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Home My WebLink AboutAnalysis of Voltage Drop & Energy Losses Seward 1982SEW 006 ANALYSIS OF VOLTAGE DROP AND ENERGY LOSSES PREPARED FOR: CITY OF SEWARD SEWARD ALASKA OCTOBER, 1982 BY: DWANE LEGG ASSOCIATES 7526 OLD HARBOR RD. ANCHORAGE, ALASKA 99504 PHONE 337-2303 INDEX I. INTRODUCTION II. LOAD HISTORY AND PROJECTIONS III. VOLTAGE DROP AND ENERGY LOSSES IV. POSSIBLE ACTION V. ANALYSIS VI. CONCLUSION AND RECOMMENDATIONS I. INTRODUCTION This report is presented in response to purchase order 7463 from the City of Seward. The report is not intended to be an exhaustive original work, but rather a summary of and careful analysis of existing information, together with brief projections of future conditions. The City of Seward is experiencing brownout (low voltage) problems during periods of peak load. This is not a new problem. It is addressed in detail in the "City of Seward Electric System Planning Study" by CH2M Hill, Inc., August, 1979. Considerable new commercial/industrial construction is underway in Seward. More is in advanced planning/design stages and should appear as new electrical loads in the very near future. These new loads along with normal load growth will further aggravate existing problems. Chugach Electric Association (CEA) provides power at wholesale to the City of Seward via a 14.4/24.9 kv line from Daves Creek to Lawing, a distance of approximately 16 miles. The City of Seward owns a 69 kV line, operated at 14.4/24.9 kv, from Lawing to Seward, A distance of 18 miles. The City of Seward supplies several consumers from this line before it reaches Seward. At the outskirts of Seward, the voltage is reduced to 7.2/12.5 kv for additional distribution. PAGE 1 Seward owns two 1500 kW and one 2500 kW diesel-generators. During periods of peak load these generators are operated in order to maintain proper voltage levels at Seward. When supply voltage at Lawing is increased even to 130 V on a 120 Volt base, the voltage at Seward is 110 V or below during peak loads. When a CEA outage occurs, the supply from CEA is opened and the Seward generators supply the Seward Load. When the CEA supply is re-established, the CEA no-load voltage is too high to close the tie. PAGE 2 II. LOAD HISTORY AND PROJECTIONS Historical kW demand and kWh consumption information was obtained from utility records and from previous engineer- ing studies. This information indicates that consumption grew at an annual rate of 10% per year from 1967 through 1981. Data for the first 8 months of 1982 indicates that consumption in 1982 will probably be about 14% above 1981. Peak demand grew at an average rate of 10.6 percent from 1967 through 1978, experienced an unusually high value of 6697 kW in 1979, and has remained at slightly above 5000 kW since 1980. Since 1980, demand has been relatively stable, growing at less than 5% per year. It is most probable that the 1982 peak will be in the range of 5200- 5600 kW. It should be noted that the indicated peak load values are at the CEA metering point at Lawing. Seward generators are used to shave the peak, therefore peak load values are actually higher than the indicated values by an unknown amount. PAGE 3 A number of major new loads are under construction or planned for the very near future. The most prominent are listed below. DESCRIPTION : STATUS LOAD State grain terminal Being constructed 500-1000 kw AVTEC Student Center Construction/Design 300-500 kw Fourth of July Shiplift Being constructed 500-1000kwW Fourth of July Industrial Planned 1000-2000kW Reactivate Lumber Mill Uncertain 500kW Total 2300-5000kW These loads will be in addition to normal growth, and will likely spur additional growth in residential and light commercial sectors as well. Figures 1 and 2 are graphs indicating historical peak load and consumption, as well as several possible future growth rates. Based upon historical information and known load additions, it is only remotely possible that load growth will be as low as 5%. However, even ignoring the peak shaving by Seward generation, peak load will be 6000kW by 1985. If 10% growth is realized, peak load will be 7800 kW by 1985. Further analysis in this report will be based upon the top curve of 20% growth through 1983, and 10% thereafter. If, in fact, peak loads during 1980 and 1981 have been artificially depressed by peak shaving, even these projections could be low. The magnitude of these voltage drops and energy loss PAGE 4 problems are so imminent and so drastic in nature that immediate corrective action is needed, PAGE 5 46 5250 cA SEMI-LOGARITHMIC 2 CYCLES X 200 DIVISIONS KEUFFEL & ESSER CO. MADE IN USA KE ‘A my NNUAL 7a 71 70 1961 6? 