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Cordova-Valdez DC Transmission Tie Line Feasiblity 1982
Alaska Power Authority LIBRARY COPY CORDOVA - VALDEZ DC TRANSMISSION TIE LINE FEASIBILITY REPORT By Alcat Engineering (f08 Burg eA) E. CORDOVA-VALDEZ DC TRANSMISSION TIE LINE FEASIBILITY REPORT MAY 1, J. HARRINGTON, P. E. 1982 A. W. MOODY, P. E. Gar O22 TABLE OF CONTENTS INTRODUCTION SCOPE OF ANALYSIS TRANSMISSION PLANS CONVERTER SUBSTATION AND CABLE TERMINAL LOCATIONS TECHNOLOGY AND COST CONSIDERATIONS A. DC PLAN AC PLAN MONOPOLAR VERSUS BIPOLAR TRANSMISSION LOSS CONDUCTOR SIZE SELECTION VOLTAGE LEVEL GROUND ELECTRODES CABLE CONSTRUCTION - CABLE INSTALLATION AND ROUTING J. AC OVERHEAD LINE K. AC SUBMARINE CABLE L. DC OVERHEAD LINE M. COMMUNICATION CHANNELS N. SYNCHRONOUS CONDENSERS . sie ie HmaADHONwW OPERATION AND MAINTENANCE A. OPERATION OF DC SYSTEMS B. SYSTEM AVAILABILITY (1) Cable Failure Rate, Repair Time (2) Converter Availability, Repair Time (3) Ancillary Equipment (Synchronous Condensers, etc.) (4) Overhead Line Outage Rate (5) Summary - Outage Rates of Cordova-Valdez Line C. OPERATING COST ITEMS - OPERATORS D. MAINTENANCE AND REPAIR COSTS E. SUMMARY OF SYSTEM OPERATION AND MAINTENANCE COSTS ENVIRONMENTAL ASPECTS OF DC SYSTEM A. GROUND ELECTRODES B. OVERHEAD LINES SUMMARY PAGE NO, 1 WOUWDMDDINAUS > BPRRERH rFHOOO 12 12 12 12 13 13 14 14 14 15 15 16 16 19 20 TABLE OF CONTENTS (Continued) PAGE NO. 9. TABLES AND MAPS TABLE 1 - CORDOVA-VALDEZ DC TIE LINE COST - 12000 KW 22 TABLE 2 - CORDOVA-VALDEZ DC TIE LINE COST - 9000 KW 25 TABLE 3 - CORDOVA-VALDEZ AC TIE LINE COST - 12000 KW 28 TABLE 4 - CORDOVA-VALDEZ AC TIE LINE COST - 9000 KW 30 FIG. 1 - MAP OF DC CABLE ROUTE FIG. 2 - MAP OF CORDOVA TERMINAL AND OVERHEAD LINE ROUTE FIG, 3 - MAP OF VALDEZ TERMINAL AND OVERHEAD LINE ROUTE 10. APPENDIX 1 SITING SEA ELECTRODES A-1 SEA ELECTRODE COSTS A-5 SEA ELECTRODE DESIGN A-6 SAMPLE CALCULATIONS A-8 FIG, 1 A-11 FIG. 2 A-12 COMPASS ERRORS CAUSED BY DC CABLES A-13 SAMPLE CALCULATIONS A-14 PRELIMINARY FEASIBILITY STUDY OF DC TRANSMISSION CABLE FROM CORDOVA TO VALDEZ, ALASKA INTRODUCTION This study was undertaken as part of the "Cordova Power Supply Alternatives Feasibility Analysis" sponsored by the Alaska Power Authority. It includes an investigation of AC and DC submarine cables as a means of interconnecting Cordova and Valdez. Power flow may be in either direction. The amount of power to be transferred is 12000 KW and an estimate of the cost of a 9000 KW system is also included. Although, the majority of the inter- connection is made with underwater cable, there will be short runs of overhead line at each end connecting the converter sta- tions with the point where the cable emerges from the water. Also, an overhead line will be used at each end, running from the converter ground terminal to the shore adjacent to the location of a salt water immersed ground electrode. SCOPE OF ANALYSIS The report describes the component parts of the system and also lists the estimated cost of the various parts, including the labor of installation. Costs are based on 1982 dollars. Fig- ures on the major items, such as cables and converter stations, have been obtained from the manufacturers of such equipment, and the remainder estimated by our engineers. Estimated losses, outage rates, operating costs, maintenance and cable repair costs have also been calculated or estimated by staff members. Route selection was made from chart studies and one helicopter flight over the route. No underwater or land surveys are in- cluded. The optimum voltage level and conductor size were not investigated in this study but were based on a previous study! in which a range of values was investigated to determine, approxi- mately, the most economical values. No taps or intermediate substations were considered for the DC system, but the AC system requires one or more intermediate substations for compensating reactors. TRANSMISSION PLANS - ALTERNATING CURRENT VERSUS DIRECT CURRENT Building overhead AC transmission lines in Southern Alaska is costly for the following reasons: A. Lack of roads along transmission routes. l"Snettisham-Ketchikan Transmission System". DOE Contract No. 85-79 AP10008.00 3. (Continued) B. Heavily timbered rights-of-way that have extremely high clearing costs. C. Rugged, mountainous terrain in some areas. D. Many bays and inlets along the shore, requiring long spans or underwater cable crossings, E. Severe wind loading, particularly where lines go over ridges or cross valleys requiring long spans. F. Heavy snow and ice loading in some places, G. Tall trees which require removal or wider rights-of-way to minimize outages caused by falling trees, H. Environmental restrictions, An alternative to overhead lines, especially for terminals lo- cated near the sea shore is to use underwater cable, AC trans- mission is possible up to about 50 miles over cable, and above this distance intermediate compensating reactors are needed along the way. When long cables are needed to connect two points on a power system, it becomes more economical to convert the power to DC at the source end and back to AC at the load end, This eliminates the problems caused by charging current on AC cables. For the cables considered in this study, the charging current at each end equals the thermal current rating of the cable (230 amps) for a cable 70 miles long, if no compensating reactors are used. The converters for changing AC to DC and DC to AC in this analysis are identical, so that power flow can take place in either direction. The converters use all solid state devices and have been demonstrated to have a very high degree of reliabili- ty. Converters cost considerably more than the substations normal- ly used at the ends of an AC transmission tie line, but this added cost may be easily offset by the saving in cable. The monovolar DC system proposed for the Cordova-Valdez tie requires only one cable. The return current flows through the earth via the ground electrodes. Since DC is involved, this return current flows deep in the earth and causes no interference with other equipment, as long as the ground electrodes are properly de- signed and located. The saving resulting from using one cable with DC versus three cables for AC usually offsets the added cost of the DC converters for distances in excess of 30 miles. This report includes a cost estimate on both an AC and a DC system. The DC system costs were substantially lower. B= as (Continued) The AC and DC cable alternatives both have an 11 mile length of overhead line from Jack Bay to the City of Valdez and short sections of overhead line from Cordova to Bluff Point and across Hawkins Island. The total length of overhead line is 18.3 miles. For the purpose of having a complete cost for the cable approach to this transmission problem, an approximate cost for the overhead line has been included, Dryden and LaRue may wish to replace the overhead estimates with more accurate figures. This analysis includes estimates of systems with power carry- ing capability of 12000 KW and 9000 KW. The cost of underwater cable used for this application is not very sensitive to conductor size. Therefore, little difference is shown between the cable costs for a 9000 and 12000 KW system, either AC or DC. Since DC converter cost estimates were based on an installed cost of $159 per KW, there is a modest saving by dropping from the 12000 KW to 9000 KW rating on the DC system, The sub- Station transformers are the only items in the AC system which show a significant cost reduction when the size is reduced from 12000 to 9000 KVA. For the above reasons, the cost reduction in going from a 12000 KW to a 9000 KW system is very modest. CONVERTER SUBSTATION AND CABLE TERMINATION LOCATIONS CORDOVA Appendix 1 includes a discussion of several alternate locations for the underwater cable termination and the ground electrode. For this analysis, it was assumed that the DC converter station would be located on the outskirts of Cordova and that an over- head line would be run to Bluff Point, a distance of about 7.3 miles. This DC wood pole line would carry the main power conductor, 336 MCM ACSR, insulated for 70 KV DC to ground. In addition, it would carry a ground wire of the same size insulated for 5 KV DC to ground. At Bluff Point, both conduc- tors would be changed to armored submarine cable for the Orca Inlet crossing. The cables would be ditched across the inlet to eliminate problems caused by anchors, fishing gear, or shifting mud and sand. On emerging from the water on Hawkins Is- land, both cables would continue with overhead construction to the South end of Canoe Passage, where the ground conductor would terminate at a sea electrode submerged in Canoe Passage. The 70 KV conductor would continue in a Northwesterly direction along Canoe Passage for at least one mile before entering the sea and heading toward