used for terminating alternating-current power cables hav- ing extruded, solid, or laminated insulation which is reated 2.5 kV and above is known as a high-voltage cable termination. (1) Provisions. Such terminations are covered by IEEE 48 which requires terminations to be able to pro- vide one or more of the following: TM 5-811-1/AFM 88-9 Chapter 1 CONVENTIONAL TAPED JOINT Resin overcast type Resin pressure-filled type (35 kV maximum) ‘ jas eee .5 kV maximum) Gam RESIN SYSTEM JOINT CABLE SPLICE KIT JOINT CONSTRUCTION @® Conductor strand Connector Conductor removal length Strand shielding Semicon tape (does not include length of connection) C Cable insulation 3 Insulating tape 6"-15kV, 9s"-25kV, 13"-35kV D Shield bedding 4 Shielding tape II Cable pencil length E Tape cable shielding 5 Ground braid 3/4"=15kV, Us"-25 kV, 235"-35kV F Cable bedding 6 Jacketing tape G Jacket 7 Spacer tape H Wire cable shielding 8 Restricting tape 9 Resin injection fitting 10 Electrical putty = BASEPON DATA FROM THE 3M COMPANY DRAWING C 2047, B2 AND REPRINTED WITH THE PERMISSION OF THE 3M COMPANY, ST. PAUL, MINNESOTA Figure 7-2. Conventional taped or resin system cable joints TM 5-811-1/AFM 88-9 Chapter 1 (a) Electric stress control for the cable insula- tion shield terminus. (b) Complete external leakage insulation be- tween the cable conductors and ground. (c) A seal at the end of the cable against the en- trance of the external environment which also main- tains the pressure, if any, of the cable system. (2) Types. Termination types are defined by IEEE 48 as Class 1, which provides all of the above three conditions (and includes potheads, a term now rapidly becoming obsolete), Class 2 which provides the first two conditions, and Class 3 which provides only the first condition. The first two classes include both in- door and outdoor types, but Class 3 can only be used indoors. Protection from direct exposure to solar radia- tion or precipitation is required for outdoor types. (3) Requirements. Class 2 terminations with their unsealed ends are subject to tracking when exposed to humidity changes occurring inside outdoor equipment. Class 3 terminations with their exposed length in addi- tion to the exposed end, can be more difficult to main- tain plus more dangerous to maintenance personnel. Since the use of the more expensive Class 1 type causes an almost unnoticable overall cost increase in the pro- vision of a medium-voltage cable installation, only Class 1 terminations will be used. Either taped or pre- formed Class 1 terminations are acceptable. Use of the next higher BIL rating in contaminated areas is not recommended, as it is generally preferable to have a cable failure at the termination rather than within the cable length. (4) Installation. A taped Class 1 outdoor termina- tion is shown on figure 7-3. Dimensions are shown for 133 percent insulation. A preformed slip-on Class 1 outdoor termination is shown on figure 7-4. Some manufacturers provide a cap and shield adaptor which eliminates the need for tracking tape. Indoor Class 1 terminations are similar, except that weather and ultra-violet protection are unnecessary. The skirted in- sulator provides the weather protection and the type of materials used are ultra-violet resistant. An indoor termination similar to figure 7-3, would not require tracking tape. An indoor termination similar to figure 7-4 might not require a preformed skirted insulator; two half-lap wraps of self-fusing silicon rubber tape might provide adequate protection dependent upon the manufacturer. Also available are heat-shrinkable terminations which consist of a connector lug, a heat- treated tube providing stress control, and heat-treated skirts. For indoor applications, skirts may not be necessary. Potheads will be used to terminate mul- tiple-conductor cables as other types of termination are made only for single-conductor cable. The use of a spreader head and single-conductor terminations is more costly than a pothead and provides one more point subject to stress. 7-6 e. Fireproofing. High current arcs can cause heat or even flames which can destroy cables adjacent to the arc. To limit damage to the cable producing the arc, cables are often fireproofed in manholes and vaults. In general, fireproofing should be limited to cables carry- ing voltages of more than 600 volts. Fireproofing can be provided by wrapping with fireproof tapes or spray- ing with flame retardent coating. Figure 7-5 shows cable fireproofing details for a taped installation. Polymeric elastomer tapes will be used; asbestos tapes are not permitted. f. Insulation tests. Cable testing will be specified to be performed and successfully completed before cable installations are accepted. Cable testing will include the testing of the adequacy of any cable splices, stress- relief cones, or potheads, as applicable. Cables will be disconnected from equipment when equipment is not rated to withstand the test voltage. When equipment is adequately rated, circuit breakers or switches asso- ciated with the tested cable will be opened to allow complete cable testing procedure to be performed. The first high-potential testing of new cables is performed by the cable manufacturer at the factory, and is per- formed in accordance with industry standards. The first high-potential testing of cable following installa- tion in the field should be limited to 75 percent of the test voltages used at the factory. The designer should specify the actual field test voltages or refer the con- struction contractor to the applicable industry stand- ard that list the types of tests permitted and the value of the test voltages to be used for cables with different voltage ratings. 7-3. Duct lines. Duct lines will be installed below the frost line at the project site location. In clay soil, not less than a 3-inch layer of sand should cover the bottom of the duct trench before ducts are placed. Ducts should be cov- ered with not less than a 6-inch layer of sand after they are placed. Metallic conduit should not be used when concrete encasement is provided. a. Construction. (1) Wall thickness. Nonmetallic ducts are manu- factured with thin-wall and heavy-wall thicknesses. The thin-wall type is designed to be used with an add- ed concrete encasement. The heavy-wall type is used without encasement in concrete; this type of duct is in- stalled with an earth fill separating the ducts in a bank, except that under areas used for vehicular traf- fic concrete encasement is necessary. Guidelines indi- cating where concrete encasement is necessary to pro- vide in chapter 5. 126 (2) Shape. Most ducts have round exteriors with a round bore; however, octagonal and square exteriors are available, as are square bores. Square or octagonal exteriors may make stacking easier in some cases, but TM 5-811-1/AFM 88-9 Chapter 1 3/4"-15kV, Lg"=25kV, 255"-35kV sae 20"-15kV, 25"-25kV, 35"-35kV ey 5/8"-15kV, 3/4"-25kV, 1"-35kV 6"-15kV, 8"-25kV, 10"-35kV CABLE TERMINATION KIT TERMINATION CONSTRUCTION (a) Conductor strand Connector lug Conductor removal length (does not strand shielding Semicon tape include length of connector lug) C Cable insulation 3 Insulation tape Il Cable pencil length D Shield bedding 4 Shielding tape Ili Stress cone length E Tape cable shielding 5 Ground braid IV Stress cone depth F Cable bedding 6 Jacketing tape G Jacket 7 Tracking tape * BASED ON DATA FROM THE 3M COMPANY DRAWING C 2047, B2 AND REPRINTED WITH THE PERMISSION OF THE 3M COMPANY, ST. PAUL, MINNESOTA Figure 7-3. Medium-voltage taped termination TM 5-811-1/AFM 88-9 Chapter 1 CABLE TERMINATION KIT NOMINAL REQUIREMENTS @) Conductor strand @ Connector lug Strand shielding Semicon tape Cable insulation Shield bedding Tape cable shielding Cable bedding Jacket Preformed skirted insulator Shield strap Ground wire Preformed stress cone Tracking tape ommoa NOUSY US Army Corps of Engineers Figure 7-4. Medium-voltage preformed slip-on termination and stress cone 7-8 TM 5-811-1/AFM 88-9 Chapter 1 End bell Cable protector for metallic-sheathed cable only Fireproofing tape Cable Duct DUCT ENTRANCE Fireproofing tape Cable STO Do not build up at this location Cable joint CABLE JOINT REQUIREMENTS Fireproof only medium-voltage circuits (over 600-volts), Fireproof cables their entire length within the manhole and into the duct entrance as indicated. US Army Corps of Engineers Figure 7-5. Fireproofing of insulated cables round bores are preferable for cable pulling. (3) Number. Ducts are typically available in a sin- gle raceway configuration. Although some ducts are available in multiple duct units with from two to nine raceways in each length, this type should not be used especially for electric power cables. b. Systems. Duct lines for both electric power and communication circuits will be provided concurrently. Communication cables will be completely isolated from electric power cables which requires separate ducts and access points, such as manholes, for each. For reasons of economy and space conservation, elec- tric power and communication ducts may be installed in the same trench and manholes may be adjacent, when such arrangements suit the communication cir- cuit requirements of the appropriate communication agency. c. Sizes. The nominal diameter of raceways for me- dium-voltage, communication, and other cables in ducts between manholes will be 4 inches, with larger ducts provided where 15 kV cables larger than No. 4/0 AWG are to be installed. Low-voltage connections to building services will also be 4 inches, except that for small building services of 100 amperes or less, 2-inch ducts are adequate. However, the communication serv- ice duct to any building will not be less than 3 inches in diameter. Exterior loads supplied from a building such as multiple lighting, control, or motor loads should be served with not less than 1-inch ducts. In general, sizes of underground raceways installed should be the nomi- nal 4-inch, 3-inch, 2-inch, or 1-inch size, except where large numbers of secondary ducts make this uneco- nomical, as for instance, on tank farms. d. Spare capacity. A sufficient number of spare ducts will be provided in duct systems between man- holes to provide for at least a 25 percent increase in the number of cables. The number of spare ducts should be increased as required for future service to 7-9 TM 5-811-1/AFM 88-9 Chapter 1 planned expansion. However, such spare provisions do not apply to building service ducts, unless there is a definite planned expansion or a planned increase in reliability requires provision for duplicate feeders. e. Installation. Installation requirements for con- crete-encased duct lines are shown on figure 7-6. Fig- ure 7-7 indicates drainage requirements for under- ground ducts. (1) Maximum number of conduits in a duct run. Electric power cables generate heat dependent upon 3" ELECTRIC OR COMMUNICATION DUCT BANK US Army Corps of Engineers the cable loading and resistance. Dissipation of this heat is usually no problem because of diversity of cable loading, as previously noted. Normally, more than eight ducts entering at any one point in a manhole pro- vide a cable congestion which makes maintenance time-consuming and costly. Where the use of more than eight ducts in a single run is necessary, the mini- mum manhole size required, as noted later, will be in- creased as necessary. More than two duct entrances may require larger manhole sizes. 3" ELECTRIC AND COMMUNICATION DUCT BANK No. 4 bars at 6" to 8" on centers No. 8 wire loop approximately 8" on centers Figure 7-6. Concrete encased duct details 7-10 Minimum cover, as required TM 5-811-1/AFM 88-9 Chapter 1 ee eae 4 inches Minimum slope DUCT LINE ELEVATION US Army Corps of Engineers Figure 7-7. Duct line drainage (2) Configurations. Generally accepted arrange- ments for electric (E) or communication (C) ducts are given below: AUTOM AO! io oie secrete 2 ducts wide by 2 deep OAT A( 5 5145 tones) nets 4 ducts wide by 2 deep eT CeCe ere Le 3 ducts wide by 2 deep Gand OCs: P6085. 6 ducts wide by 2 deep (3) Miscellaneous. (a) Jacking. Where ducts are jacked under exist- ing pavement or used for exposed installations, rigid steel conduit will be installed because of its strength. To protect the corrosion-resistant conduit coating re- quires pre-drilling or installing conduit inside a larger iron pipe sleeve when conduits are jacked. (b) Duct line markers. Duct line markers will be provided only for long stubouts where the location of the end of the stubout is not otherwise defined. 7-4, Manholes, handholes, and pullboxes. In traffic areas, design will be for a H20 wheel loading as defined by AASHTO HB-12. a. Manholes. Manholes will be located at street in- tersections, and will be spaced not more than 600 feet apart to provide maximum flexibility. On curved sec- tions the maximum distance will be limited to 300 feet. These spacings limit pulling tensions to accept- able values for the usual types and sizes of cables in- stalled. Where curves are required to avoid obstruc- tions or because of right-of-way or other space limiting requirements, the curve will be the maximum suitable for the installation, but not less than a radius of ap- proximately 25 feet. The use of 90° bends is permitted only for pole risers or equipment risers to transformer stations, switches, or similar devices. Risers will be not more than 150 feet from the manhole where the race- ways originate. (1) Criteria for construction. Manholes will not be less than 6 feet in depth, by 6 feet in length, by 4 feet in width with an access opening to the surface above (outer air) of not less than 30 inches in diameter. Man- holes will provide a minimum wall space of 6 feet on all sides where splices will be racked. Duct entrances into the manhole can be located near one end of long walls so that sharp bends of cables at the duct mouth are avoided, or else sufficient space will be provided for a reverse bend before the cable straightens out on the wall on which the cable is racked. Manhole eleva- tions and elevations of duct lines entering manholes will be shown. For non-metallic-jacketed cables, the minimum bending radius will be six times the overall cable diameter. Metallic-jacketed cable bends will be in accordance with ICEA/NEMA requirements. Figure 7-8 shows details of factors which affect lengths of manholes. A scale example of a specific cable size in- stalled in a manhole is shown on figure 7-9. (2) Types of manholes. A combination electric power and manhole suitable for use with most electric power and communication duct arrangements is shown on figure 7-10. Other arrangements are accept- able, but minimum inside dimensions and reinforcing will match requirements shown on figure 7-10. Gener- ally, manhole drawings indicate the requirements for a cast-in-place concrete manhole. Precast manholes may be a contractor’s option, when they provide the same inside dimensions, strength, and sealed joints compar- able to the monolithic construction of cast-in-place manholes. Prefabricated vaults of other than concrete construction will be restricted to direct-burial cable systems. (3) Prohibited devices. Electrical equipment such as transformers or switches will not be installed in manholes or underground vaults, except in manholes adjacent to airfields where such installations may be necessary to meet airfield clearance requirements and then equipment will be of the type which can be sub- mersed. Where the water table is high enough to flood 7-11 TM 5-811-1/AFM 88-9 Chapter 1 ELEVATION | LEVEL OFFSET CABLE ELEVATION NONLEVEL OFFSET CABLE US Army Corps of Engineers - \-4 LA ELEVATION LEVEL CABLE TURN | For offset of reverse cable curvature, about 2 to 3 feet for large 15 to 35 kV cables when based on a minimum bend radius of six times the cable diameter, B Length needed for cable joint and supporting racks. C Clearance from duct entrance to start of* bend. D Cable adjustment length where ducts enter and leave manholes at radically different elevations. E For additional cable bend needed since cable turns. "Based on data from the "Underground Construction Handbook" and reprinted with the permission of Bermico Company. Figure 7-8. Factors influencing manhole design manholes, water should be removed by portable pumps operated on a regular schedule. Permanently connect- ed sump pumps will not be installed, except in special instances. Permanent ladders will not be installed; portable ladders will be used when required. (4) Manhole appurtenances. Ground rods will be installed in one corner of each electric manhole for me- tallic shield or sheath grounding to reduce induced po- tential gradients. Dangerous gradients are not induced by communication circuits, so rods will not be installed in communication manholes. Other manhole appurte- nances are shown on figure 7-11. Square covers will not be used because of the danger of the cover slipping through the opening. The traffic cover shown on fig- ure 7-11 is suitable for H20 wheel loadings. Pulling-in irons will be provided opposite each duct entrance or where there are provisions for future duct entrances. Sufficient cable racks will be installed to properly sup- port cables on both sides of any cable splice and else- where as needed. Rack horizontal spacing will be about 3 feet to 4-1/2 feet for electric power cables dependent upon the nature of the cable bends. At least two racks should be located on each wall, except where duct en- trances would interfere. For communication cables, racks will not be more than 30 inches apart horizontal- ly. 7-12 b. Other types of cable access points. Where splicing or pulling of low-voltage cables requires an access point, but the volume provided by a manhole is unnec- essary, handholes or pullboxes will be provided as ap- propriate. (1) Handholes. Handholes are used on laterals from manhole and ductline systems or other sources for low-voltage power and communication supply to building services. A handhole suitable for most electric power or communication usage is shown on figure 7-12. Generally at least four racks should be installed. Where more than two splices occur, a manhole may be more appropriate. (2) Pullboxes. Pullboxes are generally used for electric circuits supplying low-voltage electric loads which require conductors no larger than No. 1/0 AWG and no more than one 2-inch conduit entrance at each side. Where larger conduits are installed, handholes or manholes will be used. Because pullbox depths are less than 2 feet, conduits must always slope up into the pullbox. Pullboxes are also suitable for fire alarm, pub- lic address, and control circuits. Pullboxes will not be used for telephone circuits without the approval of the * appropriate communication agency. Figure 7-13 shows standard sizes of pullboxes routinely used for low-voltage installations. Pullboxes will not be used in TM 5-811-1/AFM 88-9 Chapter 1 @ ' Scale t t i s mes eo rele were 4 0" eae ad z +: 4 Yo e ws a age Cable diameter — -——-—- -— fatal 7. Bre r Minimum bend redius = six times , cable diameter a 2 aaa t ’ , *% 6 2 Tr i 2 5 Gs hs 2 e ze 4 | 4 - Splice . . B) \ <5 d A ; 2 oy Pees 4 att 350 kemil, 15 kV ae es, single-conductor pe oe XLP cable an # | \ Pee a e da 8 f — Manh. S \ =, 2 aaa nhole wall J a) * . i we e | : +O i ate + en boo 4S et Bb Miscig, e 4 Note: For definitions of(4).(), ana(c) see figure 7-8. US Army Corps of Engineers Figure 7-9. A scale example of a cable installed in a manhole 7-13 TM 5-811-1/AFM 88-9 Chapter 1 30" minimum opening ee = ¥ Construction requirements + ae Clear minimum inside dimensions for installation and Nea as maintenance purposes p= fou eee io : Sump ee tee Height | Length | Width deoeh. cover ES as Ae } and = 6 feet |6 feet | 4 feet | 1‘ foot frame - Pulling-in iron Cable rack PLAN an Manhole frame and cover Grade irons Ground rod Sump SECTION A-A US Army Corps of Engineers Minimum concrete thickness Manhole walls, top, and floor Sump walls and floor 8 inches 4 inches Minimum reinforcing” 1. Bars will be a minimum of No. 4 round deformed. 2. Walls and floor will have {|{ bars at 12 inches minimum on centers with a minimum 12 inch hook at corners and intersections. 3. The top will have bars installed as shown at 4 inches on center minimum laterally and longitudinally as appropriate, except that at openings also provide an additional bar at a two-inch spacing and two diagonal bars, each way at 45° to and located above lateral or longitudinal bars. ee ed ®Reinforcing will be increased where required to suit actual installation. Figure 7-10. Typical double manhole areas subject to vehicular traffic. In such areas, hand- holes will be installed. The use of a pullbox at the base of a lighting pole is unnecessary in most cases. 