POWER PLANT ELECTRICAL REFERENCE SERIES VOLUME Power nansformers Authors A W Goldman and C G Pebler Written by Stone & Webster Engineering Corporation 245 Summer Street Boston Massachusetts 02107 Electric Power Research Institute 3412 Hillview Avenue Palo Alto California 94 304 EPRI Project Manager D K Sharma Ordering Information Requests for copies of this series should be directed to Research Reports Center (RRC), P.O Box 50490, Palo Alto, CA 94303, (415) 965-4081 For further information on EPRI's technical programs contact the EPRI Thchnical Information Division at (415) 855-2411, or write directly to EPRI's Thchnical Information Center at P.O Box 10412, Palo Alto, CA 94303 EL-5036, Volume Project 2334 ISBN 0-8033-5001-5 volume ISBN 0-8033-5015-5 series Topics: Power transformers 'Ii"ansformer ratings Taps and connections Station auxiliary systems Installation and maintenance Voltage regulation Copyright© 1987 Electric Power Research Institute, Inc All rights reserved Reprinted in 1998 by Energy Conversion Division, Steam-Turbine, Generator, Balance-of-Plant Target Electric Power Research Institute and EPRI are registered service marks of Electric Power Research Institute, Inc Notice This series was prepared by Stone & Webster Engineering Corporation as an account of work sponsored by the Electric Power Research Institute, Inc (EPRI) Neither EPRI, members of EPRI, Stone &, Webster Engineering Corporation, nor any person acting on behalf of any of them: (a) makes any warranty, express or implied, with respect to the use of any information, apparatus, method, or process disclosed in this series or that such use may not infringe privately owned rights, or (b) assumes any liabilities with respect to the use of, or for damages resulting from the use of, any information, apparatus, method, or process disclosed in this series FOREWORD In the past, several electrical equipment manufacturers published reference books dealing with specific technical areas Many utilities have stated that these reference books have been very useful to them in dealing with plant emergencies and in making decisions on design, system planning, and preventive maintenance Unfortunately, manufacturers today seldom publish or update reference books on electric power apparatus, mainly because of tighter budget constraints Until now, utilities have had no upto-date industrywide practical reference manual covering the various electric power apparatus and electrical phenomena commonly encountered in power plants The Power Plant Electrical Reference Series was planned to fill this need EPRI believes that the series will save utilities time and money It will aid plant engineers in • Prevention of forced outages through proper installation, application, and protection of station auxiliary equipment • Recognition of potential problems and their prevention • Selection of appropriate methods of maintenance to ensure trouble-free equipment operation • Reduction of equipment installation time and expense • Proper specification of equipment being ordered • Better coordination and integration of system components This volume deals with power transformers A power transformer connects the generator to the high-voltage transmission system Another power transformer connects the generator to the plant medium-voltage auxiliary power system 'Iransformer impedance is the major factor in the voltage regulation of the auxiliary power system, as well as in the short-circuit duty of the switchgear Selection of transformers for use in power stations requires knowledge of the power system and various parameters A wealth of information about transformers is available in the transactions of the IEEE and in the ANSI/IEEE standards and applications guides EPRI has also published a great deal of information on transformers, including studies of transformer life characteristics (EL-2622), dielectrics, accessories, and monitoring equipment The purpose of this book is to bring out the concepts that are most useful to power plant personnel, without requiring an understanding of the rigorous engineering analysis necessary for the basic design transformers D K Sharma Electrical Systems Division Electric Power Research Institute ABSTRACT The unit transformer in a generating station connects the electric power output of the generating unit to the high-voltage electric transmission gridi the unit auxiliaries transformer, station service transformer, and secondary-unit substation transformers supply the electric auxiliaries required for operation of the power plant In the lower range of sizes, power transformers may be of standard design types, but many of the transformers used in power plants and all of the larger ones are custom-designed-similar, but seldom identical, to others built previously This volume covers the practical aspects of the selection, specification, installation, operation, testing, and maintenance of these power transformers lransformer designs of particular interest to power plant operators include liquid-immersed, dry-type, and vapor-cooled transformers ranging in size from 500 kVA to 1200 MVA The function and application of each design are described in detail, from load considerations to noise criteria Photographs show the various types of oilpreservation systems, transformer connections, and bushings A variety of gages, monitors, and indicators may be provided for liquid-immersed transformersi these accessories are also discussed ACKNOWLEDGMENTS The authors wish to acknowledge the help they received from many technical publications prepared by people in the industry They also express their appreciation to the following people for their reviews, suggestions, and guidance in general Electric Power Research Institute D K Sharma, Project Manager R Steiner, Associate Director, Electrical Systems Division J C White, Program Manager G Addis, Project Manager Stone & Webster Engineering Corporation G Buffington, Project Manager P Garfinkel A R Fitzpatrick A P Stakutis EPRI Review Committee J R Boyle, Thnnessee Valley Authority L E Brothers, Southern Company Services J Erlingsson, Pacific Gas and Electric Company R G Farmer, Arizona Public Service Company R G Hodgson, Los Angeles Department of Water & Power J A Maxwell, Georgia Power Company W L Nail, Jr., Mississippi Power& Light Company D G Owen, Duke Power Company B K Patel, Southern Company Services R A Schaefer, Public Service Company of Oklahoma J E Stoner, Jr., Duke Power Company D M Van Thssell, Jr., Florida Power& Light Company J E White, Thmpa Electric Company The authors owe special thanks to W J McNutt, General Electric Company, member of the Transformers Committee of IEEE, who reviewed the final manuscript CONTENTS SECTION PAGE SECTION _Figures 2-xi Secondary Unit Substation 'Iransformers 2-14 Grounding 'Iransformers 2-14 Tables .