CHAPTER 3. MARKET AND TECHNOLOGY ASSESSMENT 

TABLE OF CONTENTS 

3.1 INTRODUCTION ..................................................... 3-1


3.2 DISTRIBUTION TRANSFORMER DEFINITION ........................... 3-1


3.3 PRODUCT CLASSES .................................................. 3-6


3.4 NATIONAL SHIPMENT ESTIMATE ..................................... 3-7


3.5 MANUFACTURERS OF DISTRIBUTION TRANSFORMERS ................. 3-9


3.5.1 Small Business Impacts .......................................... 3-10


3.5.2 Distribution and Sales Channels ................................... 3-10


3.6 TOTAL OWNING COST EVALUATION ................................. 3-12


3.7 VOLUNTARY PROGRAMS ........................................... 3-13


3.7.1 National Electrical Manufacturers Association TP 1 Standard ............ 3-13


3.7.2 Energy Star Transformers ........................................ 3-15


3.7.3 Consortium for Energy Efficiency .................................. 3-16


3.7.4 Federal Energy Management Program ............................... 3-16


3.7.5 Efficiency Vermont ............................................. 3-16


3.7.6 Idaho Power ................................................... 3-17


3.7.7 National Grid .................................................. 3-17


3.7.8 NHSaves ..................................................... 3-17


3.7.9 Northeast Utilities .............................................. 3-18


3.7.10 Seattle City Light ............................................... 3-18


3.7.11 Tacoma Power ................................................. 3-19


3.7.12 Two Rivers Water and Light ...................................... 3-19


3.7.13 United Illuminating ............................................. 3-19


3.7.14 Wisconsin Public Power ......................................... 3-20


3.7.15 Xcel Energy ................................................... 3-20


3.8 REGULATORY PROGRAMS .......................................... 3-20


3.8.1 Arizona Efficiency Standard ...................................... 3-21


3.8.2 California Efficiency Standard ..................................... 3-21


3.8.3 Connecticut Efficiency Standard ................................... 3-21


3.8.4 Maryland Efficiency Standard ..................................... 3-21


3.8.5 Massachusetts Efficiency Standard ................................. 3-21


3.8.6 Minnesota Procurement Efficiency Standard .......................... 3-23


3.8.7 New Jersey Efficiency Standard ................................... 3-23


3.8.8 New York Efficiency Standard .................................... 3-23


3.8.9 Oregon Efficiency Standard ....................................... 3-23


3.8.10 Rhode Island Efficiency Standard .................................. 3-24


3.8.11 Washington Efficiency Standard ................................... 3-24


3.8.12 Wisconsin Efficiency Standard .................................... 3-24


3.8.13 Burlington, Vermont Efficiency Standard ............................ 3-24


3.8.14 Proposed State Efficiency Standards ................................ 3-24


3.8.15 U.S. National Energy Bill - EPACT 2005 ............................ 3-25


3.8.16 Canadian Efficiency Standard ..................................... 3-25


3.8.17 Mexican Efficiency Standard ...................................... 3-28


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3.9 TECHNOLOGY ASSESSMENT ........................................ 3-33


3.9.1 

3.9.2 

3.9.3 

Table 3.3.1 

Table 3.4.1 

Table 3.7.1 

Table 3.7.2 

Table 3.7.3 

Table 3.7.4 

Table 3.7.5 

Table 3.7.6 

Table 3.7.7 

Table 3.7.8 

Table 3.8.1 

Table 3.8.2 

Table 3.8.3 

Table 3.8.4 

Table 3.8.5 

Table 3.8.6 

Table 3.8.7 

Table 3.9.1 

Figure 3.4.1 

Figure 3.4.2 

Figure 3.5.1 

Figure 3.9.1 

Figure 3.9.2 

Distribution Transformer Types .................................... 3-34


Transformer Efficiency Levels ..................................... 3-34


Transformer Losses ............................................. 3-36


LIST OF TABLES 

Distribution Transformer Product Classes ............................. 3-7


National Distribution Transformer Shipment Estimates for 2001 ........... 3-8


NEMA Efficiency Levels for Liquid-Immersed Distribution Transformers .. 3-14


NEMA Efficiency Levels for Dry-Type Distribution Transformers ........ 3-15


Efficiency Vermont Rebate Amounts ............................... 3-16


National Grid Design 2000 Rebate Amounts ......................... 3-17


NHSaves’ New Equipment and Construction Program Rebate Amounts .... 3-18


Northeast Utilities Energy Conscious Construction Rebate Amounts ....... 3-18


Tacoma Power Transformer Rebate Amounts ......................... 3-19


United Illuminating Transformer Rebate Amounts ..................... 3-20


Comparison of Massachusetts State Energy Efficiency Standards for MV Dry-


Type Distribution Transformers to DOE NOPR TSLs .................. 3-22


Canadian Efficiency Regulations for Dry-Type Transformers ............ 3-28


Characteristics of Regulated Distribution Transformers in Mexico ........ 3-29


Minimum Efficiency Levels for Transformers in Mexico ................ 3-30


Maximum Allowed Losses for Transformers in Mexico ................. 3-31


Transitional Standards for Small Manufacturers in Mexico .............. 3-32


Transitional Maximum Losses for Small Manufacturers in Mexico ........ 3-33


Options and Impacts of Increasing Transformer Efficiency .............. 3-37


LIST OF FIGURES 

Liquid-Immersed Distribution Transformer Shipment Estimate, 2001 ....... 3-8


MV Dry-Type Distribution Transformer Shipment Estimate, 2001 ......... 3-8


Market Delivery Channels for Distribution Transformers ................ 3-11


Transformer Losses Vary with Load (75 kVA Dry-Type) ................ 3-35


Transformer Efficiency Varies with Load ............................ 3-36


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CHAPTER 3. MARKET AND TECHNOLOGY ASSESSMENT 

3.1 INTRODUCTION 

This chapter provides a profile of the distribution transformer industry in the United 

States. The Department developed the preliminary market and technology assessment presented 

in this chapter primarily from publicly available information. This assessment is helpful in 

identifying the major manufacturers and their product characteristics, which form the basis for 

the engineering and the life-cycle cost (LCC) analyses. 

3.2 DISTRIBUTION TRANSFORMER DEFINITION 

The definition of a distribution transformer was presented in the Energy Policy Act 

(EPACT) of 2005, and then further refined by DOE when it was codified into the Code of 

Federal Regulations (CFR) on April 27, 2006. 10 CFR 431.192; 71 FR 24972. 

EPACT 2005 established that the definition of a distribution transformer would be as 

follows: 

The term 'distribution transformer' means a transformer that -

(i)	 has an input voltage of 34.5 kilovolts or less; 

(ii)	 has an output voltage of 600 volts or less; and 

(iii)	 is rated for operation at a frequency of 60 Hertz. 

The term 'distribution transformer' does not include -

(i)	 a transformer with multiple voltage taps, the highest of which equals at least 

20 percent more than the lowest; 

(ii)	 a transformer that is designed to be used in a special purpose application and 

is unlikely to be used in general purpose applications, such as a drive 

transformer, rectifier transformer, auto-transformer, impedance transformer, 

regulating transformer, sealed and non-ventilating transformer, machine tool 

transformer, welding transformer, grounding transformer, or testing 

transformer; or 

(iii)	 any transformer not listed in clause (ii) that is excluded by the Secretary by 

rule because -

(I)	 the transformer is designed for a special application; 

(II)	 the transformer is unlikely to be used in general purpose applications; and 

(III) the application of standards to the transformer would not result in 

significant energy savings. 

The term ‘low-voltage dry-type distribution transformer’ means a distribution transformer that— 

(A) has an input voltage of 600 volts or less; 

(B) is air-cooled; and

(C) does not use oil as a coolant. 

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The term ‘transformer’ means a device consisting of 2 or more coils of insulated wire that 

transfers alternating current by electromagnetic induction from 1 coil to another to change the 

original voltage or current value. 

In the April 2006 final rule, DOE clarified some of the exemptions which were not 

defined in the statute, based on the test procedure rulemaking which had been developing the 

definition of a distribution transformer. These definitions were based on primarily industry 

sources including IEEE and NEMA. In addition, EPACT 2005 did not provide kVA ranges 

which were used by DOE in this rulemaking proceeding to bound its scope of coverage. 

Therefore, in the April 2006 final rule, DOE established kVA ranges that were consistent with 

the scope of applicability for the test procedure and energy conservation standards rulemakings 

DOE had been conducting on distribution transformers. This means that DOE’s coverage 

authority granted by Congress is broader than that subset of distribution transformers that are 

being regulated in this proceeding. 

The following text includes all the definitions that were codified into 10 CFR 431.192 in 

the April 2006 final rule for distribution transformers. As discussed in today’s final rule, the 

revision to the definition of an Uninterruptible Power Supply transformer is included in this 

definition. 

Autotransformer means a transformer that: 

(a) Has one physical winding that consists of a series winding part and a common 

winding part; 

(b) Has no isolation between its primary and secondary circuits; and 

(c) During step-down operation, has a primary voltage that is equal to the total of the 

series and common winding voltages, and a secondary voltage that is equal to the common 

winding voltage. 

Basic model means a group of models of distribution transformers manufactured by a 

single manufacturer, that have the same insulation type (i.e., liquid-immersed or dry-type), have 

the same number of phases (i.e., single or three), have the same standard kVA rating, and do not 

have any differentiating electrical, physical or functional features that affect energy consumption. 