7-5. Direct-burial cable installations. Cables should be installed not less than the minimum depth required by the NEC or as necessary to be below the frost line, whichever is greater. a. Protection. In some locations, nonmetallic-jackets may not provide sufficient cable protection. Metal ar- mor provides protection from rodents. Underground residential distribution (URD) cable should be installed in plastic duct, not because the duct will prevent corro- 7-14 sion of the concentric neutral, but because cable re- placement is facilitated. Where buried cable warning is necessary, tape manufactured for this purpose will be provided. Where installed under traffic areas, ca- bles will be installed in concrete-encased duct for pro- tection. b. Markers. Markers are required at the ends of di- rect-burial systems, at each splice, at approximately every 200 feet along straight runs, and at changes of direction. Where cable is used for lighting circuits and the lighting poles effectively provide indication of di- rection changes, markers are not required. Markers will be similar to the one shown on figure 7-14. ENTRANCE COVER 3-1/2" | | ses ve —Identification ~ Cover handle Grout Duct DUCT WINDOW TM 5-811-1/AFM 88-9 Chapter 1 2" wide sheet copper flashing Edge of duct window 1" embedment TF: eS SUMP FRAME AND COVER SEALING Fasten by means of F 2-1/2" by 1/2" bolts and expansion shields— 2-1/4" a / 2-1/4" Ht. —- oa in 27-1/2", \ Saat, : | I, si —_y | | 7/8" 1-1/2" 4— ‘ 2-5/8" radius | porcelain i insulator J 3" tet ENTRANCE FRAME PULLING-IN IRON CABLE RACK Fed. Spec. RR-F-621 Dimensions classification inches Appurtenance Remarks Type Style Size Nominal A B c D E F 30A 1-3/8 Nontraffic Manhole frame III A 2 80 32 2 Se hele et Traffic 30A 1-3/8 2-5/8 Nontraffic Manhole cover D - 30B 30 31-7/8 2 3-1/6 - - - Traffic 36A 1-3/8 Nontraffic Handhole frame III A 36c 36 38 2 36 47 4 10 Traffic 1-3/8 2-5/8 Nontraf fic Handhole cover D - a 36 37-7/8 2 31/4 - = . Tratfic Sump frame VIL = oe 12 15 1/2 12 13 3/8 = b Sump cover I - - 12 - 1/2 - 13 - - b "Modified to suit a 36-inch frame. bcircular instea US Army Corps d of square shaped. of Engineers Figure 7-11. Manhole appurtenances 7-15 TM 5-811-1/AFM 88-9 Chapter 1 Adjacent communication handhole, where applicable, shall be of the same construc- tion as electric handhole, Construction requirements except without ground rod Clear minimum inside requirements} for installation and maintenance purposes 36" minimum opening Handhole Ta and floor PLAN Minimum [ae 2" Bars will be a minimum of No. 4 round deformed. Walls and floor will have bars at 8 inches maximum End bells on centers with a minimum Grade Brick collar where 12 inch hook at corners required and intersections. to bring conte racks The top shall have bars cover to installed as shown at a desired minimum of 2 inches from grade Slope to the opening and with a drain minimum 4 inches spacing Pulling-in between bars. iron, provide one opposite each duct entrance "Reinforcing shall be increased where required to suit actual installation. Minimum require- ments are for a H20 wheel SECTION A-A loading (AASHTO). Ground rod US Army Corps of Engineers Figure 7-12. Electric or communication handhole 7-16 TM 5-811-1/AFM 88-9 Chapter 1 One conduit on 1 three sides only One conduit on | maximum fu sides maximum t I Lift holes Cas =e) Mark cover appropriately Increase width J 1/2" diameter, to 18" where a 3" long with conduits enter on 2" arm for hold all four sides down bolting PLAN PLAN Provide wire fabric reinforcing. Grade 6" deep gravel capillary fill 2" duct max. Pullbox without cover used as an extension 2' max. distance to where conduit must be 2' min. ELEVATION below grade ELEVATION TYPE A TYPE B Minimum requirements: Box Minimum requirements: Box interior size, 22" long by interior size, 17" long by 12" wide with 1-1/2" thick 10" wide with 1" thick walls walls and 1-7/8" thick cover and 1-5/8" thick cover US Army Corps of Engineers Figure 7-13. Pullbox installation 7-17 TM 5-811-1/AFM 88-9 Chapter 1 Items impressed or 3-inch letter "C" for direct-burial cable, cast in top will "D" for duct line be V-shaped and have a minimum stroke of at least 3-inch arrow parallel to and 3-inch letter pointing 1/4-inch wide by to item marked for straight runs. Substitute an 1/4-inch deep angular arrow pointing at item marked for runs PLAN changing direction with angle matching bend 1/2-inch chamfer all around where appropriate 6-inch round or square Grade Suggested projections | Concrete Direct-burial cable installation i 1'-6" Paved areas Grassed areas subject to mowing Graveled areas 2'-0" to right of item marked Uncultivated areas ELEVATION US Army Corps of Engineers Figure 7-14. Underground system marker 7-18 TM 5-811-1/AFM 88-9 Chapter 1 CHAPTER 8 TRANSFORMER INSTALLATIONS 8-1. Definitions. Transformers are classified in various ways according to their construction and application. In order to clar- ify usage in this manual, transformer terminology is defined below. a. Utilization transformers. Transformers which convert distribution voltage to utilization voltage can be classified by capacity or by integral devices provid- ed with the transformer. (1) Capacity designations. Designations relating to capacities are as follows: (a) Distribution transformers usually have a rat- ed capacity of 500 kVA or less, although pad-mounted compartmental units are considered distribution type up to their upper limit of 2,500 kVA. (6) Power transformers usually have a rated ca- pacity of over 500 kVA. (2) Integral protection types. Designations relat- ing to the integral protection provided with the trans- former are as follows: (a) Conventional transformers are not provided with integral overcurrent protection for either the pri- mary or the secondary, but have connections suitable for underground or overhead line terminations. (6) Pad-mounted compartmental transformers have high-voltage and low-voltage compartments where primary or secondary protective devices can be installed and are assembled in an integral tamper- resistant and weatherproof unit. Units are suitable for underground entrance of cables only. (c) Load center transformers have integral pri- mary protection and secondary switchgear and are also known as articulated secondary unit substations. Integral load center transformers have a terminal com- partment or a secondary panelboard. Nonintegral load center transformers have a secondary switchgear line- up or secondary switchboard. Units are suitable for un- derground entrance of cables only. b. Main electric supply station transformers. Trans- formers which convert transmission voltage to distri- bution voltage include the following types: (1) Substation transformers do not have integral primary or secondary protection and are generally con- nected to aerial lines. (2) Primary unit substation transformers do have integral connections to secondary switchgear and may also have integral primary protection. Generally, the primary side is connected to an aerial line and the sec- ondary switchgear supplies underground cabling. 8-2. Installation of distribution-to-utilization voltage transformers. a. Aerial mounting. (1) Unit capacities, mountings, and types. Aerial transformer installations may utilize a three-phase unit or banked single-phase units. Transformers, ei- ther singly or in banks, having an individual unit or combined capacity greater than 100 kVA will not be mounted on single wood poles. Aerial mounting will be single pole, cluster or crossarm mounted. Cluster mounting for transformer banks is preferred over crossarm mounting as less visually objectionable. Simi- larly, the cluster or 3-phase bracket mountings will be permitted for mounting of surge arresters and cutouts if acceptable to the Using Agency responsible for the operation and maintenance of transformer installa- tions. Figure 8-1 indicates a cluster-mounted trans- former bank installation and figure 8-2 indicates a crossarm-mounted transformer bank installation. Pole-platform mounting (two-pole structure) should not be used, except where other mounting methods are not satisfactory. For three-phase installation of 225 to 500 kVA, pad-mounted compartmental transformers are more economical than pole-mounted units in most cases and should be provided, except where ground space is unavailable. Self-protected transformers have internal primary fuses that should be replaced only by experienced personnel. Therefore, self-protected trans- formers should not be specified. (2) Location. Aerially mounted installations nor- mally supply several buildings. When that is the case, transformers should be installed at the pole location closest to the center of the secondary loads served. Sec- ondary wiring may drop directly to the buildings served, if the span does not exceed 125 feet; otherwise, intermediate poles are required. b. Ground level mounting. (1) Types and capacities. Transformer units will normally have an incoming, transforming, and outgo- ing sections manufactured as one or more subassem- blies. The use of conventional-type transformers, with connections to separate primary and secondary protec- tive devices, is not permitted since that type of instal- lation is more dangerous, generally more difficult to 8-1 TM 5-811-1/AFM 88-9 Chapter 1 Climbing space Climbing space i 7. Th CAN io: 4271) — 90° maximum VIEW B-B Minimum 50-foot pole, class 2 or 3 Surge arrester ground 4 Surge arresters A Primary neutral, where required Primary fuse cutout Stand-off insulator Cluster-mounted transformers Transformer frame (case) ground, where required Neutral-supported Ground wire secondary cable Molding Grade 12 inches minimum Secondary neutral ground 6 feet minimum ELEVATION US Army Corps of Engineers Figure 8-1. Cluster-mounted transformer bank installation — Minimum TM 5-811-1/AFM 88-9 Chapter 1 50-foot pole, class 2 or 3 10-foot crossarm Primary fuse cutout | Stand-off | insulator Crossarm- Secondary mounted neutral transformers ground ELEVATION THRU CONSTRUCTION Note: US Army Corps of Engineers Transformer frame (case) ground, where required SIDE VIEW DEADEND CONSTRUCTION Installation shown without surge arresters; provide and ground as shown on figure 8-l. Figure 8-2. Crossarm-mounted transformer bank installation maintain, requires more space, and there is rarely a significant cost saving. (a) Units, 500 kVA and less. Load center trans- formers, shown in figure 8-3, or pad-mounted com- partmental transformers, shown in figure 8-4, will be used. Pad-mounted compartmental units should not be used where the primary voltage exceeds 15 kV, where fault currents are so large that standard equipment does not provide the required primary interrupting duty, or where capacities exceed 500 kVA. Deadfront, group-operated, load-break features for primary switching of pad-mounted compartmental units are not available for capacities over 500 kVA. Integral load center transformers may be utilized in lieu of non- integral load center units when appropriate; however, since neither type is tamperproof, fencing is required. (b) Units larger than 500 kVA. Nonintegral load center or integral load center transformers will be used. Normally transformers larger than 1,500 kVA for 480/277 volt service and 500 kVA for 208Y/120 volt service should be avoided, because of the magni- tude of their secondary fault currents. However, in some cases, it may be more feasible and cost effective to provide 2,000 kVA transformers for 480Y/277-volt service and use current-limiting fuses in conjunction with circuit breakers. The use of higher than standard impedance should be minimized, since value engineer- ing after design may eliminate a necessary require- ment because its necessity is not apparent. Transform- ers 750 kVA or larger will be provided with a watthour demand meter. The Using Agency will stipulate if a re- cording type demand meter is required. (2) Location. Exterior installations are usually preferred over interior installations because space 8-3 TM 5-811-1/AFM 88-9 Chapter 1 Incoming switching and protective devices, as required 8-inch thick concrete pad reinforced with 6 x 6 - W2.9 x W2.9 wire mesh Medium voltage cable termination 4-inches Load center —____— Overhead secondary busway, if required Outgoing secondary protective devices and metering, as required Fence Gravel fill Outgoing underground Gravel fill Incoming primary conduit secondary conduit, if required 6-inch well compacted subgrade ELEVATION Incoming section Transformer section | Extend pad 12 inches minimum beyond unit on all sides 10-foot minimum width for equipment removal gate Incoming primary conduit 6 feet minimum up to 25kV primary, 8 feet minimum for 34.5 kV 3) feet iain Location of front for nonintegral load center Note: For grounding see figure 9-3. US Army Corps of Engineers Outgoing section 3 feet minimum Location of front for integral load center 3 feet minimum to side of section, 4 feet minimum to front of section Fence 3-foot minimum width for personnel gate PLAN Figure 8-3. Load-center transformer installation costs are less; however, secondary feeder lengths may require an interior location or make interior installa- tions economical in some cases. (a) Exterior installations. _Ground-mounted units should be installed as close to the building served as is permissible and as near as practicable to the sec- ondary distribution center. The location should be chosen to be compatible with the architectural concept and protected from vehicular traffic. Architectural compatibility can be obtained by the proper location in relation to landscaping, the addition of shrubbery around pad-mounted compartmental transformers, or the use of screened fence enclosures. The primary serv- ice will be underground. When primary supply is from 8-4 an aerial system, the medium-voltage riser pole should be located as close as practicable to the transformer in- stallation, subject to reasonable aesthetic considera- tions. Medium-voltage riser pole installations are cov- ered in chapter 9. Secondary building connections should use underground cables or bus duct; however, the use of more than two underground cables in paral- lel should be minimized as complexity of connection can lead to maintenance and space problems. (b) Interior installations. Transformers will be located as close to the center of the load as is practica- ble. Open ventilated dry-type transformers will not be installed in interior areas having a dusty or a corrosive atmosphere. High-fire-point, liquid-immersed trans- TM 5-811-1/AFM 88-9 Chapter 1 Incoming primary Primary protection Ground Secondary circuit breaker, where required Outgoing secondary SINGLE LINE DIAGRAM High voltage section ———-——___. --——----—-—_-__——- Pad-mounted compartmental- type transformer Seal around base with resilient sealant --__—-—— Low-voltage section mane — 8-inch concrete pad z reinforced with 6 X 6 - W2.9 X W2.9 wire mesh 4 inches ——~ \ 6-inch well compacted Ground rod subgrade ——————___—_— % ——————__—— Conduit ELEVATION Concrete pad Extend gravel fill a minimum of 1 foot beyond pad on all sides Extend pad a minimum of 6 inches beyond unit on-all sides Pad-mounted compartmental- type transformer Transformer — Secondary neutral ground, section aa where required Surge protection ground, where applicable -—-___-__— crt Ground rod i. Incoming primary Outgoing secondary conduit No. 2 AWG mipimtmse eset AF Equipment ground — US Army Corps of Engineers Figure 8-4. Pad-mounted compartmental transformer installation TM 5-811-1/AFM 88-9 Chapter 1 formers should be provided with curbs to contain any liquid spilled, and drainage will be in accordance with NEC requirements for transformer vaults. Pipes and duct systems should not be routed above units. c. Underground mounting. Transformers in under- ground vaults are not permitted except where required to meet airfield clearances. Requirements are given in chapter 7 for equipment in underground vaults. 8-3. Provision of transmission-to-distribu- tion voltage transformers. These transformers are installed generally as part of the main electric supply station, since the secondary voltage normally will be of the 15 kV Class or larger. Primary unit substation transformers should be used to meet the criteria contained in chapter 4. 8-4. Insulation for transformers having windings rated 1,000 volts or more. a. Mineral-oil-immersed units. Mineral-oil-im- mersed units will normally be used for outdoor instal- lations. However, because of the flammability of min- eral oil, certain restrictions apply to their installation. Units with this type of dielectric will not be located in close proximity to flammable structures. Close prox- imity is defined as being within 25 feet radially from combustible construction or building openings such as windows and louvers, but not including solid-metal doors. When located indoors, units will be installed in vaults meeting NEC requirements. b. Other liquid-immersed units. Approved high-fire- point, liquid-immersed transformers will be installed indoors generally and will be required for outdoor in- stallations where mineral-oil-immersed units cannot meet the proximity to flammable construction require- ments. Polychlorinated biphenyl (PCB), commonly known as askarel, has been used as a nonflammable- liquid insulation but has been proven to be environ- mentally unacceptable and therefore is no longer being manufactured. Other insulating liquids must be listed or approved by either Underwriter’s Laboratories or Factory Mutual Corporation as high-fire-point, non- flame-propagating liquids (as defined by the NEC) and as suitable for use as dielectric mediums in transform- ers conforming to NEMA requirements. Units having windings rated at more than 35 kV must be installed in a vault. c. Open ventilated dry-type transformers. This type of transformer is acceptable only for indoor installa- tions. Units will meet required BIL ratings, tempera- ture rise requirements, and winding insulation char- acteristics. Vault construction is required for windings above 35 kV. d. Cost analysis. Where other than oil-immersed units are proposed for installations, a cost analysis shall be provided in the project design analysis cover- 8-6 ing the acceptable alternatives and indicating that the most cost effective transformer insulation medium has been selected. Costs shall include all features neces- sary to provide a proper installation, including vaults, curbs and drains, exterior screening, interior floor space, and additional wiring as applicable. 