Valdez, This arrangement keeps the ground electrode away from other known submarine cables or man-made metallic structures which might suffer from ground currents. —3e 4. (Continued) VALDEZ Appendix 1 includes a discussion of alternative locations, For this analysis, it was assumed that the converter location would be near where Solomon Creek enters Port Valdez (bay). From here a DC wood pole line would carry the main power conductor, 336 MCM ACSR, insulated for 70 KV DC to ground. In addition, it would carry a ground wire of the same size insulated for 5 KV to ground. At a bay located midway between Sawmill Spit and Anderson Bay, the ground wire would be terminated at a sea electrode located in this bay. From here the wood pole line carry- ing only the power conductor would continue southwesterly over a mountain pass to an inlet on the north side of Jack Bay. This arrangement insures good isolation of the ground electrode from the power cable ground sheath or any other known metallic structures which might suffer from ground currents. A substantial saving in transmission line cost could be effected by having the main power cable enter the sea at Anderson Bay, thus saving the mountain crossing. The Anderson Bay location, however, may be dangerous because of the precipitous nature of the shore where the cable must go to reach deep water. It is possible that further investigation may reveal this to be a more economical location than the Jack Bay location used in this analy- sis. A. C. SYSTEM For the purpose of appraising an AC cable transmission tie, it was assumed that a 3 conductor 187 MCM, 70 KV (line to line) armored cable followed the same path as the DC cable. The over- head line portion of the 3 phase AC circuit would follow the same route as the DC overhead power cable. A compensating reactor would have to be located about midway between the Canoe Passage and Jack Bay cable termination. This would in- volve a cable landing and a substation near Goose Island off Knowles Head. TECHNOLOGY AND COST CONSIDERATIONS A. DC PLAN The DC plan requires a converter at each end of the line to convert power from DC to 60 HZ AC. These converters are planned to be identical and they allow power to be trans- ferred in either direction. A DC system requires a syn- chronous machine at the receiving end of the line. Since it is possible that Cordova might wish to shut down its synchronous generators and obtain all of its power from Valdez on some occasions, a synchronous condenser has been included in the -4- Si A. (Continued) plans to permit such operation. The synchronous condenser consumes no power except for its losses. A new machine was included in the estimate, but a great many synchronous con- densers are available on the surplus market, and it is almost certain that one could be purchased for a fraction of the new machine cost. The converters used in this estimate are solid state devices. They have 15% redundancy in the SCR circuitry, so that several SCR's could fail simultaneously and still not require shut- ting the converter down. The manufacturer who supplied the prices advised that he is willing to guarantee an availabili- ty of 98% for each converter and that the forced outage rate is 1.4% per converter. DC transmission systems have the advantage that they can be set to transfer a fixed amount of power between two AC systems, regardless of load or frequency variations. on the AC systems. Controls can also be provided to vary the amount of power transferred between two systems, so as to hold constant frequency on the receiving system, if desired. The estimated cost of the DC system is shown in the cost summaries of Tables 1 and 2. AC PLAN An AC transmission tie line from Cordova to Valdez via sub- marine cable was also estimated. A minimum cost system was selected to see if there was any chance that it could compete in capital cost with DC for so long a cable tie. The volt- age selected was 70 KV (line to line). A 187 MCM, 3 con- ductor armored cable was used for the underwater portion and 4/0 ACSR for the overhead portion. The transmission losses are approximately 20%. The voltage drop at full load is 15% which would be tolerable if step voltage regulators were properly applied. The estimated cost of a 12000 KW AC tie, including both underwater and overhead portions, terminal substation and compensating reactors is $46,394,000. This is $16.6 million more than the DC system. In addition, the full load losses are more than double and the voltage drop more than triple that of the DC system proposed. It is also significant that the outage probability is greater with either 3 conductor cable or 3 single phase cable used for the AC system. In view of the great superiority of the DC system, it is recommended that the AC cable system be dropped from further consideration. 5. (Continued) Cc. MONOPOLAR VERSUS BIPOLAR Most of the DC transmission systems that have been installed worldwide are of the bipolar type. This means that there are two converters at each terminal, connected in series, with the midpoint grounded. Two cables are required be- tween terminals, and the current in normal operation, flows down one cable and back the other. If one cable or one converter fails, the bipolar system can still operate at half capacity by shutting one-half down and letting the return current flow through the earth, There are also a few systems installed which work only in the monopolar mode. These systems have one converter at each end and one interconnecting cable. The earth carries the return current continuously rather than during emer- gencies only. Monopolar systems require a good ground such as the sea provides. Also, it is desirable to have the sea electrode located a mile or more from armored cables or Pipelines, Both of these ground electrode requirements can be met by the seaport cities in Southern Alaska, without having to run long lines to the electrodes. A monopolar system can always be converted to bipolar operation later, but this requires adding a new cable and converters at each end, It is an economical way of delaying part of the investment, if future expansion is planned, since adding the second pole and cable doubles the transmission capacity. The fact that only one cable is required for a monopolar system makes it more attractive for installations some distance apart, since the cable is often the most expen- sive item in the package. The monopolar system requires somewhat more elaborate ground electrodes, but this is only a minor part of the system cost. ‘ It is recognized that a monopolar system has a greater probability of a total transmission outage than a bipolar, which can operate at half capacity for either a cable or converter failure. On the other hand, it is probable that Cordova would not wish to place total dependence for power on a transmission tie, anyway. To avoid being totally shut down, the city will probably wish to maintain 100% back-up capacity in Cordova. If this is so, then a large expendi- ture for a small gain in transmission tie availability is hard to justify and the monopolar system would be the economic choice. The Isle of Gotland, off the coast of Sweden has been successfully served by such a monopolar sys- tem since 1954. 5. (Continued) D. TRANSMISSION LOSS A loss optimization calculation is beyond the scope of this study, but previous work has indicated that the high value of power in the Cordova area dictates the use of oversize trans- mission conductors for maximum system economy. With this in mind, 300 MCM copper cable was used in the DC analysis even though the current is only 171 amperes. Prices were obtained from a cable manufacturer on 70 KV DC., copper con- ductor, paper insulated, lead covered, armored cable, F. O. B. Seattle, as follows: 300 MCM $ 97,750/mile 500 MCm 104,150/mile As can be seen, the sensitivity to conductor size is not as great as one might suppose, The total resistance of the 72.2 mile cable and the 18.3 miles of 336 MCM ACSR overhead DC line is 18.5 ohms and the loss is 4.5% for a 12000 KW load. Adding the converter loss at each end brings the total line loss to 7.0%. At 48% load factor, the loss factor would be about 0.30. The 10000 KVA synchronous condenser operating at 48% load factor would add about 53 KW average loss. Estimated Losses at 48% Load Factor for Cordova-Valdez Line DC System Power Rating 9000 KW 12000 KW Cable size, MCM 225 300 Converter loss in KW (both ends) 146 195 Cable loss in KW (at 48% load factor, .30 loss factor) 22) 163 Synchronous condenser loss 40 53 Total estimated loss in KW 308 411 Percent total loss at 48% load factor 3.4% 3.4% CONDUCTOR SIZE SELECTION A comprenehsive loss optimization study requires that the effects of changing the system operating voltage and the effect of changing conductor size be analyzed simultaneous- ly, which is beyond the scope of this analysis. The 300 MCM ey E. (Continued) cable