· 2-xiii Executive Summary 2-xv 2.10 Introduction 2-1 2.11 Bushings 2-15 2.12 Accessories 2-18 2.2 Definition of Terms 2-1 2.3 General Liquid Level Gage 2-18 Thmperature Indicators 2-18 Flow Indicator 2-20 Bushing Current 'Iransformers 2-20 Resistance Thmperature Detectors 2-20 Sudden Pressure Relay 2-20 Gas Detector Relay 2-21 Fault Gas Monitor 21 Pressure Relief Device 21 Lifting Eyes and Jack Bosses 2-·22Lightning Arresters 2-22- 2-3 Liquid-immersed 'Iransformers 2-3 Dry-type 'Iransformers 2-3 2.4 Rating Basis and Temperature Rise 2-4 2.5 Insulation Level 2-5 2.6 Cooling Methods-Single-, Dual-, and 'D:iple-rated 'D:ansformers 2·5 2.13 Liquid-immersed 'Iransformers 2-5 Water-cooled 'Iransformers 2·7 Dry-type 'Iransformers 2·7 2.7 Application Considerations 22Maximum Sustained Load 2-2Altitude 2-25 Ambient Thmperature 25 Number of Windings 2-2-5 Voltage Ratings and Overexcitation 25 'Iransient Overvoltage 2·26 Load Current Waveform 2-26 Harmonic Current Derating 2-27 Impedance Voltage and Regulation 2-28 Impedance and Through-Faults 2-29 Phasing Out Three-Phase Circuits 2-29 Loss Evaluation 2-30 Noise Criteria 2-30 Losses 2-7 Evaluation method 2-7 Application of Loss Values 2·8 2.8 Oil Preservation Systems 2-8 Sealed.:nmk System 2-8 Inert Gas System 2-9 Modified Conservator System 2-9 2.9 'D:ansformer Connections 2-10 U'IS 2-11 UA'IS 2·12 SS'IS 2-12 Taps 2-14 No-Load Thp Changers 2-14 Load Thp Changers (LTCs) 2-14 Acronyms & Abbreviations 2-xvii 2.1 PAGE 2.14 Shipping Considerations 2-32 2-x CONTENTS SECTION 2.15 PAGE Specific Applications 2·32 UTh 2·32 UA'IS 2·45 SS'IS 2·46 Load Center Substation 'Transformers 2·4 Auxiliary 'Transformers 2·4 Grounding 'Transformers 2-4 2.16 Transformer Testing 2-48 Shop Thsting 2-48 Field Thsting 2-49 2.17 Foundations 2·51 2.18 Provision for Oil Spills 2·51 2.19 Fire walls and Barriers 2·51 2.20 Water-Spray Fire Protection 2-51 2.21 Installation 2·52 Liquid-immersed 'Transformers 2·52 Dry-type 'Transformers 2.22 Maintenance 2·53 Visual Inspection 2·53 Oil Conditioning 2·54 Gasing 2-54 Dryout 2-54 Cleaning Bushings 2·54 Appendix A: Loss Evaluation 2·55 References 2·59 Bibliography 2·61 Index 2·65 2·54 POWER PLANT ELECTRICAL REFERENCE SERIES 'Iransformers with LTCs require additional maintenance of this electromechanical equipment, which can be done only with the transformer out of service One manufacturer recommends that the first detailed inspection be done after the first year of operation 'Iransformers with LTCs also have insulating fluid systems for the LTC that are separate from those for the core and coils and that can be sampled while the transformer is in service In general annual inspection may suffice unless the application requires very frequent tap changes Owners of LTC transformers would be well advised to plan their maintenance schedules on the basis of frequency of tap-changing operations and to perform maintenance in accordance with the relevant maintenance instructions OIL CONDITIONING Periodically taken oil samples are expected to withstand approximately 30 kV in the standard test cup Breakdown below 26 kV is generally regarded as unsatisfactory Water, sludge, and other forms of contamination can often be removed, even with the transformer in service, by circulating heated oil through a transportable oil-conditioning system while testing repeatedly to monitor the improvement Such a system may include heaters, Fuller's earth beds, and a vacuum dehydrator through the windings at low voltage This procedure must be carried out with care to avoid the formation of hot spots that may degrade the insulation The heating must be combined with vacuum or other methods to remove the moist vapor Each manufacturer can furnish detailed procedures for such operations CLEANING BUSHINGS Outdoor apparatus bushings have skirted, glazedporcelain rain shields to provide a long surfaceleakage path from terminal to flange In areas where the air is contaminated with particulate matter, the porcelain may collect a heavy coating of dust, which will become conductive when wet and can lead to bushing flashover The porcelain should be cleaned as often as necessary with a nontoxic solvent Some users have found that a coating of silicone grease will break up the conductive leakage path and thus prolong the interval between washings GASING Significant evolution of bubbles or concentration of gases dissolved in oil requires close monitoring and may dictate taking the transformer out of service for further investigation (14) The gas may be produced by decomposition of oil or of cellulosic insulating materials due to local heating If the problem cannot be localized by tests in the field (Section 2.16), it may be necessary to remove the transformer to a service shop, where more sophisticated diagnostic procedures and, ultimately, untanking may be feasible DRYOUT If the kraft paper insulation of any transformer has absorbed a significant amount of water (a condition that may be diagnosed by insulation power factor or even Megger testing), it may be necessary to employ a combination of methods, including heating, to dry it out In general dryout can be accomplished without untanking The most common method of heating is circulating alternating current • APPENDIX A LOSS EVALUATION In both indoor and outdoor applications transformer losses incur significant future cost beyond that attributable to heat removal That cost has two components: a demand cost and an energy cost The demand cost is based on the amount of capacity that the losses make ungross available to the power system for meeting its peak customer demand The aggregate level of such power losses will ultimately require that a new generating unit be added to the system one year earlier than would otherwise be necessary Thus, the demand penalty to be invoked for losses is based on their magnitude under peak system load conditions and on the