8-5. Transformer characteristics. a. Capacities. Capacities should be in accordance with industry standards. Standard sizes recommended for distribution-to-utilization voltage applications are shown in table 8-1. Pad-mounted compartmental units are not available for ratings of less than 25 kVA for single-phase units or 75 kVA for three-phase units. Generally transformer capacities selected will provide a rated capacity equivalent to not less than 90 percent of the load requirement figured in accordance with guide lines covered in chapter 2, except that distribu- tion transformers serving Family Housing Units will be sized in accordance with the demand factors given in Appendix A. ANSI loading factors may need to be taken into account also. Table 8-1. Standard kVA Capacities Single-phase Three-phase kVA kVA 5 15 10 30 15 45 25 75 37.5 112.5 50 150 75 225 100 300 167 500 750 1,000 1,500 2,000 2,500 * From paragraph 3.1.1 of ANSI/IEEE C57.12.00-1979 and re- printed by permission of the Institute of Electrical and Electronics Engineers, Inc. b. Transformer life. Transformer life is dependent upon the thermal aging of the transformer. Normal life expectancy is based on operating transformers continuously at rated capacity to the limiting contin- uous duty temperature of the insulation. Thus the transformer operating temperature is the sum of the temperature rise (the increase in temperature of the transformer due to the load) and the ambient tempera- ture (average temperature of the immediate air outside the transformer). (1) Load duration. Aging of a transformer is a function of time and temperature. Transformers may be operated above rated load for short periods pro- vided units are operated for much longer periods at TM 5-811-1/AFM 88-9 Chapter 1 Table 8-2. Daily Allowable Peak Loads for Normal Life Expectancy * Oil-immersed, self-cooled units Dry-type, self-cooled, ventilated units Peak Allowable peak load in percent of rated capacity following load and followed by the indicated percent constant load » duration hours 50% 70% 90% 1/2 MOF ede se son MOG ares centers 162 1 NOS sie viem sacs os MB st ene 138 2 Das is arn ae sis TB eid ad sista ares 123 4 Dace ben muiead UES «tater sities sortie 113 8 POG soecturoctaruones Re ait kee cetr 106 ® This material is reproduced with the permission of the American National Standards Institute from the ANSI Standards entitled “Guide for Loading Oil-Immersed Distribution and Power Transformers” ANSI C57.92, copyright 1962 and “Guide for Loading Dry-Type Distribution and Power Transformers” ANSI C57.96, copyright 1959. > At 30° C ambient temperature. loads below these limits, since thermal aging is a cumulative process and there is a time lag in insulation temperature rise. Table 8-2 indicates loads consistent for normal life expectancy at a 30° C average ambient temperature. Table 8-3 may be used for approximat- ing the loads permitted at other ambient tempera- tures, or the designer may use the tables in the ap- plicable ANSI standards. Correction factors apply only from 0° to 50° C. Temperatures not in this range must be checked with the manufacturer. For further discus- sion on loading of transformers, see ANSI standards shown in table 8-3 plus ANSI C57.91 for 65° C opera- tion of overhead transformers. (2) Temperature ratings. Transformers are rated for a hottest-spot temperature which will give normal life expectancy based on rated kVA loading. (a) Temperature rise. Normally the temperature rise specified will be 65°C for oil-immersed trans- formers having a 105° C insulation and 80° C for ven- tilated dry-type transformers having a 220° C insula- tion. If thermally upgraded insulation (greater wind- ing temperature rise rating) is specified then the trans- former will have a longer life at rated capacity and will have more overload capacity. Oil-immersed trans- formers specified to have a 55° C temperature rise at rated kVA and to have an insulation upgraded to 65° C (55°/65° C rise) can carry continuously 112 per- cent of rated kVA. Likewise ventilated dry-type trans- formers with 220°C insulation having 80°/150° C temperature rise can carry continuously 135 percent of rated kVA. Thermally upgraded insulation is not normally a requirement for oil-immersed trans- formers, except at main electric supply stations. Thermal upgrading is required for dry-type trans- formers, as is vacuum-impregnated winding insu- lation. (b) Ambient. Since the actual temperature of the insulation is the sum of the ambient temperature and the temperature rise, the ambient temperature very largely determines the load which can reasonably be carried by transformers in service. An average am- bient temperature of 30°C is used as the basis for nameplate ratings. Average ambient temperatures for the actual cooling air are then based on daily operation and the maximum ambient operating temperature in any 24-hour period can be no more than 10° C above the average ambient temperature. The Using Agency should be contacted to determine the average ambient temperature if ANSI load factors are taken into ac- count in transformer loadings. Most load estimates are sufficiently conservative to take into account any nameplate derating for units located in high ambient temperature areas. Low ambient temperature should not be a deciding factor in sizing of transformers, ex- cept where the installation has an average daily am- bient of 20° C or less. (c) Use of ANSI loading factors. The influence of operating temperatures and load durations on trans- former life should be taken into account in sizing transformers. c. Cooling provisions. The rated capacities of 750 kVA and larger transformers can be increased by the addition of cooling fans, with the exception of pad- mounted compartmental units. ANSI C57.12.10 and Table 8-3. Loading on the Basis of Ambient Temperatures * For each degree C that the average ambient temperature is above or below 30° C the percent of rated kVA shall be Increased for Decreased for lower ambient higher ambient Oil-immersed, self-cooled units .. .....1.5..... .......1.0 Dry-type, self-cooled ventilated UDINE oss cig Litany 53 ieo% inne en DG incest inte hp aie 0.6 * This material is reproduced with the permission of the Amer- ican National Standards Institute from the ANSI Standards entitled “Guide for Loading Oil-Immersed Distribution and Power Trans- formers” ANSI C57.92, copyright 1962 and “Guide for Loading Dry- Type Distribution and Power Transformers” ANSI C57.96, copy- right 1959. Transformer 8-7 TM 5-811-1/AFM 88-9 Chapter 1 C57.12.30 cover both the initial installation of cooling fans and the provisions which permit addition of fu- ture forced-air-cooling. Fan cooling can be controlled by either top-liquid temperature or winding tempera- ture. Usually the type of control should be left to the option of the manufacturer. (1) Main electric supply stations. Forced-air-cool- ing will be provided in accordance with the criteria of chapter 4. (2) Load center transformers. Since load center transformers supply electric energy for direct utiliza- tion by motors, lights, and other devices, initial forced- air-cooling is not necessary in most cases. Provisions for addition of future forced-air-cooling should be pro- vided only when such cooling equipment is a cost effec- tive way to satisfy future load increases. d. Basic impulse levels. Insulation characteristics for voltage surges of high magnitude but short dura- tion, such as lightning or switching surges, are deter- mined by impulse tests. The most common test is the application of either a 1.2 x 50 microsecond or a 1.5 x 40 microsecond full impulse voltage wave, dependent upon the industry specification. The crest value of the voltage wave is called the basic impulse insulation level (BIL) of the equipment involved. Standard basic impulse insulation levels have been established for each voltage reference class; however, equipment rated 15 kV and below is often built to a so-called “dis- tribution-class” BIL rather than to the standard or “power-class” BIL. The distribution class BIL require- ment is normally even lower for ventilated dry-type transformers than for oil-immersed transformers as shown in table 8-4, although BIL levels equivalent to those for distribution-class oil-immersed units can be obtained for some voltages at a relatively small cost in- crease. Ventilated dry-type transformers will always be provided with a BIL rating equivalent to oil-im- mersed units of the same rating. Use of external de- vices such as surge arresters to provide an adequate BIL protective level is not acceptable. e. Three-phase connections. The wye-wye connec- tion of two-winding transformers requires that a fourth wire (neutral or ground) be installed throughout the length of distribution lines, and the solid ground- ing of the primary and secondary windings of trans- formers. Loss of either the primary or secondary ground and unbalanced loading can cause interference on communication circuits and result in excessive heating of the tanks of 3-phase transformers. For those reasons, the wye-wye connection of two-winding transformers will be avoided whenever possible. A delta primary connection eliminates objectionable odd harmonic paths and a wye-secondary connection pro- vides enhanced protection against low magnitude ground fault currents. Therefore, connections will be delta-wye, except where other connections are techni- cally advantageous. When wye-wye connections can- not be avoided, a three-winding transformer should be specified. The tertiary winding will be specified to be delta connected to provide a path for the third harmonic currents. Elimination of ferroresonance is not an acceptable reason for providing a wye primary connection. f. Impedance. Standard impedances should be used to the greatest extent possible for reasons of economy. However, industry standards do not specify the per- cent impedance voltage for overhead transformers or for pad-mounted compartmental distribution trans- formers of 500 kVA and less. Manufacturers typically supply these units with such low impedances that normal interrupting duties for protective devices may be inadequate. For this reason, it may be necessary to specify minimum impedances for three-phase pad- mounted compartmental and overhead type trans- formers. These impedances should be no more than are required by industry standards for load center trans- Table 8-4. Basic Impulse Insulation Levels Basic impulse level (BIL) kV Oil-immersed units Ventilated dry-type units Normal Insulation duty for 57.12.00 * reference insulation (57.12.00 requirement for class reference requirement for distribution 57.12.00 # Available and kV class power class class > requirement mandatory Di pege Sorat ae ees 60 EE eos sss 3 60 MOF o.oo BoP ae tee 60 TB pe saree eae te 110 UNO soe os hiss one, 95 GOTH Sri als 95 Be ee aie nai 150 ack Ossie view VUE Ce 150 AO sce beasciastesie de sas 150 Pini tad Piya amie 200 OO: Fo caie cis 5 Nise Fas tye 200 OA aed oii chats - * From tables 4, 5, 6, and 7 of ANSI/IEEE C57.12.00-1979 and reprinted with the permission of the Institute of Electrical and Electronics Engineers, Inc. » Rating also applicable to primary and secondary unit substations. ¢ Rating not C57.12.00 listed, but available. TM 5-811-1/AFM 88-9 Chapter 1 Table 8-5. Standard Load Center Percent Impedances Maximum three-phase short circuit Percent amperes Transformer impedance, kVA when primary 208Y/120 volts 480Y/277 volts cei . From 100% motor From 100% motor transformer contribution transformer contribution DA vre-cinrec 5s 2 sty 5 oes ewe ons 9b 4 oars 2.0 TBGUD oo.s sae 4 ace 5 ops suse dws oreabms 1,,300 150. . iol 220 20,800... . 1,700 225... eid AO. 31,300. . . 2,000 300. . 2 4.5 EEN ON cia, de evans » rv tines, HRs 3,300 500. . ow a ROEM Sia svexsss Giles piri 6 od oes ae ee 5,600 750. . ». 575 36,200. 8,300 1,000. . sae BedO 48,300. 11,100 1,500. . vera Dado 72,500. 16,700 2, OOO bbe bald sicie vise in ree ois 5.75 QE re hieiees t,o sotcearesel dpe's tie te 22,200 ® These impedance values are reproduced by permission from NEMA Standards Publication No. 210-1970 (R 1976) entitled “Secondary Unit Substations.” > Transformer short circuit current based on unlimited utility company contribution. former stations of the same kVA rating as shown on table 8-5. Where the designer feels that circumstances warrant specifying a minimum impedance for over- head and single-phase pad-mounted compartmental units, the values of table 8-5 should be used. Values greater than 1.5 percent for transformers 75 kVA and smaller are not justified usually. g. Voltage taps. Power transformers are normally provided with manual voltage taps at no additional cost. Taps are not always required by NEMA or ANSI standards for smaller distribution transformers. Where available, taps should be required on trans- formers. h. Factory tests. ANSI C57.12.00 requires two kinds of factory tests, routine and optional. Routine tests required on transformers, or in some cases for one unit of given rating, are winding resistance meas- urements; voltage ratio, polarity and phase relation tests; current, impedance, excitation, and load loss measurements; and temperature and low-frequency di- electric tests. Optional tests which can be required are impulse, insulation power factor, switching surge, and front-of-wave tests, which for transformer voltages and capacities encountered on military installations, are rarely necessary to the degree covered by ANSI. (1) ANSI impulse tests. A full-wave impulse test demonstrates the basic impulse insulation (BIL) with- stand to traveling waves entering the transformer over the incoming circuit. This test is used in conjunc- tion with a reduced-wave impulse test which repre- sents the characteristic wave shape of the combined transformer winding and the impulse generator. An- other test is the chopped wave impulse test which simulates a wave traveling along a line after flashing over an insulator some distance away from the trans- former. Also covered is the front-of-wave impulse test which represents a direct lightning stroke. (2) Usual impulse test requirements. Normally, the only impulse test necessary is a production-line im- pulse test which consists of first imposing a reduced wave and then a full wave on each fully insulated primary terminal. Since such a test is mainly for qual- ity control, tests must be run for each transformer. Prototype tests do not indicate quality control defi- ciencies. (3) Optional NEMA impulse tests. Optional NEMA impulse tests include either a nominal test se- quence consisting of a reduced full wave, two chopped waves, and one full wave or a combined test sequence which interposes two or more front-of-wave tests be- tween the reduced full wave and the two chopped wave tests on the nominal test sequence. These tests are ex- pensive and manufacturers will ordinarily not provide them for distribution transformers. Such tests are nor- mally specified only by utilities and only for their large transformers (50 MVA and larger) or where re- duced insulation is provided on transformer windings rated 115 kV and above. TM 5-811-1/AFM 88-9 Chapter 1 CHAPTER 9 SURGE PROTECTION AND GROUNDING 9-1. Voltage surges and potential gradients. Even the best designed electric system is subject to overvoltages resulting from physical conditions not subject to the owner’s control. Dangerous potential gradients can result also from improper design. a. Causes. Lightning imposes voltage surges on aerial lines either by direct strokes or by induction. Such surges can be transmitted to underground lines. Opening and closing circuits in large generating plants or switching stations can raise voltages to two or three times normal for a brief period of time. In addition, ex- cessive voltages and currents can result from short cir- cuit conditions when line-to-line or line-to-ground faults occur, because of inductive/capacitive character- istics of the line between the electric power source and the fault location. Transformer ferroresonance can create overvoltages also as discussed in chapter 5. b. Elimination. Since voltage surges can result in personnel injuries from electrical shock, insulation damage to equipment, and possibly fire, surge ar- resters are used to provide safe dissipation of these surges. Grounding systems should limit potential gradients to safe values. Proper relaying should pro- vide isolation and disconnection of faulty equipment and lines when a short circuit occurs. 9-2. Methods of controlling voltage surges and potential gradients. a. Surge arresters. Surge arresters are used to safe- guard apparatus against hazards caused by abnormally high voltage surges. Such overvoltage can cause serious damage if arresters are not correctly coordi- nated with the insulation strength of the protected equipment, and are unable to discharge the energy properly. To function correctly, arrester protective levels must be lower than the insulation withstand strength of equipment to be protected. The usual margin is 20 percent which allows for some insulation deterioration due to equipment age. b. Characteristics. An arrester’s characteristics of impulse sparkover voltage, discharge voltage, and voltage rating will have protective margins coordi- nated with the equipment insulation characteristics of insulation lightning impulse, basic impulse level (BIL), and line-to-ground voltage rating. Lead lengths must also be taken into account. (1) Impulse sparkover voltage. Impulse sparkover voltage is the highest value of voltage attained by an impulse of a designated wave shape and polarity ap- plied across the terminals of an arrester prior to the flow of discharge current. This voltage plus the lead length voltage contribution is the highest that can be impressed on protected equipment because, at this level, the arrester will sparkover and discharge the surge to ground. Arrester front-of-wave sparkover voltage is compared to the insulation lightning im- pulse (chopped-wave) crest value that the protected equipment is required to withstand for purposes of de- termining the protective margin. (2) Discharge voltage. Discharge voltage is the voltage that appears across the terminals of an ar- rester during passage of discharge current. Arrester maximum discharge voltage is compared to the BIL value that the protected equipment is required to with- stand for purposes of determining the protective margin. (3) Voltage rating. The nameplate voltage rating of an arrester is the maximum permissible operating voltage at which the arrester can operate correctly. (a) Operation. An arrester has a maximum volt- age level above which the arrester cannot seal off the 60 Hz line (follow) current, after sparkover on surge voltage. If the correct nameplate rating is used, the ar- rester can interrupt 60 Hz line current even though there may be a line-to-ground fault on another phase. If the 60 hz follow current is not immediately extin- guished, the arrester may fail. (b) Sizing. On a modern overhead grounded wye primary distribution system (effectively grounded sys- tem), the arrester is able to reseal at a voltage level that does not exceed 1.25 times the nominal line-to- ground voltage. For a main electric supply station with a 13,200Y/7,620 volt secondary, the minimum ar- rester rating would be 1.25 x 7.62 = 9.53kV. A9-kV arrester might not reseal so a 10-kV arrester, which is the next higher standard rating, should be provided. For ungrounded systems, ratings should equal or ex- ceed the phase-to-phase system voltage dependent upon the size of the maximum ground fault that could occur. (4) Lead length. Lead length is the length of line connecting the line terminal of an arrester to the ener- gized line (line lead) plus the length of the line (ground lead) connecting the ground terminal of an arrester to a common ground. On riser poles the common ground is the conducting shield or sheath of cable at the cable 9-1 TM 5-811-1/AFM 88-9 Chapter 1 termination. Leads should be kept as short as prac- ticable, since voltage drops of both leads must be added to the sparkover and discharge voltages of the arrester when figuring protective margins. A common- ly used figure for lead voltage drop is 2 kV per foot of length. c. Classification. Arrester classification is based on specified test requirements. Of the six classifications available, only the four valve arrester types which are designated as station, intermediate, distribution, and secondary have suitable operating characteristics. Table 9-1 indicates protective margins for oil-im- mersed transformers of various primary voltages. The discharge values are for a 10 kA impulse current crest, the current commonly used as a basis for insulation co- ordination on a medium-voltage distribution systems. (1) Distribution class. Distribution arresters, with the lowest protective margins for voltage systems above 1,000 volts, are primarily used as an economical way of providing lightning surge protection for distri- bution equipment. Aerial to underground risers re- quire surge protection, as do transformers, capacitors, and regulators mounted on poles. (2) Station class. Station arresters are capable of discharging the most surge energy and, therefore, will be used at main electric supply stations for protection of incoming aerial lines and where needed for protec- tion of equipment not within the protective radius of an incoming line arrester such as transformers and regulators. (3) Intermediate class. Intermediate class ar- resters have protective characteristics and costs some- where between those of station class and distribution class types. Intermediate arresters are required to pro- tect pole-mounted transformers and §aerial-to- underground risers at munitions areas. Elsewhere, when such units are proposed as a substitute for other classifications, their use should be justified, except where such use is the installation’s normal policy. (4) Secondary class. Secondary arresters are normally required only for low-voltage service at munitions areas. Arresters will be located as close to the electrical service entrance as possible and a sep- arate ground from the secondary service entrance will be bonded to the munition building counterpoise. Range of voltage ratings is 0.175 kV to 0.650 kV. d. Location. Arresters should be located as close to the equipment protected as is practicable. Arresters will be connected to line conductors ahead of any over- current protective devices immediately adjacent. (1) Underground connections. Procedures for esti- mating magnitudes of surge voltages at distances re- mote from the transition arrester location are very complex. An IEEE committee report recommends doubling both the sparkover and the discharge plus lead voltage for the arrester and then requiring a 15 percent margin over the equipment insulation. This recommendation will be followed in areas with numer- ous lightning storms and may require intermediate ar- resters at transition poles, arresters at transformer stations, or both provisions for adequate protection. (2) Main electric supply station connections. On Table 9-1. Aerial-Mounted Oil-Immersed Transformer Surge Protective Margins Protective ratio comparison * Arrester Transformer Voltage Sparkover > Discharge > insulation level Classification kV Arrester Trans. Ratio Arrester Trans. Ratio kV kV kV BIL 4,160 Distribution’. . 