size was selected as being adequately large to keep the losses low, but may be larger than required for opti- mum economy. The value of power in southern Alaska is high enough to warrant careful analysis of losses in a transmission sys- tem. Previous work done on this subject! indicated that a conductor rated at two or more times the rated system current could be justified. VOLTAGE LEVEL The price of AC to DC converters is not terribly sensi- tive to the operating voltage level of the line. From 40 to 70 KV, one manufacturer advised the price per KW of capacity would only increase about 5% per KW. Cable prices drop very slightly if the voltage rating is increased and the current rating (conductor size) is decreased pro- portionally for the cables considered on this project. Thus, both major components of a DC transmission system vary only slightly for a modest change in voltage. Based on experience with other studies, 70 KV is believed to be close to the optimum voltage for a 12000 KW DC cable system. GROUND ELECTRODES In order to minimize the tendency for current from the sea electrodes to travel in the power cable armor, the plans call for locating the sea electrodes at least one mile from the power cable or any other armored cable. The details for an electrode suitable for a 30-year life carrying 175 amps DC at 48% load factor are shown in Appendix 1. Only the anode electrode is consumed, but in order to provide for in- stantaneous reversal of power flow, an anode has been in- cluded in the plans for each end of the line. Thus, power flow can occur in either direction without the need for polarity reversing switches. It is desirable that the ground electrode be located where the sea water salinity is not decreased by fresh water dilution. It should also not be exposed by the tide. It should be in deep water or a protected area, where anchors or trawl boards will not disturb it. It is proposed to support the individual electrodes in a concrete box that prevents fish from getting too close. (See Appendix 1 for more information.) lsee "Snettisham-Ketchikan Transmission System", a report prepared for U. S. Department of Energy, Alaska Power Administration, Contract No. 85-79 AP 10008.00 -8- 5. (Continued) H. CABLE CONSTRUCTION The DC cables proposed in this report are insulated with oil impregnated paper, encased in a lead sheath. A 300 MCM copper conductor is proposed. A polyethelene cover will go over the lead sheath and underneath the galvanized iron armor wires. It may be desirable to specify that the individual armor wires be polyethelene covered, so that cathodic protection could be added, if necessary. The current rating of this cable is over 450 amps. CABLE INSTALLATION AND ROUTING It is proposed that the cable be manufactured in one con- tinuous length for each run, 66 miles for the longer run and 6.6 miles for the one across Orca Inlet. These could both be shipped on one special cable laying ship or barge directly to the Cordova area, even if foreign manufacturers are involved. Information on cable installation was furnished by the firm, "Jacobson of Seattle", which has laid a large num- ber of cables, including the 138 KV ones across Taku in- let near Juneau. It is proposed to bury the line ends out to a depth of 50 feet or greater, if there is heavy ship traffic in the area. Burial would be to a depth of four feet in the earth. It is also proposed to bury the cables crossing Orca Inlet for their entire length. In selecting the route for the 66 mile cable run from Hawkins Island to Jack Bay, the following criteria should be considered. 1. The shore ends of the cable must be protected so that damage will not result from storms, wave action, ice, tidal currents, ship traffic, etc. 2. The cable must not pass over sharp projections or ledges sufficient to damage it, either immediately or long term. 3. The cable should not traverse slopes greater than 45°F, If this is unavoidable, it should be securely anchored at intervals. 4. Cable must not be subject to strong water currents (tidal or other). If such are unavoidable, -9- 5. Lie (Continued) Suitable protection must be provided, such as bury- ing, anchoring, covering with cement bags, etc. 5. The cable location should avoid areas where ship anchors, beam trawls, etc,, are likely to cause damage. Ship lanes should be avoided unless the depth is adequate to avoid these problems. 6. Areas where electrical gradients exist should be avoided. If this is not possible, cathodic pro- tection should be provided. AC OVERHEAD LINE Short sections of AC overhead lines are included at the cable ends. No detailed work on the 70 KV wood pole line design was done. Costs were estimated on the basis of similar lines through similar terrain. Dryden and LaRue may elect to modify these costs, since they have the responsibility for options involving AC overhead lines. AC SUBMARINE CABLE The AC cable considered for this option had an aluminum conductor, 187.5 MCM cross-section with a current rating of 230 amps. Full load current at 12000 KW and .95 P. F. is 104 amps. The insulation is oil impregnated paper. Outside of the insulation is an insulation screen, a 1 mm lead sheath, armor bedding, 42-5.6 mm armor wires, and a polypropylene yarn and asphalt outer covering. It has an impedance of .563 + J.241 ohms per mile and a capacitance to ground of .43 mfd. per mile. No attempt was made to optimize the conductor size for this option. The AC cost estimate was much higher than the DC alternative. Assuming full load at 95% power factor and compensating reactors at the middle and the two ends, the loss on the AC tie is about 20%. DC OVERHEAD LINE Two types of DC overhead construction are proposed for the short sections of overhead lines needed at the extremi- ties of the DC system. It is assumed that the isokeraunic level in this area does not make an overhead ground wire necessary for lightning protection. Therefore, in situations where the ground return circuit has already entered the sea, only one conductor is needed for the DC overhead lines, -10- 5. L. (Continued) It would probably be most economical to use a single post type insulator on top of the pole, In situations where the ground wire must be included to carry current to a ground electrode, the overhead DC transmission line must carry two wires. Post type insulators could be used with a 5 KV insulator on top carrying the ground wire and a 70 KV DC post type insulator mounted horizontally for the power con- ductor. Line insulation behaves differently under DC stress than AC. Voltage distribution over the line insulator is deter- mined primarily by the capacitance in the AC case and by leakage in the DC case. Special, long creep insulators have been developed for DC that reduce the tendency for contamination flashovers and work is still proceeding in this area2. The cost of DC overhead lines is significantly less than AC and the amount is dependent, in part, on whether one conductor or two is required for the DC line. The cost estimates reflect this saving. COMMUNICATION CHANNELS A DC transmission system is designed to be self-regulating at a preset current level. Thus, if there is a breakdown in communication between the rectifying station and the in- verting station, the system will continue to transmit the same amount of power, Nevertheless, communication is nec- essary whenever the receiving power system desires to change the amount of power it is receiving, Also, communi- cation is extremely important during emergencies and faults. For purposes of this report, it is assumed that two reliable voice grade channels will be required for communication be- tween the terminal stations. One of these would be used for voice and the other for multiple tones. For this study it has been assumed that voice grade tele- phone channels can be leased for $10.00 per airline mile per month. The airline distance between Cordova and Valdez is approximately 45 miles and the estimated charge for two voice grade channels would then be $900 per month or $10,800 per year. SYNCHRONOUS CONDENSERS As mentioned previously under 5A, a synchronous condenser or synchronous generators must be on line at the receiving end of a DC transmission system to insure proper commuta- tion. Since Cordova may, at times, wish to shut down all of its generators, a synchronous condenser has been included 2"contamination of DC Insulators", EPRI Report EL-2016 =11- Seno Ne (Continued) in the plans. It could be an indoor or outdoor machine, but for a unit in Alaska, an indoor unit is recommended. If hydro generators are later installed on the Cordova sys- tem, it is probable that the synchronous condenser can be shut down or retired, If no local generators are running, the synchronous con- denser provided must have a rating that will produce a short circuit KVA equal to three times the converter terminal KW rating based on its transient reactance, For the 9 MW system a 7500 KVA synchronous condenser is pro- posed and for the 12000 KW system a 10000 KVA condenser. 