### September 16, 1996

Ms. Ingrid M. Watson Program Manager Office of Codes and Standards U. S. Department of Energy 1000 Independence Avenue, S.W. Washington, DC 20585
Dear Ms. Watson: NEMA is pleased to provide you with NEMA Standards Publication TP-1, "The Guide for Determining Energy Efficiency for Distribution Transformers." This standard was developed by the Transformer section and is available for use by the electrical industry to promote the use of high efficiency transformers and to assist users in the selection of such transformers. As with other NEMA standards, this publication is periodically reviewed by the Transformer section ofNEMA for revisions necessary to keep it up to date with advancing technology. In the Department of Energy's Interpretative Rule, it is indicated that additional consideration will be given to market-driven and voluntary programs. The transformer industry respectfully requests that DOE consider this standard as evidence of the industry's pro-active efforts toward energy efficiency in lieu of a mandatory standards program. If you have any questions regarding this document, please feel free to contact me (703) 841-3245.

National Electrical Manufacturers Association 1300 North 17th Street, Suite 1847 Rosslyn, VA 22209 (703) 841-3200 FAX (703) 841-3300

### NE A STANDARDS PUBLICATION TP 1-1996

Guide for Determining Energy Efficiency for Distribution Transformers

Published by National Electrical Manufacturers Association 1300 North 17th Street, Suite 1847 Rosslyn, Virginia 22209

©1996 by National Electrical Manufacturers AssociationTP 1-1996 Page i TABLE O F CONTENTS

Foreword .............................................................................................................................. i Section 1 General ...................................................... ..........................................................................1 Section 2 Efficiency Evaluation for Electric Utilities .............................................................................5 Section 3 Evaluation Parameters for Commercial and Industrial Transformers .................................7 Section 4 Table of Energy Efficiency ...................................................................................................9 Appendix A Temperature Correction Factor for Dry Type Transformers .............................................. 11 Appendix B Bibliography .......................................................................................................................13TP 1-1996

Page ii 

### Foreword This standard has been developed by the Transformer section and has been approved for publication by the National Electrical Manufacturers Association. It is available for use by the electrical industry to promote the use of high efficiency transformers and to assist users in the selection of such transformers. This standard consists of two parts, sections 2 and 3, which offer a simplified methodology for the user to apply to determine the equivalent first cost of core and load losses. This information will permit the manufacturer to tailor the transformer design to the unique situation of each user. Section 4 defines the minimum efficiency, based on kVA and voltage considerations, that is recommended if the user elects not to follow the suggested methodology. It must be clearly understood that certain design criteria or conditions of use may preclude the application of this standard. These exceptions are detailed in the body of this document. User needs and safety have been considered throughout the development of this document. This publication is periodically reviewed by the Transformer section of NEMA for any revisions necessary to keep it up to date with advancing technology. Proposed or recommended revisions should be submitted to: Vice President, Engineering Department National Electrical Manufacturers Association 1300 North 17th Street, Suite 1847 Rosslyn, Virginia 22209 This Standards Publication was developed by the Transformer Products Section of the National Electrical Manufacturers Association. At the time it was approved, the Transformer Products Section had the following members.

-ABB Power T & D Company-Jefferson City, MO Acme Electric Corporation-Lumberton, NC -Cooper Power Systems-Waukesha, WI Eaton Corp., Cutler-Hammer-Pittsburgh, PA 'General Electric-Hickory, NC Hammond Mfg. Co.-Guelph, Ontario Kentucky Assn. Elec. Cooperatives, Inc.-Louisville, KY Magnetran Inc.-Voorhees, NJ Niagara Transformer Corporation-Buffalo, NY North American Transformer-Milipitas, CA Olsun Electrics Corporation-Richmond, IL Pauwels Transformers-Washington, MO PDI-Sandston, VA R.E. Uptegraff Mfg. Company-Scottsdale, PA Siemans Energy & Automation-Jackson, MS SMIT Transformers, Inc.-Ladson, SC Southern Transformer Company-East Point, GA Square D Company-Lexington, KY Vantran Electric Corporation-Waco, TX Virginia Transformer Corporation-Roanoke, VA Waukesha Electric Company-Goldsboro, NCTP 1-1996 Page 1