dollars-per-kilowatt cost of new generating capacity The energy cost of losses is based on the delivered cost of extra fuel burned to generate the loss energy All other components of generating cost, such as fixed charges, maintenance, and operating costs other than fuel, are essentially unaffected by the incremental kilowatthour production Fuel use on the system is not directly proportional to electrical load Each generating unit is more efficient near full load than at light load At no load a turbine requires input energy to overcome losses from several sources: friction and windage losses incurred in running the turbine generator and many of its auxiliaries at full speed; throttling losses in partially open inlet steam valves; pump and piping losses in the circulatingwater system incurred in maintaining condenser and heat losses incurred in maintaining masses of metal at high operating temperatures The result is that lightly loaded generating units are inefficient Their average fuel cost in cents per kilowatthour is high Near full load inlet steam throttling losses are reduced because the valves are nearly wide open On some turbines, however, a new form of loss appears near full load: a discharge loss caused by "choking" in the exhaust annulus at high steam fiow Nevertheless, the aggregate of all losses at full load becomes a small fraction of the total input, most of which then produces useful output The result is that heavily loaded generating units are more efficient than lightly loaded units Their average fuel cost in cents per kilowatthour is lower Incrementally, fuel cost is different When a unit moves away from the no-load condition, fuel use increases slowly in essentially direct proportion to load added This rate, also measured in cents per kilowatthour, remains nearly constant up to the point at which choking begins Somewhere near full load average fuel cost, which has been decreasing, and incremental fuel cost, which has started to rise, become equal It is not feasible to operate all generating units near their full-load point at all times Inevitably, some units will be lightly loaded They must be on the line, however, to provide "spinning reserve" to meet rapid increases in customer demand or to replace a unit that trips off the line because of a malfunction At any given time the system load dispatcher arranges to have enough generating capacity online to satisfy the customer demand expected during the next few hours, to supply the system losses associated with that load flow, and to provide appropriate spinning reserve The system load dispatcher must then apportion the load among the operating units in such a way as to achieve minimum production cost The manner in which that load dispatching is done is germane to the subject of loss evaluation Load dispatching is a computer-aided process in which each kilowatt of new load is assigned by automatic load-frequency control equipment to the generating unit that can supply it at lowest incremental cost Similarly, any load reduction, including a reduction in system losses, reduces production cost at the incremental rate The result is that all generating units adjust, within their stable operating limits, to the incremental fuel cost, which is then the system incremental cost for that load condition The system incremental fuel cost for a given combination of operating units always increases with system load 'li'ansformer losses are a partially avoidable increment of load on the system A reduction of those losses reduces system fuel cost at the incremental rate If average fuel costs were used in loss evaluation, it would lead to a larger initial outlay for loss reduction than can be justified by the future fuel savings that are likely to result 2·56 POWER PLANT ELECTRICAL REFERENCE SERIES As previously explained, transformer load losses vary as the square of transformer load current When the energy value of the losses is determined, it is not necessary to establish the time of day when they reach a particular level as long as there is a fairly well defined relationship between transformer loss magnitude and system load, which provides a key to incremental fuel cost 1ransformer no-load losses remain essentially constant during all of the hours the transformer is energized Their energy value is therefore related to the annual average system incremental fuel cost When loss values for a transformer at a nuclear power plant are established, it is not appropriate to use the incremental fuel cost at that plant, because the nuclear units are base loaded whenever possible The loss energy, in effect, is produced elsewhere by generating units having higher incremental fuel cost 1b justify consideration of these complexities, one need only recognize that the present worth of losses over the life of a large UT is generally greater than the initial cost of the transformer The present worth of a future cost depends on (1) the magnitude of that cost at current cost els; (2) the year in which the cost will be incurred; (3) the anticipated rate of inflation; and (4) the owning company's internal rate of return (IROR) (Eq A·l) Where: CI = present worth of the outlay in the year of first commercial operation f = annual inflation rate (decimal) P = quoted or estimated price, valid in the "price year" M = number of years between the price year and the year of first commercial operation N2 = greater than the number of years between commercial operation and payment (It is greater to reflect the convention of beginning-of-year measurement of end-of-year cash flow.) k Price Year Future costs may be estimated at the levels prevailing on the day of the estimate or on historical record The price year is that year in which the estimate was valid IROR IROR, expressed as a percentage, is a function of capitalization structure, cost of money, and statutory tax rate The proper worth to use in loss evaluation should be obtained from a financial officer of the company owning the plant IROR cannot be calculated from fixed charge rate Fuel Cost Attributable to Transformer Loss· Energy It is customary to predict the future loading of a new generating unit by constructing a table of the kind shown below: Percentage of Time at Each Load PRESENT WORTH OF FUTURE COSTS Cl = (1 + jJM X P£(1 + jJ/(1 + k)JM the future, because the components of present worth may not be