Differences in voltage and differences in basic impulse insulation level (BIL) rating are examples 

of differentiating electrical features that affect energy consumption. 

Distribution transformer means a transformer that– 

(1) Has an input voltage of 34.5 kV or less; 

(2) Has an output voltage of 600 V or less; 

(3) Is rated for operation at a frequency of 60 Hz; and 

(4) Has a capacity of 10 kVA to 2500 kVA for liquid-immersed units and 15 kVA to 

2500 kVA for dry-type units; but 

(5) The term “distribution transformer” does not include a transformer that is an– 

(i) Autotransformer;

(ii) Drive (isolation) transformer;

(iii) Grounding transformer;

(iv) Machine-Tool (Control) Transformer;

(v) Nonventilated Transformer;

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(vi) Rectifier Transformer;

(vii) Regulating Transformer;

(viii) Sealed Transformer;

(ix) Special-Impedance Transformer; 

(x) Testing Transformer;

(xi) Transformer with Tap Range of 20 percent or more; 

(xii) Uninterruptible Power Supply Transformer; or 

(xiii) Welding Transformer.

Drive (isolation) transformer means a transformer that: 

(a) Isolates an electric motor from the line; 

(b) Accommodates the added loads of drive-created harmonics; and 

(c) Is designed to withstand the additional mechanical stresses resulting from an 

alternating current adjustable frequency motor drive or a direct current motor drive. 

Efficiency means the ratio of the useful power output to the total power input. 

Excitation current or no-load current means the current that flows in any winding used to 

excite the transformer when all other windings are open-circuited. 

Grounding transformer means a three-phase transformer intended primarily to provide a 

neutral point for system-grounding purposes, either by means of: 

(a) A grounded wye primary winding and a delta secondary winding; or 

(b) A transformer with its primary winding in a zig-zag winding arrangement, and with 

no secondary winding. 

Liquid-immersed distribution transformer means a distribution transformer in which the 

core and coil assembly is immersed in an insulating liquid. 

Load loss means, for a distribution transformer, those losses incident to a specified load 

carried by the transformer, including losses in the windings as well as stray losses in the 

conducting parts of the transformer. 

Machine-tool (control) transformer means a transformer that is equipped with a fuse or 

other over-current protection device, and is generally used for the operation of a solenoid, 

contactor, relay, portable tool, or localized lighting. 

Medium-voltage dry-type distribution transformer means a distribution transformer in 

which the core and coil assembly is immersed in a gaseous or dry-compound insulating medium, 

and which has a rated primary voltage between 601 V and 35 kV. 

No-load loss means those losses that are incident to the excitation of the transformer. 

Nonventilated transformer means a transformer constructed so as to prevent external air 

circulation through the coils of the transformer while operating at zero gauge pressure. 

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Phase angle means the angle between two phasors, where the two phasors represent 

progressions of periodic waves of either: 

(1) Two voltages; 

(2) Two currents; or 

(3) A voltage and a current of an alternating current circuit. 

Phase angle correction means the adjustment (correction) of measurement data to negate 

the effects of phase angle error. 

Phase angle error means incorrect displacement of the phase angle, introduced by the 

components of the test equipment. 

Rectifier transformer means a transformer that operates at the fundamental frequency of 

an alternating-current system and that is designed to have one or more output windings connected 

to a rectifier. 

Reference temperature means 20 °C for no-load loss, 55 °C for load loss of liquidimmersed distribution transformers at 50 percent load, and 75 °C for load loss of both lowvoltage and medium-voltage dry-type distribution transformers, at 35 percent load and 50 percent 

load, respectively. It is the temperature at which the transformer losses must be determined, and 

to which such losses must be corrected if testing is done at a different point. (These temperatures 

are specified in the test method in Appendix A to this part.) 

Regulating Transformer means a transformer that varies the voltage, the phase angle, or 

both voltage and phase angle, of an output circuit and compensates for fluctuation of load and 

input voltage, phase angle or both voltage and phase angle. 

Sealed Transformer means a transformer designed to remain hermetically sealed under 

specified conditions of temperature and pressure. 

Special-Impedance Transformer means any transformer built to operate at an impedance 

outside of the normal impedance range for that transformer’s kVA rating. The normal 

impedance range for each kVA rating for liquid-immersed and dry-type transformers is shown in 

Tables 1 and 2, respectively. 

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Table 1 – Normal Impedance Ranges for Liquid-Immersed Transformers 

Single-Phase Transformers Three-Phase Transformers 

kVA Impedance (%) kVA Impedance (%) 

10 1.0-4 .5 15 1.0-4 .5 

15 1.0-4 .5 30 1.0-4 .5 

25 1.0-4 .5 45 1.0-4 .5 

37.5 1.0-4 .5 75 1.0-5 .0 

50 1.5-4 .5 112 .5 1.2-6 .0 

75 1.5-4 .5 150 1.2-6 .0 

100 1.5-4 .5 225 1.2-6 .0 

167 1.5-4 .5 300 1.2-6 .0 

250 1.5-6 .0 500 1.5-7 .0 

333 1.5-6 .0 750 5.0-7 .5 

500 1.5-7 .0 1000 5.0-7 .5 

667 5.0-7 .5 1500 5.0-7 .5 

833 5.0-7 .5 2000 5.0-7 .5 

2500 5.0-7 .5 

Table 2 – Normal Impedance Ranges for Dry-Type Transformers 

Single-Phase Transformers Three-Phase Transformers 

kVA Impedance (%) kVA Impedance (%) 

15 1.5-6 .0 15 1.5-6 .0 

25 1.5-6 .0 30 1.5-6 .0 

37.5 1.5-6 .0 45 1.5-6 .0 

50 1.5-6 .0 75 1.5-6 .0 

75 2.0-7 .0 112 .5 1.5-6 .0 

100 2.0-7 .0 150 1.5-6 .0 

167 2.5-8 .0 225 3.0-7 .0 

250 3.5-8 .0 300 3.0-7 .0 

333 3.5-8 .0 500 4.5-8 .0 

500 3.5-8 .0 750 5.0-8 .0 

667 5.0-8 .0 1000 5.0-8 .0 

833 5.0-8 .0 1500 5.0-8 .0 

2000 5.0-8 .0 

2500 5.0-8 .0 

Temperature Correction means the mathematical correction(s) of measurement data, 

obtained when a transformer is tested at a temperature that is different from the reference 

temperature, to the value(s) that would have been obtained if the transformer had been tested at 

the reference temperature. 

Test Current means the current of the electrical power supplied to the transformer under 

test. 

Test Frequency means the frequency of the electrical power supplied to the transformer 

under test. 

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Test Voltage means the voltage of the electrical power supplied to the transformer under 

test. 

Testing Transformer means a transformer used in a circuit to produce a specific voltage 

or current for the purpose of testing electrical equipment. 

Total Loss means the sum of the no-load loss and the load loss for a transformer. 

Transformer with Tap Range of 20 percent or more means a transformer with multiple 

voltage taps, the highest of which equals at least 20 percent more than the lowest, computed 

based on the sum of the deviations of the voltages of these taps from the transformer’s nominal 

voltage. 

Uninterruptible Power Supply Transformer means a transformer that is used within an 

uninterruptible power system, which in turn supplies power to loads that are sensitive to power 

failure, power sags, over voltage, switching transients, line noise, and other power quality 

factors. 

Waveform Correction means the adjustment(s) (mathematical correction(s)) of 

measurement data obtained with a test voltage that is non-sinusoidal, to a value(s) that would 

have been obtained with a sinusoidal voltage. 

Welding Transformer means a transformer designed for use in arc welding equipment or 

resistance welding equipment. 

3.3 PRODUCT CLASSES 

The Department divides covered products into classes by: (a) the type of energy used; (b) 

the capacity; or (c) any performance-related features that affect consumer utility or efficiency. (42 

U.S.C. 6295(q)) Different energy efficiency standards may apply to different product classes. In 

the advance notice of proposed rulemaking (ANOPR), the Department proposed 10 product 

classes, and received general support on these product classes. The 10 product classes divided up 

the population of distribution transformers by: 

a) Type of transformer insulation - liquid-immersed or dry-type, 

b) Number of phases - single or three, 

c) Voltage class - low or medium (for dry-type units only), and 

d) Basic impulse insulation level (for medium-voltage, dry-type units only). 

On August 8th, 2005, the President signed into law EPACT 2005, which contained a 

provision establishing energy conservation standards for two of the Department’s product classes 

(PCs)—PC3, low-voltage, single-phase, dry-type and PC4, low-voltage, three-phase, dry-type. 

With standards thereby established for low-voltage, dry-type distribution transformers, the 

Department is no longer considering these two product classes for standards. Table 3.3.1 below 

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presents the eight product classes that remain within the scope of this rulemaking analysis, and 

provides the kilovolt-ampere (kVA) range associated with each. 

Table 3.3.1 Distribution Transformer Product Classes 

PC # * Insulation Voltage Pha se BIL Rating kVA Range 

PC1 Liquid-Immersed Med ium Single - 10-833 kVA 

PC2 Liquid-Immersed Med ium Three - 15-2500 kVA 

PC5 Dry-Type Med ium Single 20-45kV BIL 15-833 kVA 

PC6 Dry-Type Med ium Three 20-45kV BIL 15-2500 kVA 

PC7 Dry-Type Med ium Single 46-95kV BIL 15-833 kVA 

PC8 Dry-Type Med ium Three 46-95kV BIL 15-2500 kVA 

PC9 Dry-Type Med ium Single >96kV BIL 75-833 kVA 

PC10 Dry-Type Med ium Three >96kV BIL 225-2500 kVA 

* Note: PC 3 and PC 4 we re the p rod uct class es for lo w-volta ge, dr y-type tran sform ers, whic h were remo ved from th is 

rulemaking when EPAC T 20 05 becam e law. For consistency with prior Notices and to maintain schedule, the 

Dep artment did no t renumbe r the liquid-immersed and me dium-voltage, d ry-type produ ct classes. 