64 46 5250 KeE SEMI-LOGARITHMIC 2 CYCLES X 200 DIVISIONS KEUFFEL & ESSER CO. MADE IN USA III. VOLTAGE DROP AND ENERGY LOSS Voltage drop and energy loss calculations were performed for a range of loads from 4 to 20 mW for three configura- tions. Table 1 is for the present configuration, table 2 is for operation of the line from Daves Creek to Seward at 69 kv, and table 3 is for operation of the line at 115 kV. All cases assume unit voltage at Daves Creek. Adding 5% boost at Daves Creek, at Lawing, and at Seward substation will increase the supply voltage at Seward by 15%, but losses will remain approximately the same. Table 4 is a summary of expected load, service voltage conditions, and energy losses through 1990. PAGE 8 TABLE 1 VOLTAGE DROP AND ENERGY LOSSES EXISTING SYSTEM CALCULATED AT .90 POWER FACTOR 1000 KW LOAD AT MOOSE PASS KW LOAD ———0 VOLTAGE"- <—“6----— ANNUAL MWH LOSSES---- SEWARD LAWING SEWARD D.C-LAWING LAWING-SEWARD TOTAL 4000 -899 -806 1413 1081 2494 5000 883 e771 2063 1690 3753 6000 -867 -738 2839 2433 5272 7000 853 -708 3738 3312 7050 8000 -840 -680 4761 4326 9087 9000 827 -654 5909 5476 11385 10000 -816 -630 7179 6760 13939 11000 805 -608 8574 8180 16754 12000 2795 587 10092 9735 19827 13000 - 786 567 11735 11425 23160 14000 -778 -549 13502 13257 26753 15000 -769 O32 15.392 15211 30603 16000 -762 2515 17407 17307 34714 17000 754 -500 19545 19538 39083 18000 748 485 21808 21905 43713 19000 741 -472 24194 24406 48600 20000 135 ~459 26703 27043 53746 PAGE 9 TABLE 2 VOLTAGE DROP AND ENERGY LOSSES 69 kV OPERATION CALCULATED AT .90 POWER FACTOR 1000 KW LOAD AT MOOSE PASS 69kV, 556.5 MCM ACSR, TP-69 CONSTRUCTION DAVES CREEK-LAWING EXISTING LINE LAWING-SEWARD KW LOAD ---PU VOLTAGE-- = -------- ANNUAL MWH LOSSES-------- SEWARD LAWING SEWARD D.C-LAWING LAWING-SEWARD TOTAL 4000 992 2-977 50 141 191 5000 -990 972 74 220 294 6000 -988 -967 103 318 421 7000 987 -962 136 432 568 8000 985 -956 174 565 739 9000 -983 951 215 725 930 10000 981 -946 262 883 1145 11000 -980 941 313 1068 1381 12000 978 936 369 1272 1641 13000 -976 “931 429 1492 1921 14000 3975 -926 494 LASI 2225 15000 973 921 563 1987 2550 16000 -971 917 637 2261 2898 17000 -970 -912 715 2552 3267 18000 -968 -907 798 2862 3660 19000 -967 -902 885 3188 4073 20000 -965 -898 977 3533 4510 PAGE 10 TABLE 3 VOLTAGE AND ENERGY LOSSES 115 kV OPERATION CALCULATED AT .90 POWER FACTOR 1000 KW LOAD AT MOOSE PASS 115 KV, 336. MCM ACSR, TH1A STRUCTUES KW LOAD =—-=PU: VOLTAGES— | #=5=-=<=— ANNUAL MWH LOSSES-------- SEWARD LAWING SEWARD D.C-LAWING LAWING-SEWARD TOTAL 4000 997 «992 18 50 68 5000 -996 -990 26 79 105 6000 -996 -988 37 114 Lod 7000 2995 -986 48 155 203 8000 6995 -984 62 203 265 9000 994 982 77 257 334 10000 993 -980 93 318 411 11000 993 978 112 384 496 12000 992 -976 132 457 589 13000 991 974 154 S37 691 14000 991 973 178 623 801 15000 -990 971 202 715 917 16000 -990 -969 228 814 1042 17000 989 967 257 919 1176 18000 988 -965 287 1030 1317 19000 988 963 318 1148 1466 20000 987 961 351 1272 1623 PAGE 11 YEAR 1982 1983 1984 1985 1986 1987 1988 1989 1990 LOAD MW 6.4 7.7 8.5 953 10.3 Les 12.4 13.6 15.0 SERVICE VOLTAGE-P.U. TABLE 4 PROJECTED CONDITIONS 24.9kV 69kV 115kV 73 69 67 65 62 -60 58 -56 253 96 95 295 95 94 94 93 93 92 98 -98 -98 -98 -98 98 98 97 97 (1) Losses from Lawing to Seward (2) Losses from Daves Creek to Seward, <= LOSSES-MWH---- 24.9kV 69kV 115kV (1) (1) (2) 2784 364 2 4022 525 246 4901 640 303 5861 765 357 7186 939 437 8647 1129 524 10411 1360 630 12521 1635 AST PS211 1987 917, metering point is moved to Daves Creek assumming the PAGE 12 IV. POSSIBLE COURSES OF ACTION Several possible courses of action are available. They are listed below and discussed in brief detail. 1. CONTINUE AS AT PRESENT. This alternative will continue to produce substandard service voltages and high energy losses. It will be mandatory that the Seward generators be operated at peak-load times to prevent voltage levels from dipping to completely unacceptable levels. As system load continues to grow, it will be necessary to operate the generators more hours each month which will cause fuel and operating costs to rise. 2. ADD POWER FACTOR CORRECTING CAPACITORS. Correcting power factor with capacitors will cause a measurable but not significant increase in voltage level, and decrease in energy losses. This would at best be only a temporary , patch. 