affected equally by inflation A $100,000 loan at 8% interest will cost $8000 per year, regardless of inflation But 100 t of coal, which might cost $6000 this year, are likely to cost more in each future year = IROR expressed as a decimal rather than as a percentage Inflation Inflation must be considered in evalu- ating any series of costs extending some years into Period in Years 2-5 6-10 11-15 16-30 100% 75% 50% 250Al Load -30 Load Load 40 10 20 25 10 15 15 20 20 -Load 60 50 40 20 0 22 0% Load 20 15 15 15 32 It is necessary to combine all the numbers in this table into a single number that will represent the present worth of future energy cost per kilowatt of no-load loss and to combine them in a slightly different manner for each kilowatt of (fullload) loss For no-load loss the kilowatthours for each year are found by adding together the operating hours for that year Thus, for the thirtieth year the unit will be in operation 68% of the time Each kilowatt of no-load loss will be present 0.68 times 8760, or 5957 h It will therefore consume 5957 kWh of electrical energy in that year If the system annual average incremental fuel cost is $0.027 (price year cost) per kilowatthour, the cost of fuel will be 5957 times 0.027, or $160.83 for each kilowatt of loss For transformer load loss the calculation becomes more complex, because load loss, which includes P.R loss and stray losses, varies as the square of load, becoming equal to the measured value only at rated load, and because each quantity of loss will occur at a different system incremental POWER TRANSFORMERS fuel cost Thus, the hours at 25% load will be multiplied by 0.0625, those at 50% by 0.25, and those at 75% by 0.5625 to find the kilowatthours for that year Each product must then be multiplied by the applicable incremental fuel cost Except for hydroelectric plants and nuclear plants, it is assumed that a generating unit will operate at 50% load when its incremental fuel cost at that load matches the system incremental fuel cost for that system load condition The incremental fuel cost for the unit can be calculated from the net station incremental heat rate at that load and the applicable fuel cost per British thermal unit For example, assume that the incremental heat rates for the unit at 100, 75, 50, and 25% load are 12,000, 10,000, 9180, and 8770 Btu/kWh, respectively, and the fuel cost is $2.50 (price year per million Btu) Then, if the unit (and its UT) are at 50% load, it is because the system incremental fuel cost is $2.50 times 0.00918, or $0.0295/kWh The extra fuel cost incurred in the thirtieth year by kW of (full-load) loss during the 20% of time in which the unit is at 50% load will be: 0.20 X 8760 X 0.25 X 0.0295 = $10.05 Adding costs similarly calculated for other loads during that year brings the total to $72.64/kW of (full-load) load loss The totals for each of the earlier 29 years can be calculated in a similar manner When these annual totals are summed, however, each must be increased to account for escalation and discounted at the IROR rate Combining Future Costs The present worth is expressed in Equation A-1 An example will illustrate the use of this expression in finding the present worth of fuel cost increment attributable to kW of (full-load) transformer load loss in the thirtieth year Assume that the plant will go into operation in 1990 and that fuel costs are based on 1984 prices Then N1 = For the year 2020 N2 = 30 Assume fuel cost escalation rate is 6% and IROR is 12.5% CI = (1 + 0.06) X 72.64 ((1 + 0.06)/(1 + 0.125)] 30 = 1.4185 X 72.64 X 0.1677 = $17.28 When the fuel cost increments for all earlier years have been adjusted similarly, they can be summed to fmd the total present worth of fuel cost attributable to kW of transformer (full-load) load loss Thble A-1 shows a sample calculation for the 30-year period It may be noted that, for the first 2-57 years, the present worth is greater than the "cost:' These higher present worths occur because the cost shown· here is based on 1984 fuel cost The present-worth column shows these values increased by inflation and discounted at the IROR rate The combined effect of these two multipliers, starting from the first year of commercial operation, is to overtake in the sixth year the escalation that occurred between the price year and the operating date The totals at the bottom of the present-worth columns must be added to the demand cost to obtain the total present worth per kilowatt of each type of loss 2-58 POWER PLANT ELECTRICAL REFERENCE SERIES Table A-1 Year of commercial operation Fuel cost, cents per million Btu Fuel price year Fuel cost escalation rate, percentage System average incremental fuel cost cents per kilowatthour Internal rate of return, percentage 1990 250 1984 6.00 2.70 12.50 Transformer Loss Energy Evaluation Incremental net station heat rate, cents per million Btu 12,000 at 100% load 10,000 at 75% load 9,180 at 50% load 8,170 at 25% load Projected Unit-loading Schedule Year Percentage of Time at Each Load 100% 75% 50% Load Load Load 30 25% Load Copper 0% Load Calculated Results per kilowatt of Full-Load Loss Iron Present Cost Value Cost Present Value 60 60 60 50 40 10 10 10 10 20 10 15 15 15 15 15 0 0 0 20 15 15 15 15 15 189.22 201.04 201.04 201.04 201.04 201.04 252.90 253.18 238.55 224.77 211.78 199.55 133.14 177.54 177.54 177.54 177.54 163.58 177.95 223.58 210.66 198.49 187.02 162.36 10 11 12 50 50 50 50 40 40 20 20 20 20 25 25 15 15 15 15 20 20 0 0 0 15 15 15 15 15 15 201.04 201.04 201.04 201.04 201.04 201.04 188.02 177.15 166.92 157.27 148.19 139.62 163.58 163.59 163.58 163.58 145.97 145.97 152.98 144.14 135.81 127.96 107.59 101.38 13 14 15 16 17 18 40 40 40 20 20 20 25 25 25 6 20 20 20 20 20 20 0 22 22 22 15 15 15 32 32 32 201.04 201.04 201.04 160.83 160.83 160.83 131.56 123.96 116.79 88.04 82.95 78.16 145.97 145.97 145.97 72.64 72.64 72.64 95.52 90.00 84.80 39.76 37.47 35.30 19 20 21 22 23 24 20 20 20 20 20 20 6 6 6 20 20 20 20 20 20 22 22 22 22 22 22 32 32 32 32 32 32 160.83 160.83 160.83 160.83 160.83 160.83 73.64 69.39 65.38 61.60 58.04 54.69 72.64 72.64 72.64 72.64 72.64 72.64 33.26 31.34 29.53 27.82 26.22 24.70 25 26 27 28 29 30 20 20 20 20 20 20 6 6 6 20 20 20 20 20 20 22 22 22 22 22 22 32 32 32 32 32 32 160.83 160.83 160.83 160.83 160.83 160.83 51.53 48.55 45.75 43.10 40.61 38.27 72.64 72.64 72.64 72.64 72.64 72.64 23.27 