1.1 SCOPE 

### Section 1 GENERAL

This standard in intended for use as a basis for determining the energy efficiency performance of the equipment covered and to assist in the proper selection of such equipment. This standard covers single-phase and three-phase dry-type and liquid-filled distribution transformers as defined in the following table:

Voltage Class Liquid Rating Dry Rating Single Phase Three Phase Single Phase Three Phase 34.5 kV and Below 600 Volts and Below 10-833 kVA 15-2500 kVA 15-833 kVA 15-2500 kVA Note: Includes all products at 1.2kV and below Products excluded from this standard include:

a. b. C. d. e. f. 9- h. i. J• k. 1. M. n. 0. p• Liquid-filled transformers below 10 kVA Dry-type transformers below 15 kVA Drives transformers, both AC and DC All rectifier transformers and transformers designed for high harmonics Autotransformers Non-distribution transformers, such as UPS transformers Special impedance, regulation and harmonic transformers Regulating transformers Sealed and non-ventilated, transformers Retrofit transformers Machine tool transformers Welding transformers Transformers with tap ranges greater than 15% Transformers with frequency other than 60 Hz Grounding transformers Testing transformers 1.2 REFERENCE STANDARDS Transformers shall meet the requirements for liquid-filled and dry-type transformers as contained in the latest revision of the following standards: American National Standards Institute, Inc.

11 West 42nd Street New York, NY 10036 Primary Voltage Secondary Voltage

C57.12.00-1993 IEEE Standard General Requirements for Liquid-Immersed Distribution, Power and Regulating TransformersTP 1-1996

Page 2 C57.12.01-1989 IEEE Standard General Requirements for Dry-Type Distribution and Power Transformers including those with Solid Cast and/or Resin-Encapsulated Windings C57.12.90-1993 IEEE Standard Test Code for Liquid-Immersed Distribution,Power and Regulating Transformers and IEEE Guide for ShortCircuit Testing of Distribution and Power Transformers C57.12.91-1979 IEEE Standard for Test Code for Dry-Type Distribution and Power Transformers National Electrical Manufacturers Association

1300 North 17th Street Arlington, VA 22209 TR 1-1993 Transformers, Regulators and Reactors
ST 20-1992 Dry-Type Transformers for General Applications 1.3 DEFINITIONS 1.3.1 EC = Avoided cost of energy ($/kWhr-yr): The levelized avoided (incremental) cost for the next kWh produced by the utility's generating units. 1.3.2 Efficiency tolerance : The nameplate efficiency is the value calculated based on the specified losses of the transformer. A transformer is considered to be within an acceptable tolerance of its nameplate efficiency if its no load and total losses meet the single unit tolerances defined in ANSI standards C57.12.00 or C57.12.01. 1.3.3 FCR(%) = Fixed charge rate : The cost of carrying a capital investment. 1.3.4 HPY (hours): Hours per year (HPY) used in the A- and B-factor equations is generally taken as 8760. However, there may be exceptions, such as transformers connected to irrigation loads. In this case, the transformer may be de-energized a portion of the year and hence, a value less than 8760 would be used for HPY. On the other hand, this transformer may remain energized all year but loaded only part of the year. In this case, a reduced equivalent loss factor could be used to account for the unloaded portion of the year while retaining the use of 8760 hours per year in both the A- and B-factor formulas. 1.3.5 LsF (%) - Loss factor : A measure of the annual average load losses to the peak value of load losses on the distribution transformer. 1.3.6 LL: Load Loss watts at rated temperature rise plus 20°C, i.e., 85° C for 65° C rise and 170° C for 150°C rise.
1.3.7 LM - Loss multiplier (%): A measure of system losses from generation through the transmission and distribution system. 1.3.8 Nameplate efficiency : Rounded efficiency to 1/10 of 1 percent. This calculated number which is derived from the parameters of output kVA divided by out put kVA plus losses multiplied by 100% at a given percent load and at specified reference temperature.TP 1-1996 Page 3 Mathematically, the relationship is as follows: %E= 100x(PxkVAx1000) PxkVAxl000+NL+LLxP2 xT