0:35.26 63 6 Intermediate.......... 6 12,000 Y/6,930 Distribution or Intermediate He 12,470Y/7,200 SURGE 5, ose donee 13,200Y/7,620 Distribution ......... 10 : or Intermediate . és al Oil-immersed 13,800 I hy cis hs ain a 12 Distribution. .... ..:. '. 18 24,940Y/14,400 Intermediate......... 21 MAMON G5 93 sis 298 6 5 21 Distribution ......... 27 34,500Y/19,920 Intermediate......... 30 SCAND sis hid «ors 30 @ Lead length not included. > Characteristics are median of the range of maximums listed in ANSI (62.2 and are reproduced with the permission of the American Na- tional Standards Institute from the ANSI Standard entitled “Guide For the Application of Valve-Type Lightning Arresters for A.C. Systems,” copyright 1969. 9-2 main electric supply stations, the incoming aerial line switching devices and the transformer primary termi- nals are normally the main elements requiring surge protection. (a) Incoming lines. Arresters should be located on the line side of any incoming line fuse to prevent the lightning discharge from passing through the fuse. Arresters need not be installed on the line side of group-operated disconnect switches. However, ar- resters should be connected close enough to protect the switch adequately when the switch is closed. Line en- trance gaps may be used on the line side of any switch for protection when the switch is open. Normally where two-column structures are provided as in figure 4-6, arresters are mounted on the load side as this structure configuration does not lend itself to line side connection. Other structures, such as a double square bay structure, have a configuration which makes loca- tion of the arrester on the line side of the switch the most practicable arrangement. (b) Transformers. Economics makes it desirable to protect both incoming line devices and the trans- former with the same set of arresters, which may re- quire mounting the arresters some distance away from the transformer terminals. The permissible separation distance depends upon various factors, but a lead length kept to less than 50 feet appears to provide an adequate protective margin. In regions of high light- ning incidence, surge arresters will be mounted on each of the incoming aerial line structures and directly on each of the main supply transformers. (c) Generators. In addition to surge arresters at transition points between aerial and underground lines, surge protection may be necessary within a gen- erator plant. Surge arresters in parallel with surge pro- tective capacitors may need to be installed either at the terminals of the generator switchgear bus for over- all machinery protection or at the terminals of each generator, dependent upon the degree of protection re- quired. Surge protective capacitors reduce steep wave fronts, which if imposed on rotating machinery could result in stresses exceeding a machine’s insulation impulse strength. e. Overhead ground wires. Overhead ground wires are run parallel to and above electrical lines, in order to shield lines from a direct lightning stroke. (1) Transmission and distribution lines. Overhead ground wires are used for protection of transmission lines, but rarely is such an installation economical for distribution lines. Overhead ground wires will not be installed to protect distribution lines, unless such an installation is necessary to be consistent with local usage. (2) Main electric supply stations. Shielding should be provided because of the cost and importance of such stations. Transformer stations with incoming aerial TM 5-811-1/AFM 88-9 Chapter 1 lines-above 15 kV should be shielded because of equip- ment cost. Such shielding reduces possible surge volt- ages. This shielding may take the form of lightning masts located on top of the station metal structure to provide the required cone of protection for apparatus and circuits within the station area. The incoming line should be shielded for at least 1/2 mile from the sta- tion to provide sufficient line impedance between the nonshielded line and the station, otherwise high dis- charge currents could occur resulting in excessive ar- rester discharge voltages. When the incoming lines be- long to the serving utility and shielding cannot be pro- vided, design calculations must assure adequate surge arrester protection or other methods of limiting travel- ing wave sizes. (a) Zone of protection. The zone of protection of a shielding system is the volume of space inside which equipment is considered to be shielded. The shaded areas on figure 9-1 illustrate the zones of protection for both single and double mast or wire systems plus the range of angles often used and the maximum angles recommended. (b) Strength of wire. Breakage of shield wires could result in outage and damage to equipment. To minimize possible damage, ground wires should be at least 7/16-inch, high-strength, zinc-coated steel (ASTM A 475) with a minimum breaking strength of 14,500 pound-force (1bf) and maximum design tension should be limited to 2,000 pounds per conductor. f. Grounding. For safety reasons, electric power sys- tems and equipment are intentionally grounded, so that insulation failure results in operation of protec- tive devices to deenergize circuits, thus reducing risk to personnel. The word “grounding” is commonly used in electric power system work to cover both “system grounding” and “equipment grounding”; however, the distinction between system and equipment grounding should be recognized. A system ground is a connection to ground from one of the conductors of an electric cir- cuit, normally the neutral conductor. An equipment ground is a connection to ground from noncurrent carrying metallic parts of the installation such as con- duit and equipment cases of apparatus connected to an electric circuit. IEEE 142 discusses grounding practice in greater detail. (1) System grounding. Wye-connected electric dis- tribution systems should be provided with a grounded neutral connection. Such intentional grounding mini- mizes the magnitude and duration of overvoltages, thereby reducing the probability of insulation failure and equipment damage. Where systems are delta-con- nected, no ground will be provided. Neutrals for each voltage level should be grounded independently at each electric power source; that is, at transformer secondaries and at generators. (a) Transformer neutral grounding. Trans- 9-3 TM 5-811-1/AFM 88-9 Chapter 1 Angle w> Single mast or shield wire US Army Corps of Engineers Degrees 20 to 60 40 to 60 Degrees recommended Figure 9-1. Zones of protection for masts and shield wires formers which have wye-connected secondaries should normally be solidly grounded. Solid grounding is the least expensive method of limiting transient overvolt- ages while obtaining enough ground fault current for fast selective fault isolation. Other methods of ground- ing are resistance grounding and reactance grounding, but in most caess, reactance grounding of transform- ers provides no advantages over solid grounding. A disadvantage of systems grounded through resistors is that surge arrestors should be sized as if used on un- grounded-neutral systems, that is, with a voltage rat- ing at least equal to the line-to-line voltage. 1. Voltage above 15 kV. Because of the pro- hibitive cost of grounding equipment and the in- creased surge arrester cost, systems should usually be solidly grounded. 2. Voltage from 2.4 to 15 kV. Overhead distri- bution systems and underground distribution systems which supply transformers protected by primary fuses require enough fault current to melt primary fuses on a ground fault, so that solid grounding is generally preferable. However, in some cases, resistance ground- ing may be needed to limit ground fault currents to values less than withstand ratings of equipment when such equipment is designed for direct connection to voltages of the 2.4 to 15 kV level. 3. Low-voltage systems. Use of other than solidly grounded systems must be justified on the basis of a paramount necessity for service continuity. How- ever, if a policy of immediate repair is not enforced such a system may actually degrade service continuity by its more sensitive response. (b) Generator neutral grounding. Normally gen- erating units are provided with reactor grounding only when solid grounding would cause ground-fault cur- rent to exceed the short-circuit current for which the unit is braced and when harmonic current circulation needs to be minimized. (2) Equipment grounding. Intentional equipment grounding maintains metallic surfaces at low poten- 9-4 tials above ground, thereby decreasing possibility of electric shocks. System grounds and equipment grounds are usually interconnected at some point. Some state safety orders do not permit grounding of enclosure cases supported on wood poles, when acci- dental contact with bare aerial lines might occur. g. Ground fault relaying. Two types of ground fault relays are in general use. Overcurrent relays are used on medium- and high-voltage systems, and the less ex- pensive ground fault protector is used on low-voltage systems. Since no current or voltage is present in the ground conductor under normal balanced system oper- ation, ground relays can be made very sensitive. Ground relays can also be set to operate very quickly since coordination between voltage levels is not a con- straint. Their use permits isolation of faulty equip- ment before short circuits can cause damage. (1) Medium- and high-voltage systems. The ground fault relay used should have the same time- overcurrent characteristics as the overcurrent relays used for phase protection. The ground fault relay is interposed in the residual connection between the cur- rent transformers in each of the three phases and senses the fault current of a grounded wye connection. For further information on ground fault relaying see “Applied Protective Relaying” and “The Art and Sci- ence of Protective Relaying” (see app. B). (2) Low-voltage systems. Where low-voltage ground fault protection is required by the NEC, pro- tection is normally installed as a part of the building secondary main switchboard, but some instances make installation advisable at the exterior transformer sta- tion. Although overcurrent relays can be used to meet NEC requirements, normally the less expensive ground fault protector is satisfactory. (a) Single electric source systems. Ground fault protectors should utilize sensors of the vectorial sum- mation type which either requires one sensor for each phase and the neutral (residual sensing) or one window type sensor around all three phases and the neutral (zero sequence sensing). Use of a single sensor on the grounding electrode conductor is not acceptable, be- cause the additional grounding connection at the transformer station provides a second path of fault current which is not sensed. (b) Multiple source electric systems. Erroneous ground fault response can occur in multiple-source, three-phase, four-wire distribution systems. The com- mon neutral conductors have multiple ground points providing alternate paths for fault currents, which if not properly monitored, can cause nuisance tripping or failure to trip. For such systems, a detailed analysis may be necessary to ensure ground fault protection that will trip appropriate circuit breakers dependent upon the fault location. 9-3. Ground electrodes. The most elaborate grounding system that can be de- signed may prove ineffective unless the connection of the system to earth is adequate and has a sufficiently low resistance. Since the desired resistance varies in- versely with the fault current to ground, the larger the fault current the lower the resistance must be. For main electric supply stations and plants generating at medium voltages, the earth resistance should not ex- ceed 5 ohms. In some cases, lower values of earth re- sistance may be necessary. For electrical installations other than generator plants or main electric supply stations, the NEC requirement of 25 ohms maximum is usually acceptable. a. Resistivity of the soil. The resistivity of the earth varies dependent upon its composition, as indicated in table 9-2. More moisture in the soil or a higher soil temperature usually decreases soil resistivity. For most cases, a 5/8-inch by 8-foot ground rod is ade- quate. The methods of providing earth connections given in this manual should be used to provide the re- quired resistance to ground, except when the installa- tion or the local utility indicates that special tech- niques are necessary. In that case, local practice should be followed. b. Elements of the system. Ground cables should be copper. Other metals or metal combinations should be used only in those cases where the mechanical strength of copper is inadequate. In general, driven TM 5-811-1/AFM 88-9 Chapter 1 copper-clad steel ground rods should be used as ground electrodes since such rods have a higher conductivity than most other types. High conductivity pure copper ground rods, because of their low strength are easily damaged when driven into the ground. Galvanized steel ground rods have a much shorter life, especially in soils with lime content; however, such rods may be required where guys are grounded as covered in chap- ter 6. Stainless steel ground rods are expensive. While connection to an extensive metallic water system usu- ally provides a ground resistance of less than 3 ohms, there is the possibility that water main maintenance or other work might result in accidental disconnection of grounds and create a hazardous condition. There- fore, such connections should only be provided as a sec- ondary backup to made electrodes. (1) Additional electrodes. Whenever the 5/8-inch by 8-foot ground rod does not provide the required ground resistance, either longer or additional ground rods may be necessary. Since ground resistance usually decreases with depth, the use of longer ground rods normally is the most economical method. However, where rock is encountered, use of more rods, a ground counterpoise, or a ground grid may be necessary. Ideal- ly space between rods should be no more than the length of a rod, but never less than 6 feet. (2) Other made electrodes. Butt grounds or ground plates are sometimes provided on poles as an economical method of grounding the overhead ground wire, but as their use is permitted only in areas with low soil resistance, such grounding methods should be used only where such an installation is local practice. These made electrodes can not be used as the sole grounding electrode for apparatus or neutral grounds, which require a ground rod installation as a minimum. 9-4. Grounding details and requirements. Grounding will be provided in accordance with the ap- plicable area code. a. Main electric supply stations. Because of the equipment layout within a station, steep voltage gradi- ents might occur if each apparatus “island” were sepa- rately grounded. (1) Ground grid. In order to prevent steep-voltage gradients and also to design for maximum voltage ex- Table 9-2. Resistance of One 5/8-Inch by 8-Foot Ground Rod in Various Soils * Resistance in ohms Type of soil Minimum Average Maximum Ashes, cinders, brine waste... . . Gees eet SEs eM LENT onthe RAO) miracle Fontes ki SRA Ud 28 Clay, shale, gumbo, loam....... dts. tk. has ee, Hae LOE RS se i nate LE Ae ak 66 Same, but with sand and gravel ... MA... 5c oipsiedclvtatet ss SVG Pbiy 6S) 2 nuns d ceo osles Paving 541 Gravel, sand, stones, little clay orloam.................. exis! ie sxene' oko tsk bE oly OPO waa s yn soon a at le le 1,825 * Based on the resistivity of soils and formulas for calculation of resistance given in tables 7 and 10 of IEEE 142-1972. The use of such data is by permission of the Institute of Electrical and Electronics Engineers. Inc. Use of a 3/4-inch diameter rod of the same length decreases re- sistivity less than 5 percent. TM 5-811-1/AFM 88-9 Chapter 1 cursions at the station, without the use of an excessive conductor size, a grid system is installed below grade enveloping the fenced area. Figure 9-2 shows such a system for solidly grounded transformers. Ground wire spacings of approximately 10 to 12 feet are com- monly used. Exact spacing may be slightly more or less to suit station configurations. The perimeter ground wire should be installed not less than 2 feet outside the station fence to protect approaching personnel from step-and-touch potential exposure. (2) Special danger points. Equipment operating handles are a special danger point because of the higher probability for coincidence of adverse factors, namely, the presence of a person contacting grounded equipment and performing an operation that can lead to electrical breakdown. If the grounding system is de- signed conservatively for safe mesh potentials, then the operator is not exposed to unsafe voltages. How- ever, due to the uncertainty inherent in substation grounding design, a metal grounding platform, con- nected to the operating handle and to the grid in at least two places, should be placed so the operator must stand on the platform to operate the device (see figure 9-2). This arrangement should be provided regardless 9-6 of whether the operating handle is insulated. b. Other installations. Overhead transformer instal- lations will be grounded in accordance with figures 8-1 and 8-2. Pad-mounted compartmental-type trans- formers will be grounded as shown on figure 8-4. Load center transformer stations and enclosing fence will be grounded as shown on figure 9-3. Medium-voltage riser poles will be provided with surge arresters, even in areas having a low lightning incidence, and grounded as shown on figure 8-4. c. Miscellaneous. On low-voltage systems, any equipment supplied from a grounded electric source shall, in addition to the local grounding electrode, be provided with a continuous metallic conductor (either a metal conduit or a grounding wire) extending from the equipment ground point back to the system (neu- tral) ground point for that voltage level. Conductive poles such as metal or reinforced concrete will always be provided with an individual ground electrode con- nection. Possibility of mechanical damage, corrosion, and other conditions which can degrade the continuity of a grounding system make such multiple-grounding points necessary. ™ Grounded luminaire Flexible grounding connectors Grade ELEVATION A-A eet Ground grid ground rods “ams Po (12 minimum) ae ASE . SF fai oe Ground grid cee system cable 10°. to\12" grid spacing Surge arrester Incoming line metal switching structure Surge arrester ground system reconnection 5-811-1/AFM 88-9 Chapter 1 Grounded switch operating handle Grounded metal switch operating platform Equipment ground grid < Battery house ht—Fence Unit substation : 2 ito 5" Metal structure ground Surge arrester ground rod (two minimum each three-phase set) Transformer case ground Fence ground © US Army Corps of Engineers Figure 9-2. Grounding of a main electric supply station Neutral ground Switchgear ground bus Gate flexible ground 9-7 TM 5-811-1/AFM 88-9 Chapter 1 Load center transformer Fence Concrete pad Ground wire Ground rod ELEVATION Transformer sect ion——. Secondary neutral ground, where required Primary sect ion— _ Secondary section Primary equipment grouni + ety x Equipment removal gate x J Fence ground f Secondary equipment Surge arrester x ground ground, where required ¥ Fence + Ground rod Counterpoise Transformer case ground Flexible gate ground —Personnel gate PLAN US Army Corps of Engineers Figure 9-3. Grounding of a load center transformer station TM 5-811-1/AFM 88-9 Chapter 1 ——-_— surge arrester Primary fuse cutout Medium-voltage cable terminator. Ground wire Seal end of conduit Molding Riser conduit Ground rod connection not shown, similar to figure 8-1 SIDE VIEW ELEVATION . US Army Corps of Engineers Figure 9-4. Provision of surge arresters at a medium-voltage riser pole TM 5-811-1/AFM 88-9 Chapter 1 CHAPTER 10 ROADWAY AND AREA LIGHTING 10-1. General. Quantity and quality of illumination will conform to the latest issue of the Illumination Engineering So- ciety’s (IES) Lighting Handbook, except as modified in this chapter. Data contained in IES RP-8 provides a basic reference relating to the principles of standard roadway lighting practice. Unless otherwise indicated, illuminances are always on the horizontal plane at ground level. Where directed, illuminances shall be modified to be in conformance with current energy conservation policies. 