21.93 20.66 19.47 18.34 17.28 60 REFERENCES U.S Congress Th;dc Substances Control Act Washington, D.C.: Government Printing Office, Octeber 12, 1976 15 USC 2601, et seq., PL 94-469 Code of Federal Regulations "Protection of Environment: Polychlorinated Biphenols (PCBs) Manufacturing, Processing, and Distribution in Commerce, and Use Prohibitions:' Washington, D.C.: Government Printing Office, June 7, 1978 40CFR761 Field Determination of PCB in Tl"a.nsformer Oil Vols and Final Report Palo Alto, Calif.: Electric Power Research Institute, October 1984 EL-3766 "The Products of Combustion of Cast Biphenol-A Epoxy 'Iransformer Coils:' Palatine, ill.: SquareD Co., July 1983 File 730, Product Data Bulletin No EIP 19 General Requirements for Liquid-Immersed Distribution, Power and Regulating Tl"a.nsformers New York: American National Standards Institute, 1980 ANSI Std C57.12.00-1980 General Requirements for Dry-7}pe Distribution and Power Tl"ansformers New York: American National Standards Institute, 1979 ANSI Std C57.12.01-1979 Test Code for Dry-7jpe Distribution and Power Tl"ans- Electric Power Research Institute, June 1982 EL-2443 14 Guide for the Detection and Determination of Generated Gases in Oil-Immersed Tl"ansformers and Their Relation to the Serviceability of the Equipment New York: American National Standards Institute, 1978 ANSI Std C57.104-1978 15 Basic Research on Transformer Life Characteristics Palo Alto, Calif.: Electric Power Research Institute, September 1982 EL-2622 16 Guide for Loading Mineral Oil-Immersed Tl"ansformers Up to and Including 100 MVA With 55°C or 65°C Winding Rise New York: American National Standards Institute, 1981 ANSI Std C57.92-1981 17 Guide for Loading Dry-7}pe Distribution and Power Tl"ansformers New York: American National Standards Institute, 1959 ANSI Std C57.96-1959 18 Recommended Practice for Establishing Tl"ansformer Capability When Supplying Nonsinusoidal Load Currents New York: American National Standards Institute, 1985 ANSI Std C57.110/D7-1985 formers New York: American National Standards Institute, 1979 ANSI Std C57.12.91-1979 19 R M Kerchner and G F Corcoran AlternatingCurrent Circuits New York: John Wiley and Sons, 1960 Tl"ansformers, Regulators, and Reactors Washington, D.C.: National Electrical Manufacturers Association, 1980 NEMA Std TR 1-1980 20 D G Fink and H W Beaty, eds Standard Handbook for Electrical Engineers, 11th ed New York: McGrawHill Book Co., 1978 Terminal Markings and Connections for Distribution 21 W J McNutt and M R Patel "The Combined Effects of Thermal Aging and Short-Circuit Stress on 'Iransformer Life:' In IEEE Tl"ansactions on Power Apparatus and Systems, val PAS-95, no 4, July/August 1976, pp 1275-83 and Power Tl"ansformers New York: American National Standards Institute, 1978 ANSI Std C57.12.70-1978 10 Requirements for Load-Tap-Changing Tl"a.nsformers :?-30,000 Volts and Below, 3750/4687 Through 60,000180,0001100,000 kVA Three-Phase New York: American National Standards Institute, 1977 ANSI Std C57.12.30-1977 11 Standard Electrical, Dimensional and Related Requirements for Outdoor Apparatus Bushings New York: Institute of Electrical and Electronics Engineers, 1984 IEEE Std 24-1984 12 General Requirements and Test Procedures for Outdoor Apparatus Bushings New York: American National Standards Institute and Institute of Electrical and Electronics Engineers, 1976 ANSI/IEEE Std 21-1976 13 Basic Tl"ansformer Life Characteristics Vol 2, Evaluation of a Fluoroptic™ Thermometer as a Hot Spot Sensor for Power Transformers Palo Alto, Calif.: 22 T M McCauley "Through-Fault Capability for Unit Auxiliary 'fransformers:' In IEEE Tl"ansactions on Power Apparatus and Systems, vol PAS-96, no 5, September/October 1977, pp 1639-47 23 U.S Department of Labor Occupational Safety and Health Administration "Title 29-Labor:' Occupational Safety and Health Administration Standards Washington, D.C.: Government Printing Office, April 1, 1981 29CFR1910 24 Terminology for Power and Distribution Transformers New York: American National Standards Institute, 1978 ANSI Std C57.12.80-1978 25 Thst Code for Liquid-Immersed Distribution, Power, and Regulating Transformers New York: American National Standards Institute, 1980 ANSI Std C57.12.90-1980 2-60 REFERENCES 26 Acoustic Emission Detection of Pa.nial Discharges in Power Transformers Final Report Palo Alto, Calif.: Electric Power Research Institute, August 1985 EL-4009 27 Improved Transformer Oil Pump Palo Alto, Calif.: Electric Power Research Institute, September 1982 EL-2619 BIBLIOGRAPHY Acker, C R "ll:ansformer Insulation Deterioration and 'fransformer Life Expectancy-A More Comprehensive Concept:' Abstract In IEEE 'Ihmsactions on Power Apparatus and Systems, vol PAS-95, no 3, May/June 1976, p 756 Alexander, G W., et al "Influence of Design and Operating Practices on Excitation of Generator Step-Up 'fransformers:' In IEEE 'llansactions on lbwer Apparatus and Systems, vol PAS-85, no 8, August 1966, pp 901-9 Distribution 11-a.nsformer Tank Pressure Study Appendix Palo Alto, Calif.: Electric Power Research Institute, February 1976 Report 325A Electric Power Systems and Equipment-Voltage Ratings (60Hz) New York: American National Standards Institute, 1982 ANSI Std C84.1-1982 Electrical11-a.nsmission and Distribution Reference Book 4th ed Pittsburgh, Pa.: Westinghouse Electric Corp., 1964, pp 96-144 Amine-enhanced Photodegradation of Polychlorinated Biphenyls Palo Alto, Calif.: Electric Power Research In· stitute, July 1982 CS-2513 El-Hawary, M E Electric lbwer Systems Design and Analysis Reston, Va.: Reston Publishing Co., 1983, sect 3.8, fig 3-24 Basic 11-a.nsformer Life Characteristics, Vol 1, Overload Characteristics and Life-'Iest Evaluation Palo Alto, Calif.: Electric Power Research Institute, June 1982 EL-2443 Evaluation of Alternative Insulating Oils for Use in 11-a.nsformers and Other Electrical Apparatus Palo Alto, Calif.: Electric Power Research Institute, February 1980 EL-809-SY Bean, R L 11-a.nsformers for the Electric lbwer Industry Pittsburgh, Pa.: Westinghouse Electric Corp., 1959 Blume, L F Transformer Engineering New York: John Wiley and Sons, 1951 Chen, K "Evaluation of the Sunhio PCBX Process for Reclamation of ll:ansformer Oils Containing PCBs:' In IEEE Transactions on Power Apparatus and Systems, vol PAS-102, no 12, December 1983, pp 3893-98 Conformance Standard