3. ADD AUTOMATIC VOLTAGE REGULATORS. This also would be a temporary fix. It would be possible, by installing a sufficient number of regulators, to provided proper levels of service voltage, but losses would continue to mount. The ultimate limitation will be the 16 mVA rating of the 4/0 transmission conductor at 24.9 kV 4. CONVERT TO 69 kV TRANSMISSION VOLTAGE. This would be implemented by operating the existing line from Lawing to Seward at 69 kV and by building a new 69 kV line from Daves Creek to Lawing or converting the existing one. It would provide a good solution for now and the near future. PAGE 13 However, by the time the system load reaches 15-20 mw (1990-1995), voltage drop and energy losses will again become of concern, 5. CONVERT TO 115 kV TRANSMISSION VOLTAGE. This would require rebuilding or replacing the total line from Daves Creek to Seward. It would accommodate 10% per year load growth for up to 30 years. 6. COMBINATION 115/69 kV TRANSMISSION. This would require a new 115 kv line from Daves Creek to Lawing, a 115-69 kV substation at Lawing, and operation of the exist- ing line from Lawing to Seward at 69 kV. It would hold down immediate construction costs, but it would still be necessary to convert to 115 kV from Lawing to Seward within a few (say 5) years. PAGE 14 V. ANALYSIS Seward is experiencing approximately 20% system energy loss. The losses appear to be split approximately evenly between the distribution system and the 24.9kV trans-— mission system. At the present wholesale rate of 2.5 cents per kwh, the losses in the transmission system have a real cost of $64,000 per year. The cost of these losses will increase many fold during the next few years as a result of increased consumption and wholesale rate increases. Any of the possible actions to reduce voltage drop will also reduce system losses, but not sufficiently to pay for the improvements. The improvements will represent a cost which is made necessary by the require- ment to maintain acceptable system voltages. Options 1, 2 and 3 are not considered for further analysis, as they do not provide a lasting solution to the problem. Option, 4, convert to 69 kV, would provide relief for a few years. However, it would require a major expenditure to upgrade the Daves Creek-Lawing line to 69 kV and that would soon be inadequate. Therefore the final analysis is a comparison of option 5, convert to 115 kV, and option 6, use a combination of 69 kV and 115 kV. PAGE 15 Option 5, convert 115 kV will require the following approximate expenditures: 1983-84 34 miles 115 kv line at $400,000/mi $13,600,000 20 mVA 115kV substation at Seward 200,000 115kV tap at Daves Creek 100,000 Local 12.5 or 24.9 kv underbuild 240,000 Total $14,140,000 Option 6, operate at 115/69 kV will require the following approximate expenditures: 1983-84 Expenditures 16 mi 115kV, Daves Creek-Lawing at $400,000 $6,400,000 20 mVA 115kvV to 69/24.9 kV sub at Lawing 200,000 115 kV tap at Daves Creek 100,000 Local 12.5 or 24.9 kV underbuild 240,000 Total 1983-84 $6,940,000 1988-89 Expenditures (1983-84 dollars) 18 miles 115 kv, (Lawing-Seward) at $400,000 $7,200,000 Relocate 115 kV sub from Lawing to Seward 100,000 Total 1988-89 $7,300,000 PAGE 16 Cost of debt service will vary, depending upon the interest rate and length of loan. The following factors, multiplied by the amount of the loan, will approximate the annual repayment amount for the terms and rates indicated. TERM/ RATE 6% 8% 10% 12% 15% 15 years -10296 -11683 13147 - 14682 17102 20 years -08718 -10185 -11746 -13388 -15976 25 years -07823 -09368 11017 ~12750 -15470 30 years -07265 -08883 -10608 -12414 -15230 Using, for example, a factor of 0.10608 for 10%, 30 years, the repayment schedule for option 5 will be $1,500,000 per year. It would require an average retail rate increase of about $0.038/kWh in 1983 to pay the debt service. In later years, as kWH consumption increases, the cost would be spread over the larger number of kwh and would be less per kWH. Using this same factor, the repayment schedule for option 6 would be $736,000 per year from 1983-87 and $1,511,000 beyond 1988. This would require a retail rate increase of $0.019/kwh in 1983 and an additional $0.005/kWh in 1988. These analysis are all based upon constant 1983-84 dollars. PAGE 17 VI. CONCLUSION AND RECOMMENDATIONS The City of Seward should immediately proceed with de- tailed engineering analysis/design for transmission system improvements, and should immediately investigate methods of financing construction. This engineer's recommendation, based upon only a brief study and subject to verification by a more detailed study, is that option 6 be implemented. This would construct in 1983-84 a 115 kV line from Daves Creek to Lawing, a 115 kV to 69/24.9 kV substation at Lawing, convert the line from Lawing to Seward to 69 kV, and build local 12.5 or 24.9 kV underbuild as required on the line from Lawing to Seward. In 1988-89 the line from Lawing to Seward would be converted to 115 kV and the 115 kv to 69/24.9 kV substation would be relocated to Seward. This plan will require an approximate retail rate increase of $0.019/kwh in 1983 and an additionl $0.005 in 1988. PAGE 18