10-2. Roadway lighting design. a. Illuminances. The average maintained horizontal illumination recommended by IES is based on the type of traffic flow and the character of the surrounding area. On military installations, the values for road and area classification used will range usually from 0.4 to 1.4 foot candles. Luminaires located along roadways and intersections at spacings ranging from 150 to 200 feet can provide illumination within this range as shown in table 10-1. The definitions of the IES classi- fications in table 10-1 can be found in the current IES Lighting Handbook. Spacings are approximate and may vary somewhat dependent upon the actual lumi- naire type, mounting height, roadway width, and other conditions applying. b. Luminaires. Normally luminaires of the enclosed type utilizing high-pressure sodium (HPS) lamps will be used. A discussion of the characteristics of various light sources is presented later in this chapter. Figure 10-1 indicates a typical roadway lighting installation. Bracket length is dependent upon the location of the luminaire and the roadway width, but should not ex- ceed 25 percent of the mounting height normally. Light distribution characteristics of any luminaire will suit the mounting height, road geometry, and uni- formity required. Vertical and lateral light distribu- tion and control of these characteristics should be indi- cated for each luminaire. (1) Vertical. Vertical light distributions, based on spacing-to-mounting height ratios, are categorized as short, medium, and long distribution. Short distri- bution is suitable for pole spacings no greater than 4.5 times the mounting height; medium distribution is suitable for pole spacings from 4.5 to 7.5 times the mounting height; and long distribution is suitable for pole spacings from 7.5 to 12 times the mounting height. Normally, medium distribution is the most appropriate choice for the mounting heights and spac- ings utilized on military installations. (2) Lateral. Lateral light distributions, based on the shape of the half candlepower isocandela trace which falls within the longitudinal distribution range, are classified as Types I through V. A general guide to their use, compiled from data in IES RP-8, is shown on figure 10-2. Selection is dependent upon whether the luminaire is situated at the side or at the center of the road, whether the luminaire is located between intersections or at an intersection, and the roadway width to mounting height ratio. Since most luminaires are mounted at the side of the road, Types II, III, or IV are used more often. Type II is used to light narrow roads, and types III and IV are used for lighting pro- gressively wider roadways. (3) Control. Control of the amount of light in the upper portion of the beam above maximum candlepow- er is classified as cutoff, semicutoff, or noncutoff. Semicutoff limits the lumen output above the nadir to 5 percent at 90° horizontally and to 20 percent at 80°, whereas cutoff reduces these two percentages by one- half, and noncutoff places no limitations. Semicutoff Table 10-1. Illumination Versus Spacing Required HPS IES classification average maintained Spacing lamp footcandles * feet » Area OB Nic hears meine es ares axes os 5 ae + 5 Me eis aos ps, alah s axes Residential OD. 5s, ARR REN. sow Fett 200 . Intermediate Le ee ae en eee eee eS eer on Intermediate ® With a uniformity ratio meeting IES requirements. » Based on units mounted 30 feet above the roadway on the same side. For intermediate areas, road width is assumed to be 40 feet and for residential areas to be 30 feet. US Army Corps of Engineers 10-1 4—_—_——Indicate TM 5-811-1/AFM 88-9 Chapter 1 ae | Slip fitter mounting height Ground line Elevation CONCRETE POLE Indicate bracket length and diameter }+—Tapered hollow shaft, octagonal or round. Ground rod Elevation CONCRETE POLE EMBEDDED BASE US Army Corps of Enginee rs ee bracket length and diameter Slip fitter T__Iadicate be Steel or mounting aluminum shaft height Elevation METAL POLE Indicate diameter of bolt circle Top view Provide ornamental covering when Door opening bolts are exposed Ground line Concrete — it footing (indicate |, size Anchor bolts (indicate length) Elevation CONCRETE OR METAL POLE ANCHOR-BOLT-MOUNTED BASE Figure 10-1. Typical roadway lighting installation TM 5-811-1/AFM 88-9 Chapter 1 Width of roadway in Luminaire multiples of mounting height (MH) pie location Distribution Pabaher with respect pattern shape coxtondvay Width Placement 2 a Up to Center I Center Canine O—— oe) 2 x MH suspension a ee / iS Local 4 i Center pete roadway yay W)77 intersections One side II Side ete; or oe staggered Local 4 a Side ee So roadway way al intersections Up to as) Sclaee One side Boo § Side —.. : ew eee see 1.5 x MH Staggered and over or opposite Up to ee Se pn 15: ia One side ee oe 1.5 x MH Staggered and over or opposite A Y Local Up to Vv Center 2 x MH roadway a wy intersections “This material is reprinted by permission of the Illumination Engineering Society from 1ES RP-8-1977 entitled "Standard Practice for Roadway Lighting." Figure 10-2. Lateral lighting distributions 10-3 TM 5-811-1/AFM 88-9 Chapter 1 is most generally selected as a compromise between noncutoff, where high brightness in the upper part of the beam produces both discomfort and disability glare, and cutoff, where lumen control necessitates closer spacings to satisfy uniformity requirements. c. Placement. Luminaires will be located to provide uniformity of illumination with an average-to-mini- mum spacing ratio not to exceed three to one, except for local residential streets where the ratio may be as high as six to one; actual requirements should be checked against the IES Lighting Handbook guide- lines. Generally, luminaires for two and three lane roads should be placed on one side of the street for rea- sons of economy. Adequate coverage should be pro- vided so that security is not degraded. For four lane roads, poles may have to be placed on both sides of the road for uniformity. The illumination at intersections should be at least twice that required on the intersect- ing roads. Figure 10-3 indicates that to meet this re- quirement, two luminaires are normally all that are necessary for two and three lane roads; but for inter- sections of four lanes or those with merging traffic, four luminaires are usually necessary. 10-3. Area lighting design. a. Illuminances. Muminances will conform to the re- quirements contained in the IES Lighting Handbook for average maintained illumination, except as fol- lows: (1) Normal vehicle parking (including minor re- pair). Areas will have 2 footcandles maximum, except where higher illuminances are approved. Often, road- way rather than floodlighting luminaires may be more suitable. (2) Sports lighting. The classifications shown in table 10-2 will be used. Table 10-2. Sports Lighting TES classification Municipal and semi-professional Industrial league . Class III or IV Recreational US Army Corps of Engineers (3) Storage areas. Where lighting is required for nighttime use, a maximum of 2 footcandles will be pro- vided, except where additional lighting has been justi- fied or is required by the Using Agency. (4) Aircraft service areas. Aircraft service areas will be illuminated in accordance with the criteria given in AFM 88-15. b. Luminaires. Adjustable floodlights or roadway luminaires, with beam pattern selected for half over- Luminaire required for continuous lighting (roadway) = se 1 TWO LANE ROADS | r it ; || -Luminaire required for ;f partial lighting (intersection) “s— ' Sees . ' aid] a = FOUR LANE ROADS “This material is reprinted by permission of the Illumination Engineering Society from IES RP-8-1977 entitled "Standard Practice for Roadway Lighting" Figure 10-3. Intersection lighting placement 10-4 lap, are generally used as area lighting units. To pro- vide economical coverage, a minimum of 60 percent of the beam lumens should fall within the area to be lighted. Normally floodlights will be enclosed type, either Heavy Duty (Class HD) or General Purpose (Class GP). A description of floodlight construction re- quirements is discussed in chapter 11. Use of Class 0 and Class 01 units, which are open types and accumu- late more dirt, should be avoided. c. Placement. Only areas with nighttime activities will be lighted. Floodlighting is not justified when used only for aesthetic purposes. Floodlights should be located on buildings, where practicable, or on poles or metal towers. Roadway luminaires adjacent to areas to be floodlighted may be utilized for both roadway and area lighting, where mounting height and spacing of units is appropriate for both types of illumination. Lo- cation of floodlights for apron and hardstands is cov- ered in AFM 88-15. 10-4. Walkway and bikeway lighting design. Normally roadway lights and building exterior lights can serve also as walkway and bikeway lights. Maxi- mum use should be made of multiple-purpose lighting systems. a. Intensities. Values are dependent upon whether walkways and bikeways are adjacent to roadways or are isolated from vehicular traffic. (1) Adjacent to roadways. Walkways and bike- ways will be illuminated to not less than one-half the maintained illumination required for adjacent road- ways. Areas having changes in grade, such as stairs and ramps, may require special treatment. Crosswalks in the middle of the block will be illuminated to 1.5 to 2 times the normal roadway lighting level. (2) Remote from roadways. Walkways and bike- ways remote from roadways will have a minimum of 0.5 footcandle illumination. Pedestrian tunnels, stair- ways, and overpasses will have a minimum 4.0, 0.6, and 0.3 footcandles illumination, respectively. TM 5-811-1/AFM 88-9 Chapter 1 b. Pole design. Where pole-mounted lights illumi- nate only walkways or bikeways, shorter poles are the most suitable, but luminaire height should not be less than 10 feet. Construction should be such as to mini- mize vandalism by use of break-resistant lenses, tam- perproof screws, and sturdy poles. 10-5. Light sources. a. Selection. Normally, selection of the light source will be made from high intensity discharge (HID) sources. However, minor additions to existing systems may justify use of other sources. In general, HPS lamps should be used because of their luminous effi- cacy. b. Advantages and disadvantages. The advantages and disadvantages of various sources are listed in Table 10-3. c. Discussion. HPS lighting is the most energy effi- cient source which has an acceptable color rendition. (1) Other acceptable sources. Metal halide lamps have a good color rendition, but luminous efficacy, lu- men maintenance (lumen output diminishes more rap- idly throughout life), length of life, and restrike time make them a less than desirable source for many appli- cations. Mercury vapor luminaires, on an initial cost basis, can be less expensive than HPS units when used for minor extensions to existing systems; however, a life cycle cost analysis normally makes the selection of mercury vapor lamps more costly due to lower lumi- nous efficacies. (2) Unacceptable sources. Fluorescent lighting has not been included in table 10-3 due to its relatively low luminous efficacy and the limited control possible with the tubular shape. Low-pressure sodium lighting is also not included, as the color is monochromatic and therefore is not considered suitable for general use. The amount of sodium in low-pressure sodium lamps requires special disposal methods if such lamps are not to pose a fire hazard. Incandescent lighting is included only to indicate the extremely low luminous efficacy Table 10-3. Characteristics of Light Sources * Light sources High-intensity discharge Hnearicieecedt Characteristics HPS Metal halide Mercury vapor Luminous efficacy (lumens/watt)” .......... AOAAZD: i508 se bbs tsb an BOARD oe. 8088 dG. BODO AR. a bis... 15-25 Ten mainpenanod £0046)... 2 9s Ee oe Lamp life (kilohours)................. ze SAMMI ie oa eeu cale cuss lately sabe Startup te Gninutes): os. he es ea Restrike time (minutes). ... 60.5.5 05ss0.00% CCS ROEMAEEION lo) 5 5c) oes ois ei Selon sieve < sie, Neutral surface color effect * Courtesy of Keller & Gannon. » Ballast losses are included. © Computed based on 4,000 burning hours a year. 10-5 TM 5-811-1/AFM 88-9 Chapter 1 and short lamp life provided by this light source. d. Lamp designations. In general, lamps will be des- ignated in accordance with the requirements of ANSI C78.380 in order to provide nationally applicable and convenient lamp identification symbols. These desig- nations ensure interchangeability of lamps bearing the same symbol. Each lamp bearing an ANSI designation has been provided with that specific designation in ac- cordance with the method shown on figure 10-4. Al- though technically low-pressure sodium lamps are not HID lamps, they are included under ANSI C78.380 as a convenience. e. Ballast characteristics. Ballast circuits and operating characteristics vary dependent upon the type of ballast circuit provided. Both ANSI C82.4 and manufacturer's terminology for ballasts can be confus- ing and sometimes appear contradictory. For that rea- son, HID ballasts should be specified by the operating characteristics desired. When ballast specifications cover indoor lamps the ANSI lamp ambient tempera- ture range of 50° F and above may be more appropri- ate than extending the range down to 5° F, — 22° F, or -40° F which are also available. r-Lamp classification ‘Lamp wattage 10-6. Lighting control and wiring system. a. On-off control. Luminaires for dusk to dawn operation will normally be controlled by a photo-elec- tric cell installed on each luminaire; however, central control may be more economical for luminaires having fixed hours of operation. Generally an automatic sys- tem using a time switch with an astronomical dial or a manual on-off control is used for such cases. b. Type of system. Multiple wiring systems will be installed, except for extensions to existing series sys- tems or for long access roads where voltage drops ex- ceeding that permitted for multiple lighting systems (chapter 5) would occur. Circuits for multiple lighting should be designed to utilize the highest low-voltage level appropriate for the installation in order to keep wire sizes and voltage drops to a minimum. Normally lamps will be connected phase-to-neutral rather than phase-to-phase. Where practicable, units should be connected to transformers which serve other loads. Protection and disconnection of lighting circuits will be provided. Electrical characteristics two-digit number assigned in order of existence Physical characteristics twe-letter symbol arbitrarily assigned Special supplementary symbols (not issued by ANSI) + « « « Self-ballasted mercury vapor lamp + + + » Mercury vapor lamp + « « » High-pressure sodium lamp . » « « « Low-pressure sodium lamp B H M.. . . Metal halide lamp s I “This material is based on information provided in the ANSI Standard enti- tled "Method for the Designation of High-Intensity-Discharge Lamps" ANSI C78.380. Figure 10-4. Key to standard HID lamp designations 10-6 TM 5-811-1/AFM 88-9 Chapter 1 CHAPTER 11 PROTECTIVE LIGHTING 11-1. General Quantity and quality of illumination will conform to the latest edition of the Illuminating Engineering Soci- ety’s (IES) Lighting Handbook, except as modified in this chapter. Data contained in IES EP-10 provides a basic reference relating to the principles of standard protective (security) lighting practice. Specific require- ments for protective lighting are covered by AR 50-5 for nuclear security; AR 50-6 for chemical exclusion areas; AR 190-11 for weapons, ammunition, and ex- plosives; and FM 19-30 for physical security. Other protective lighting requirements peculiar to classified areas may be obtained from the Department of De- fense. For Air Force security requirements, AFR 207-1 will be used. In all cases, project construction requirements will apply when such requirements are more rigorous than those given in this manual. 11-2. Authorization. The Using Agency determines where protective light- ing is necessary to illuminate boundaries and areas so that unauthorized intrusion is visible to those respon- sible for security. Normally the Using Agency will des- ignate the maximum acceptable period for which loss of illumination can be tolerated so that acceptable backup sources, as covered later, can be provided. In absence of specific data, 2 minutes is to be considered the maximum outage period acceptable. 11-3. Use of protective lighting systems. Protective lighting systems are employed in connec- tion with security operations and provide illumination of boundaries, sensitive inner areas, and entry points. The type of system is determined by the installation environment and the intended use. Often two or more types of lighting systems are used within a single area. a. Objective. The fundamental objective is that any system or combination of systems must always work to the maximum advantage of the security force and to the maximum disadvantage of the intruder. Lights will be spaced and located so that a single lamp failure does not leave a vulnerable area in darkness and ex- posed to entry or damage. b. Coordination. Where installed on airfields, pro- tective lighting must be coordinated with the Flight Safety Officer so that aircraft takeoff, landing, and ground operations are not impaired. Where lighting near navigable waters is required, the US Coast Guard will be contacted to see whether the system provided requires their approval. 11-4. Types of areas to be lighted. Three distinct types of areas are lighted. a. Boundary lighting. Ilumination of a restricted area boundary includes exterior and interior clear zones adjacent to boundary barriers (fences) or, in some cases, the area between multiple barriers. The de- sign will provide adequate light on the bordering area, glare light in the eyes of the trespasser, and minimum light on guard personnel. Glare which handicaps guards or authorized operations should be avoided. Poles will be placed inside the boundary fence and be- tween the patrol road and boundary. Distance of poles from fence should not be less than 5 feet and this mini- mum distance should be used only where the patrol road is close to the fence. Either glare projection or controlled lighting will be provided. Generally glare projection lighting provides better protection and should be used to illuminate flat areas free of obstruc- tion for at least 150 feet outside the fence. Controlled lighting, which does not project masking glare, should be used only when it is necessary to limit the width of the exterior lighted area, because glare would interfere with authorized activities. Figure 11-1 shows how beam direction differs between glare and controlled lighting. b. Sensitive inner area lighting. The lighting for sensitive inner areas should be discussed with the ap- propriate security agency. Lighting installed and fo- cused to illuminate the interior of a restricted area as- sists security forces in locating unauthorized individ- uals. The system will be designed so that detection of an intruder within the restricted area is virtually as- sured. Shadows, except those cast by intruders, should be avoided. Sensitive areas or structures may include pier and dock areas, vital buildings, storage areas, and vulnerable areas of the communication, power, and water distribution systems. (1) Luminaires. Lighting units can range from or- dinary floodlights or pivotable, individual spotlights or searchlights to more elaborate pole-mounted fix- tures capable of illuminating comparatively large sec- tors of adjacent terrain, such as those used for stadium lighting. Where night operations are conducted, work area lighting can be used to facilitate the detection of unauthorized approach. Special purpose lighting may TM 5-811-1/AFM 88-9 Chapter 1 Beam location for controlled lighting —-- cea \ G \ Xx To patrol road Mounting height 10' to 20' for glare lighting, 25' minimum for controlled lighting. Beam location for glare projection Boundary fence US Army Corps LU 20 (5' minimum) of Engineers Figure 11-1. Boundary lighting beam directions be necessary for some applications. (2) Towers. Security towers, whether continuous- ly or intermittently occupied, should be provided with a movable luminaire or searchlight which is controlled at the tower. High intensity illumination at long range is the essential characteristic of a movable lighting system. c. Entry point lighting. Lighting is installed at en- try points to facilitate accurate and rapid identifica- tion of personnel requiring entry into the area and complete inspection within and under vehicles. Entry point lighting will be installed in any restricted area for which entry controls are required during normal operations. Fixtures will be placed so that light sources are above and behind the entry guard and facing per- sons approaching the area. If the area is equipped with a boundary lighting system, the entry point light pat- tern will extend outward from the boundary or gate of the area. The entry guard position, in such instances, should be inside the area in comparative darkness. 