for Liquid-Filled 11-a.nsformers Used in Unit Installations Including Unit Substations, Ex· eluding Pad-Mounted Compartmentals!JJ'pe 'llansformers New York: American National Standards Institute, 1982 ANSI Std C57.12.13-1982 The Cost of Energy From Utility-owned Solar Electric Systems Pasadena, Calif.: California Institute of Thchnology, Jet Propulsion Laboratory, 1976 Degeneff, R C., et al "'fransformer Response to System Switching Voltages:' In IEEE 11-a.nsactions on lbwer Ap· paratus and Systems, vol PAS-101, no 6, June 1982, pp 1457-70 Development of a Portable Field Monitor for PCBs Palo Alto, Calif.: Electric Power Research Institute, January 1983 CS-2828 Disposal of Polychlorinated Biphenyls (PCBs) and PCBContaminated Materials Vol 2, Suggested Procedure for Development of PCB Spill Prevention Control and Countermeasure Plans Palo Alto, Calif.: Electric Power Research Institute, October 1979 FP-1207 Distribution 11-a.nsformer Tank Pressure Study Palo Alto, Calif.: Electric Power Research Institute, February 1976 Report 325 Fire Codes Vol 15, chaps and Quincy, Mass.: National Fire Protection Association, 1983 Frantz, T P., and D M Korinek "Low-Impedance Generator Step-Up ll:ansforrners: Improvements in System Performance:' The Line, Summer 1975 GasNapor- and Fire-Resistant Transformers Palo Alto, Calif.: Electric Power Research Institute, June 1980 EL-1430 General Electric Co 1tansformer Connections Schenectady, N.Y.: General Electric Co., June 1960 GET-2G Goldman, A W "Selection of Generator Step-Up ll:ansformer Ratings:' In IEEE 'llansactions on lbwer Apparatus and Systems, vol PAS-100, no 7, July 1981, pp 3425-31 Guide for Application of 1tansformer Connections in Three-Phase Distribution Systems New York: American National Standards Institute, 1978 ANSI Std C57.105-1978 Guide for Installation of Oil-Immersed EHV 1tansformers 345 kV and Above New York: American National Standards Institute, 1980 ANSI Std C57.12.12-1980 Guide for Installation of Oil-Immersed 1tansformers (10 MVA and LargeTj and 69 kV to 287 kV Ratings) New York: American National Standards Institute, 1980 ANSI Std C57.12.11·1978 Guide for 11-a.nsformer Impulse 'Jests New York: American National Standards Institute, 1968 ANSI Std C57.98-1968 Hall, J., and T Orbeck "Evaluation of New Protective Coating for Porcelain Insulators:' In IEEE Transactions 2-62 BIBLIOGRAPHY on Power Apparatus and Systems, vol PAS-101, no 12, December 1982, pp 4689-96 Heinrichs, F W., Jr "Theoretical and Statistical Dependence of the 'Iransformer Thst Regime on the StressLife Characteristics of Insulation Systems:• In IEEE 'Iransactions on Power Apparatus and Systems, vol PAS-95, no 4, July 1976, pp 1159-64 High-Ampacity Potheads Palo Alto, Calif.: Electric Power Research Institute, October 1975 Report EL-7817 Horne, I J "Writing Specifications for Generator StepUp 'Iransformers:' The Line, Winter 1977 Ignitability of High-Fire Point Liquid Spills Palo Alto, Calif.: Electric Power Research Institute, March 1981 NP-1731 Installation, Application, Operation, and Maintenance of Dry-'J}pe General-Purpose Power and Distribution 'Iransformers New York: American National Standards Institute, 1982 ANSI Std C57.94-1982 Janis, W J., et al "Dechlorination and Reclamation of PeE-Contaminated Insulating Fluids:• In IEEE 'Iransactions on Power Apparatus and Systems, vol PAS-102, no 12, December 1983, pp 3928-32 Kelly, J J "'Iransformer Fault Diagnosis by Dissolved Gas Analysis:' In IEEE 'Iransactions on Industry Applications, vol IA-16, no 6, November/December 1980 McNutt, W J., et al "Short-Time Failure Mode Considerations Associated with Power 'Iransformer Overloading:• In IEEE 'Iransactions on Power Apparatus and Systems, vol PAS-99, no 3, May/June 1980, pp 1186-97 - - "'Iransformer Short-Circuit Strength and Standards-A State-of-the-Art Paper:' In IEEE 'Iransactions on Power Apparatus and Systems, vol PAS-94, no 2, March!April1975, pp 432-43 Miners, K "Particles and Moisture Effect on Dielectric Strength of 'Iransformer Oil Using VDE Electrodes:' In IEEE 'Iransactions on Power Apparatus and Systems, vol PAS-101, no 3, March 1982, pp 751-56 Moore, C L., and G F Mitchell, Jr "Design and Performance Characteristics of Gas/Vapor 'Iransformers:• In IEEE 'Iransactions on Power Apparatus and Systems, vol PAS-101, no 7, July 1982, pp 2169-70 Nelson, P Q., and I S Benko "Determination of 'Iransient Inrush Currents in Power 'Iransformers Due to Out-of-Phase Switching Occurrences:' In IEEE 'Iransactions on Power Apparatus and Systems, vol PAS-90, no 4, July/August 1971, pp 1511-21 Oommen, T V "Adjustments to Gas-in-Oil Analysis Data Due to Gas Distribution Possibilities in Power 'Iransformers:' In IEEE 'Iransactions on Power Apparatus and Systems, vol PAS-101, no 6, June 1982, pp 1716-22 Oommen, T V., H R Moore, and L E Luke "Experience with Gas-in-Oil Analysis Made During Factory Thsts on Large Power 'Iransformers:' In IEEE 'Iransactions on Power Apparatus and Systems, vol PAS-101, no 5, May 1982, pp 1048-52 Oommen, T V., and E M Petrie "Particle Contamination Levels in Oil-Filled Large Power 'Iransformers:' In IEEE 'Iransactions on Power Apparatus and Systems, vol PAS-102, no 5, May 1983, pp 1459-65 PCB Removal From 'Iransformers Palo Alto, Calif.: Electric Power Research Institute, May 1984 EL-3345 Performance Characteristics and Dimensions for Outdoor Apparatus Bushings New York: American National Standards Institute and Institute of Electrical and Electronics Engineers, 1982 ANSI/IEEE Std 24-1982 Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems New York: Institute of Electrical and Electronics Engineers, 1975 IEEE Std 242-1975 Requirements for Sealed Dry-'J}pe Power 'Iransformers, 501 kVA and I.a.rger, Three-Phase With High-Voltage 601 to 34,500 Volts, Low-Voltage 208YI120 to 4160 Volts New York: American National Standards Institute, 1981 ANSI Std C57.12.52-1981 Requirements for 7i"ansformers 230,000 Volts and Below, 833/958 Through 10,417 kVA Single-Phase and 7501862 Through 60,000180,0001100,000 kVA Three-Phase New York: American National Standards Institute, 1978 ANSI Std C57.12.10-1977 Requirements for 'Iransformers 230,000 Volts and Below, 8331958 Through 8333/10,417 kVA Single-Phase and 7501862 Through 60,000180,000/100,000 kVA ThreePhase New York: American National Standards Institute, 1978 ANSI Std C57.12.10a-1978 Requirements