Basic impulse insulation levels (BIL) refer to the level of insulation wound into a 

transformer, dictating its design voltage. Generally, higher BIL ratings have lower transformer 

operating efficiencies because the additional insulation and necessary clearances increase the 

distance between the core steel and the windings, contributing to higher losses. In addition, as 

the overall size of the windings increases due to additional insulation surrounding each wire, the 

core window through which the windings pass must increase, creating a larger core and 

increasing losses in the core. Recognizing this important aspect of transformer design, and after 

consultation with industry experts, the Department determined that differentiation of the energy 

efficiency standards by BIL level would be necessary for medium-voltage (MV), dry-type units, 

since these transformers experience significant variability in efficiency due to their BIL ratings. 

This decision is consistent with NEMA’s TP 1-2002 (described in section 3.7.1). 

3.4 NATIONAL SHIPMENT ESTIMATE 

To prepare an estimate of the national impact of energy conservation standards for 

distribution transformers, the Department needed to estimate annual transformer shipments. For 

accuracy in this calculation, unit shipments were required by product class and kVA rating within 

each product class. Detailed shipment information like this is highly sensitive to manufacturers, 

many of whom indicated to the Department they would not able to disclose their shipments. The 

Department researched public sources of transformer shipment information, such as the data 

compiled by the U.S. Census Bureau, but found that the data are aggregated, with many kVA 

ratings bundled in one value. Thus, the Department determined that it would not be possible to 

create an accurate estimate of transformers by kVA rating using Census Bureau data. 

Instead, to develop its shipments estimate, the Department contracted a company with 

considerable knowledge of the U.S. transformer industry. This contractor has collectively more 

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than 80 years of experience working in both the liquid-immersed and medium-voltage, dry-type 

transformer industry in the U.S. The Department tasked the contractor with using its knowledge 

of the market, plus a limited number of consultative calls, to compile a national estimate of 

shipments for liquid-immersed and medium-voltage, dry-type transformers. 

Figure 3.4.1 MV Dry-Type Distribution Transformer Shipment Estimate, 2001 

Figures 3.4.1 and 3.4.2 present the total aggregate shipment estimates for liquidimmersed and medium-voltage, dry-type units. These pie charts show the estimated shipments 

for 2001 in both number of transformers and cumulative megavolt-ampere (MVA) of transformer 

capacity. The superclasses are subdivided into two principal groups—single-phase and threephase. A detailed breakdown of the shipment estimates by product class and kVA rating appears 

in the shipments analysis (Chapter 9 of this TSD). 

Figure 3.4.2 Liquid-Immersed Distribution Transformer Shipment Estimate, 2001 

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Table 3.4.1 presents the actual shipment estimates by product class and the estimated 

value of these shipments, approximately $1.3 billion in 2001. 

Table 3.4.1 National Distribution Transformer Shipment Estimates for 2001 

Distribution Transformer Product Class Units 

Shipped 

MVA Capacity 

Shipped 

Shipment Value 

(2001 US$million) 

Liquid-imm ersed, med ium-voltage, single-phase 977,388 36,633 698 .8 

Liquid-imm ersed, med ium-voltage, three-pha se 79,367 42,887 540 .4 

Dry-type, medium-voltage, single-phase, 20-45 kV B IL 119 18 0.5 

Dry-type, medium-voltage, three-phase, 20-45 kV BIL 650 776 13.5 

Dry-type, medium-voltage, single-phase, 46-95 kV B IL 121 22 0.6 

Dry-type, medium-voltage, three-phase, 46-95 kV BIL 2,371 3,913 68.1 

Dry-typ e, med ium-vo ltage, sing le-pha se, >96 kV B IL 20 4 0.1 

Dry-typ e, med ium-vo ltage, thre e-pha se, >96 kV B IL 187 367 6.4 

Total 1,060,224 84,621 1,328 

Overall, liquid-immersed distribution transformers are a much larger market segment than 

MV dry-type. On a unit basis, 1,056,756 liquid-immersed units were shipped compared to just 

3,468 MV dry-type units. On an MVA shipped basis, liquid-immersed were 94 percent of the 

capacity shipped in 2001, compared to 6 percent for MV dry-type. 

Within the liquid-immersed market, single-phase distribution transformers dominate the 

unit-shipments, comprising 92 percent of the shipments in 2001. However, on an MVA capacity 

shipped basis, three-phase units dominate, representing 54 percent of the liquid-immersed 

capacity sold in 2001. For the medium-voltage, dry-type market, three-phase distribution 

transformers dominate, representing 93 percent of the unit shipments and 99 percent of the MVA 

capacity shipped in 2001. 

In preparing its estimates of the distribution transformer market, the Department’s 

contractor identified differences between its 2001 shipment estimates and the Oak Ridge 

National Laboratory (ORNL) Determination Analysis shipment estimates for 1995.1 The 

differences and the understanding behind some of these differences are discussed below. 

1.	 Compared to 1995, the 2001 shipment data suggest that more single-phase, liquidimmersed transformers were purchased as pad-mounts in 2001 than in 1995. Total 

single-phase, liquid-immersed transformer shipments remained close to the traditional 

one million units per year; however, the average kVA size has risen in both pole- and 

pad-mounted transformers by approximately 10 percent between 1995 and 2001. 

2.	 The three-phase, liquid-immersed transformer market was considerably larger in 2001 

than in 1995. This difference could be attributed to a more robust commercial and 

industrial expansion in 2001 compared to 1995. 

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3.	 The three-phase, medium-voltage, dry-type transformer market was smaller in volume 

than ORNL determined in 1995, but with larger kVA ratings. These larger three-phase, 

medium voltage, dry-type distribution transformers are most commonly used inside 

commercial and industrial buildings when power requirements are sufficiently large that 

direct feed from a liquid-immersed external transformer would be uneconomical. 

3.5	 MANUFACTURERS OF DISTRIBUTION TRANSFORMERS 

In total, there are more than 60 manufacturers and importers of distribution transformers 

operating in the U.S. today.a Of these, 16 major companies represent about 80 percent of both 

the liquid-immersed and medium-voltage, dry-type markets. 

From a manufacturing point of view, the six largest companies operating in the 

liquid-immersed distribution transformer market are (in alphabetical order): ABB Power T&D 

Company, Cooper Power Systems, ERMCO, General Electric Power Systems, Howard 

Industries, and Kuhlman Electric Corporation. Together, these six companies represent more 

than 80 percent of the sales revenue of liquid-immersed distribution transformers in the U.S. 

For medium-voltage, dry-type distribution transformer manufacturers, the seven largest 

companies operating in the U.S. include (in alphabetical order): ABB Power T&D Company, 

Eaton Electrical, Inc., Federal Pacific Transformer Company, General Electric, Olsun Electrics 

Corporation, Siemens Corporation, and Square D Company. Together, these companies 

represent more than 80 percent of the sales revenue of medium-voltage, dry-type distribution 

transformers in the U.S. 

3.5.1	 Small Business Impacts 

The Department considered the possibility of small businesses being impacted by the 

promulgation of minimum efficiency standards for distribution transformers. The Department is 

aware that there are small distribution transformer manufacturers, defined by the Small Business 

Administration as having 750 employees or fewer, who would be impacted by a minimum 

efficiency standard. The Department studied the potential impacts to these small businesses in 

greater detail during the manufacturer impact analysis (MIA), which it conducted as part of the 

notice of proposed rulemaking (NOPR) analysis. 

Following the MIA, the Department concluded that small businesses may be adversely 

impacted by an energy conservation standard due to the incremental magnitude of capital 

investment for transformer manufacturing equipment. Distribution transformer manufacturers 

may be required to purchase additional core-cutting machines, coil winding machines, annealing 

furnaces, or other necessary equipment due to the increased size of more energy-efficient 

a

 This estimate is based on a review of the Thomas B usiness Registry (June 2005), United Laboratories (UL) Listings 

(June 2005), Canadian Standards Association (CSA) Listings (June 2005), Factory Mutual (FM) Listings (June 2005), 

the OR NL c ontact datab ase from the D etermination A nalysis,1

 and participants in DO E’s Distribution Transformers 

Framework Workshop meeting held November 1, 2000 in Washington, DC. 

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distribution transformers. Many small businesses do not possess the capital needed to purchase 

this additional equipment. There are a limited number of producers of distribution transformer 

manufacturing equipment, therefore the cost of such equipment is generally equivalent for all 

distribution transformer manufacturers. Chapter 12, describing the MIA, addresses impacts on 

small businesses in greater detail. 

3.5.2 Distribution and Sales Channels 

A schematic of the structure of the distribution transformer market is shown in Figure 

3.5.1.1

 This illustration depicts the major market players and the level of interaction between 

them. The solid lines show more common distribution and sales channels and dashed lines less 

frequently used channels. 

Figure 3.5.1 Market Delivery Channels for Distribution Transformers 

Source: ORNL, Determination Analysis of Energy Conservation Standards for Distribution 

Transformers, 1996. 