6. OPERATION AND MAINTENANCE A. OPERATION OF DC SYSTEMS The normal mode of operation for a two terminal DC line is constant current. This results in constant power if the DC voltages remain constant. If the system AC voltages vary at the converters, the DC power transmitted will vary. AC voltages at the converter terminals should be regulated. Automatic frequency control of the receiving system may be accomplished by controlling the power transmitted over the line with signals from a time standard. SYSTEM AVAILABILITY (1) Cable Failure Rate, Repair Time The 1980 Cigre Report on HV DC systems, 14-08 stated that for all DC cable systems, the cable outage rate for the four-year sampling period was one outage per 100 KM/year. This corresponds to 1.6 per 100 miles/year. The Cigre report also indicates that almost none of the outages were caused by electrical failures of the cables, and those that were reported were at splices. (No cable splices are planned for the proposed Cordova-Valdez DC cable.) The mechanical failures were almost all caused by trawl boards or anchors and were effectively eliminated by burying the cables in shallow waters. It is also noted that on the two most recent installations, installed since these pro- tective procedures were developed, only one cable fail- ure has been reported for both installations, These two are across the Skagerrak, the Strait of Georgia, Vancouver to Vancouver Island, Their outage rate works out to be .24 outages per 100 miles/year, == 6. B. (1) (2) (3) (Continued) It should he noted that on the long cable from Hawkins Island to Jack Bay, 92% of the lay will be ata depth over 50 fathoms (300 feet), which virtually elimin- ates trawl board or anchorage problems, The line ends of this run would be ditched out to about a 50 foot depth and the cable across Orca Inlet would be ditched for its entire length. With proper installation tech- niques, it should be possible to reduce the incidence of cable failure well below the .24 outages per 100 miles/year figure reported above. Based on an outage rate of ,24 per 100 miles/year, we could expect to have .,174 outages per year on the 72.6 miles of cable between Cordova and Valdez. Advice from Jacobson of Seattle, marine cable laying and repair experts, indicates that for less than one outage per year, it is more economical to hire the nec- essary equipment for repair rather than purchasing it. The price for hiring the necessary men and equipment is estimated at $15,000 per day or $450,000 per month, The estimated time to recover, repair and replace a damaged cable section in average weather is 1 month. If we add 20% for contingencies, we arrive at an esti- mated cost for repair operations of $540,000 per month of repair time. Multiplying by the annual failure rate, we get annual cable maintenance costs and outage times as follows: -174 repairs/year X $540,000 = $94,000/year -174 X 30 days = 5.22 days (125 hours) /year The estimated scheduled outage time for inspection and maintenance is 16 hours per year. Converter Availability, Repair Time The estimated converter availability is 98%, but this includes .6% for scheduled maintenance. The remaining 1.4% is forced outage time and comes to 2.8% for both terminals. This is equal to 245 hours or about 10 days/ year. Scheduled outages are 105 hours per year. Ancillary Equipment (Synchronous Condenser, Ground Electrodes, etc.) There is very little data available on outage rates for these types of equipment, and it is proposed to use a figure of one-half of one converter's outages to cover -13- 6. B. (3) (4) (5) (Continued) all of it. This results in 0.7% or 61 hours (2,5 days) per year. For scheduled maintenance, three days or 72 hours/year has been assumed, Overhead Line Outage Rate For the 18,3 miles of overhead DC line, it is assumed that the forced outage rate is ,06 per mile/year, or one-third the rate being experienced on the Snettisham- Juneau 138 KV line on which good records are avail- able. This results in a forced outage time as follows; -06 X 18.3 X 12,5 hours/outage = 14 hours/year The scheduled outage time for the overhead line portion is estimated at 10 hours per year. Summary + Outage Rates of Cordova-Valdez Line Forced outages: Hrs/Year % of Time Cable 125 1,4 Converters (both ends) 245 2.8 Ancillary equipment 61 af Overhead line 14 pte Total 445 i. Scheduled outages; Hrs/Year % of Time Cable 16 oa Converters (both ends) 105 Lig Ancillary equipment We 8 Overhead line 10 eel Total 203 Das, OPERATING COST ITEMS, OPERATORS It is assumed that an operator will be on duty at the Solomon's Gulch Hydro Plant, and if so, no additional opera- tor would be required for a DC converter added at that loca- tion. There is no need of an operator on continuous duty at the Cordova converter. The system operator could advise the -14- 6. Cc. (Continued) operator at Solomon's Gulch of any changes in power orders if they were on a fixed schedule. If frequency control of the Cordova system is to be accomplished with the DC tie line, the amount of DC power transmitted must be under auto- matic control of the time-frequency control system. MAINTENANCE AND REPAIR COSTS It is estimated that one maintenance man, trained in the servicing of DC converter stations, would be needed at each terminal. There would not be enough work to keep one man busy eight hours per day, but the need for prompt maintenance would probably justify having one man located at each station, He could handle other duties for the utility, as well. Assuming the cost per man at $96,000 per year, including overhead, the charge for maintenance labor would be $192,000 per year. It is estimated that each converter station would require $5,000 per year in specialized maintenance labor and the $20,000 per year in repair parts for a total of $50,000 per year for the two stations, The estimated maintenance cost from part 6B (1) is $94,000 per year for the submarine cable. The maintenance of ancillary substation equipment is esti- mated at $10,000 per year per station and for the 18,3 miles of overhead line, $15,000 per year. SUMMARY OF SYSTEM OPERATION AND MAINTENANCE COSTS Cost per Year 1. Additional maintenance manpower at converter stations $192,000 2. Converter station, specialized main- tenance and parts (for both converters) 50,000 3. Cable maintenance 94,000 4. Ancillary equipment (two stations) 20,000 5. Overhead line 15,000 Total $371,000 Contingencies at 20% 74,000 Grand Total $445,000 -15- 7. ENVIRONMENTAL ASPECTS OF DC SYSTEM A. GROUND ELECTRODES Several possible locations for ground electrodes were selected by aerial survey or from maps of Cordova and Valdez. Only seawater locations were considered because the expense is reduced and the performance improved com- pared to ones located in the earth. Known environmental effects are listed below. (1) (2) (1) In sea water, chlorine gas is released at the anode surface. (2) Electrical voltage gradient can affect sea life - principally fish, (3) Buried or submerged metallic structures may form part of the earth return current path, resulting in corrosion or loss of metal at locations where the current leaves the structures, (4) Magnetic compass deviation may occur. Chlorine Release. Where a sea electrode is designed with electrode area great enough to produce the low resistance desired, and a voltage gradient low enough that the effect on marine life is acceptable, the chlorine release will be diluted in such a large volume of water that effects will be negligible. Effects on Marine Life, Considerable research has been done on the electrical gradient effect upon fish, and maximum gradient criteria have been established by several agencies and researchers throughout the world. These criteria can be met by incorporating sufficient surface area in the electrode to hold the gradient to less than the established maximum, The British Columbia Department of Fisheries, for example, requires that the voltage gradient be limited to 1.65 volts per meter in areas accessible to large fish, The design proposed in Appendix 1 limits the gradient to .6 volts per meter outside of the concrete shield. The concrete shield would prevent fish from getting close to the electrode surface. Therefore, no bad effects on fish are anticipated with the electrode design proposed. -16- 7. A. (Continued) (3) Galvanic Corrosion, This phenomena is not directly related to the electrode but to the use of the earth as a current path, The electrode comes into the pic- ture because it is only in the vicinity of the electrode that the voltage gradient becomes great enough to create a problem. Any metallic structure in contact with the earth or sea will be subject to the passage of electric currents. These currents may enter and leave the structure at few or many locations, Mainly, these