11-5. Lighting guidelines. a. Area definitions. (1) The boundary is considered to be the perimeter fence, unless there is no fence in which case the prop- erty line is considered the boundary. (2) An isolated fenced boundary is where the area outside the fence is clear of obstructions for 150 feet or 11-2 more, and the fence is at least 100 feet from any inner buildings or operating areas. (3) A semi-isolated fenced boundary is where the area outside the fence is clear for only 60 to 100 feet. (4) A nonisolated fenced boundary is where the fence is adjacent to operating areas within the installa- tion, or to public thoroughfares or other installations outside the boundary. The width of the lighted area is dependent upon the clear distances available. (5) A sensitive inner area is a storage or open work space inside a lighted boundary where additional protective lighting is required, particularly for aisles and passageways. (6) A sensitive inner structure is either within 20 feet of a lighted lighting or houses critical operations (such as structures or buildings for power, heat, water, communications, explosive materials, critical materi- als, delicate machinery, classified material, and valu- able finished products) where additional protective lighting is required so that doorways and insets will not be in shadow. (7) An entry point is where access to protected areas requires complete inspection of pedestrians, pas- senger cars, trucks, and freight cars entering or leav- ing. b. Intensities. The type of lighting system, area to be covered, and minimum levels of illumination are shown in table 11-1, except that requirements for nu- TM 5-811-1/AFM 88-9 Chapter 1 Table 11-1. Protective Lighting Requirements Application Illuminated width Minimum illumination feet Type Lighting Area Outside Footcandles * Location Glare Isolated 150 0.2> Outer lighted edge 0.4 At fence Boundary Controlled Semi-isolated 70 0.2 Outer lighted edge 0.4 At fence 0.4 Outer lighted edge Controlled Nonisolated 20-30 30-40 0.5 Within General - 0.2-0.5°¢ Entire area Sensitive Area inner area At structures = pf Out from structure fs Pedestrian 25 2 Entry pavement Entry point Controlled and sidewalk Vehicular 50 1 * Horizontal plane at ground level unless otherwise noted. » Vertical plane, 3 feet above grade. © Use higher value for more sensitive areas. US Army Corps of Engineers clear and chemical sites will be obtained from HQDA (DAEN-ECE-E). Typical application of protective lighting systems are shown on figure 11-2. 11-6. Light sources. High intensity discharge (HID) lamps are more energy- conserving than incandescent lamps as shown in table 10-3; however, because of operating characteristics, HID lamps do not provide maximum illumination at initial energization. Because of their longer restrike times, mercury vapor and metal halide lamps are not normally acceptable for use in protective lighting sys- tems. Fluorescent lamps normally cannot be provided with the type of directional control needed, but may be used where such control is unnecessary, such as at guardhouses. Either high-pressure sodium (HPS) lamps or incandescent lamps are acceptable, but the energy savings that HPS lamps provide make their in- stallation preferable. Incandescent lamps should be used only when a life cycle cost analysis indicates such a source is the most economical choice or when re- quired by operational considerations. When lighting remains “off” during normal nighttime conditions, but is turned “on” during alerts, such as in the use of searchlights, the 3-to-4-minute warmup time for HPS units cannot be tolerated, so incandescent lighting is an operational requirement. Tungsten-halogen incan- descent lamps, also known as quartz-iodine, with their generally longer lamp life than the conventional tung- sten type, should be considered for incandescent lamp applications where appropriate. Low-pressure sodium lamps may be considered provided procurement and installation is in accordance with current Army Serv- ices Procurement Regulations (ASPR). 11-7. Electric power sources. a. Alternate electric power requirement. In the event of an outage of normal electric power, a reliable alternate electric power source is necessary to ensure continuous illumination. Normally, a Class “C” (emer- gency) generator will be used as the alternate source for applications, except where the electric power re- quirements of the lighting system are small enough to make battery backup more economical. Automatic or manual starting of the generator and load transfer will be provided dependent upon the permissible electric power outage duration. In some cases, portable genera- tors or portable battery-operated lights are required in addition to stationary auxiliary electric power sources. Provision of portable units is normally not the design- er’s responsibility, beyond providing a connection point when directed by the Using Agency. 6. Uninterruptible electric power requirement. Most protective lighting systems can tolerate the nor- mal 10 to 17 seconds outage time occasioned by gener- ator startup time. (1) Additional outage (restrike) time for HID lamps. When HID lighting is used, the generator start- up outage time is extended by the amount of time re- quired to restrike the arc in an HID lamp plus the time required for the lamp to reach full lumen output. The shortest restrike time, as shown in table 10-3, applies to HPS lamps and is less than one minute from a hot- lamp state. A lamp is considered to be hot for 3 min- utes after loss of electric power. Cold-start time of 2 to 4 minutes for HPS lamps does not apply when aux- iliary electric power is supplied. As is shown on figure 11-3, total time lapse on loss of normal electric power to full HPS lamp illumination including allowance for TM 5-811-1/AFM 88-9 Chapter 1 For sensitive inner area 7 fy o.2 to 0.4Fc lighting, see isolated bel boundary ot area Patrol road NY 0. 2 5 Ss 0.2 to 0.4fc Luminaire semi-isolated boundary area Outer lighted edge Fence 0.4 to 0.5fe nonisolated boundary area For entry point lighting, see below Public thoroughfare BOUNDARIES 8 Lighted storage aisle Sensitive area within an illuminated boundary area - | iil — Y LL LE MUU: WILE A 0.2 fe general area lighting & 1.0 fe area lighting near structures Critical structure Lighted areas 50' all sides SENSITIVE INNER AREAS Fence Pedestrian entry 50' 50' Lighted areas Vehicular entry A 1.0 fe vehicular entry 3 2.0 fc pedestrian entry ENTRY POINTS US Army Corps of Engineers Figure 11-2. Application of required lighting intensities 11-4 TM 5-811-1/AFM 88-9 Chapter 1 100 75 Generator startup time Percent illumination 5° 25 HPS lamp illumination ee Sr ee me rs 40 Time in seconds from loss of normal power * Courtesy of Ketter & Gannon Figure 11-3. HPS outage time for normal to emergency source transfer engine-generator startup is 72 seconds. (2) Tolerable outage time. Where the Using Agen- cy has determined that the outage time must be less than 72 seconds, then an uninterruptible power sys- tems (UPS) will be required, if the more energy-con- serving HPS lamps are used. Where a UPS unit is pro- vided in addition to the Class “C” generating unit, the UPS unit will be sized as directed. A life cycle cost analysis is required in those cases where interruption of full illumination cannot exceed 12 to 15 seconds. The analysis should include the costs of the methods of providing a combined incandescent and HPS system versus costs of an incandescent system. 11-8. Luminaires. a. Type. Generally, luminaires will be the enclosed type with light distribution characteristics selected for the type of lighting system required. Characteristics of roadway type luminaires are discussed in chapter 10. Floodlights will be constructed to meet the require- ments of NEMA FA 1. Tables 11-2 and 11-3 describe various beams and classes of floodlights which are ap- propriate for protective lighting applications. b. Specific usage requirements. Detailed informa- tion on floodlight or roadway luminaire types is cov- ered in IES EP-10. The following is given for general guidance. (1) Boundaries. For boundary area applications, Table 11-2. Floodlight Beam Descriptions * NEMA type Beam spread Beam designation degrees description REND GO Fos s'e are Narrow 0 SO 8 dis eg Medium-narrow « SAO EO 5.6 5 sia 5 id Medium TI WO 100 ise. acd 0 sie Medium-wide 100 up to130......... Wide glare projection luminaires should have the asym- metrical distribution pattern that a floodlight with a wide horizontal distribution and a narrow vertical dis- tribution, (type 6 by 2) provides. Controlled lighting luminaires should have the wide spread that roadway types I through III or floodlights with a medium to wide vertical distributions (types 4, 5, and 6) provide. (2) Inner Areas. Inner area luminaires should have the wide symmetrical distribution that a roadway type V or floodlight types 4 to 6 provide. Where there is a general area lighting requirement for nighttime activity, as defined in chapter 10, luminaires may pro- vide both protective lighting and area or roadway illu- mination. (3) Entry Areas. Luminaires with symmetrical light distribution and a medium to wide spread beam are suitable for entry area lighting. Luminaires should be aimed at check points from several directions to fa- cilitate inspection. Table 11-3. Floodlight Class Descriptions * NEMA class designation Description Recommended use HD Enclosed with an Permanent installa- for outer housing into tions or where sub- heavy duty which is placed a ject to rough use or separate and re- exposed to severe at- movable reflector or mospheric or corro- an enclosure in siveconditions. which a_ separate housing is placed over the reflector. GP Enclosed with aone- Allowed only at per- for piece housing where manent installations general purpose the inner surface where light weight serves as a reflector and the outer sur- face is exposed to the elements. is a prime considera- tion or in canton- ment areas. “ This table is reproduced by permission from NEMA Standards Publication No. FA 1-1973 entitled “Outdoor Floodlighting Equip- ment.” * This table is reproduced by permission from NEMA Standards Publication No. FA 1-1973 entitled “Outdoor Floodlighting Equip- ment.” 11-5 TM 5-811-1/AFM 88-9 Chapter 1 (4) Special purpose applications. Special purpose applications may require use of spotlights, floodlights, or searchlights, dependent upon the type of security required. Searchlights are appropriate where it is nec- essary to spot moving objects at great distances; the beam spread should be only about 6°. Size and candle- power of searchlights are dependent upon the length of throw required, and the atmospheric conditions likely to be encountered. A one-million beam candle- power searchlight (approximately 1,000 watts) has an effective range of approximately 1,000 feet. Where stationary lighting must be supplemented, truck- mounted units are available, but provision of such units is normally not the designer’s responsibility. 11-9. Wiring and control. a. Multiple wiring systems. Multiple systems will be installed, except where their use is clearly impractica- ble. The circuit protective devices, transformer, and 11-6 wiring will be within the restricted area. Wiring should be located underground to minimize the possi- bility of sabotage or vandalism. Equipment and design should provide for simplicity and economy in system maintenance. b. On-off control. On-off control will be automatic, manual, or manual/automatic as appropriate. (1) Automatic. Boundary and area lighting on-off control is normally automatic, and is activated during periods of darkness or at other times when visibility is reduced. In hostile environments, automatic on-off control must be capable of being deactivated which may require either manual/automatic or manual on-off control depending upon the site. (2) Manual. Wherever manual on-off control is ap- propriate, on-off controls will be accessible to and operable only by authorized personnel. Systems which are designed to remain “off” until needed should have “on-off” control at the surveillance location. TM 5-811-1/AFM 88-9 Chapter 1 CHAPTER 12 DESIGN ANALYSIS 12-1. General requirements. The designer preparing plans and specifications for work covered in this manual will also prepare an ac- companying design analysis. The design analysis will be used also to justify decisions recommended in con- cept or feasibility studies, although a separate section is not required if necessary material and computations are contained in a study, either in the body or in an ap- pendix. 12-2. Scope. The design analysis will cover completely the electrical design requirements for electric power supplies and distribution systems necessary to the project. The analysis will be submitted in two parts, a basis for de- sign and design computations. 12-3. Basis for design. The first part, the basis for design, serves to present a concise outline of functional features, including a de- scription of existing systems and other considerations affecting the design. In addition, a full description of any special requirements and justification for any pro- posed departure from standard criteria are required. a. Exterior electric distribution systems. The de- scription of exterior electric distribution systems will include statements on all features relevant to the spe- cific project as follows: (1) Electric power sources. Electrical characteris- tics of the electric power supply to an entire installa- tion, or that portion of the installation involved, in- cluding circuit interrupting requirements and voltage regulation will be covered. A statement discussing the adequacy of the existing electric power supply (includ- ing primary feeders) at the point of take-off will be giv- en. If the electric power source is inadequate, a state- ment of the measures proposed to correct the defi- ciency will be included. If a new electric power source or local electric generation is required, the various pos- sibilities will be covered, except where the design di- rective has stipulated requirements. The advantages and disadvantages of various suitable methods should be analyzed and cost comparisons submitted. Where a design directive permits a choice among alternatives, the merits of each alternative should be examined. If the use of a certain system or equipment has been di- rected and the designer recommends another ap- proach, the designer will indicate any deviation from the directed design and justify such deviations. (2) Loading. An estimate of total connected loads, power factors, demand factors, diversity factors, load profiles where required, resulting demands, and sizes of proposed transformers to serve either the complete project or the various portions involved will be provid- ed. Transformer peak loads and load cycling should be analyzed for transformers when appropriate (chapter 8). (3) Electric distribution systems. The basis for se- lection of primary and secondary distribution volt- ages, and of overhead or underground construction is necessary. The proposed type of conductors such as copper or aluminum, bare or insulated, where each type is used, and any special basis for selection are re- quired. Statements describing pertinent standards of design such as voltage drop, maximum primary circuit interrupting requirements, physical characteristics of overhead or underground circuits, switching, circuit protection, lightning protection, type of lighting units, and lighting intensities are necesary. Any provisions for communication circuits to be installed by others, either aerially or underground, will be described. (4) Underground justification. The basis for de- sign will justify proposed underground construction by citing either criteria (chapter 9) or authority for waiv- er of criteria. (5) Work performed by others. If functional ade- quacy of the design is contingent on work to be per- formed by the Using Agency or the local utility, the basis for design should describe the limits of such work and the responsible agency. b. Electric generating plants. Wherever electric generating plants are required, pertinent data should be included in the basis for design. (1) Loading. The estimated connected load, maxi- mum demand, average demand, minimum demand, number of units proposed, their kW ratings, and rea- sons for the selection of these units should be indi- cated. The maximum revolutions per minute, the maximum brake mean effective pressure, and the esti- mated horsepower rating of engines should be given. (2) Engine class. The class of plant “A”, “B”, or “C”, type of starting system, type and grade of fuel, and approximate storage capacity should be covered. The type of plant, whether completely manual, fully automatic, or semiautomatic, with reasons for the se- lection should be noted. 12-1 TM 5-811-1/AFM 88-9 Chapter 1 (3) Voltage selection. The selected voltage should be given and reasons for the choice; for borderline cases, cost comparisons should also be provided. Bor- derline cases are those where the advantages of the optimum voltage level are not clearly apparent. If com- mercial electric power is not provided, the reasons why electric power is not used should be stated. If operation in parallel with the serving utility is planned, a writ- ten utility company statement is necessary affirming agreement with this mode of operation. (4) Voltage regulation. Engine governor and volt- age regulating requirements, including requirements for parallel operation, should be listed. A statement should be made that standard equipment is to be speci- fied; where special equipment such as precise electric power equipment is proposed, this special equipment should be fully justified. The additional cost of special equipment should be given. (5) Cooling and heat recovery systems. The type of cooling system and reason for selection is required, along with a description of the type of waste heat re- covery, if any. An explanation is required to justify not utilizing waste heat. c. Uninterruptible power systems (UPS). Where de- sign for Class “D” or UPS systems utilizes government furnished property (GFP), adequate coverage of elec- trical and environmental requirements is necessary. Justification for system design should include the maximum voltage and frequency deviations (as given by the Using Agency) that the critical load can toler- ate. Installation of non-GFP units is permitted only when such units supply real property loads, and a statement must be made that this is the justification for their provision. d. Main electric supply stations. Where a main elec- tric supply station is provided, the utility’s system will be described including the utility’s recommendations. Where pertinent, the utility’s system should also be de- scribed relative to adequacy and dependability, alng with other applicable data covered in the requirement for engineering studies (chapter 3). 12-4. Design computations. Computations will be provided to indicate that materi- als and systems are adequate, but not overdesigned, and are correctly coordinated. Generator and trans- former capacities and protective device current ratings will be calculated. Voltage drop calculations may be necessary for primary feeders whose kilovoltampere loading exceeds that permitted by criteria (chapter 5). Short circuit calculations should be provided, except for short line extensions. Protective device coordina- tion is necessary when relay and circuit breaker trip settings must be determined. Pole line strength analy- ses are necessary when other than normal pole strengths and spans are used (chapter 6). 