The market delivery channel for electric utilities is generally direct, with the majority of 

these customers placing orders directly with manufacturers. It is estimated that electric utilities 

purchase over 90 percent of their distribution transformers directly from manufacturers, 

specifying their desired features and performance.1 There are also utilities, such as some rural 

cooperatives and municipalities, that make transformer purchases through distributors. When 

placing an order, the electric utility provides a specification, including the value it places on 

future core and coil losses over the life of the transformer (see section 3.6 for a discussion of total 

owning cost). This market dynamic leads manufacturers to develop custom designs in their 

contract bid, reflecting the customer’s performance requirements and the dynamic costs of 

material, equipment, and labor at a transformer manufacturer’s facility. 

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The delivery channel for commercial and industrial customers can be complex, working 

through intermediaries such as stocking distributors and electrical contractors. Electrical 

contractors typically purchase transformers using specifications written by themselves or by 

agents. Some larger industrial customers buy transformers directly from distributors or 

manufacturers based on specifications drafted by in-house experts. Any large-volume or customorder purchases made (e.g., orders from the petrochemical or the pulp and paper industry) are 

typically made directly with transformer manufacturers. Similarly, original equipment 

manufacturers (OEMs) know the exact specification they require for their finished products and 

typically work directly with manufacturers when placing an order. 

Transformers with major damage are usually replaced rather than repaired. However, 

when a repair does take place (e.g., when failure occurs within the warranty period), it may be 

carried out by a repair shop or at the manufacturer’s facility. Additionally, some utilities may 

choose to carry out their own repairs if this option is less expensive than disposal and 

replacement. 

3.6 TOTAL OWNING COST EVALUATION 

In 1995, there were an estimated 44 million liquid-immersed distribution transformers in 

service, of which approximately 90 percent were owned by electric utilities.1

 For dry-type 

transformers, there were approximately 12 million units in service, which were primarily used by 

commercial and industrial customers.1

 The liquid-immersed market, dominated by the electric 

utility sector, drove efficiency ratings higher over time, encouraging more efficient materials and 

manufacturing methods. A detailed discussion of these improvements and efficiency trends 

between the years 1950 and 1993 can be found in two ORNL reports.1, 2 

Following the energy price shocks of the 1970s, utilities started using total owning cost 

(TOC) evaluation formulae (Equation 3.1), incorporating core and winding losses into their 

purchasing decisions. The TOC consists of the quoted transformer price and energy losses in the 

core and winding over the anticipated life of the unit. 

Expressed as a formula, 

TOC = (NL × A) + (LL × B) + Price Eq. 3.1 

where: 

TOC = total owning cost ($),


NL = no-load loss (Watts),


A = equivalent first-cost of no-load losses ($/Watt),


LL = load loss at the transformer’s rated load (Watts),


B = equivalent first-cost of load losses ($/Watt), and 


Price = bid price (retail price)($).


The capitalized cost per watt of no-load and load losses, the A and B factors, vary from 

one electric utility to another. They are derived from several variables, including the avoided 

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costs of system capacity, generation capacity, transmission and distribution capacity and energy, 

the levelized fixed charge rate, the peak responsibility factor, the transformer loss factor, and the 

equivalent annual peak load.3 For a detailed discussion on the development and use of the TOC 

formula, including examples, see the draft industry standard document, Institute of Electrical and 

Electronics Engineers, Inc. (IEEE) PC57.12.33. 

Utilities that use A and B factors compare two or more proposals from manufacturers and 

select the one that offers them the lowest total owning cost—i.e., the lowest combination of first 

cost and operating cost over the life of the transformer. Before electric utility deregulation 

started in North America, 30 years was considered the operating life and the depreciation period 

of a liquid-immersed transformer. In the last five years, deregulation has raised concerns about 

payback periods, since electric utilities are not sure if they will own the transformer for its entire 

life. This uncertainty has forced some electric utilities to reduce their A and B factors, equating 

to a decreased emphasis on losses, and therefore a reduction in transformer efficiency ratings. 

In 1996, ORNL estimated that “more than 90 percent” of electric utilities used the TOC 

method of loss evaluation at the time of purchase, which drove the market toward increasingly 

efficient designs.1 More recently, however, the possibility of deregulation and the associated sale 

of distribution networks has meant that utilities purchasing transformers today may not own them 

in 5 or 10 years, and thus will not recover the higher initial cost of a more efficient design. These 

regulatory changes and the general uncertainty surrounding deregulation have driven some 

utilities to purchase designs with lower first costs and higher losses. 

The IEEE draft standard PC57.12.33 has a chapter discussing transformer efficiency for 

commercial and industrial customers3 (i.e., typical users of medium-voltage, dry-type 

transformers). The medium-voltage, dry-type transformer market functions similarly to the 

liquid-immersed market, in that manufacturers receive custom-build orders with specifications or 

design criteria from the customer. Because these customers pay for (and are concerned about) 

the electricity lost in their own distribution systems, they are concerned about the performance of 

the transformers they order. 

3.7 VOLUNTARY PROGRAMS 

The Department reviewed several voluntary programs promoting efficient distribution 

transformers in the United States. These include the National Electrical Manufacturers 

Association (NEMA) TP 1 Standard, the U.S. Environmental Protection Agency’s Energy Star 

Transformers program, the Consortium for Energy Efficiency’s Commercial and Industrial 

Transformers Initiative, and the Federal Energy Management Program’s TP 1 purchase program. 

The Department also reviewed several voluntary programs operating at a regional level that 

affect distribution transformers, including Efficiency Vermont, Idaho Power, National Grid, 

NHSaves, Northeast Utilities, Seattle City Light, Tacoma Power, Two Rivers Water and Light, 

United Illuminating, Wisconsin Public Power and Xcel Energy. Because the national standard 

for low-voltage, dry-type distribution transformers took effect on January 1, 2007, many of these 

programs will cease to exist in 2007. However, these programs are still recorded in this TSD 

chapter, to show the level of interest in improving the energy-efficiency of distribution 

transformers that existed before the national regulatory actions of Congress and the Department. 

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3.7.1 National Electrical Manufacturers Association TP 1 Standard 

The NEMA TP 1 standard establishes a voluntary efficiency standard for distribution 

transformers.4 It encompasses liquid-immersed distribution transformers, single- and threephase, as well as dry-type, low-voltage and medium-voltage, single- and three-phase units. 

NEMA established this national voluntary efficiency standard in 1996, and revised it in 2002. 

Manufacturers must meet or exceed the minimum efficiency targets presented in Tables 3.7.1 and 

3.7.2 at the appropriate loading points. TP 1 efficiency levels are adopted by States and other 

agencies that are interested in establishing a standard. At the national level, Congress established 

TP 1 as the standard for low-voltage dry-type transformers (EPACT 2005, August 8th, 2005). 

More information about TP 1 can be obtained by contacting NEMA, tel: 703-841-3200, or by 

visiting http://www.nema.org/stds/tp1.cfm#download. 

Table 3.7.1 NEMA Efficiency Levels for Liquid-Immersed Distribution Transformers 

Liquid -Immer sed, Single-P hase Liquid -Immer sed, Thr ee-Ph ase 

kVA Min Efficiency (%) kVA Min 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 99.4 

No tes: Temperature: load-loss 85oC, no-load loss 20oC 

Efficiency levels at 50 percent of unit nameplate load 

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Table 3.7.2 NEMA Efficiency Levels for Dry-Type Distribution Transformers 

Dry-Type, Single-Phase Dry-Type, Three-Phase 

Min Efficiency (%) Min Efficiency (%) 

kVA Low- Medium-Voltage kVA Low- Medium-Voltage 

Voltage <60 kV BIL >60 kV BIL Voltage < 60 kV BIL > 60kV BIL 

15 97.7 97.8 97.6 15 97.0 97.2 96.8 

25 98.0 98.1 97.9 30 97.5 97.6 97.3 

37.5 98.2 98.3 98.1 45 97.7 97.8 97.6 

50 98.3 98.4 98.2 75 98.0 98.1 97.9 

75 98.5 98.5 98.4 112 .5 98.2 98.3 98.1 

100 98.6 98.6 98.5 150 98.3 98.4 98.2 

167 98.7 98.8 98.7 225 98.5 98.5 98.4 

250 98.8 98.9 98.8 300 98.6 98.6 98.5 

333 98.9 99.0 98.9 500 98.7 98.8 98.7 

500 - 99.1 99.0 750 98.8 98.9 98.8 

667 - 99.2 99.0 1000 98.9 99.0 98.9 

833 - 99.2 99.1 1500 - 99.1 99.0 

- - - - 2000 - 99.2 99.0 

- - - - 2500 - 99.2 99.1 

No tes: Temp erature: 75oC for both low- and medium-voltage 

Low-voltage efficiency levels at 35 percent of unit nameplate load 

Medium-voltage efficiency levels at 50 percent of unit nameplate load 

3.7.2 Energy Star Transformers 

The U.S. Environmental Protection Agency (U.S. EPA) and DOE manage a program 

called Energy Star Transformers to overcome market barriers preventing industrial/commercial 

customers and utilities from purchasing more energy-efficient, dry-type, low-voltage, single- and 

three-phase units. The minimum efficiency that a transformer must meet or exceed to be 

classified as an Energy Star transformer is the same as NEMA’s TP 1. The activities of this 

program include use of the Energy Star label, marketing assistance to manufacturers and 

distributors, and free software tools for end users (including a downloadable cost evaluation 

model and an energy-efficiency calculator). This program is sponsored and promoted by the U.S. 