currents arise from three sources. One is due to galvanic cells set up by electro-chemical action between the struc- ture and other material which is higher or lower in the electromotive series. A second source is earth currents that are present due to natural causes (sun- spot activity) which may enter and leave the structure if it parallels their path. The third source is man- made currents that may be created by installations such as the DC system under discussion. Currents entering and leaving a metallic structure create problems because metal is removed at the points where the current leaves the structure. This action can be prevented by making sure that any current enter- ing the structure leaves it by way of a metallic path connecting it to an anode some distance away through which the current returns to earth or sea. This anode material is sacrificed in lieu of the protected struc- ture. Current flow in the proper direction is established by choosing an anode material higher in the electromotive series than the metallic structure, or by interposing a DC current source of correct polarity and of sufficient voltage to overcome any gradients that would tend to cause current to leave the structure at locations other than the established metallic path. Such an approach is termed a cathodic protection system, It is termed a passive system if current flow is established by using an anode material higher in the electromotive series and an active system if the desired current flow is set up by a separate DC source. Metallic structures in contact with earth over a wide area such as buried pipe lines may have very low resistance to earth. To protect such structures over their entire length would require numerous anodes and current sources and involve the circulation of a large amount of current. To overcome this problem, the pipe line or structure can be coated with a low cost insulating material. If this =) 7 7. A. (3) (Continued) material were to be installed and maintained perfect- ly, no cathodic protection would be necessary. Inas- much as this would be both difficult and costly, cathodic protection is applied to prevent the departure of current at any locations where the insulation is flawed. This holds the number of cathodic protection sources and the current flows to reasonable values. Large marine installations where insulation is im- practical, such as sheet piling, etc,, may require the circulation of thousands of amperes to insure protection, From the above, it may be concluded that it is of prime importance that the terminal sea electrodes be located in an area sufficiently remote from buried metallic structures. For a land electrode, this separation may amount to several miles. In the case of a sea electrode, if the salinity of the water is high, a separation of approximately one mile usually brings the gradient to the point where the current contribution from the trans- mission system will be minor. If sufficient separation cannot be achieved, any accel- eration of corrosion of the structure can usually be avoided by increasing the existing cathodic protection or adding such protection, if non-existent. One metallic structure that will frequently be in the vicinity of the converter station is the armored AC submarine cable, For this reason, it may become nec- essary to locate the sea electrode some distance from the converter station. If such separation conflicts with other structures, it may be necessary to decrease the electrode separation and add cathodic protection to the cable armor. For this to be practical, insulated armor wires may be required and this will add to the cost of the cable. Costs used in this study were based on cables armored with bare galvanized wire, The jute-asphalt covering over this armor is not of a quality to constitute in- Ssulation of the armor. If these cables are to be "fished" and repaired in case of fault after laying, it is essential that the armor remain intact over the life of the cable. Final design of the cable should include an indepth study of the factors affect- ing life of the armor in the Alaskan environment, effect of ground electrode and possible savings by lo- cating it closer to the terminal, etc. Results of such study may make it prudent to insulate the armor and incorporate cathodic protection on some or all of the cable installations. Care should be exercised to choose an insulation method that is amenable to laying without high risk of damage, -18- 7. A. (3) (Continued) The scope of this study covers only a somewhat cursory exploration of electrode sites with little search for the presence of structures susceptible to damage by ground current; therefore, it can only be stated that the sites mentioned have a reasonable chance of being acceptable. (4) Compass Deviation. A monopolar DC system using sub- marine cable has an uncancelled magnetic field sur- rounding the cable. If this field is misaligned with earth's magnetic field, it can produce an error of deviation of any magnetic compass in the vicinity. The magnitude of the error is contingent upon a num- ber of factors, all of which are known. This allows the deviation to be calculated, The appendix contains material illustrating how these calculations can be made and typical curves plotted from computed data. These curves illustrate two facts: (1) The compass deviation can be relatively large where the cable lies in shallow water, but becomes small for areas 100 feet or more from cable centerline, (2) Compass deviation becomes relatively in- significant for all areas where cable depth is 250 feet or greater. Inasmuch as all but a very small portion of the cable can be laid at depths greater than 250 feet, no serious problem due to compass deviation is anticipated, OVERHEAD LINES The environmental impact of a DC overhead line is, in all respects, less than a comparable AC line. A single con- ductor monopolar line probably achieves the irreducible minimum as far as overhead line impact is concerned. Such a line can be located so as to avoid eagle nesting Places and involve minimum right-of-way clearing and danger-tree removal. Poles would be minimum height and would blend with the background. Use of a single conductor and the absence of crossarms appreciably reduces visual impact. At the voltage contemplated, audible noise is essentially non-existent, television interference should impose no problems, and, even though some radio interference may be present during foul weather conditions, this effect will -19-+ Te Be (Continued) exist only in close proximity to the line, Furthermore, radio interference created by DC voltages is tolerable to a much greater extent than that produced by AC voltages. In addition, if reliability factors dictate the use of the oversize conductor as contemplated in this study, radio noise during foul weather will be considerably less than the more common construction where, conductor selection is based more on economic factors, It is worth repeating: A single conductor, monopolar, over- head DC line, if properly designed and located, probably achieves the minimum environmental impact possible for overhead line construction, 8. SUMMARY: A. COST The use of DC instead of AC makes long submarine cable interconnection more economically attractive. In this report, AC and DC cable systems are compared for a 90.9 mile interconnection over the same route with costs as follows (Data from Tables 1 through 4): Cost in Millions of $ 9000 KW 12000 KW AC 45.4 46.4 pc 28,1 29.8 ENVIRONMENTAL In an area known for its natural beauty, a submarine cable causes less degradation of the scenery than overhead trans- mission line. No attempt has been made to place a dollar value on this feature. (See Section 7). FORCED OUTAGE RATE The predicted forced outage rate for the proposed DC cables (including the 18.3 miles of overhead lines) is 139 hours per year. (See Section 6B). By comparison, a 68 mile 138 KV overhead line would have an estimated outage rate of -178/mile/year and an average repair time of 12.5 hours3, This results in a forced outage time of 151 hours per year. Statistically, the estimated outage time of the submarine 3Data from Alaska Power Administration for 138 KV line from Snettisham to Juneau, February 2, 1977, through March 3, 1979. -20- (Continued) cable tie line appears to be about the same as a 63 mile overhead line in the rugged terrain of Southern Alaska. OPERATION AND MAINTENANCE The estimated operating and maintenance cost for either the 9000 KW or 12000 KW DC system is $445,000 per year (from Section 6E). COMMUNICATION CHANNELS The charges for communication channels needed for operation of the DC system are estimated at $10,800 per year for the 9000 or 12000 kW size. REPLACEMENT POWER No attempt was made to calculate the cost of replacement power since power costs in this area are not known, The estimated forced outage time for the DC system is 445 hours and the scheduled outage time 203 hours for either the 9000 or 12000 KW DC system, It should be noted that the cost per KW of DC systems goes down rapidly with size in the 10 to 20 MW capacity range. A report on a similar system in Southeast Alaska showed that its capacity could be doubled for a 30% increase in cost, 2) TABLE 1 CORDOVA-VALDEZ DC TIE LINE 12000 KW SYSTEM COST Cost in 1,000's 72.6 mi. of 70 KV, 300 MCM, armored cable at $97,750/mi, delivered in Seattle, includ- ing duty charges. Engineering and administration at 103% Laying 66 mi. cable run from Canoe Passage to Jack Bay at $52,800/mi. Engineering and administration at 20% Laying and ditching 6.6 mi, cable run across Orca Inlet, (Includes ground cable). Engineering and administration at 20% Cost of 4 cable terminations, including ditching at Canoe Passage and Jack Bay terminals, (Orca ditching included in Item 3 above). Engineering and administration at 20% Total installed cable cost 7 mi. of 2 conductor overhead line, Solomon Gulch to ground electrode. 