Where: P = Per unit load

0.35 for low voltage (600 volt class) dry type transformers = 0.50 for medium voltage liquid and dry transformers kVA = nameplate kVA rating NL = No load (core) loss at 20`C in watts LL = Load loss at its full load reference temperature, consistent with

C57.12. 00 (liquid ) and C57.12.01 ( dry) in watts. T = Load loss temperature correction factor to correct specified

temperatures, i.e., 75°C for dry- and 85°C for liquid-transformers. For liquid-filled transformers, the factor T is 1.0, since efficiency is stated at 85°C. Dry type transformers are significantly affected because 75°C is well below the full load rise. For dry-type transformers, the factor T assumes 10% winding eddy loss, as described in the appendix; however, the actual winding eddy loss may be different than 10%. 1.3.9 P : Per unit load. 1.3.10 PL- Equivalent annual peak load (on the transformer): The average annual peak load seen by the transformer that is equivalent to an initial peak load with an estimated load growth rate and a maximum allowable load before change-out is required. 1.3.11 RF (%)-Peak loss responsibility factor : A measure of the diversity of the load on the transformer. 1.3.12 SC = Avoided cost of system capacity ($/kW-yr): The average avoided (incremental) cost of generation, transmission and primary distribution capacity required to supply the next kW of load to the distribution transformer coincident with the peak load.TP 1-1996

Page 4TP 1-1996 Page 5



### Section 2 EFFICIENCY EVALUATION FOR ELECTRIC UTILITIES

Electric utilities purchase distribution transformers based on a life-cycle cost methodology which accounts for the economic value of electrical losses over the useful life of the transformer. The following is a brief summary of the equivalent first cost (EFC), total owning cost (TOC) method which is most commonly utilized: TOCEFC = Transformer first cost + Cost of core IossEFC + Cost of load IossEFC Transformer first cost = Cost of acquisition Cost of core IossEFC = A($/Watt) x core loss watts Cost of load IossEFC = B($/Watt) x load loss watts Where: A = Equivalent first cost of no load losses ($/Watt) B = Equivalent first cost of load losses ($/Watt) The A and B factors are functions of the energy costs and the capacity costs associated with the transformer no-load losses and load losses (including financial costs). Avoided costs are generally used in the calculation of total owning cost (TOC) evaluations for distribution transformers. As previously described, components of TOC are the costs to the utility to supply distribution transformer core (no load) and load losses, commonly referred to as the A- and B-factors. These distribution transformer losses represent additional (incremental) load that the utility must serve over the life of the transformer. If the utility's avoided costs reflect its long-range incremental costs taken over the transformer's economic life, they can be used to determine the system capacity and energy cost of the transformer core and load losses. Most utilities regularly determine their avoided costs of capacity and energy. Assuming that those values reflect the continuing economic impact over the transformer's life, they should be used directly in the loss evaluation process. Avoided costs of energy and generating capacity that are used in evaluating distribution transformers should be determined on a long-range incremental cost basis, using generation production costing and expansion planning. The long-range incremental cost factors include the utility load characteristics, projected peak loads (demand), existing and future generation capability and availability, generation maintenance, generation reliability, costs associated with construction of new generation plants, current and projected fuel prices, short-range purchase/sale contracts and long-range purchase/sale contracts. The generation expansion includes planning reserve margins sufficient to maintain system reliability at a high level based on objective criteria. The application of the TOC methodology using A- and B-factors, as described above, is common place in the electric utility industry.TP 1-1996