EPA and DOE, with additional promotional support from the Consortium for Energy Efficiency 

(CEE). For more information about this program, please contact the U.S. EPA tel: 1-888-STARYES or CEE, tel: 617-589-3949. 

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3.7.3 Consortium for Energy Efficiency 

The CEE’s Commercial and Industrial Transformers Initiative, launched in 1997, 

promotes the manufacture and sale of high-efficiency transformers. Partnering with the Energy 

Star Transformers Program, CEE and participating members promote high-efficiency 

performance guidelines for low-voltage distribution transformers specified by the NEMA TP 1 

standard. CEE members and other participating organizations include electric utilities, and 

statewide or regional efficiency organizations, which may be utility-based. CEE published an 

Initiative Description and Market Assessment, which identifies the transformer market barriers to 

efficiency for interested utilities and other organizations. For more information, contact Ted 

Jones at tel: 617-589-3949, ext. 230. 

3.7.4 Federal Energy Management Program 

The Department manages the Federal Energy Management Program (FEMP), which helps 

Federal buyers identify and purchase energy-efficient equipment, including distribution 

transformers. The FEMP standard for distribution transformers is based on the NEMA TP 1 

standard, and includes all units listed in TP 1. FEMP offers buyers support tools such as 

efficiency guidelines, cost-effectiveness examples, and a cost calculator. FEMP also offers 

training, on-site audits, demonstrations, and design assistance. For more information, interested 

stakeholders can contact FEMP at tel: 1-800-363-3732. 

3.7.5 Efficiency Vermont 

Efficiency Vermont, an organization offering technical assistance and financial incentives 

to encourage energy efficiency in the State of Vermont, offers rebates for Energy Star 

three-phase, low voltage, dry-type transformers meeting the NEMA TP 1 standard.5 The 

maximum rebate amounts are presented in Table 3.7.3. Efficiency Vermont also provides simple 

payback calculations for various transformer sizes, and a comparison of the life-cycle cost for a 

dry-type, low voltage 225 kVA standard transformer and an Energy Star 225 kVA transformer. 

For more information, contact Efficiency Vermont at tel: 802-860-4095. 

Table 3.7.3 Efficiency Vermont Rebate Amounts 

Dry -Typ e, Low -Vo ltage, Th ree-P hase 

kVA M axim um in cen tive p er un it kVA M axim um in cen tive p er un it 

15 $250 112 .5 $500 

30 $275 150 $700 

45 $400 225 and higher $1200 

75 $450 - -

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3.7.6 Idaho Power 

Idaho power manages the Industrial Efficiency Program, which aims to encourage and 

assist large commercial and industrial customers in the use of high-efficiency transformers. 

Financial incentives are offered for any project that results in kWh savings. Projects are 

evaluated on a case-by case basis and take into account existing loads on both sides of the 

transformer to calculate transformer losses under actual operating conditions. These values are 

compared with those of the new transformer under similar loading conditions. The difference in 

the transformer losses multiplied by the operating hours gives an approximation of kWh savings. 

Financial incentives include $0.12 per annual kWh saved, or 50 percent of the project cost. 

Between the two incentives, the lesser of the two will be awarded. Idaho Power also provides 

energy-efficient education, project monitoring and verification, and energy-efficient 

demonstration projects. For more information, contact Idaho Power at tel: 208-388-2200. 

3.7.7 National Grid 

National Grid manages the Design 2000 Plus Program, which works to promote energy 

efficiency in design and construction practices in new and renovated commercial and industrial 

buildings.6 The target equipment of this program is NEMA TP 1 dry-type, low-voltage, threephase units. The program offers rebates in Rhode Island territories (the participating utility is 

Narragansett Electric). These rebates cover 75 percent of a compliant transformer's incremental 

cost over the least expensive TP 1 model, or they buy down the unit cost until it offers a 1.5-year 

payback. The maximum rebate amounts are presented in Table 3.7.4. The program also offers 

training for transformer specifiers and provides marketing activities to promote Energy Star 

units. For more information, contact National Grid at tel: 508-389-2000. 

Table 3.7.4 National Grid Design 2000 Rebate Amounts 

Dry -Typ e, Low -Voltage, Single-Phase 

kVA M axim um in centive p er un it kVA M axim um in centive p er un it 

15 $130 112 .5 $520 

30 $190 150 $560 

45 $250 225 $1150 

75 $440 - -

3.7.8 NHSaves 

The NHSaves Program is a collaborative of New Hampshire’s electric utilities that aims 

to promote energy efficiency, while advancing the economy of the state.7 NHSaves’ New 

Equipment and Construction Program offers incentives for the installation of NEMA TP 1 

dry-type, low-voltage, three-phase distribution transformers in commercial/industrial new 

construction or renovations. The maximum rebate amounts available are presented in Table 

3.7.5. For more information, contact the Public Service of New Hampshire at tel: 

1-800-662-7764, Granite State Electric Company (GSECo) at tel: 1-800-322-3223, New 

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Hampshire Electric Cooperative (NHEC) at tel: 1-800-698-2007, or Unitil Energy Systems, Inc. 

at tel: 1-888-886-4845. 

Table 3.7.5 NHSaves’ New Equipment and Construction Program Rebate Amounts 

Dry -Typ e, Low -Voltage, Th ree-Phase 

kVA M axim um in centive p er un it kVA M axim um in centive p er un it 

15 $130 112 .5 $520 

30 $190 150 $560 

45 $250 225 $1150 

75 $440 - -

3.7.9 Northeast Utilities 

Northeast Utilities manages the Energy Conscious Construction Program, which provides 

incentives to builders and contractors to support the purchase of energy-efficient transformers.8 

The target equipment of this standard are NEMA TP 1 dry-type, low-voltage, three-phase 

distribution transformers. The program focuses its efforts on projects within the customer area of 

Northeast Utilities, covering 70 to 100 percent of the additional incremental cost for a TP 1 

transformer, depending on measured energy savings. The maximum rebate amounts available 

are presented in Table 3.7.6. For more information, contact Northeast Utilities at tel: 

1-800-286-5000. 

Table 3.7.6 Northeast Utilities Energy Conscious Construction Rebate Amounts 

Dry -Typ e, Low -Voltage, Th ree-Phase 

kVA M axim um in centive p er un it kVA M axim um in centive p er un it 

15 $640 150 $1140 

30 $480 225 $1440 

45 $570 300 $1800 

75 $670 500 $2550 

112 .5 $700 - -

3.7.10 Seattle City Light 

Seattle City Light manages the Energy Smart Services Custom Incentive Program.9 The 

program provides incentives for distribution transformers that exceed the State-mandated NEMA 

TP-1 future standards for low voltage, dry-type distribution transformers. The standards were 

mandated through An Act Relating to Energy Efficiency, which becomes effective on January 1, 

2007 in Washington State. Incentives provided cover up to 70 percent of the cost for qualifying 

equipment, or $0.23 per kWh saved. Usually incentives are applied to utility-owned equipment. 

For more information contact Seattle City Light at tel: 206-684-3000. 

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3.7.11 Tacoma Power 

Tacoma Power manages a Transformer Rebate Program, offering rebates to their 

commercial and industrial customers who choose to install Energy Star-qualified distribution 

transformers.10 This program applies to NEMA TP 1 dry-type, low-voltage, three-phase 

distribution transformers. The incentives were offered until January 1, 2007, at which point the 

NEMA TP 1 standard took effect nationally. The maximum rebate amounts that were available 

are presented in Table 3.7.7. For more information, contact Tacoma Power at tel: 253-502-8619. 

Table 3.7.7 Tacoma Power Transformer Rebate Amounts 

Dry -Typ e, Low -Voltage, Th ree-Phase 

kVA M axim um in centive p er un it kVA M axim um in centive p er un it 

15 $210 112 .5 $665 

30 $310 150 $825 

45 $445 225 or higher $1810 

75 $505 - -

3.7.12 Two Rivers Water and Light 

Two Rivers Water and Light in Wisconsin offers incentives for Energy Star low-voltage, 

dry-type transformers that meet the NEMA TP 1 efficiency standards.11 Incentives are provided 

on a customized basis, based on an energy savings calculation, project cost, and simple payback 

to complete installation. Two Rivers Water and Light directs its program marketing efforts at 

customers, electricians, and local vendors. For more information, contact Two Rives Water and 

Light at tel: 920-792-5550. 

3.7.13 United Illuminating 

United Illuminating manages an energy-efficiency initiative in Connecticut called the 

Energy Blueprint Program.12 This program works to promote energy-efficient buildings and 

commercial equipment, including lighting; building envelope; heating, ventilation, and air 

conditioning (HVAC) equipment; motors; and other energy components of commercial and 

industrial systems. For transformers, Energy Blueprint promotes Energy Star transformers. The 

program offers cash incentives ranging from $640 to $2,550. The maximum rebate amounts 

available are presented in Table 3.7.8. For more information, contact United Illuminating at tel: 

1-800-722-5584. 

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Table 3.7.8 United Illuminating Transformer Rebate Amounts 

Dry-Type, Low-Voltage 

kVA M axim um in cen tive p er un it kVA M axim um in cen tive p er un it 

15 $640 150 $1140 

30 $480 225 $1440 

45 $570 300 $1800 

75 $670 500 $2550 

112 .5 $700 - -

3.7.14 Wisconsin Public Power 

Wisconsin Public Power manages a program called the Energy Star Transformer 

Incentive, which is based on promoting the market for Energy Star Transformers.13 A cash 

incentive is provided, based on realized energy savings. Before purchasing a transformer, the 

buyer must contact one of the sponsoring electric utilities to receive a rebate for purchasing an 

Energy Star transformer. For more information, contact Wisconsin Public Power at tel: (608) 

834-4500. 