6.2 mi. of 2 con- ductor OH line, Cordova to ground electrode. Total 13.2 mi. 2 conductor OH line at $150,000/mi. Engineering and administration at 20% 4 mi. 1 conductor, OH line from Valdez ground electrode to Jack Bay and 1 mi. 1 conductor, OH line from Canoe Passage ground electrode to Canoe Passage cable entry. Total 5 mi. 1 con- ductor OH line at $125,000 mi, Engineering and administration at 20% =22= Cost in 1,000's $7,097 710 3,480 696 1,740 348 600 120 1,980 396 625 125 $14,791 TABLE 1 (Continued) CORDOVA-VALDEZ DC TIE LINE 12000 KW SYSTEM COST Cost in 1,000's Cost in 1,000's ee See 8. Total cost of OH line $ 3,126 9. Valdez converter cost at $159/KW installed* $1,908 Engineering and administration at 10% 191 10. Sea electrode 105 Engineering and administration at 20% 21 11. AC substation including 13.8 KV breaker, bus and dis- connects, installed 250 Engineering and administration at 20% 30 12. Site preparation at Solomon Gulch 500 Engineering and administration at 20% 100 13. Total for Valdez terminal “$ 3,005 14. Cordova converter cost at $159/KW installed* 1,908 Engineering and administration at 10% 191 15. Sea electrode 105 Engineering and administration at 20% . 21 16. AC substation including 34.5 KV breaker, bus and disconnects, installed 200 Engineering and administration at 20% 40 17. Site preparation at Cordova 500 Engineering and administration at 20% 100 *Installed turnkey estimating price supplied by manufacturer, =235 18. 19. 20. TABLE 1 (Continued) CORDOVA-VALDEZ DC TIE LINE 12000 KW SYSTEM COST Cost in 1,000's Cost in 1,000's 10,000 KVA synchronous con- denser, with circuit break- er, regulator, and start- ing motor, installed $ 700 Engineering and administration at 20% 140 Total for Cordova terminal $ 3,905 Total $24,827 Contingencies at 20% ~ 4,965 Project cost $29,792 -24- TABLE 2 CORDOVA-VALDEZ DC TIE LINE 9000 KW SYSTEM COST d2e 6M). OL704KV,.225)MCM, armored cable at $95,000/mi. delivered in Seattle, in- cluding duty charges Engineering and administration at 10% Laying 66 mi. cable run from Canoe Passage to Jack Bay at $52,800 Engineering and administration at 20% Laying and ditching 6.6 mi. cable run across Orca Inlet. (Includes ground cable). Engineering and administration at 20% Cost of 4 cable terminations, including ditching at Canoe Passage and Jack Bay terminals, (Orca ditching included in Item 3 above). Engineering and administration at 20% Total installed cable cost 7 mi. of 2 conductor overhead line, Solomon Gulch to ground electrode. 6.2 mi. of 2 con- ductor OH line, Cordova to ground electrode. Total 13.2 mi. 2 conductor OH line at $150,000 mi. Engineering and administration at 20% 4 mi. 1 conductor, OH line from Valdez ground electrode to Jack Bay and 1 mi. 1 conductor, OH line from Canoe Passage ground electrode to Canoe Passage cable entry. Total 5 mi. 1 con- ductor OH line at $125,000 mi. Engineering and administration at 20% -25- Cost in 1,000's $6,897 690 3,485 696 1,740 348 600 120 1,980 396 625 25) Cost in 1,000's $14,576 10. ll. 126 phic 14. 15. 16. Lis TABLE 2 (Continued) CORDOVA-VALDEZ DC TIE LINE 9000 KW SYSTEM COST Total cost of OH line Valdez converter cost at $159/KW installed* Engineering and administration at 10% Sea electrode Engineering and administration at 20% AC substation including 13.8 KV breaker, bus and dis- connects, installed Engineering and administration at 20% Site preparation at Solomon Creek Engineering and administration at 20% Total for Valdez terminal Cordova converter cost at $159/KW installed* Engineering and administration at 10% Sea electrode Engineering and administration at 20% AC substation including 34.5 KV breaker, bus and disconnects, installed Engineering and administration at 20% Site preparation at Cordova Engineering and administration at 20% Cost in 1,000's $1,431 143 100 20 150 30 500 100 1,431 143 100 20 200 40 500 100 $3,126 $ 2,474 *Installed turnkey estimating price supplied by manufacturer. -26- TABLE 2 (COntinued) CORDOVA-VALDEZ DC TIE LINE 9000 KW SYSTEM COST Cost in.2,000"s) Cost in 7),.000*s 18. 7,500 KVA synchronous con- denser, with circuit break- er, regulator, and start- ing motor, installed $ 560 Engineering and administration at 20% ne. 19. Total for Cordova terminal Si Sipe 2015 | | Total. $23,383 Contingencies at 20% 4,677 Project cost $28,060 27 TABLE 3 CORDOVA-VALDEZ AC CABLE TIE LINE 12000 KW SYSTEM COST 72.6 mi. of 3 conductor 187 MCM, 70 KV armored cable at $273,000/ mi. Engineering and administration at 10% Laying of cable run from Canoe Passage to Jack Bay - 66 miles at $68,000/mi. Engineering and administration at 20% - Laying and ditching cable across Orca Inlet - 6.6 miles Engineering and administration at 20% Cost of 6 cable terminations including ditching at Canoe Passage and Jack Bay. (Orca ditching included in Item 3 above). Engineering and administration at 20% Total installed cost of cable 2-15000 KVA and 1-30000.KVA shunt reactors at $25/KVA, installed. Engineering and administration at 20% Site preparation of compensating reactor station on Goose Island Engineering and administration at 20% 2-13.3 MVA-70 KV substations, including power transformer, HV and LV breaker at 500,000 each, installed Engineering and administration at 20% Total installed cost of sub- stations -28- Cost in 1,000's $19,820 1,982 4,490 898 1,740 348 1,160 232 1,500 300 500 100 1,000 200 Cost in 1,000's $30,670 $_3,600 TABLE 3 (Continued) CORDOVA-VALDEZ AC CABLE TIE LINE 12000 KW SYSTEM COST Cost in 1,000's Cost in 1,000's 10. 18.3 mi. of 70 KV, 3 phase, overhead transmission line at $200,000/mi. $ 3,660 Engineering and administration at 20% 732 ll. Total cost of overhead lines $ 4,392 12. Total $38,662 Contingencies at 20% Tetae Project cost $46,394 =29= TABLE 4 CORDOVA-VALDEZ AC CABLE TIE LINE 9000 KW SYSTEM COST 72.6 mi. of 3 conductor i87 MCM, 70 KV armored cable at $265,000/ mi. Engineering and administration at 10% Laying of cable run from Canoe Passage to Jack Bay - 66 miles at $68,000/mi. Engineering and administration at 20% Laying and ditching cable across Orca Inlet - 6.6 miles Engineering and administration at 203% Cost of 6 cable terminations including ditching at Canoe Passage and Jack Bay. (Orca ditching included in Item 3 above). Engineering and administration at 20% Total installed cost of cable 2-15000 KVA and 1-30000 KVA shunt reactors at $25/KVA, installed Engineering and admistration at 20% Site preparation of compensating reactor station on Goose Island Engineering and administration at 20% 2-10 MVA-70 KV substations, including power transformer, HV and LV breaker at 425,000 each, installed Engineering and administration at 20% Total installed cost of sub- stations -30- Cost in 1,000's $19,239 1,924 4,490 898 1,740 348 1,160 2312, 1,500 300 500 100 850 170 Cost in 1,000's $30,031 $ 3,420 10. il. 12. TABLE 4 CORDOVA-VALDEZ AC CABLE TIE LINE 9000 KW SYSTEM COST Cost in 1,000's Cost in 1,000's 18.3 mi. of 70 KV, 3 phase, overhead transmission line at $200,000/mi. $ 3,660 Engineering and administration at 20% 732 Total cost of overhead lines Total, Contingencies at 20% Project cost ~31- $ 4,392 $37,843 7,569 $45,412 aut Onan Catsing Me. Penta Ltt 4 ligne may be pbtained ‘4 the Ottiey of the Commander. 178 Cost Reber to sechan'numbers shown ith * Navigation regulations are published in LeChapter 2. 418 Diarret Capnenr. Carpe of Eagan” in ‘the regulations may be ebjained at the Offiee © Anchorage, Ala Netiee te Ml : Teweed regulations Informabon concerning Anchorage ree Guard District im Juneau, Alaska. SUUINVINGS IN FALHOMS SSS ao A itll rite i a Cry VAL D gzo Sat 147° FSseSs~s! 3 WNOBHINOS —_ Ppa 0 SS set SOUNDINGS IN FATHOMS AT MEAM LOWER LOW WATER ALASKA — SOUTH COAST ee ee 20' fant PRINCE WILLIAM. SOUND |. SCALE 1:63360 } o 1 2 a 4 MILES 3000 6000 9000 12000 15000 18000 21000 FEET —— = eel 5 ° 1 2 3 4 5 KILOMETERS CONTOUR INTERVAL 100 FEET DATUM IS MEAN SEA LEVEL DEPTH CURVES AND SOUNDINGS IN FEET-DATUM IS MEAN LOWER LOW WATER SHORELINE SHOWN REPRESENTS THE APPROXIMATE LINE OF MEAN HIGH WATER THE AVERAGE RANGE OF TIDE IS APPROXIMATELY 10 FEET FOR SALE BY U.S. GEOLOGICAL SURVEY FAIRBANKS, ALASKA 99701. DENVER. COLORADO 80225 OR WASHINGTON, D. C. 20242 CABL © weremon-ceoLoaca sunvey, wherncTOn OC 1973 Men 0e QUADRANGLE LOCATION Yd ea Deep Ba J V4 & Z Ee Wy : eae ; Hartney | Z a ariney } ay 58” 5610006. 