12-2 a. Voltage drops. An example of an aerial line volt- age drop calculation is given on figure 12-1. This ex- ample uses the approximate formula method which ig- nores angle $ and which is sufficiently accurate for all but abnormal conditions, such as where system power factors are extremely low. Proximity effects, sheath currents, and geometric construction may need to be taken into account in calculations of impedance for un- derground circuits. Various tables and voltage drop curves are available from manufacturers for under- ground circuits. For aerial circuits, impedance may be determined using values of resistance and reactance. (1) Resistance. For conductors of 500 kcmil and less at 60 Hz frequencies, the skin-effects of alternat- ing current are negligible and direct-current resistance values can be used. (2) Reactance. Normal practice is to separate in- ductive reactance into two components. X, is the reac- tance which results from flux within a radius of 1 foot of the conductor plus the internal reactance of the con- ductor. X, is the reactance which results from flux be- tween the radius of 1 foot and the equivalent conduc- tor spacing based on a mean distance (D). The two values of reactance can be found in conductor tables and added together for the total alternating-current reactance. b. Short circuit calculations. Short circuit calcula- tions for a simple radial feeder are shown on figure 12-2. Only reactances are used, since for most medi- um-voltage systems the effect of resistance will be neg- ligible. Two methods of computation are shown, the per unit method and the Million Volt Amps (MVA) method. The MVA method has been developed using formulas based directly on Ohm’s law thus eliminating conversion to a common base and the small decimal values of the per unit method. (1) Per unit method. The per unit method adds re- actances, which for series circuits are added directly and for parallel circuits are added reciporcally. (2) MVA method. The MVA method adds admit- tances (reciprocals of reactances) and therefore, paral- lel circuits are added directly and series circuits are added reciprocally. c. Protective device coordination. A main electric supply station will have relays which must be set to provide coordination of the system. Since maintaining a continuous supply of electric power to as much of the entire system as possible under fault conditions is de- sirable, the protective device closest to the fault on the electric power source side should be set to operate first as is shown in figure 12-3. If this device fails, the next device towards the source should take over and open the circuit and so on in ascending order of trip settings. Coordination of in-line protective devices is required to achieve this selectivity. For example a much larger current is needed to trip circuit breaker IMPEDANCE FACTORS TOR + f (Ke + Xd) occcccccccceec(l) Where: 60 Hz resistance 60 Hz inductive reactance at 1l-foot spacing 60 Hz inductive reactance for additional spacing D { (ab) (Dbe) (Dea) ]2/3 .....(2) TM 5-811-1/AFM 88-9 Chapter 1 APPROXIMATE VOLTAGE DROP FORMULAS IR cos6 IX sin6 Source voltage Receiving voltage Line-to-line voltage drop = 1.732 I (R cos6 + X sin® ).... Where: I = Line current in amperes 6 = Phase angle between voltage and current or cos6 = power factor R = Resistance of line in ohms, one conductor X = Reactance of line in ohms, one conductor Formula (3) can be converted as follows to calculate percent voltage drop: % voltage drop = kva [R cos + (Xa + Xq) sind) (4) 10 (ky)? Where: kVA is three-phase kVA and kV is line-to-line kilovolts. For single-phase circuits the percent drop is twice this value, and kVA is single-phase kVA. oeeecececeeee(3) EXAMPLE No. 4/0 AWG copper x 4.4')1/3 2 4.08" (Tavle 4-29)4 (Table 4-29)? (Vable 4-34) (355"..x 4.4" 0.278 2mile 0.503 2/mile 0.171 2/mile 0.278 + j0.674 Q/mile NxXx BO ae Given: cos@ = 0.90 sin® = 0.436 kVA = 15,000 kv = 13.8 Find voltage drop for one mile of line Percent voltage drop = 15 noo {0.278 0.9) + (0.674 0.436)) 10(13.8)2 = 4.28% voltage drop ..cccceeccccsccccccscces (4) @Tables are from Standard Handbook for Electrical Engineers (Eleventh Edition). Figure 12-1. An example of a voltage drop calculation 12-3 TM 5-811-1/AFM 88-9 Chapter 1 69 kV utility line 500 MVA system contribution 7.5 MVA 69 to 13.8 kV 7.0% impedance SINGLE LINE r—13.8 kV switchgear bus 1 mile No. 4/0 AWG copper aerial line X = 0.687 ohms fe po 1,000 kVA 13.8 kV to 480 volts 5.75% impedance FORMULAS xe = System per-unit reactance MVA, = System MVA Xy = Transformer per-unit reactance MVAy = Transformer MVA X~ = Cable per-unit reactance MVA, = Cable MVA kVAg = Base kVA xy = Percent impedance kV, = Base kV kVA, = Transformer kVA B Xe = (kVAg) = (MVAZ x 1,000)... . ~~ (1) MVA, = As given. 2... 2.27 ee + (4) Xp = (Xz) x (kVAg) = (kVAp x 100). . . . (2) NVA, = (kVBp) + Cy) x (10). 2 2 ee - SD Xo = (X) x (KVAg) = (kV? x 1,000). . . - (3) mval = (kv) = (x) Pro, Se a sc 7 (MVA) x (1,000) + (1.732) x (kV). (7) CALCULATIONS PER UNIT METHOD MVA METHOD MVAg KVA_ = 500,000 kVA kVp = 13.8 kV Beh et, oS ee PY Oe neem eee ee (4) 500 MVA Xe ie 02000) 70k ss ws) 8 (500) (1,000) oer = 7,500/(7 x 10) ee cecccccccccceecs ervccceee (5S) a (7.0) (500,000) . y, (500) (107) _ “1 £ %y" G50) ado) 7 7 + + @) Boron + 02 AVA MVAc = (13.8)7/0.687 eoccceee ovcccccccecce(6) x = £0.687)-500 000) =1.8. © € Xe “ (3.8)2(1,000) ees ee ee 88 + 277 MVAT, = 1,000/(5.75 x 10) x = 65.75) (500,000) _ ln woe eecccerevececevosees aie 105) T2 € %t2" (7,000) (100) 28 at (67) (17.4) ovata 67 + 17.4 x Xtotal = 36.3 per unit 500 MVA: a i Total " 365 13.8 MVA Ipc = 623-8) (1,000) , sc (1.732) (0.48) 16,600 amperes. .... (7) US Army Corps of Engineers Figure 12-2. Examples of short circuit calculations 12-4 1006 800 809 700 600 500 400 300 200 70 60 40 20 TIME IN SECONDS 03 F-- 08 o7 oe 95 F- “3 02 TM 5-811-1/AFM 88-9 Chapter 1 30 40 50 60 7080908 3 4 5 678910 55 aoe fot te ' SETTINGS @) ae toe er. jh TIME a ; DIAL. |INSTAN.. E 7% IMPEDANCE 13.8 kV BUS L. s2 52 c 1ooe 1000kVA 13.8xV-480V I 35.75 % IMPEDANCE 1600 a)-(0) ee TRANSFORMER. WITHSTAND —t ET] TRA MAXIMUM INRUSH | EHH | | ++ opener: : py ae ager atats AXIMUM 39 FAULT CURRENT=480V—44| |: | 13.8xv-+— 14 | eee EE eee i | i is 1s 87 8810 36 a0 0 6 JonoDg 2 & © 282888 2 i FETE CURRENT IN AMPERES x 10-39(I3.8kV BASE) © Foe BR REEE US Army Corps of Engineers Figure 12-3. An example of protective device coordination 12-5 TM 5-811-1/AFM 88-9 Chapter 1 “B” than circuit breaker “C” and the same type of selec- tivity applies to all protective devices shown on figure 12-3. No instantaneous setting is provided on circuit breaker “B”, since such a setting could introduce non- selective tripping with circuit breaker “C” under some conditions and does not improve bus fault protection appreciably. Various steps are required in order to de- termine system requirements. (1) Short circuit study. A short circuit study, as shown on figure 12-2, is made first to establish the fault currents available at the various voltage levels. These points are then plotted on a time-current log-log graph on a common voltage basis. The device farthest from the source should be plotted first. The other de- vices will then be plotted in order towards the source. Relays with the same shape curve should be used. Very-inverse-time relay curves are generally selected as the most suitable shape where coordination with fuses is necessary. (2) Device selection. Pickup currents and operat- ing times of protective devices should be chosen so that transient overloads such as inrush currents of transformers and motors will be overridden. Trans- former withstand points can be determined from data in ANSI C57.12.00. Transformer protective devices will be selected to lie between the withstand point on the source side and the inrush point on the down- stream side. (3) Preferred selectivity. Selectivity is always de- sirable between protective devices. (a) Between like devices. Like devices have curves of the same shape. A time interval (coordinat- 12-6 ing time) of approximately 0.4 seconds between opera- tion of a protective device and a similar device (fuse and fuse or circuit breaker and circuit breaker) up- stream will insure proper selectivity. (6) Between unlike devices. Complete selectiv- ity with no overlapping of the characteristic curves of unlike protective devices is desirable, but sometimes difficult to obtain. (4) Ground fault coordination. Ground fault pro- tective devices on opposite sides of delta-wye trans- formers cannot be coordinated, since this type of con- nection isolates each voltage level with respect to the flow of ground (zero-sequence) fault currents. d. Aerial line analyses. An example of an aerial con- ductor strength calculation is shown on figure 12-4. This type of calculation requires making an assump- tion (in this case that conductor sag equal 2.06 feet) and then checking the validity of the assumption, which can be tedious and time-consuming. The various conductor manufacturers have computer programs which have been developed for use on a suitable pro- grammable calculator. The assumed value of 2.06 feet of sag and 3,350 pounds tension are different from the values given in table 6-3 where the values listed are 2.4 feet of sag and 2,870 pounds tension. The variation results because of elastic creep; however, the variation in values of about 15 percent, in this case, provides a more conservative design or an additional safety fac- tor. Figure 12-5 gives an example of a pole strength analysis. An example of a guy strength analysis has been previously given on figure 6-10. TM 5-811-1/AFM 88-9 Chapter 1 @ USING VALUES BELOW IN FORMULAS BELOW Ww. = Conductor weight, unloaded (1b/ft) eet = Length of pole spacing (ft) T aaa ah Pate ah ce ee eee CD d = Conductor sag (ft) = Tension (1b) OL = Length conductor is greater than pole spacing Ae a2 Ds 3242 (2) based on parobolic formula (in) es L eBay: A) ay & D, = Conductor diameter (in) Dy = De + (2 x ice thicknese®) . , (3) . Dy = Conductor plus NESC additional ice thickness ik e requirement (in) Ice thickness from NESC table 250-1 if W = NESC wind force requirement (1b/ft2) WDn . ™, Horizontal loading (1b/ft) MP che erent einer ov oe G) Iy = Ice weight factor of 0.396 1b/ft per in? 57 lb/ft based on NESC weight of ice ( /£t3) ee Lop,2 a pi2piguctie Sate 8 PTE (5) wy = Weight of ice (1b) Wy = Vertical loading (1b/ft) Me We WE nd Goes ot a aes rs COD k = Constant to be added to resultant from NESC table 251-1 2p ys Wc] = Conductor weight, loaded (1b/ft) Wel = (wy? + wy?) “uit OD) Tg = Stringing tension (1b) T, = Tension under NESC loading conditions (1b) APS Ty ts, eee eed 2 B®) AST = Increase in loaded tension over stringing tension (1b) | A, = Conductor cross-section (in?) at © AS = Increase in stress (1b/in2) 4s TUAey ans ee eS ERAe awe ey (9) E «= Modulus of elasticity of conductor As(12L) AL, = Increase in length from stress increase (in) AL, = ea FW oes ier of ies aime te (10) X = Thermal expansion coefficient per (° F) At = Change in temperature between stringing ALe ‘= Z(At)(L2L): 55s ee es = (1) temperature and loaded temperature (° F) AL_ = Decrease in length from temperature decrease (in) EXAMPLE FOR HEAVY LOADING DISTRICT INITIAL CONDITIONS FINAL LOADED WEIGHT FINAL LOADED CONDITIONS E Primary ~ 4[0.563 + (2 x 0.5)}\,. _ (1.38)(200)? | #4/0 AWG ACSR “bh T2 Tr = 602.06) 3,350 1b... (1) De = 0.563 in : = 0.521 1b/ft..(3),(4)|AT = 3,350 - 1,455 = 1,895 1b..(8) Ac = 0.194 in: Po. 2008-? | e We = 0.291 1b/£t “%y 0 as = 20893 = 9,773 i/in? .....(9) EB -11.5x ioe 60° F stringing | 0.291 + i156? - 0.5632) (0.396) = i Sedaeeiateal temperature 1591952 1b/Et. x.-%-s ocs.- +0255), (6) Ale w= aa i = 2.04". .(10) Bi ‘ Ty = £0297) 200)" = 1,455 1b..(2)] wey = ALt = 10.5 x 10-6(60 - 0)(12 x 200) « sana? (0.9522 + 0.5212)/2 + 0.30= WTSI, cocaseidls sista saiataelge C11) 4L = oe © 0.16" .....000000(2)| 1.38 ID/Et 2... cceccccccccsesee (7)| Loaded AL = 2.04 - 1.51 + 0.16 é Rated breaking strength of conductor = 8,350 1b 0.69 2 NESC requirement for maximum load = 8,350 x 60% = 5,190 1b “a & 32(2.06) if oe 3,350 1b (1) < 5,190 1b eee 200 Os 68-2) 4The value 2.06 in the formula ae was assumed bo Courtesy of Ketter & Gannon Figure 12-4. An example of an aerial conductor strength analysis 12-7 TM 5-811-1/AFM 88-9 Chapter 1 USING VALUES BELOW D_ = Conductor diameter (in) Ss " Conductor plus NESC additional ice thickness requirement (in) W = NESC wind pressure requirement (1b/ft2) L = Length of pole spacing (ft) N = Number of conductors at same height above grade H_ = Height of conductor above grade (ft) M_ = Bending moment at base of pole from conductor (£t-1b) P_ = Wind pressure on pole at the top® Pe Wind pressure on pole at the ground? a " Circumference of pole at top (in) C_ = Circumference of pole at grade (in) H_ = Height of top of pole above grade (ft) M_ = Bending moment at base of pole from wind on P pole (ft-1b) S_ = Section modulus at base of pole Gap O, = Overload factor from NESC table 261-3 F_ = Fiber stress in pole (1b/in”) Pe IN FORMULAS BELOW Do “8, + (2 x ice thickness*) | |. . (1) "Ice thickness from NESC table 250-1 D_WLNH a c ig i ns ee oe Force = Py x H Moment arm = H/2 2 Moment = Pr = —force = 1/2(Pg - P_)(H) Moment arm = H/3 M (P Pe) Ww loment = - Pe al A e 6 — (Pg-P)/2 2 ww Mp = He ¥ fac, + Oo aie (* Bh mcm ater, 709 /c\3 ¢3 x /c\3_c¢ i eR) eRe tas. bs cs. 40:3) digo Pc RAD 2 Ei) 3207 (M+ M p= 22 \Me a % (5) o7—tet an EXAMPLE FOR HEAVY LOADING DISTRICT Primary lines ans ' 1.25 Check whether pole will carry load: Cc No. 4/0 AWG ACSR Doy = 0.563 in PY SN ise Dy = De + 2(0.5) Day = 1-563" Dap = 3" Dy3 = 2.88" (1) Dn4LNHe _ DnLNHe _ (1.563) (200) (1) (39-75) Secondary eal ~~ Me = Ty 94 5 4 No. 2 AWG CU (1.563) (200) (2) (35.75) Deg = 2 in—- ~ 2 3 29.75" i + (3)200) (2) (29.75 Communication 3 200 pair No. 22 AWG ¢ Gir 4 42-88) (200) (2) (20) Do3 = 1.88 in 3 Tuas = 21,380 ft-lb (oS) 3°) 7 =: @) 2 2 Class 3,douglas fir HY (4) He with Cp = 23 in = rr Mp = Sy (2Cp + Cg) = gq (46 + 37.5) a oh anger 2 = 2,190. ft=1b [i552 tae . (Gd = in 5 : 37.5)3 maximum | Sy - Gis 167 ind oe ew 12 (21,380 + 2,190) x 4 _ 2 Poles located 6.5' Fsi= 167 6,775 lb/in® . - - (5) ‘ 200' apart 1 | | | 6,775 1b/in? < 8,000 1b/in?: pole will carry load a . Lb per foot of circumferences p Courtesy of Ketter & Gannon Figure 12-5. An example of a pole strength analysis 12-8 TM 5-811-1/AFM 88-9 Chapter 1 CHAPTER 13 UNINTERRUPTIBLE POWER SUPPLY SYSTEMS (CLASS “D" PLANTS) 13-1. General. An uninterruptible electric power supply system is necessary for certain equipment, generally electronic, that performs critical functions and requires contin- uous disturbance-free electric power to operate proper- ly. This type of electric power system provides regu- lated electric power to critical loads under any condi- tion. Uninterruptible power system (UPS) units pro- vide instantly accessible and constantly available elec- tric energy thus preventing any interruption of elec- tric power even for milliseconds, except for automatic bypassing on some installations. In addition, the iner- tia of rotary UPS units also eliminates any transients resulting from lightning, switching surges, or other causes of dynamic, as opposed to steady-state, varia- tions in voltage and frequency. UPS units will be pro- vided for facilities where authorized by AR 420-43 for Army Projects and AFR 91-4 and AFM 88-15 for Air Force Projects. 13-2. Types. Both static and rotary types of UPS systems are avail- able. a. Static systems. The incoming (prime) electric serv- ice is converted to direct current by a static rectifier and transformed back to alternating current by a static inverter. A battery connected between the recti- fier and the inverter floats on the system and provides instant electric energy when there is a prime source outage. The conversion from alternating current to di- rect current and back to alternating current is de- signed so as to provide an electronic flywheel thus vir- tually eliminating transients. Automatic and manual bypass circuits isolate UPS units under fault condi- tions or when maintenance is necessary. Figures 13-1 and 13-2 indicate typical single-line diagrams of static uninterruptible power system (UPS). b. Rotary systems. The incoming electric service is connected to a motor which under normal conditions drives a synchronous generator and a flywheel. Upon loss of normal power, the flywheel provides energy during the time it takes the diesel engine to become fully operational. Figure 13-3 shows a simplified dia- gram of a typical rotary UPS Unit. Some systems utilize a flywheel driven by a separate motor at an ele- vated speed. Other systems have a diesel engine and a synchronous machine which functions either as a generator or a motor as necessary, and are known as on-line systems. A combination staticrotary system has a static rectifier and a floating battery supplying a direct-current motor which drives an alternating-cur- rent generator. Because many rotary type installations have not operated satisfactorily and usually require excessive maintenance, such units cannot be used without prior approval of HQDA (DAEN-ECE-E) for Army projects and HQUSAF/LEEEU for Air Force projects. 13-3. Definitions. For a better understanding of uninterruptible power system design, the following definitions are provided. a. Critical technical load. That part of a facility technical load that requires continuous precise electric power for successful operation. b. Uninterruptible power supply (UPS) system. A system designed to provide electric power without de- lay or transients, during any period when the normal electric power supply is incapable of performing ac- ceptably. An uninterruptible power supply system con- sists of (UPS) equipment, backup power sources, en- vironmental equipment, switchgear, and controls which together provide a reliable continuous precise electric power system. c. UPS devices. One or more UPS modules, an elec- tric energy storage battery, and accessories as required to provide a reliable and precise electric power supply. The UPS isolates the load from the prime and emer- gency sources, and in the event of an electric power in- terruption provides regulated electric power to the critical technical load for a specified period dependent upon battery capacity. d. UPS module. The static power conversion portion of the UPS system consisting of a rectifier, an invert- er, and associated controls along with synchronizing, protective and auxiliary devices. UPS modules may be designed to operate either individually or in parallel. e. UPS battery. A battery providing constantly available or instantly accessible source of electric ener- gy which eliminates electric power interruptions. Nor- mally units are sized sufficiently large enough to sup- ply the critical technical load for the interval before auxiliary power units assume load, plus an electric en- ergy allowance for implementation of catastrophic 13-1 TM 5-811-1/AFM 88-9 Chapter 1 Incoming primary electrical service ie Auxiliary generating units i, Technical bus ) UPS circuit Bypass circuit Technical Nontechnical loads loads UPS module 11_—_—— Battery Synchronizing circuit Manual bypass (make-before-break) circuit breaker Static switch transfer in less than 1/4 cycle (4 milliseconds) Critical technical loads US Army Corps of Engineers Figure 13-1. Single-line diagram of anonredundant configuration 13-2 TM 5-811-1/AFM 88-9 Chapter 1 Incoming primary electrical service a Auxiliary generating units a Nontechnical bus Technical bus UPS circuits Nontechnical Technical loads loads Bypass | circuit | fifi | Battery | in a ee ee —S>— —— ooo “ Critical | | technical load switchboard i = | | 7. | WY | | | | a ae | US Army Corps of Engineers Figure 13-2. Single-line diagram of a redundant configuration 13-3 TM 5-811-1/AFM 88-9 Chapter 1 Incoming electrical service [—-—— Motor starter Bypass circuit crn ee ee ee ee Synchronous or low slip induction motor Synchronous generator Diesel engine Electric clutch Flywheel ritical technical loads US Army Corps of Engineers Figure 13-3. Simplified diagram of a rotary UPS unit procedures in the event auxiliary power unit do not start. f. Nonredundant UPS configuration. A configura- tion consisting of one UPS module with automatic (static) and manual bypass circuits and a battery. Upon failure of the UPS module, the static bypass circuit au- tomatically transfers the critical technical load to the prime or emergency source with only a 4 millisecond interruption to the load (figure 13-1). g. Parallel nonredundant UPS configuration. A con- figuration consisting of two or more UPS modules with each rated less in kilovoltampere capacity than the kilovoltampere requirements of the critical loads. The parallel nonredundant system will be required when the capacity of commercially available UPS equipment is insufficient to supply the loads to be served by a single UPS module. This type of system shall have a common battery and system control cabi- net. h. Parallel redundant UPS configuration. A config- uration providing redundancy if it consists of an ade- quate number of UPS modules rated to supply critical loads in the event one of the modules must be taken out of service for maintenance or if any of the modules fail. A static interrupter will disconnect the failed module from unfaulted modules without an interrup- tion of power to the critical loads (figures 13-2). The 13-4 parallel redundant system shall include a common UPS battery and system control cabinet. 