3.7.15 Xcel Energy 

Xcel Energy manages the Custom Efficiency Program in Minnesota to help reduce peak 

load demand of commercial and industrial customers.14 Based on the NEMA TP 1 standard for 

low- and medium-voltage, dry-type distribution transformers, this program offers financial 

incentives of up to US$200 per kilowatt of average demand savings achieved during the system 

peak period by utilizing an energy-efficient distribution transformer. For more information, 

contact Xcel Energy at tel: 1-800-328-8226. 

3.8 REGULATORY PROGRAMS 

On August 8th, 2005 the President signed into law EPACT 2005. This legislation 

establishes the energy conservation standard for low-voltage, dry-type distribution transformers 

at the industry voluntary program level of TP 1-2002. This Federally mandated standard is the 

national standard, preempting any State efficiency standards for these products when it took 

effect on January 1, 2007. This section identifies those State-level regulatory programs that 

existed before the Federal action, including: Arizona, California, Connecticut, Maryland, 

Massachusetts, Minnesota, New Jersey, New York, Oregon, Rhode Island, Washington, 

Wisconsin, and the city of Burlington, Vermont. Standards were also proposed in Colorado, 

Maine, New Hampshire, Pennsylvania, and Vermont. At the international level, the Department 

is aware of standards in both Canada and Mexico that may impact the companies servicing the 

North American market. Summaries of all these regulatory programs are provided in this 

section. 

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 EE-RM/STD-00-550 COMMENT 196
3.8.1 Arizona Efficiency Standard 

An Arizona Act Relating to Appliance and Equipment Energy Efficiency Standards was 

signed into law on April 25, 2005.15 According to the law, all low-voltage, dry-type transformers 

sold or installed in the State must meet NEMA TP 1 efficiency levels beginning January 1, 2008. 

For more information, contact the Arizona House Information Desk at tel: 602-542-4221. 

3.8.2 California Efficiency Standard 

The Title 20 Appliance Efficiency Regulations mandate that transformers manufactured 

after March 1, 2003 and sold in California be NEMA TP 1 compliant.16 Title 20 was approved 

by the California Energy Commission in November 2002. For more information, contact the 

California Energy Commission at tel: 916-654-4058. 

3.8.3 Connecticut Efficiency Standard 

As of July 1, 2005 all low-voltage, dry-type distribution transformers sold, offered for 

sale, or installed in the State of Connecticut must meet the NEMA TP 1 efficiency level.17 The 

Connecticut Act Concerning Energy Efficiency Standards affects new and remodeled buildings, 

and is enforced by periodic inspections of distribution transformer distributors and retailers. For 

more information, contact the Connecticut Energy Research and Policy Development Department 

at tel: 860-418-6297. 

3.8.4 Maryland Efficiency Standard 

The Maryland Energy Efficiency Standards Act requires that all low-voltage, dry-type 

distribution transformers sold or installed in the State after March 1, 2005 meet the NEMA TP 1 

efficiency level.18 This act applies to all manufacturers, wholesalers, retailers, distributors, 

commercial installers, and consumers in the State. The Maryland Energy Administration intends 

to maintain a database on their website listing products that are in compliance with the standard. 

For more information, contact the Maryland Energy Administration at tel: 1-800-735-2258. 

3.8.5 Massachusetts Efficiency Standard 

Since December 31, 1999, Massachusetts law, under section 313 of the Massachusetts 

Electric Industry Restructuring Act of 1997, required that all distribution transformers sold or 

installed in the State meet the NEMA TP 1 efficiency level.19 Since passage of this standard, 

transformer specifiers have become more familiar with TP 1 through training provided by the 

Massachusetts Board for Building Regulations and Standards. The standard impacts new and 

remodeled buildings as well as electric utilities, and is enforced by building code inspectors. 

In late 2005, the Massachusetts’ State government revised the efficiency standards for 

single-phase and three-phase medium-voltage dry-type distribution transformers. In November 

2005, Governor Romney signed into law a bill encompassing a range of energy-efficiency 

measures. This bill included a higher standard for medium-voltage dry-type distribution 

transformers than was previously required.20 These efficiency levels, which take effect on June 

1, 2006, are set at NEMA TP 1 plus three-tenths of a percent for all medium-voltage dry-type 

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 EE-RM/STD-00-550 COMMENT 196
kVA ratings. Table 3.8.1 presents the newly enacted Massachusetts State standards (see column 

labeled “Massachusetts Standard”), and compares it to the DOE’s NOPR TSLs for each kVA 

rating. If the Massachusetts standard falls between two TSLs, the next highest TSL is reported. 

The table shows that by applying a constant three-tenths of a percent increase in 

efficiency over TP 1 establishes efficiency levels that are different than those being considered by 

the DOE. In fact, for the Massachusetts standard, as the kVA ratings of the transformers 

increase, so do the equivalent DOE TSLs. For instance, a 150 kVA transformer having a BIL 

rating less than or equal to 60 kV would have to meet the Department’s TSL2 under the new 

Massachusetts standard; while a 1500 kVA transformer with the same BIL rating must meet a 

level equivalent to TSL5. 

Table 3.8.1 Comparison of Massachusetts State Energy Efficiency Standards for MV 

2002 Standard 

Corresponding 

Standard 

2002 Standard 

Corresponding 

Standard 

# #

kVA (%) (%) TSL number (%) (%) TSL number 

15 96.8 97.1 TSL2 96.8 97.1 TSL2 

30 97.3 97.6 TSL2 97.3 97.6 TSL2 

45 97.6 97.9 TSL2 97.6 97.9 TSL3 

75 97.9 98.2 TSL2 97.9 98.2 TSL3 

98.1 98.4 TSL2 98.1 98.4 TSL3 

150 98.2 98.5 TSL2 98.2 98.5 TSL3 

225 98.4 98.7 TSL2 98.4 98.7 TSL3 

300 98.6 98.9 TSL3 98.5 98.8 TSL3 

500 98.8 99.1 TSL3 98.7 99.0 TSL4 

750 98.9 99.2 TSL4 98.8 99.1 TSL4 

1000 99.0 99.3 TSL4 98.9 99.2 TSL4 

1500 99.1 99.4 TSL5 99.0 99.3 TSL4 

2000 99.2 99.5 TSL5 99.0 99.3 TSL4 

2500 99.2 99.5 TSL5 99.1 99.4 TSL4 

Dry-Type Distribution Transformers to DOE NOPR TSLs 

Medium-Voltage, Three-Phase Dry-Type Distribution Transformers 

NEM A TP 1­ M assachusetts 

DOE T SL 

to M ass. 

NEM A TP 1­ Massachusetts 

DOE T SL 

to M ass. 

60 kV B IL 60 kV B IL 20-45 kV BIL >60 kV BIL >60 kV BIL 46-95 kV BIL 

Efficiency Efficiency Efficiency Efficiency

112 .5 

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 EE-RM/STD-00-550 COMMENT 196
3.8.6 Minnesota Procurement Efficiency Standard 

The Minnesota Building Code requires that TP 1-compliant transformers be installed in 

new and remodeled buildings for which permit applications were received on or after July 20, 

1999.21 This standard affects both dry-type, low- and medium-voltage, single- and three-phase; 

and liquid-immersed, single- and three-phase transformers. The market impact for this standard 

is being evaluated, as the TP 1 exemption of harmonic transformers resulted in expansion of the 

market for K-4 units (harmonic tolerating transformers), which are often less efficient than the 

baseline transformers targeted by the State Building Code. Harmonic tolerating transformers are 

classified as “K-type” transformers, with the number after the letter K representing the severity of 

the harmonics the transformer can tolerate. Minnesota has taken steps to close this apparent 

loophole by requiring documentation in the building permit application demonstrating that a 

harmonic transformer is legitimately needed before it can be substituted for a transformer 

meeting the minimum efficiency standard. For more information, contact the Minnesota 

Department of Public Service, tel: 651-297-2313. 

3.8.7 New Jersey Efficiency Standard 

On March 8, 2005, acting New Jersey Governor Richard J. Codey signed an act 

concerning energy efficiency, mandating a NEMA TP 1 efficiency standard for all low-voltage, 

dry-type transformers sold in the State after March 8, 2007 or installed in the State after March 8, 

2008.22 The New Jersey Act Concerning Energy Efficiency will impact new and remodeled 

buildings, and will be enforced by periodic inspections of distribution transformer distributors 

and retailers. For more information, contact the New Jersey State Legislature at tel: 609-292-

4840. 

3.8.8 New York Efficiency Standard 

New York State adopted the TP 1 standard for commercial buildings.23 The Energy 

Conservation Construction Code of New York State formally mandated the TP 1 standard 

starting July 2002. The Code covers dry-type, low- and medium-voltage, single- and threephase; and liquid-immersed, single- and three-phase transformers. The Code is focused on new 

buildings and renovations, and compliance is enforced by State building inspectors. For more 

information, contact the New York Department of State, tel: 518-474-0050. 

3.8.9 Oregon Efficiency Standard 

The Oregon Structural Specialty Code took affect January 2005.24 This standard requires 

the NEMA TP 1 efficiency level for liquid-immersed and dry-type, low- and medium-voltage, 

single- and three-phase, distribution transformers installed for non-process loads in nonresidential buildings. For more information, contact the Oregon Department of Energy, tel: 

503-378-4040. 