145 %t gr _.Mapped, edited, and published by the Geological Survey Control by USGS and USC&GS Topography by photogrammetric methods from aerial photographs taken 1950, field annotated 1951. Map not field checked Selected hydrographic data compiled from USC&GS Charts 8520, 8525, and 8551 (1:200, 000 scale) This information is not intended for navigational purposes Universal Transverse Mercator projection, 1927 North American datum CORDOVA (C-6), ALASK /10.000 - foot grid based on Alaska coordinate system, zone 3 1 000-meter Universal Transverse Mercator grid ticks, | 5 er a N6030—W14552.5/15X22 6, in blue 1950 MINOR REVISIONS 1963 R.4W. ROAD CLASSIFICATION Trails predetermined by the Bureau of Land Management lene ne © An stand lines represent unsurveyed and unmarked locations \‘—-- CORDOVA TERMINAL intrance | ,Pellew g[- Island es C en ee Soom os 3 Wr 5 Anderson, Boy 2 - ~-Yyouolas © 2.560 000 FEET / , 676 ote 35° = (CORDOVA D-7) ; ¥ eT sy ” Mapped, edited, and published by the Geological Survey : : } 5 : SCALE 1:63360— ; _ an yt Control by USGS and USC&GS Pigs eos = °@ T oiy by piol attic inert ial chet Ry 3000 oO 3000 6000 9000 12000 15000 18000 21000 FEET FI 3 ‘opography by photogrammi methods from aerial photographs = = | ( 5 ry taken 1957, field annotated 1960. Map not field checked = [= ee u z z a Semele Mediu, Selected hydrographic data compiled from USC&GS 2 & | Charts 8519 (1947) and 8551 (1963). This information is not | & eee EAs VALDEZ TERMINAL intended for navigational purposes El = DEPTH CURVES AND SOUNDINGS IN FEET.OATUM IS MEAN LOWER LOW WATER na Universal Transverse Mercator projection, 1927 North American datum i$ SHOE Se MOAN RANGE OF NOES APPRONMATELY 1OFEET ‘4 10,000-foot grid based on Alaska coordinate system, zone 3 APPROXIMATE MEAN. . 0. 00 AE 1000-meter Universal Transverse Mercator grid ticks, DECLINATION, 1960 ‘QUADRANGLE LOCATION VALDEZ (A-7), ALASKA zone 6, shown in blue FOR SALE BY U.S. GEOLOGICAL SURVEY N6100-W14615/15X22.5 Land lines represent unsurveyed and unmarked locations FAIRBANKS, ALASKA 99701, DENVER, COLORADO 80225, OR WASHINGTON, D. C. 20242 - 9 ese a abet lated hl eceace A FOLDER DESCRIBING TOPOGRAPHIC MAPS AND SYMBOLS IS AVAILABLE ON’ REQUEST CAPTAIN § 1960 MINOR REVISIONS 1970 APPENDIX 1 Siting Sea Electrodes Sample Calculations Sea Electrode Costs Sea Electrode Design Compass Errors Caused by D.C. Cables Sample Calculations Siting of Sea Electrodes Discussion The most crucial factor in locating a sea electrode is to achieve suffi- cient separation from other buried or marine structures to prevent electrolytic corrosion or stray current effects. This includes the effect upon the armor of the project's own submarine cable. If ade- quate separation is not possible cathodic protection may be employed. Given the current magnitude quoted for this project, electrode size assumed and a sea waterjo of not over 0.2 ohm-meter, a separation of 1 mile from the nearest buried or submerged metallic structures (pipe lines, steel piling, armored cables etc.) should be adequate. ‘Other important requirements are: Relatively deep water - but not beyond diving depths. A sound bottom not subject to silt or sand deposition or shifting i.e. stable bottom conditions. Maximum salinity - low fresh water intrusion. If fresh water in- flow cannot be avoided the site may be acceptable if little mixing occurs and the salinity at the bottom remains high. Non fishing area - not subject to disturbance in the electrode area by beam trawls, anchors, set lines etc. Tidal currents must be low. Low wave action at the shoreline is desirable to reduce burial expense. Moderate slope from feed cable entrance points at shoreline to bottom location of electrodes. Cable should not traverse slopes greater than 45° nor should it hang over ledges or span fissures unless special measures are taken to avoid early failure due to such conditions. Cordova Several potential locations for sea electrode were sighted during a helicopter survey of the Cordova terminal. Assuming the converter A-1 Cordova_ continued station will be located near the present generating plant, all potential electrode sites could be served by a wood pole overhead line which might also carry an overhead conductor connected to the submarine DC power cable shore terminus. Site #1. This location would involve a submarine cable from Cordova across Orca Inlet to the mouth of Shipyard Bay, thence overland via wood pole line to the nearest arm of Deep Bay. The Electrode would be just off shore in the Deep Bay cove. This is the nearest site and probably the one with minimum cost. It suffers from the fact that iit requires crossing the busy part of Orca Inlet with the ground cable. The site is also rela- tively close to the present cable area and area where it might be desirable to lay the DC cable. No man made marine or buried pipe structures are nearby. Site #2. This location is reached by overhead line to Bluff Point, then submarine cable across Orca Inlet toa point on Hawkins Island near the mouth of the shallow bay pointing toward Canoe Passage, then overland by pole line to a suitable location along the shore of Canoe Passage. Site #3. If it becomes essential to hold costs to an absolute minimum it might be possible to install a sea electrode on the Cordova side of Orca Inlet along the shoreline approxi- mately two thirds of the distance up the shore from the Cordova boat basin to the Orca Cannery. This location would be the least desirable because of the potential installation of pipelines, etc. sometime in the future. It is probably remote enough to avoid any trouble A-2. Cordova continued with present structures. It involves an overhead line only (mo submarine cable) and is served by a road whose right of way is probably wide enough to accept the woodpole line. Of these three preliminary sites #2 was selected for purposes of this estimate. This is a conservative approach in a number of aspects. It is most remote (12.5 miles). No manmade structures are located closer. than 5 miles (cable area 5 miles offshore). The Site may be accessed by boat and barge. It is protected from wave action. There is no major ship traffic and bottom conditions appear good as nearly as could be determined from the air. The submarine cable crosses Orca Inlet in shallow areas which should be free from any large boat traffic. The cable probably should be plowed in for protection. The cost of the ground electrode line would be reduced because it could be carried on the same wood poles that are needed to carry the main power line for the overhead portion from Cordova to Canoe Passage. Valdez Two sites, one on Jack Bay and one on Port Valdez (Bay) half way between Anderson Bay and Sawmill Spit (on Section 20 of the Valdez A-7 quadrangle) appear to be possible locations. for the ground electrode. The route over the ridge from Port Valdez (Bay) to Jack Bay could not be surveyed from the air because of the rapidly lowering ceiling and an approaching snow storm. There appears (from the map) to be a suitable route over the ridge without exceeding 2.000 foot elevation. -This involves heading approximately NE from the northern arm of Jack Bay to the shore of Port Valdez (Bay) at the N. E. corner of Section 20. If Jack Bay is selected for the power cable entry to the water, the entry could be located on the short arm on the north side of Jack Bay. The ground electrode could be located to the east of this location A-3, Valdez continued about 1 or 2 miles up the longer arm of Jack Bay. This location of the ground electrode would require bringing both the power conductor and the ground wire over the ridge from Port Waldez on a wood pole line. The other location for the ground electrode is on the south side of Port Valdez (Bay) just east of Anderson Bay at the NE corner of section 20. The marine chart of this area indicates that there is a shelf along the shore where the depth is around 5 to 10 fathoms. This should be suitable for a ground electrode. The main power conductor would then proceed over the ridge to Jack Bay on a wood pole line over the route described above. This means that the pole line over the ridge would carry only one conductor unless the lightning incidence is such that an overhead ground wire is needed. The option desc ribed in this paragraph is the one selected for this report. If the DC tie line is deemed worthy of further study, a third option should be investigated. This would involve locating the ground