Page 6TP 1-1996 Page 7



### Section 3 EVALUATION PARAMETERS FOR COMME R CIAL AND INDUSTRIAL TRANSFORMERS

3.1 INTRO D UCTION While many aspects of the TOC for industrial or commercial placed transformers parallels that used by the utility, there are, nonetheless , differences that require the use of a different procedure . This procedure would at least provide a differentiation among designs that reflect the users constraints. The following is a review of the equivalent first cost TOC method:
TOCEFC = Price + cost of core loss + cost of load loss Cost of core IOSSEFC = A($/watt) x core loss watts Cost of load IossEFC = B ($/watts) x load loss watts Where: A = Equivalent First Cost of No Load Losses

= PW(IS) (EL) (HPY) / 1000 Where: PW(IS) = Present worth of an inflation series

a = per unit inflation index i = per unit interest rate n = number of years Where: EL = purchasers cost of electricity ($/kWh)

B = Equivalent first cost of load losses = AxP2xT An alternative approach to specific no load and load losses of a transformer is to measure energy efficiency at the specific load which is most typical of how it will be used

. The general expression for energy efficiency is:

%Efficiency = 100 (output load)/(output load + losses)TP 1-1996

Page 8 This expression can be tailored to the commercial/industrial segment as:

% E= 100 x (P x kVA x l000) PxkVAxl000+NL+LLxP2 xT
Where: P = Per unit load

= 0.35 for low voltage (600 volt class) dry type transformers = 0.50 for medium voltage liquid and dry transformersTP 1-1996 Page 9



## Section 4 TABLES OF ENERGY EFFICIENCY

The following tables of energy efficiencies would define the minimum efficiency to be categorized as NEMA class 1 efficiency, per this standard. These efficiencies apply to both the utility and the commercial/industrial segment, that do not use evaluation parameters as defined in either Section 2, for utility transformers, or Section 3, for commercial/industrial transformers. Table 4-1 NEMA CLASS 1 EFFICIENCY LEVELS FOR LIQUID

-FILLED DISTRIBUTI ON TRANSFORMERS Reference Condition Temperature % of Nameplate Load Load Loss 85°C 50% No Load Loss 20°C 50%
kVA Single Phase Efficiency kVA Three Phase Efficiency 10 98.3 15 98.0 15 98.5 30 98.3 25 98.7 45 98.5 37.5 98.8 75 98.7 50 98.9 112.5 98.8 75 99.0 150 98.9 100 99.0 225 99.0 167 99.1 300 99.0 250 99.2 500 99.1 333 99.2 750 99.2 500 99.3 1000 99.2 667 99.4 1500 99.3 833 99.4 2000 99.4 2500 99.4TP 1-1996

Page 10

Table 4-2 NEMA CLASS I EFFICIENCY LEVELS FOR D RY-TYPE DISTRIBUTION TRANSFORMERS Reference Condition Temperature % of Nameplate Load Low Voltage 75°C 35% Medium Voltage 75°C 50%

Single Phase Efficiency Three Phase Efficiency kVA Low Voltage Medium Voltage kVA Low Voltage Medium Voltage 15 97.7 97.6 15 97.0 96.8 25 98.0 97.9 30 97.5 97.3 37.5 98.2 98.1 45 97.7 97.6 50 98.3 98.2 75 98.0 97.9 75 98.5 98.4 112.5 98.2 98.1 100 98.6 98.5 150 98.3 98.2 167 98.7 98.7 225 98.5 98.4 250 98.8 98.8 300 98.6 98.5 333 98.9 98.9 500 98.7 98.7 500
- 99.0 750 98.8 98.8 667

- 99.0 1000 98.9 98.9 833
- 99.1 1500

- 99.0 2000

- 99.0 2500

- 99.1TP 1-1996 Page 11



### Appendix A TEMPERATURE CORRECTION FACTOR FOR DRY TYPE TRANSFORMERS

A.1 ASSUMPTIONS a. Stray and eddy losses-10% of load loss b. Conductor material-copper and aluminum c. Candidate full load temperature rises 80, 115, 150 d. 20°C Ambient A.2 ALGORITHMS a. Electrical resistance at 75°C vs. full load reference
R75 F+75°C Rref F+Trise+Ambient