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3.8.10 Rhode Island Efficiency Standard 

The Rhode Island Energy and Consumer Savings Act of 2005 mandates that all lowvoltage, dry-type distribution transformers sold or installed in the State of Rhode Island after 

January 1, 2007 meet NEMA TP 1 efficiency levels.25 This standard will be enforced by periodic 

inspections of distribution transformer distributors and retailers. For more information, contact 

the Rhode Island State Government at tel: 401-222-2000. 

3.8.11 Washington Efficiency Standard 

The State of Washington adopted an Act Relating to Energy Efficiency on May 6, 2005.26 

According to the law, all low-voltage, dry-type transformers sold or installed in the State must 

meet NEMA TP 1 efficiency levels beginning January 1, 2007. For more information, contact 

the Washington Legislative Hotline at tel: 1-800-562-6000. 

3.8.12 Wisconsin Efficiency Standard 

The State of Wisconsin Master Specifications adopted by the Wisconsin Department of 

Administration require that TP 1-compliant transformers be installed in all new tate facility 

construction and remodeling projects starting March 2000.27 This means TP 1 is not part of the 

state building code, but in fact applies to State facility construction and renovation projects. The 

specifications cover dry-type, low-voltage, single- and three-phase distribution transformers. At 

present, there are no activities underway that might extend the TP 1 standard to commercial 

buildings. For more information, contact the Wisconsin Department of Administration, tel: 

608-266-3685. 

3.8.13 Burlington, Vermont Efficiency Standard 

The 2005 Vermont Guidelines for Energy-Efficient Commercial Construction endorse 

NEMA’s TP 1 minimum efficiency standards.28 The City of Burlington's Energy Code went a 

step further and adopted TP 1 as a mandatory standard within its jurisdiction. The mandatory 

standard took effect in Burlington in January 2001, and the voluntary, statewide standard took 

effect in January 2002. The distribution transformers covered by the Burlington Energy Code 

and the Vermont Guidelines include dry-type, low- and medium-voltage, single- and three-phase. 

The inclusion of liquid-immersed transformers will be considered in the next round of code 

revisions. To encourage compliance and adoption, Burlington Electric is offering technical 

support, code training activities, and financial incentives to increase vendor and contractor 

awareness of the standard. For more information, contact the Vermont Department of Public 

Services, tel: 802-828-2811. 

3.8.14 Proposed State Efficiency Standards 

The states of Colorado, Maine, New Hampshire, Pennsylvania, and Vermont were 

recently or are still considering NEMA TP 1 efficiency standards for dry-type distribution 

transformers. 

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Colorado House Bill 05-1162, proposing a State standard of NEMA TP 1 for all lowvoltage, dry-type distribution transformers, was vetoed by Governor Bill Owens on April 28, 

2005.29 For more information, contact the Colorado House of Representative at tel: 1-800-811-

7647. 

Maine bill number LD 1435, proposing NEMA TP 1 standard for low-voltage and 

medium-voltage, dry-type transformers, died between houses on June 9, 2005.30 For more 

information, contact the Maine Office of Legislative Information at tel: 207-287-1692. 

New Hampshire SB 105-FN, introduced during the 2003 session, proposed NEMA TP 1 

levels for all low-voltage, dry-type distribution transformers.31 For more information, contact the 

New Hampshire Senate at tel: 603-271-2111. 

The State of Pennsylvania considered two bills, HB 2035 and SB 901, during their 

2003–2004 session concerning the adoption of NEMA TP 1 efficiency levels for all low-voltage, 

dry-type distribution transformers.32 For more information, contact the Pennsylvania General 

Assembly at tel: 717-787-2342. 

The State of Vermont is considering NEMA TP 1 standards for both low-voltage and 

medium-voltage, dry-type distribution transformers.33 The 2005 Vermont Guidelines for Energy 

Efficient Commercial Construction issues the proposed standards and was open for public 

comment through the end of July 2005. For more information, contact the Vermont Department 

of Public Service at tel: 1-800-642-3281. 

3.8.15 U.S. National Energy Bill - EPACT 2005 

The U.S. Congress enacted legislation requiring that low-voltage, dry-type transformers 

manufactured on or after, or imported into the U.S. on or after January 1, 2007, meet the NEMA 

TP 1 minimum efficiency standards: 

LOW VOLTAGE DRY-TYPE DISTRIBUTION TRANSFORMERS.—The efficiency of 

a low voltage dry-type distribution transformer manufactured on or after January 1, 2007, 

shall be the Class I Efficiency Levels for distribution transformers specified in table 4–2 

of the ‘Guide for Determining Energy Efficiency for Distribution Transformers’ 

published by the National Electrical Manufacturers Association (NEMA TP–1–2002). 

This standard level preempts the Department’s rulemaking analysis for low-voltage, drytype transformers (which had been part of the Department’s scope at the ANOPR public meeting 

in 2004). For more information on EPACT 2005, contact the Committee on Energy and 

Commerce, the U.S. House of Representatives, tel: 202-225-2927. 

3.8.16 Canadian Efficiency Standard 

The Canadian Government regulates efficiency of dry-type transformers.34 The regulation 

mandates compliance with the efficiency values listed in Canadian Standards Association (CSA) 

standard C802.2-00 starting on January 1, 2005 (Canada Gazette, April 10, 2003). 

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Liquid-immersed distribution transformers are addressed by a voluntary program, which has been 

drafted to allow supervisory oversight by the Canadian Government. 

In June 1997, the Office of Energy Efficiency at Natural Resources Canada (NRCan) 

announced that it intended to develop regulated minimum performance standards for 

transformers. These proposed regulations would affect interprovincial trade and transformers 

imported into Canada. Consultative workshops followed this announcement, which included 

discussion around harmonizing with NEMA's TP 1 levels. 

The CSA drafted and published CSA C802.2-Minimum Efficiency Values for Dry-Type 

Transformers, in which efficiency is measured according to a per unit loading of 35 percent for 

low-voltage and 50 percent for medium-voltage. The efficiency levels are the same as NEMA 

TP 1 except the CSA added an additional significant digit (zero) in the hundredths place. For 

this standard, the reference winding temperature is 75°C, as in NEMA's TP 1. 

As a result of the process of working with the CSA and a range of stakeholders, NRCan 

chose to separate the regulatory processes for liquid-immersed and dry-type transformers. 

Liquid-Immersed Transformer Standards 

The process of regulating minimum efficiency levels for liquid-immersed transformers 

was stopped after several years of development. The CSA harmonized the Canadian standard 

with NEMA’s voluntary standards, selecting the range of regulated products, the efficiency 

levels, and the transformer test procedures based on NEMA TP 1 and TP 2. However, a market 

analysis revealed that the liquid-immersed transformer market in Canada is dominated by the 

nine provincially operated electric utilities, each of which had already incorporated energy 

efficiency into their transformer procurement practices. It was found that more than 95 percent 

of the liquid-immersed distribution transformers sold in Canada already met the NEMA TP-1 

efficiency levels. 

Thus, the Canadian Government decided not to continue with the development of a 

regulation for liquid-immersed distribution transformers. Instead, the major Canadian utilities 

and manufacturers, through the Canadian Electricity Association (CEA), signed a voluntary 

agreement with NRCan. Under the terms of this agreement, the electric utilities agreed to adopt 

the minimum efficiency levels based on the CSA C802.1-00 standard when purchasing liquidfilled transformers, and to report the performance of virtually all liquid-immersed transformers 

installed in Canada to NRCan. NRCan will then determine if the efficiency of the market is 

degrading and, if so, take appropriate action. 

Dry-Type Transformer Standards 

NRCan pre-published an amendment to Canada’s regulations, that includes dry-type 

transformers, on December 14, 2002. This amendment was published on April 23, 2003. This 

minimum energy performance standard for dry-type transformers became effective on January 1, 

2005. The regulations include a broad range of kVA ratings, more than are included in NEMA 

TP 1 or the Department of Energy’s proposed rulemaking on distribution transformers. 

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A consultation forum was organized in June 2005 by NRCan with the objective of 

analyzing some issues pertaining to the Canadian regulation. As a result of this focus, some 

changes were made to the regulation and modifications proposed to the CSA C802.2 standard. 

Meetings were convened in July and September 2005 involving of NRCan, the CSA C802.2 

subcommittee, transformer manufacturers and other stakeholders to address these issues. At 

these meetings, some of the key changes to the dry-type transformer regulation agreed were: 

•	 Elimination of the tap range exemption, so there is no exemption in the Canadian 

regulations based on a tap range. 

•	 Addition of an exemption for furnace transformers. This exemption was necessary due to 

the removal of the tap range exemption. Furnace transformers were defined as "a 

three-phase step-down transformer that is designed to be connected to an electric-arc 

furnace, and has a delta-wye switching arrangement plus high-voltage taps for changing 

the level of the low voltage supplied to the furnace." 

•	 Exclusion of drive transformers with two or more output windings or a low-voltage line 

current larger than 1500 Amperes. This means that drive transformers designed with one 

output winding and a low-voltage line current less than or equal to 1500 Amperes are 

subject to regulation. 

•	 Clarification that transformers with resin-cast coils (not encapsulated cores) are covered 

by the regulation. The exemptions for sealed transformers and non-ventilated 

transformers do not apply to resin-cast coil transformers. 

•	 Elimination of the minimum low-voltage values, and addition of a maximum low-voltage 

line current of 4000 Amperes. 

In addition, the following change was made to the CSA dry-type performance standard, and this 

change may be incorporated in the Energy Efficiency Regulations in a future amendment: 

•	 Adoption of two BIL groupings for medium-voltage dry-type transformers, consistent 

with the BIL groupings in NEMA TP 1-2002. 