13-4. Installation. Normal design policy is to provide UPS equipment of the static type in conjunction with the electronic equipment which requires UPS backup, that is, both are Government furnished property (GFP). In such cases, UPS equipment will be centrally procured. Design requirements covering space needed, electric loads, and environmental needs will be furnished by the Using Agency in such cases. a. Location. Equipment will be installed as close to the center of the load as is practicable. 6. Equipment rooms. UPS modules and associated battery will be installed in separate rooms from each other and from the equipment served. Construction will be of permanent type with the wall separating the UPS module room from the battery room having a 1- hour fire rating. It is recommended that, where practi- cal, space be provided in the UPS module and battery rooms for the addition of future UPS equipment or more battery capacity. c. Environmental control. Both UPS module and battery rooms will be provided with environmental control systems to maintain inside room conditions as required by the equipment manufacturer. Each envi- ENG Alaska Power Authority 010 LIBRARY COPY TM 5-811-1/AFM 88-9 Chapter 1 TECHNICAL MANUAL ELECTRIC POWER SUPPLY AND DISTRIBUTION DEPARTMENTS OF THE ARMY AND AIR FORCE SEPTEMBER 1984 \ cs ‘ eRe ES fee Penn hee ronmental control system will consist of a prime sys- tem with backup capability to support the uninterrupt- ible requirements of the electric power system. Upon failure of the prime system, automatic transfer to the backup system will occur along with alarm activation to individual equipment malfunction. d. Contractor furnished units. When procurement of UPS unit is authorized, units will be of the static type. Special attention is required to ensure that the environment is suitable with respect to dust, tempera- ture, and humidity. Normally, only one battery is fur- nished, but more than one UPS module may be re- quired in some cases. The minimum capacity of any UPS system will be 125 percent of the estimated maxi- mum demand. (1) Nonredundant systems. Systems will normally be the nonredundant or parallel nonredundant UPS configuration described above. When technical and nontechnical electric power buses are provided, the UPS modules should always be connected to the non- technical bus and the bypass circuit to the technical bus. (2) Redundant systems. Redundancy will be speci- fied only as follows: (a) Where required for fixed telecommunication stations in accordance with criteria in TM 11-695, AFM 88-15, and Military Handbook 411A. (b) Where the primary electric power supply ex- hibits an inordinate number of frequency or voltage fluctuations and 24-hour-per-day output is required. (c) Where the facility is isolated and logistic support is poor. (d) Where the frequency of the primary electric power must be converted to serve the critical technical load (that is 50 Hz to 60 Hz or 60 Hz to 400 Hz). (3) Spare units. Installation of spare units in lieu of redundant systems is not permitted. 13-5. Supporting systems. a. Battery. Lead-calcium sealed-in plastic storage cells will be used to provide an ampere-hour capacity at full load operation sufficient for a maximum period of typically 15 minutes, but not less than 5 minutes. Shorter or longer times should be justified. b. Auxiliary electric power. Class “C” (emergency) generating plants are generally installed to provide for extended outages beyond the capacity of the battery. In addition, the auxiliary generating plant will supply lighting and cooling loads which can tolerate losses of electric power for short periods, but which are neces- sary for proper operation of critical equipment. (1) Unit requirements. Emergency generators will be automatic start, automatic transfer to load upon normal electric power failure, and include provisions for automatic load shedding and load restoration where required. TM 5-811-1/AFM 88-9 Chapter 1 (2) Synchronizing capability. The capability for manual synchronizing will be specified when a single emergency generator unit is required. The synchroniz- ing features will permit the generator to be paralleled with the normal and stable electrical power source. The capability for automatic synchronizing should also be specified when the single unit is to serve essential equipment at critical facilities, such as the National Defense Command, control, and communication installations; missile sites; and munitions production facilities when the loss of power would create explo- sive hazards to personnel and production facilities. Au- tomatic and manual synchronizing capabilities will al- so be specified when two or more generating units are required. Those synchronizing features permit the generators to be operated in parallel with each other and with the normal power source. (3) Synchronizing capability precautions. Paral- leling of generating units with an unstable power source is not recommended. A long, lightly-loaded transmission or distribution line, or a lightly-load pow- er system, may have frequent and large variations in frequency, voltage, or both. The variations can serious- ly degrade the reliability of generating units and prove detrimental to the proper operation of equipment. Damage to sensitive electronic components can result also. Unacceptable variations in the normal power source may be found in some commercial power sys- tems, particularly in states with low population densi- ties; but may also be found in power systems served by onsite generating facilities within and outside of the continental United States, such as island installations. Regardless of the type, nature, or location of the nor- mal power source, precautions should be taken to in- vestigate the stability of the power source before syn- chronizing capabilities are specified. The investigation should be conducted during the implementation of the design procedures stipulated in chapter 1 of the man- ual. If the normal power source is found to have unac- ceptable stability, additional generating units should be specified to provide the desired stability, reliabil- lity, and redundancy to adequately serve the critical loads. Normally, one spare generating unit will suffice. However, two spare units may be warranted for re- mote locations and especially those which have facili- ties critical to the national defense interests. c. Bypass provisions. Bypass provisions are not con- sidered to provide redundancy. (1) Nonredundant systems. A nonredundant UPS, including the parallel nonredundant UPS, will have a fast acting static switch for automatic bypass of a faulted module. In addition, a manual circuit breaker will allow bypass of each UPS module when mainte- nance is required. The circuit breaker will be make-be- fore-break in both directions. The bypass system will contain automatic synchronizing provisions. 13-5 TM 5-811-1/AFM 88-9 Chapter 1 (2) Parallel redundant systems. A parallel redun- dant UPS will have the manual bypass circuit breaker without make-before-break contacts and synchroniz- ing provisions only between modules, but not with the bypass circuit. A static interrupter in each UPS module will isolate any UPS module which develops a fault. Where frequency conversion is provided by the UPS modules, a motor-generator set (frequency con- verter) will be required as part of the bypass provi- sions. d. Remote alarms. UPS equipment will include a re- mote alarm panel to be installed in the operating space served by the UPS unit or in another continuously occupied room, such as a guard office. Since UPS equipment rooms are usually unattended, additional remote indicating devices will be provided to monitor the environmental control and fire alarm system of UPS module and battery rooms. 13-6 13-6. Distribution systems. The UPS system serves critical technical loads only. Noncritical loads are served by separate distribution systems supplied from either the technical or nontech- nical bus as appropriate. a. Critical load protection. It is recommended that critical technical load panelboards be provided with fast acting (microsecond) fuses to shorten the tran- sient effects of undervoltages caused by load faults. Solid-state transient suppressors (metal-oxide type) should also be supplied to lessen overvoltage tran- sients caused by reactive load switching. b. Critical motor loads. Due to the energy losses and the starting current and maintenance problems inher- ent in the use of motor-generator sets, motor-genera- tor sets should be specified only when the Using Agen- cy stipulates their use. Otherwise, solid-state equip- ment should be specified. TM 5-811-1/AFM 88-9 Chapter 1 APPENDIX A SIZING OF DISTRIBUTION TYPE TRANSFORMERS FOR FAMILY HOUSING UNITS A-1. Application. areas will have the air conditioning or electric heating loads, whichever is larger, sized for 100 percent de- Design factors apply only to aerial or pad-mounted : eos mand. The rest of the load will be sized in accordance compartmental distribution transformers supplying family housing units. with the demand factors of table A-1. In no case shall secondary feeders be less than required by the Nation- A-2. Distribution transformers. al Electrical Code for dwelling units. Distribution transformers serving family housing Table A-1. Demand Factors Demand Number factor of percent units Number Demand of factor units percent ® Same demand factor applies to all quarters over 54. US Army Corps of Engineers TM 5-811-1/AFM 88-9 Chapter 1 APPENDIX B REFERENCES Government Publications Department of Defense. MIL-HBK 411 4270.1-M Long Haul Communica- tions (DCS) Power and Environmental Control for Physical Plant. Construction Criteria Man- ual. Department of the Army, Air Force, and Navy. AR 11-28 AR 50-5 AR 50-6 AR 190-11 AR 385-30 AR 420-43 FM 19-30 TM5-349 TM 5-809-11/AFM 88-3, Ch. 14 TM5-810-1 TM 5-815-2/AFM 88-36 TM 5-838-2 TM 5-852-5 TM 11-695 AFM 88-15 Economic Analysis of Pro- gram Evaluation for Re- source Management. Nuclear and Chemical Weapons and Material, Nuclear Surety. Nuclear and Chemical Weapons and Material, Chemical Surety Pro- gram. Military Police, Physical Security of Weapons, Ammunition, and Explo- sives. Safety Color Code Mark- ings and Signs. Facilities Engineering, Electric Services. Physical Security. Artic Construction. Design Criteria for Facil- ities in Areas Subject to Typhoons and Hurri- canes. Mechanical Design: Heat- ing, Ventilating, and Air Conditioning. Energy Monitoring and Control Systems. Medical Facilities De- sign—Army Arctic and Subarctic Con- struction: Utilities. Electrical Power Systems, Fixed Telecommunica- tion Stations. Air Force Design Manual Criteria and Standards for Air Force Construc- tion. Criteria for Design and Construction of Air Force Health Facilities. Operation and Mainte- nance of Electric Power Systems. Economic Analysis and Program Evaluation for Resource Management. The Air Force Physical Se- curity Program. Cold Regions Engineering Economic Analysis Hand- book. Environmental Protection Agency. Available from local Departments of EPA. PL-91-190 National Environmental Policy Act. AFR 88-50 AFR 91-4 AFR 178-1 AFR 207-1 NAVFAC DM-9 NAVFAC P-442 Executive Order. Superintendent of Documents, US Government Printing Office, Washington, D.C. 20402 EO 12003 Relating to Energy Policy and Conservation. Federal Specifications (Fed. Spec.) US Naval Publications and Forms Center, 5801 Ta- bor Avenue, Philadelphia, PA 19120 RR-F-621 Frames, Covers, Gratings, Steps, Sump and Catch Basin, Manhole. Rural Electrification Administration (REA) Publi- cations. United States Department of Agriculture, Rural Electrification Administration, Washington, DC 20250 Bulletin 43-5 List of Material Available for Use on Systems of REA Electrification Bor- rowers (July 1982). Guide for Narrow Profile and Armless Construc- tion (July 1973). Design Guide for Rural Substations (June 1978). Adequate Grounding on Primary Distribution Bulletin 61-12 Bulletin 65-1 Bulletin 83-1 TM 5-811-1/AFM 88-9 Chapter 1 Lines (March 1977). Engineering and Opera- tions Manual for Rural Electric Systems, Distri- bution Line Design (Me- chanical) (April 1982). The Application of Shunt Capacitors to the Rural Electric System (Decem- ber 1982). Nongovernment Publications. American Institute of Architects, 1735 New York Avenue, N.W., Washington, DC 20006 Life Cycle Cost A Guide for Architects. Analysis American National Standards Institute (ANSD), 1430 Broadway, New York, NY 10018 Bulletin 160-2 Bulletin 169-1 C2-1981 National Electrical Safety Code. C37.20-1969 Switchgear Assemblies, In- (R 1981) cluding Metal-Enclosing Bus. C37.20a Addenda C37.20b Addenda C37.20c Addenda C37.20d Addenda C57.12.00-1980 Liquid-Immersed Distribu- tion, Power, and Regu- lating Transformers. Transformers 230,000 Volts and Below 833/958 through 8,333/10,417 kVA, Single-Phase and 750/862 through 60,000/80,000/100,000 kVA, Three-Phase. Load-Tap-Changing Trans- formers, 230,000 Volts and Below, 3,750/4,687 kVA Through 60,000/80,000/100,000 kVA Three-Phase. Appendix to ANSI General Requirements for Distri- bution, Power, and Regulating Transform- ers. Guide for Loading Oil- Immersed Distribution and Power Transform- ers. Guide for Loading Dry- Type Distribution and Power Transformers. Guide for Application of Valve-Type Surge Ar- C57.12.10-1977 C57.12.30-1977 C57.91-1981 C57.92-1962 C57.96-1959 C62.2-1981 B-2 rester for A.C. Systems. Requirements and Test Procedure for Outdoor Apparatus Bushings. Method for the Designa- tion of High-Intensity- Discharge Lamps. High-Intensity-Discharge Lamp Ballasts (Multiple- Supply) Type. Voltage Ratings for Elec- trical Power Systems and Equipment. Galvanized Steel Bolts and Nuts for Overhead Line Construction. Threaded Galvanized Fer- rous Strand-Eye Anchor Rods and Nuts for Over- head Line Construction. Specifications and Dimen- sions For Wood Poles. Graphic Symbols for Elec- trical Wiring and Layout Diagrams Used in Archi- tectural and Building Construction. American Society of Testing and Materials (ASTM), 1916 Race Street, Philadelphia, PA 19103 A475 Zinc-Coated Steel Wire Strand. American Association of State Highway and Trans- portation Officials (AASHTO), 444 North Capi- tol Street NW, Suite 225, Washington, DC 20001 HB-12 Standard Specifications for Highway Bridges (12th Edition) 1977. Illumination Engineering Society of North America (IES), 345 East 47th Street, New York, NY 10017 IES Lighting Handbook, C76.1-1976 C78.380-1977 C82.4-1978 C84.1a-1980 C135.1-1979 C135.2-1979 05.1-1971 Y32.9-1972 (6th Edition). RP-8 Roadway Lighting. RP-10-56 Protective Lighting. (R 1970) Institute of Electrical and Electronic Engineers (IEEE), IEEE Service Center, 445 Hoes Lane, Pis- cataway, NJ 08854 No. 18-1980 No. 48-1975 Shunt Power Capacitors. Standard Test Procedures and Requirements for High-Voltage Alternat- ing Current Cable Termi- nations. Electric Power Distribu- tion for Industrial Plants. No. 141-1976 No. 142-1982 Grounding of Industrial and Commercial Power Systems. No. 493-1980 Design of Reliable Indus- trial and Commercial Power Systems. National Electrical Manufacturer’s Association (NEMA), 155 East 44th Street, New York, NY 10017 210-1970 Secondary Unit Substa- (R 1979) tions. FA 1-1973 Outdoor Floodlighting (R 1979) Equipment. SG 6-1974 Power Switching Equip- (R 1979) ment. TT 1-1977 Tapered Tubular Steel (R 1981) Structures. WC-7-1982 Cross-Linked-Thermoset- ting-Polyethylene-Insu- lated Wire and Cable for the Transmission and Distribution of Electrical TM 5-811-1/AFM 88-9 Chapter 1 Energy. WC-8-1976 Ethylene-Propylene-Rub- Incl Rev 1 through 6 ber-Insulated Wire and Cable for the Transmis- sion and Distribution of Electrical Energy. National Fire Protection Association (NFPA), Publication Sales Department, 470 Atlantic Avenue, Boston, MA 02210 No. 70 National Electrical Code. Applied Protective Relaying Handbook, Division of Relay Instrument, Westinghouse Electric Cor- poration, Newark, NJ 07101 Principles of Engineering Economy Handbook, by Grant, Ireson, and Leavenworth, John Wiley & Sons, Inc., New York, NY 10036 Standard Handbook for Electrical Engineers by Fink and Beaty, McGraw-Hill Book Company, New York, NY 10020 The Art and Science of Protective Relaying Hand- book, by Mason, John Wiley & Sons, Inc., New York, NY 10036 B-3 TM 5-811-1/AFM 88-9 Chapter 1 By Order of the Secretaries of the Army and the Air Force: JOHN A. WICKHAM, JR. General, United States Army Official: Chief of Staff ROBERT M. JOYCE Major General, United States Army The Adjutant General CHARLES A. GABRIEL General, United States Air Force Official: Chief of Staff JAMES L. WYATT, JR. Colonel, United States Air Force Director of Administration Distribution: Army: To be distributed in accordance with DA Form 12-34B, requirements for TM 5-800 Series: Engineering and Design for Real Property Facilities. Air Force: F ®% U.S. GOVERNMENT PRINTING OFFICE: 1984-421-645: 10009 RECOMMENDED CHANGES TO EQUIPMENT TECHNICAL PUBLICATIONS SOMETHING WROMG wh tus eusicationr FROM: (PRINT YOUR UNIT'S COMPLETE ADORESS) THEN. . JOT DOWN THE DOPE ABOUT IT ON THIS > A FORM, CAREFULLY TEAR IT =) OUT, FOLD IT AND DROP IT = IN THE MAIL! DATE SENT fi Date you tilled out form. PUBLICATION NUMBER PUBLICATION DATE =| PUBLICAIION TITLE IM 9-XXXX-XXX-XX Date ot IM Title ot IM BE EXACT _PIN-POINT WHERE IT IS] IN THIS SPACE TELL WHAT IS WRONG Your mailing address PAGE FiGuRE | Tas.e | AND WHAT SHOULD BE DONE ABOUT IT: no nO no 400 183 Change illustration Reason lube end shown a sembled on wrong side ot lever cam. DIZ 191 Figure 191, item 3 has the wrong NSN. Supply rejects orders tor this item. the NSN shown here 1s not listed in the AMDt or the MCRL. Please give us the correct NSN and P/N. PRINTED NAME. GRADE OR TITLE AND TELEPHONE NUMBER Jonn Smith, 8. SGI. 6/4/XXX --IF YOUR OUTFIT WANTS TO KNOW ABOUT YOUR DA FORM 9028-2 PREVIOUS EDITIONS TIVE 79 ARE OBSOLETE. RECOMMENDATION MAKE A CARBON COPY OF THIS AND GIVE IT TO YOUR HEADQUARTERS REVERSE OF DA FORM 2028-2 FILL IN YOUR UNIT'S ACORESS NY FOLO BACK DEPARTMENT OF THE ARMY POSTAGE AND FEES PAID DEPARTMENT OF THE ARMY BOO 314 OFFICIAL BUSINESS PENALTY FOR PRIVATE USE $300 HQDA DAEN-ECE-E WASHINGTON, DC, 20314 SAMPLE RECOMMENDED CHANGES TO EQUIPMENT TECHNICAL PUBLICATIONS SOMETHING WRONG wer ts eusricationr FROM: (PRINT YOUR UNIT'S COMPLETE ADORESS) THEN. . 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JOT DOWN THE DOPE ABOUT IT ON THIS FORM, CAREFULLY TEAR IT OUT, FOLD IT AND DROP IT PUBLICATION NUMBER PUBLICATION DATE PUBLICAIIONTITLE Electric Power Supply TM 5-811-1/AFM 88-9 12 September 84] 9nd Distribution BE | BE EXACT. PIN-POINT WHERE IT IS | PIN-POINT WHERE IT |S IN THIS SPACE TELL WHAT IS WRONG AND WHAT SHOULD BE DONE ABOUT IT: PRINTED NAME. GRADE OR TITLE. AND TELEPHONE NUMBER FORM DA 2028-2 PREVIOUS EDITIONS 15UL 79 ARE OBSOLETE. RECOMMENDATION MAKE A CARBON COPY OF THIS AND GIVE IT TO YOUR HEADQUARTERS PS.--IF YOUR OUTFIT WANTS TO KNOW ABOUT YOUR FILL IN YOUR UNIT'S AOORESS DEPARTMENT OF THE ARMY OFFICIAL BUSINESS PENALTY FOR PRIVATE USE $300 REVERSE OF DA FORM 2028-2 FOLO BACK HQDA DAEN -ECE-E WASHINGTON, DC, POSTAGE AND FEES PAID DEPARTMENT OF THE ARMY BOO 314 20314 SSS eee ee eee Ie OeaE: RECOMMENDED CHANGES TO EQUIPMENT TECHNICAL PUBLICATIONS SOMETHING WROMG wes tus eusricationz FROM: (PRINT YOUR UNIT'S COMPLETE ADORESS) THEN. . JOT DOWN THE DOPE ABOUT IT ON THIS FORM, CAREFULLY TEAR IT OUT, FOLD IT AND DROP IT PUBLICATION NUMBER PUBLICATION DATE PuBLiCAnionTiTLE Electric Power Supply TM 5-811-1/AFM 88-9 12 September 84] and Distribution BE EXACT. PIN-POINT WHERE IT IS IN THIS SPACE TELL WHAT IS WRONG [ AND WHAT SHOULD BE DONE ABOUT IT: PRINTED NAME, GRADE OR TITLE. AND TELEPHONE NUMBER P.S.--IF YOUR OUTFIT WANTS TO KNOW ABOUT YOUR DA FORM 2028-2 PREVIOUS EDITIONS 14uL 79 ARE OBSOLETE. RECOMMENDATION MAKE A CARBON COPY OF THIS AND GIVE IT TO YOUR HEADQUARTERS FILL IN YOUR UNIT'S AOORESS REVERSE OF DA FORM 2028-2 FOLO BACK @ DEPARTMENT OF THE ARMY OFFICIAL BUSINESS PENALTY FOR PRIVATE USE $300 POSTAGE AND FEES PAID DEPARTMENT OF THE ARMY DOO 314 HQDA DAEN-ECE-£ WASHINGTON, DC, 20314