for Ventilated Dry-7ype Power 'Iransformers 501 kVA and Larger, Three-Phase, with High-Voltage 601 to 34,500 Volts, Low-Voltage 208YI120 to 4160 Volts New York: American National Standards Institute, 1981 ANSI Std C57.12.51-1981 "Oil Spills From Substation Electrical Equipment:' Thsk Force Report In IEEE 'Iransactions on Power Apparatus and Systems, vol PAS-99, no 3, May/June 1980, pp 925-27 Rickley, A L., et al "Field Measurements of 'Iransformer Excitation Current as a Diagnostic 'Ibol:' In IEEE 7ransactions on Power Apparatus and Systems, vol PAS-100, no 4, April 1981, pp 1985-88 Seidman, A H., eta! Handbook of Electrical Calcula.tions New York: McGraw-Hill Book Co., 1984 Standard Specification for Mineral Insulating Oil Used in Electrical Apparatus Philadelphia, Pa.: American Society of Testing Materials, 1982 ASTM Std D3487-1982 Oil 'Jests in Thp Changers Palo Alto, Calif.: Electric Power Research Institute, December 1979 EL-1302 Standard 'lest for Dielectric Breakdown Voltage of Insula.ting Liquids Using Disk Electrodes Philadelphia, Pa.: Norton, E T "Specifying Tertiary Windings:' Allis Chalmers Electrical Review, fourth quarter, 1962 BIBLIOGRAPHY American Society of Thsting Materials, 1984 ASTM Std 0877-1984 State-ofthe-Art Review: PCDDs and PCDFs in Utility FCB Fluid Palo Alto, Calif.: Electric Power Research Institute, November 1983 CS-3308 Su, A "The Dechlorination of Polychlorinated Biphenyfs by Sodium Hydride and Alkylamine, W-F:' In IEEE Tl"ansactions on Power Apparatus and Systems, vol PAS-103, no 1, January 1984, pp 140-42 Surge -Characteristics and Protection of Distribution Tl"ans· formers Palo Alto, Calif.: Electric Power Research Institute, January 1984 EL-3385 'Iechnical Assistance Guide Palo Alto, Calif.: Electtic Power Research Institute, August 1977 'lest for Corrosive Sulfur in Electrical Insulating Oils Philadelphia, Pa.: American Society of Thsting Materi· als, 1967 ASTM Std 01275-1967 'lest for Dielectric Breakdown Voltage of Insulating Oils of Petroleum Origin Uncler Impulse Conditions Philadelphia, Pa.: American Society of Thsting Materials, 1985 ASTM Std 03300-1985 'lest for Dielectric Breakdown Voltage of Insulating Oils of Petroleum Origin Using VDE Electrodes Philadelphia, Pa.: American Society of Thsting Materials, 1984 ASTM Std 01816-1984 'lest for Gassing of Insulating Oils Uncler Electrical Stress and Ionization Philadelphia, Pa.: American Society of Thsting Materials, 1985 ASTM Std 02300-1985 'lest for Power Factor and Dielectric Constant of Electrical Insulating Liquids Philadelphia, Pa.: American Society of Thsting Materials, 1982 ASTM Std 0924-1982 'lest for Water in Insulating Liquids Philadelphia, Pa.: American Society of Thsting Materials, 1983 ASTM Std 01533·1983 Tl"a.nsformer Hot Spot Detector Palo Alto, Calif.: Electric Power Research Institute, October 1977 EL-573 Tl"a.nsformer Noise Abatement Using 'II.med Sound Enclosures Palo Alto, Calif.: Electric Power Research Institute, October 1977 EL-529 The Use of'IWo-Phase Heat Tl"a.nsfer for Improved Tl"ans· former Cooling Palo Alto, Calif;: Electric Power Research Institute, November 1977 EL-588 Ver, Istvan L., et al "Field Study of Sound Radiation by Power 'Iransformers:' In IEEE Tl"a.nsactions on Power Apparatus and Systems, vol PAS-100, no 7, July 1981, pp 3513-24 2-63 INDEX AA!FA, 2·7 Abnormal conditions, 2-1, 2-53 Alarm switches, 2-18, 2-20 Altitudes, 2-4, 2·22, 2·25 Ambient temperature, 2·3, 2-4, 2·5, 2-8, 2·22, 2-25, 2-53 Arrester ratings, 2-22 Arrester voltage ratings, 2-5 Arrhenius curve, 2-22 Askarel, 2-3 Autotransformer, 2-14 Double-wall tanks, 2-31 Dressing out the transformer, 2-52 Dry nitrogen, 2-9, 2-15, 2-32, 2-52 Dry-type transformers, 2-1, 2-3, 2-4, 2-5, 2-7, 2·8, 2·18, 2-23, 2-25, 2·47, 2-48, 2-49, 2-53 Barrier wall, 2·31 Basic impulse insulation level (BIL), 2-1, 2-5, 2-12, 2-16, 2-46, 2-47, 2-48, 2-49 Bushing current transformers, 2-20 Bushing deterioration, 2·50 Bushing flashover, 2-51, 2-54 Bushing maintenance, 2-17 Bushing potential tap, 2-15 Bushings, 2-8, 2·9, 2·15, 2-16, 2-20, 2·29, 2·31, 2-32, 2-48, 2-49, 2-51, 2-52, 2-53, 2·54 Factory test report, 2-25, 2-27 Fans, 2-3, 2-6, 2-7, 2-24, 2-31, 2-47, 2-53 Fault pressure relay, 2-20 Field testing, 2-49 Fire hazard considerations, 2-3 Fireproof vaults, 2·3 Fire protection, 2·31, 2-33, 2·51 Forced-air (FOA), 2-6, 2-7, 2-31, 2·32, 2-46 Forced-air cooling, 2-1 Forced-cooled transformers, 2·1, 2-7, 2-53 Forced-water (FOW), 2·1, 2·6, 2-7, 2-32 Forced-water cooling, 2·1 Foundations, 2-51 Four windings, 2-25 Fuller's earth beds, 2-54 Full-load losses, 2-5, 2-27 Cast-coil, 2-4 Combustible gas monitor, 2-21 Condenser-type bushings, 2-15 Connections for transformers, 2-46 Conservator, 2-8, 2-9, 2-10, 2-18 Conservator system, 2-8, 2-9, 2-10 Cooling auxiliaries, 2-1, 2-6, 2-7, 2·32, 2-46 Cooling fans, 2·3 Creepage path, 2-15 Current transformers, 2·18, 2-20, 2·21 Delta connection, 2-12 Demand factor, 2-1 Design center, 2-36, 2-40, 2-41, 2-43 Design tests, 2-48 Dielectric constant, 2-3 Dielectric strength, 2·2, 2-3, 2-8, 2·9, 2-25 Dielectric stress, 2-9 Dielectric tests, 2-49 Diversity factor, 2-1 Doble test, 2-50 Eddy-current loss, 2-1, 2-7, 2-8, 2·25 Efficiencies, 2-4, 2-7 Energy losses, 2-1, 2-2 Excitation current, 2-25, 2-50 Gas analysis, 2·21, 2-50 Gas detector, 2-21, 2-49 Gas-filled designs, 2-3 Gas formation, 2-1 Gas monitors, 2·1, 2·21, 2-53 Generator breaker, 2-6, 2·25, 2·26, 2-46 Graded insulation, 2-2, 2-12, 2·13, 2-49 Grounded wye, 2-11, 2-12 Grounding cap, 2-15 Grounding transformers, 2-10, 2-13, 2·14, 2-47, 2-48 Half-size three-phase units, 2-33 Harmonic current, 2-27 Harmonic factor, 2-2, 2-4, 2-27 Harsh environments, 2-4 Heat detectors, 2·51 Heat exchangers, 2-3, 2-7 Heat transfer, 2-3 Helmholz resonators, 2-31 High-current bushings, 2-16 High-impedance transformer, 2-26 Hydroelectric power plant, 2-7, 2·25, 2-26, 2·57 Hysteresis loss, 2-2, 2-7, 2-8, 2-25 Impact recorders, 2-32, 2-52 Impedance, 2·2, 2-5, 2·12, 2·14, 2-15, 2-25, 2-28, 2·29, 2-30, 2·31, 2-33, 2-35, 2·36, 2-37, 2-38, 2-41, 2-42, 2-43, 2-45, 2-46, 2-47, 2-48, 2-50 Impedance relationships, 2-46 Impedance tolerance, 2-25 Impedance voltage, 2·2, 2-5, 2-14, 2-25, 2-28, 2·38, 2-41, 2-47 Impulse tests, 2-1, 2-48, 2-49 Impulse voltage, 2-3, 2-5, 2-31, 2-35, 2-46 Incipient failures, 2-50 Inert gas system, 2-8, 2·9, 2·53 Insulating fluids, 2-1, 