elec- trode on’ the NE corner of Section 20 as described above and then run- ning the overhead line carrying the main power conductor west along the shore of Port Valdez (Bay) to the vicinity of Entrance Island, Section 14, where the main power cable would enter the water. This site for the cable entrance is dependent on being able to route the cable to deep water without running it over any under-water cliffs. The shores of Valdez inlet are so steep that it is questionable whether this is possible along the south shore. A bottom survey would be necessary before proceeding with this approach, A-4, Sea Electrode Costs Cordova Electrode Assembly Proper Materials 20 Type SM anode assemblies 20-2' x 2' x 8' concrete vaults 4 Reference electrodes 4 Buoy Units 6 Undersea connector cables (5 anode connectors + 1 reference electrode) 1 Beach control vault Estimated Material Cost $60,000.00 Labor Divers Boats, Barges, Cranes Stage and Living Expense Estimated Labor Costs 34,000.00 Engineering Environmental Studies System Design Supervision System Tests Estimated Engineering Costs 18,000.00 Total $112,000.00 Valdez Same $112,000.00 Both Terminals Total (Allowing for some engineering savings) $210,000.00 —_—_—_———_ Sea Electrode Design Discussion This design was chosen to be very similar in construction to the sea electrode on the Los Angeles end of the Pacific N.W.-Pacific S.W. DC Intertie. The voltage gradients near the electrodes are, however, much more conservative (approximately 16% of those at Los Angeles). The maximum current rating is also less than 10% of the Los Angeles design. In spite of these factors there are other differences that require the electrode to be nearly as large as that at Los Angeles. Two assumptions were made that,in turn, dictate the size and cost of the design. ae The electrode elements should have a reasonably long life and the composite electrode should be essentially maintenance free. Any maintenance required should be capable of performance with=- out taking the composite electrode out of service except for brief periods, With this in mind a minimum element life of 3Q° years was chosen, b. Resistance of the electrode should be as low as physically and economically feasible. The anodic electrode of a given composition loses material at a rate that is a function of a constant multiplied by the ampere-hours of operation. This means that for a givenpattern of operation (current flow) the desired life is achieved by installing a given weight of anode material. Fortunately, in this case, when a reasonably long life is selected for the design (30 years), all of the other criteria essential to good design are automatically satisfied. ‘ ae Current density in the immediate electrode vicinity drops to a very low value, This means very low voltage gradients with essentially no adverse effects on marine life. be. Chlorine production so low that absorption will be. practically Sea Electrode Design (continued) immediate and the density so low that effects will be prac- _tically nil. Cc. Composite electrode resistance will be quite low (approximately 0. O0330hms) per terminal. Cost of the losses in the return current path will thereby be very low. d. In the Los Angeles design, very large concrete vaults (9 tons each) are used to protect each pair of electrode elements from injury, to support them above the sea floor, to prevent burial by sediment and to keep marine life (essentially fish) out of the high electrical gradient zone. For the case at hand, the much lower gradients will allow use of a much smaller and lighter protective structure and appreciable savings as a re- sult. The gradient at vault surface will be under 0.5 V/meter. Design The design selected was a linear array of 20 elements spaced 25* apart. As in Fig. 2 each group of four elements is fed by a separate cable brought out to a shore based disconnect that will permit each group to be disconnected for service. A separate reference electrode is included to enable diagnostic checks during life of the installation. \ 4 i On the Pacific Intertie* two electrodes are suspended by polypropylene ropes from the box lid and each box is 1l feet long by 7 feet wide by 5 feet high and weighs 9 tons. For the case at hand.a vault 2 feet Square by 8 feet long should be adequate and the weight should be less than 2 tons. Any concrete reinforcement must be nonmetallic (Fibreglass for example). Fig. 1 shows the approximate gradient adjacent to an individual electrode element. * See "The Los Angeles HVDC Ocean Electrode" by G. R. Elder and D. Be Whitney. Also shown in "Direct Current Transmission", Page 475, a book by E. W. Kimbark. Sea Electrodes - Calculations Assumptions: 175 amperes continuous current Both Valdez and Cordova electrodes designed as anodes Specific resistivity of sea water at sites selected () not greater than 20 ohm-cm. 48% load factor Electrode useful life = 30 years (Based upon 50% loss of electrode material) Durco 51 Type SM electrodes (4.5" x 5' rods 220# weight. Material loss 0.85#/amp.-yr) Amperes/anode = 9 (12 would be satisfactory but 9 amps. selected to keep electrical gradient low. Calculations: Weight loss per 175 amp. @ .48 LF = 84 x .85# x 30 yrs. = 2142 # No. Rod @ 9 amp/rod = 175/9 = 19.4 (use 20) Weight loss/rod =2142/20 = 107# Each rod can stand loss of 110# of material. Therefore: 110/107 x 30 + 30.8 years actual life Anode Consumption Use 20 DURCO 51 Type SM 220#/ electrode At 175 amp. full load with 48% Load Factor Ampere hrs/yr = 175 * .48 * 24 * 365 = 736,000 amp. hr./yr or 84 amp. yrs/yr Anode Consumption (continued) Electrode Loss = 0.85#/amp. yr 175 amp. & .48% LF Loss = 0.85 * 84 = 71.4#/yr 20 electrodes may safely lose 110# each Life = 20 * 110 = 30.8 years 71.4 ——$—— Max. Amp./Rod = 175/20 Area/Rod = D*L 33.14 * .375 * 5 = 5.9 sq. ft. 8.75 amp. Current Density (max) = 8.75/5.9 = 1.48 amp/ét? 5.9 x*20 lis £t? u Total Area Los Angeles sea electrode has area 192 £t? and a resistance of 202 ohms. Ratioing areas gives 192 x .02 0.0325 ohms for this design 118 Ratioing for max gradient as compared to Los Angeles gives (E) = 2.5 x 1.48 (amp/£t?)/ 95375 (amp/£t?) (E) = 0.395 volts/meter (approx, ) or about 16% of the Los Angeles gradient near electrode. A-9 Gradient (E) = @ * 1 a (.1143)m pei St" f° = 0.2 ohm-meter A= 77 * 4,5" * 2,5 om KES xX 12) x.205 100 100 = 0.53 m? At Electrode surface (E) = 0.2 * 8.75/0.53 = 3.30 v/m At 20 cm A = 3.14 * .5143 * 1.52 2.45 sq. m 22 * 8.75 2.45 2714 v/m (E) At 40 cm A = 3.14 * 1.52 *.914 4.355 1.75/A 1.75/ 4.355 0.40 v/m (E) At 60 cm (E) 1.75/ 3.14 * 1.52 * 1.31 v ~280 v/m At 100 cm (E) = 1.757 3.14 * 1.52 * 2.11 - 2173 v/m A-10 SUOIsAIG YOUR OOL/L OVTXOOT a ‘ “W'S'N “A‘N ‘AGVLOBNSHOS ‘ANVdMOD DIN1D9713 1VY3N39 (0s) @-IzsNa A-ll VSANIIOVW “OD H3SS3 B 1344NI Ovel 9” ( S3HONT Ol X L*HONI SHL OL 02 X 02 A-12 COMPASS ERRORS CAUSED by D.C. CABLES Compass error can be calculated quite accurately if the strength of the earth's magnetic field is known. This has been checked on both the English Channel Crossing and the Konti-Skan projects. On the Gotland cable crossing a check was made when the sea was frozen and measurements made on the ice. The curves of compass error were plotted from data calculated by the following equation: & tan+(Hg,cos8/He) Where (see Figs. (a), (b) : Compass error Hgg =horizontal component of field due to cable H, =horizontal component of earth's fiela* A =angle cable makes with direction of H, Hac = qq h . Igh/2m(n?+x?) amp./meter or 3 Where: Ig= Direct current in cable, Amperes he- Height of compass above cable, meters x = Horizontal distance of compass from cable, m. r= Slant height of compass from cable, m. * He varies with latitude. It is approximately 16 A/m in the temperate zone. This value was used in the calculation. A-13 (a) (>) A-14 = 1s ee ‘| | | ey Beer hi St eS hat: ed BCRP) ba ated 4 | hae mrad ha | | : Hi a | | 1 | ky | nH | | | ' | jel: toe | | | 1 Let | | x ; | Compass Zrror Lor Verveus | bo “davis Os A Leneriel? { | ! ie ~~ pw. | | oS $ ne gp Rl acta erent ° iS . NX : ~-2.-4 \ a V4]. | Leet “4 beh soPrcnr¢ hm | % beg ae pai tie +, Oiience Camedss fait es |S te Vs placed Weratal 7O Le re of Cb le pe Coble O° +o karth fe el | | = . e pbb 7 Ft Fo ned oaks ced eS Sas 8 1 | | fyi tle SU ts cil ee «| l | | | | { | | | Coble Depth foo" Cable, Depth $0" Coble ane 250° | = | Coble Leap 177° | hc Leon 65L ” 20 #0 ; ép ; : 60 : bo Wie Sone i st | Listinee Cmpuss ts Yortial t | | | Conthr kine oF Cole 7a Come? ) 2 ee San | oy tpi eee ey bi Ts | : | ae ved rs “ ; pat ELL | | Conpess frror As ay ee Ls or | | ! Depth | | ‘ iaral | Ceble Current 250 cmp | Lartlh Freld {6 am (eh er | | pee eer cer oekacia at insane | Ee sea Q | | | v a ce Bee 7O "Fo ecors/h Siel/ | l | | g 3 ! ree | | . q | | § 6 genres UU LULL EL \ | | \ : | | Vg | is | - Wiz cotle #5 ° fo ears field F o 500 000 /500 | \ ‘a Depth of Cable fo Fee? | | | A-16 | | ' | i i {