Where:
F = thermal coefficient of resistance

Faluminum = 225 Fcopper = 234.5 Ambient = 20°C
Full Load Rise Al uminum Copper 80 0.9231 0.9253 115 0.8333 0.8376 150 0.7595 0.7651 b. Temperature correction factor TF = (LI) R75 + LE Rref

Rref R75 L, = PU load loss due to d - c resistance = 0.9 L, varies directly with temperature LE = PU load loss due to strays and eddies = 0.1 LE varies inversely with temperature

TF = 0.9 R75 + 0.1 Rref

Rref R75
Full Load Rise Al uminum Copper 80 0.9391 0.9408 115 0.8700 0.8732 150 0.8152 0.8193TP 1-1996

Page 12TP 1-1996 Page 13



### Appendix B BIBLIOGRAPHY

C57.12 .10-1988 American National Standard for Transformers - 230 KV and below, 833/958 through 8333/1041 7kVA, single phase, and 750/862 through 60000 / 80000 /100000kVA, Three Phase without Load Tap Changing; and 3750/4687 through 60000 / 80000 /100000 kVA with Load Tap Changing - Safety Requirements. C57.12.20-1988 American National Standard for Transformers - Overhead-Type Distribution Transformers, 500 kVA and Smaller; High Voltage, 34500 and Below; Low Voltage, 7970/13800Y and Below C57.12. 22-1989

C57.12. 23-1993

C57.12. 24-1988 American National Standard for Transformers - Pad-Mounted, CompartmentalType, Self-Cooled, Three-Phase Distribution Transformers with High Voltage Bushings, 2500 kVA and Smaller; High Voltage, 34500GrdY/19920 Volts and Below; Low Voltage, 480 Voltages and Below - Requirements IEEE Standard for Transformers - Underground-type, Self-Cooled, Single-phase Distribution Transformers with Separable, Insulated, High Voltage Connectors; High Voltage (24940 GrdY/14400 V and Below) and Low Voltage (240/120 V, 176 kVA and Smaller) American National Standard for Transformers - Underground-type, Three-Phase Distribution Transformers, 2500kVA and Smaller; High Voltage 34500 GrdY/19920 Volts and Below; Low Voltage, 480 Volts and Below - Requirements C57.12.25-1990 American National Standard for Transformers - Pad-Mounted, Compartmentaltype, Self-Cooled, Single-Phase Distribution Transformers with Separable Insulated High Voltage 34500 GrdY/19920 Volts and Below; Low Voltage, 240/120 Volts; 167 kVA and Smaller - Requirements C57.12.26-1992 IEEE Standard for Pad-Mounted, Compartmental-Type, Self-Cooled, ThreePhase Distribution Transformers for Use with Separable Insulated High-Voltage Connectors (34500 GrdY/19920 V and Below; 2500 kVA and Smaller C57.12. 40-1992 American National Standard for Transformers - Subway and Vault Types (Liquid Immersed

) - Requirements C57.12. 50-1981

C57.12. 51-1981

C57.12. 52-1987 American National Standard Requirements for Ventilated Dry-Type Distribution Transformers, 1 to 500 kVA, Single-Phase, and 15 to 500 kVA, Three-Phase, with High Voltage 601 to 34500 Volts, Low-Voltage 120 to 600 Volts American National Standard Requirements for Ventilated Dry-Type Power Transformers, 501 kVA and Larger , Three-Phase, with High Voltage 601 to 34500 Volts, Low Voltage 208Y/ 120 to 4160 Volts American National Standard Requirements for Sealed Dry-Type Power Transformers, 501 kVA and Larger, Three-Phase, with High Voltage 601 to 34500 Volts, Low-Voltage 208Y /120 to 4160 VoltsTP 1-1996