2-15, 2·18, 2-50, 2·54 Insulation temperature, 2-22 Internal arc, 2·20 Jack bosses, 2-22, 2-52 Kraft paper insulation, 2-15, 2-54 Leakage path, 2·54 Leakage reactance, 2-28, 2-43 Life-cycle cost, 2·7 Life expectancies, 2-4, 2·8, 2·23, 2-26, 2-48, 2·53 Lifting eyes, 2-22, 2-52 Lightning, 2-1, 2-2, 2-3, 2·5, 2-10, 2-22, 2-49, 2-51, 2-53 Lightning and switching surge impulse voltages, 2-3 Lightning arresters, 2·2, 2-5, 2-10, 2·22, 2-49, 2-51, 2·53 Lightning strikes, 2-5 Liquid-immersed transformers, 2·1, 2-2, 2-3, 2-4, 2·5, 2·7, 2·15, 2-18, 2-25, 2-32, 2-46, 2-47, 2-48, 2-49, 2·50, 2·52, 2-53 Liquid level gage, 2-10, 2-18 Load center substation, 2-47 Load growth, 2-23, 2-24 2-66 INDEX Load limits, 2-4 Load losses, 2-4, 2-7, 2-8, 2-27, 2-28, 2-30, 2-45, 2-46, 2-48, 2-56 Load rejection, 2-26 Local hot spots, 2-1 Loss evaluation, 2-7, 2-22, 2-30, 2-55, 2-56 Loss of life, 2-4 Loss reduction, 2-7, 2-8, 2-55 Low impedance, 2-6, 2-12, 2-25, 2-29, 2-43, 2-47 Low-impedance transformer, 2-6 Magnetostriction, 2-8, 2-31 Main transformer, 2-10 Manufacturing tolerances, 2-45 Masonry vaults, 2-7, 2-31 Megavars, 2-35, 2-36 Megger tests, 2-50, 2-54 Mineral oil immersed, 2-1, 2-5, 2-32, 2-47, 2-51 Multiratio ratings, 2-20 Nameplate, 2-4, 2-11, 2-24, 2-25, 2-26, 2-37, 2-38, 2-43, 2-46, 2-50, 2-52 Nameplate kilovoltamperes, 2-4 Nameplate loads, 2-23 Nitrogen, 2-9, 2-32, 2-52, 2-53 Noise control, 2-7, 2-30 Noise criteria, 2-22, 2-30 Noise measurements, 2-31 Noise ordinances, 2-30 Noise sources, 2-30 No-load losses, 2-7, 2-8, 2-27, 2-30, 2-31, 2-46, 2-48, 2-53, 2-56 No-load tap changers, 2-2, 2-14 Nonflammable fluids, 2-3 Normal station service transformer, 2-11 Oil level gages, 2-15, 2-16 Oilpreservation systems, 2-1, 2-8, 2-18, 2-50 Oil pumps, 2-6, 2-7, 2-50 Oil reservoir, 2-18 Oil samples, 2-1, 2-50, 2-54 Oil spills, 2-3, 2-31, 2-33, 2-51 Operating conditions, 2-4, 2-5, 2-25, 2-33, 2-43 Output megawatts, 2-35, 2-35, 2-36 Overexcitation, 2-25, 2-26, 2-38 Overload effects, 2-23 Overpressure, 2-9 Oversize transformer, 2-40 Performance calculations, 2-43, 2-44 Performance graphic, 2-35 Phase angle, 2-30 Phase angle difference, 2-30 Phasing, 2-10, 2-11, 2-13, 2-22, 2-29, 2-46 Phasing out three-phase circuits, 2-29 Phasing relationshp, 2-11 Phasor diagrams, 2-11, 2-43 Polarity or connections, 2-29 Polychlorinated biphenyl (PCB), 2-3 Polyphase, 2-3 Porcelain rain shield, 2-15, 2-16, 2-54 Power factor tap, 2-15 Power factor test, 2-50, 2-53 Power-frequency voltages, 2-5 Pressure relief devices, 2-10, 2-21 Primary voltage rating, 2-35, 2-36, 2-38, 2-40, 2-43, 2-44 Radiators, 2-6, 2-32, 2-51, 2-52 Radio influence voltage tests, 2-2, 2-48 Rating basis, 2-2, 2-4, 2-45 Rating selections, 2-36 Ratio error, 2-45 Reactive power, 2-27, 2-30, 2-33, 2-36, 2-37, 2-38, 2-39, 2-40, 2-41, 2-42, 2-43, 2-44, 2-45, 2-47 Real and reactive power losses, 2-33, 2-41, 2-45 Real power output, 2-33, 2-36, 2-39 Rectifiers, 2-27 Regulation, 2-28 Reliability, 2-1, 2-15, 2-43, 2-46, 2-47 Remote indication, 2-20 Reserve station service transformer, 2-11 Resin-encapsulated design, 2-4 Resin-encapsulated transformers, 2-1, 2-47 Routine tests, 2-48 Sealed-tank designs, 2-3 Secondary leads impedance, 2-15, 2-29 Secondary unit substation transformers, 2-1, 2-7, 2-14 Secondary voltage, 2-4, 2-12, 2-15, 2-25, 2-26, 2-28, 2-31, 2-35, 2-36, 2-38, 2-43, 2-44, 2-46, 2-47 Selection of size, 2-33 Selection of transformer ratings, 2-36 Self-cooled transformers, 2-1 Shipping considerations, 2-32 Shipping limitations, 2-7, 2-16, 2-32, 2-34 Shop testing, 2-48 Short circuit, 2-1, 2-29, 2-50 Short-circuit current, 2-23, 2-29, 2-48 Short-circuit limitations, 2-47 Short-circuit requirements, 2-29 Short-time overloads, 2-23, 2-24 Single-phase designs, 2-1 Single-phase units, 2-11, 2-33 Sinusoidal capacity, 2-28 Sinusoidal waveform, 2-27 Specifications, 2-4, 2-16, 2-25, 2-26, 2-27 Startup transformer, 2-11 Station service transformer (SST), 2-1, 2-2, 2-6, 2-8, 2-11, 2-12, 2-15, 2-16, 2-25, 2-29, 2-30, 2-46, 2-47 Stray currents, 2-32 Stray loss, 2-7, 2-27, 2-28, 2-43, 2-56 Substation transformers, 2-8, 2-30, 2-33, 2-46 Sudden pressure, 2-20 Surge arresters, 2-2, 2-3, 2-47 Surge voltages, 2-2, 2-22 Switching surge tests, 2-48 System voltage, 2-23, 2-33, 2-36, 2-39, 2-42, 2-45 lank rupture, 2-3 lap changing, 2-14, 2-43, 2-54 lap position, 2-15 laps, 2-4, 2-14, 2-15, 2-20, 2-28, 2-39, 2-40, 2-43, 2-46, 2-54 laut-string perimeter, 2-51 T connection, 2-10, 2-14 Thmperature indicators, 2-18, 2-2{) Thmperature rise, 2-3, 2-4, 2-5, 2-8, 2-18, 2-25, 2-26, 2-27, 2-45, 2-48, 2-49 Thrtiary, 2-12, 2-25 Thsts, 2-1, 2-4, 2-25, 2-29, 2-30, 2-48, 2-49, 2-53 Thermal aging, 2-29 Thermal expansion, 2-15, 2-22 Third-harmonic currents, 2-12 Three-phase designs, 2-1 Three-phase units, 2-11, 2-33 Three-winding transformers, 2-25, 2-46 Through-faults, 2-4, 2-22, 2-23, 2-29, 2-45, 2-48, 2-50 1bp oil temperature, 2-18, 2-20 1btally enclosed, 2-3, 2-4 1btally enclosed nonventilated designs, 2-3 INDEX 'Iransformer oil, 2-1, 2-16, 2-53 'Iransformer parameters, 2-33, 2-35, 2-36, 2-41, 2-42 'Iransformer regulation, 2-28 'Iransformer selection, 2-24, 2-35, 2-36 'Iransient overvoltages, 2-3, 2-5, 2-22, 2-26, 2-45, 2-48 'Iriple-rated transformer, 2-5, 2-6, 2-28, 2-32 1\Jrns-ratio testing, 2-50 'fum-to-turn faults, 2-50 1\vo-winding designs, 2-25 Unit auxiliaries transformer (UAT), 2-1, 2-3, 2-6, 2-11, 2-12, 2-16, 2-25, 2-26, 2-29, 2,30, 2-32, 2-33, 2-43, 2-44, 2-45, 2-46 Unit transformer (UT), 2-1, 2-3, 2-6, 2-10, 2-11, 2-12, 2-14, 2-16, 2-25, 2-26, 2-30, 2-31, 2-32, 2-33, 2-34, 2-35, 2-36, 2-37, 2-41, 2-43, 2-44, 2-45, 2-46, 2-56 Untanking, 2-51, 2-54 Vacuum dehydrator, 2-54 Vapor-cooled transformer, 2-3 Variable-speed drives, 2-26 Vaults, 2-31 Ventilated designs, 2-3 Ventilated dry-type transformers, 2-3, 2-4, 2-47, 2-53 Vibration, 2-4, 2-20, 2-22, 2-30 Voltage breakdown test, 2-50 Voltage gradients, 2-8, 2-15 Voltage profiles, 2-38, 2-47 Voltage regulation, 2-22, 2-27, 2-28, 2-42, 2-47 Voltage regulator, 2-14, 2-26, 2-31, 2-45 Volts-per-hertz protection, 2-26 Water leakage into the oil, 2-7 Water-spray fire protection, 2-51 Waveform distortion, 2-4, 2-26 Winding configurations, 2-25 Winding temperature, 2-18, 2-25 Withstand capability, 2-5, 2-26 Wye connection, 2-14 Wye-wye transformer, 2-12, 2-25 Wye-zigzag design, 2-13 Zero-sequence, 2-12, 2-25, 2-48 Zig-zag connected secondary, 2-13 Z-67