Page 14 C57.12.57-1987 American National Standard for Transformers - Ventilated Dry-Type Network Transformers 2500 kVA and Below, three-Phase, with High Voltage 34500 Volts and Below, Low-Voltage 216Y/125 and 480/277 Volts - Requirements C57.12.59-1989 IEEE Guide for Dry-Type Transformer Through-Fault Current Duration C57.12.70-1978 American National Standard Terminal Marking and Connections for Distribution and Power Transformers C57.12.80-1978 IEEE Standard Terminology for Power and Distribution Transformers C57.12.90-1993 IEEE Standard Test Code for Liquid-Immersed Distribution, Power and Regulating Transformers and IEEE Guide for Short-Circuit Testing of Distribution and Power Transformers C57.12.91-1979 IEEE Standard Test Code for Dry-Type Distribution and Power Transformers C57.91-1981 IEEE Guide for Loading Mineral-Oil-Immersed Overhead and Pad-Mounted Distribution Transformers Rated 500 kVA and Less with 65°C or 55°C Average Winding Rise C57.92-1981 IEEE Guide for Loading Mineral-Oil-Immersed Power Transformers Up to and including 100 MVA with 65°C or 55°C Average Winding Rise C57.96-1989 IEEE Guide for Loading Dry-Type Distribution and Power Transformers C57.109-1993 IEEE Guide for Liquid-Immersed Transformer Through-Fault Current Duration C57.110-1986 IEEE Recommended Practice for Establishing Transformer Capability When Supplying Nonsinusoidal Load Currents

### NEMA T.. ®TI .... i u ]'u

The purpose of NEMA standards, their classification , and status are set forth in certain clauses of the NEMA Standardization Policies and Procedures manual and are referenced below: 

## Purpose c National Electrical Manufacturers Association Standards are adopted in the public interest and are designed to eliminate misunderstandings between the manufacturer and the purchaser and to assist the purchaser in selecting and obtaining the proper product for their particular needs. Existence of a National Electrical Manufacturers Association Standard does not in any respect preclude any member or nonmember from manufacturing or selling products not conforming to the standard. 

### Definition of a Standard A standard of the National Electrical Manufacturers Association defines a product, process, or procedure with reference to one or more of the following; nomenclature, composition, construction, dimensions, tolerances, safety, operating characteristics, performance, rating, testing, and the service for which they are designed. (Standardization Policies and Procedures, p. 1) 

### D i m ensions Where dimensions are given for interchangeability purposes, alternate dimensions satisfying the other provisions of the Standards Publication may be capable of otherwise equivalent performance. (Standardization Policies and Procedures, p. 6) 

### Ca- of Standard s National Electrical Manufacturers Association Standards are of three classes, which have received the affirmative vote of at least two-thirds of the Subdivision votes cast in the affirmative or negative: 1. NEMA Standard, which relates to a product, process, or procedure commercially standardized and subject to repetitive manufacture. 2. Suggested Standard for Future Design, which may not have been regularly applied to a commercial product, but which suggests a sound engineering approach to future development. 3. Adoptive Standard, which is adopted in whole or in part from the standards of another organization, either domestic, regional, or international. (Standardization Policies and Procedures, p. 5)

A __.i_ 

### °L- ed L_ - mi 

## ng Infor

## mation Authorized Engineering Information consists of explanatory data or other engineering information of an informative character not falling within the classification of NEMA Standard or Suggested Standard for Future Design, which standard has received the affirmative vote of at least two-thirds of the Subdivision votes cast in the affirmative or negative. (Standardization Policies and Procedures, p. 5) 

### Identification of S tatus Standards in NEMA Standards Publications are identified as "NEMA Standard," "Suggested Standard for Future Design," or "Adoptive Standard." These indicate the status of the standard. A statement incorporating the auxiliary verb "shall" indicates that compliance with a requirement is mandatory for compliance with the standard. These classes of standards are identified in the foreword or throughout the text. The material identified as "Authorized Engineering Information" is designated similarly. Statements incorporating other auxiliary verbs such as "should," "may," etc. refer to the authorized engineering information and not to procedures required for compliance with the standard.