At the September 2005 meeting, an amendment to the definition of a dry-type transformer was 

also agreed as follows: 

Dry-type transformer means a transformer, including a transformer that is incorporated 

into any other product, in which the core and coils are in a gaseous or dry compound 

insulating medium and that

 (a) is either single-phase with a capacity from 15 to 833 kVA or three-phase with a 

capacity from 15 to 7500 kVA, and

 (b) has a nominal frequency of 60 Hz, 

but does not include transformers having a rated low voltage line current larger than 

4000 Amperes. 

3-27 

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Table 3.8.1 presents the efficiency requirement for dry-type transformers. 

Table 3.8.2 Canadian Efficiency Regulations for Dry-Type Transformers 

Dry-Type, Single-Phase Dry-Type, Three-Phase 

kVA Minimum 1.2 kV Class, BIL 20-150 kVA Minimum 1.2 kV BIL 20-150 

Low­ % eff. at kV, % eff. at Low- Class, % kV, % eff. 

Voltage, 

(V) 

0.35 of 

nameplate 

0.50 of 

nameplate 

Voltage, 

(V) 

eff. at 0.35 

nameplate 

at 0.50 of 

nameplate 

15 120 / 240 97.70 97.60 15 208Y/120 97.00 96.80 

25 120 / 240 98.00 97.90 30 208Y/120 97.50 97.30 

37.5 120 / 240 98.20 98.10 45 208Y/120 97.70 97.60 

50 120 / 240 98.30 98.20 75 208Y/120 98.00 97.90 

75 120 / 240 98.50 98.40 112 .5 208Y/120 98.20 98.10 

100 120 / 240 98.60 98.50 150 208Y/120 98.30 98.20 

167 120 / 240 98.70 98.70 225 208Y/120 98.50 98.40 

250 120 / 240 98.80 98.80 300 208Y/120 98.60 98.50 

333 120 / 240 98.90 98.90 500 208Y/120 98.70 98.70 

500 480 - 99.00 750 208Y/120 98.80 98.80 

667 480 - 99.00 1000 208Y/120 98.90 98.90 

833 480 - 99.10 1500 480Y/277 - 99.00 

- - - - 2000 480Y/277 - 99.00 

- - - - 2500 480Y/277 - 99.10 

- - - - 3000 600Y/347 - 99.10 

- - - - 3750 4160Y/2400 - 99.20 

- - - - 5000 4160Y/2400 - 99.20 

- - - - 7500 4160Y/2400 - 99.20 

3.8.17 Mexican Efficiency Standard 

Mexico is one of the regional leaders in promoting and regulating energy efficiency. In 

recent years, other countries, such as Argentina, Ecuador, and Peru, have requested assistance 

from Mexico in the development and implementation of national efficiency programs. 

Mexico began regulating distribution transformers more than two decades ago when it 

enacted NOM-J116 in 1977.35 However, in 1989, a presidential decree modified the Normas 

Oficiales Mexicanas (Official Mexican Standards) from mandatory to voluntary standards; 

NOM-J116 became NMX-J116, a Norma Mexicana (Mexican Standard). In 1992, the Ley 

Federal sobre Metrología y Normalización (Federal Law on Metering and Standards) reestablished the mandatory character of NOMs. In addition, this law empowered the Secretaría de 

Energía (the Mexican equivalent to the US Department of Energy) to formulate and enact 

mandatory standards for electrical equipment. 

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A new mandatory standard was enacted in 1994, NOM-001-SEMP-1994, to regulate the 

energy efficiency and safety of electrical equipment including distribution transformers. In 1997, 

Mexico’s government proposed a revision to NOM-001, and also proposed a new standard, 

NOM-002-SEDE-1997.36 NOM-002 was published in the Diario Oficial de la Federación 

(Official Registry) for public revision and enacted two years later in October 1999. 

This standard, which regulates liquid-immersed units, is the only compulsory efficiency 

regulation of distribution transformers in Mexico. Dry-type distribution transformers are used in 

Mexico, but neither government nor industry has moved to regulate them. 

Table 3.8.3 Characteristics of Regulated Distribution Transformers in Mexico 

Characteristic Specification 

Power Supply Single-phase 

Three-phase 

Nominal Capacity 5 to 167 kVA (single-phase) 

15 to 500 kVA (three-phase) 

Insulation Class Up to 15 kV 

Up to 25 kV 

Up to 34.5 kV 

Installation Application Pad; Pole; Substation; Submersible 

NOM-002 provides two sets of tables with the specified minimum efficiency levels and 

the unit losses in watts, both tested at 100 percent of nameplate load. Tables 3.8.3 and 3.8.4 

below show the efficiency requirements under NOM-002 for large manufacturers and importers 

of distribution transformers in Mexico. Tables 3.8.5 and 3.8.6 show the less stringent, 

transitional standard for small manufacturers with cumulative annual production under 9 kVA. 

The second set of tables refers to a temporary standard, established for eighteen months to 

ease the transition of small manufacturers to the new standard. In May 2001, with the transition 

period ending, officials from the Mexican Government’s Energy Secretariat met with small 

manufacturers. These officials found that small manufacturers have not had enough time to bring 

their production up to the standards in NOM-002. Because these manufacturers represent an 

important source of employment, the Mexican Government decided to extend the transitional 

period for small manufacturers, without specifying the duration of this extension.37 

While there is only one mandatory standard for distribution transformers, there are 

several Voluntary Mexican Standards. At this point, there are no plans to revise or propose 

additional standards for distribution transformers. 

3-29 

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Table 3.8.4 Minimum Efficiency Levels for Transformers in Mexico 

Type Capacity kVA 

Insulation Class 

Up to 15 kV (%) Up to 25 kV (%) Up to 34.5 kV (%) 

5 97.90 97.80 97.70 

10 98.25 98.15 98.05 

Liquid-Immersed, 

Single-Phase 

15 98.40 98.3 98.2 

25 98.55 98.45 98.35 

37.5 98.65 98.55 98.45 

50 98.75 98.65 98.55 

75 98.90 98.80 98.70 

100 98.95 98.85 98.75 

167 99.00 98.90 98.8 

15 97.95 97.85 97.75 

30 98.25 98.15 98.05 

Liquid-Immersed, 

Three-Phase 

45 98.35 98.25 98.15 

75 98.50 98.40 98.30 

112.5 98.60 98.50 98.40 

150 98.70 98.60 98.5 

225 98.75 98.65 98.55 

300 98.80 98.70 98.60 

500 98.90 98.80 98.7 

Note: These efficiency levels are applicable at 100 percent of nameplate load. 

3-30 

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Table 3.8.5 Maximum Allowed Losses for Transformers in Mexico 

Type Capacity 

kVA 

Insulation Class 

Up to 15 kV (Watts) Up to 25 kV (Watts) Up to 34.5 kV (Watts) 

Core Winding Core Winding Core Winding 

5 30 77 38 74 63 55 

10 47 131 57 131 83 116 

LiquidImmersed, 

SinglePhase 

15 62 182 75 184 115 160 

25 86 282 100 294 145 274 

37.5 114 399 130 422 185 405 

50 138 495 160 524 210 526 

75 186 648 215 696 270 718 

100 235 826 265 898 320 946 

167 365 1322 415 1443 425 1603 

15 88 226 110 220 135 210 

30 137 397 165 400 210 387 

LiquidImmersed, 

Three-Phase 

45 180 575 215 587 265 583 

75 255 887 305 915 365 932 

112.5 350 1247 405 1308 450 1379 

150 450 1526 500 1630 525 1759 

225 750 2094 820 2260 900 2410 

300 910 2734 1000 2951 1100 3160 

500 1330 4231 1475 4598 1540 5046 

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Table 3.8.6 Transitional Standards for Small Manufacturers in Mexico 

Type Capacity kVA 

Insulation Class 

Up to 15 kV (%) Up to 25 kV (%) Up to 34.5 kV (%) 

5 97.50 97.40 97.30 

10 97.75 97.70 97.60 

Liquid-Immersed, 

Single-Phase 

15 97.95 97.90 97.80 

25 98.15 98.10 98.00 

37.5 98.35 98.25 98.15 

50 98.50 98.40 98.25 

75 98.60 98.50 98.40 

100 98.70 98.55 98.50 

167 98.80 98.60 98.55 

15 97.50 97.40 97.30 

30 97.80 97.70 97.60 

Liquid-Immersed, 

Three-Phase 

45 98.00 97.90 97.80 

75 98.15 98.05 97.95 

112.5 98.25 98.15 98.05 

150 98.35 98.25 98.15 

225 98.45 98.35 98.20 

300 98.50 98.45 98.25 

500 98.55 98.50 98.35 

Note: These efficiency levels are applicable to manufacturers with less than 9 kVA annual production, and should be 

achieved at 100 percent of nameplate load. 

3-32 

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Table 3.8.7 Transitional Maximum Losses for Small Manufacturers in Mexico 

Type Capacity 

kVA 

Insulation Class 

Up to 15 kV (Watts) Up to 25 kV (Watts) Up to 34.5 kV (Watts) 

Core Winding Core Winding Core Winding 

5 36 92 45 88 74 65 

10 61 169 71 164 103 143 

LiquidImmersed, 

SinglePhase 

15 80 261 93 229 141 196 

25 110 361 123 361 176 334 

37.5 139 490 157 511 221 486 

50 166 595 190 623 254 637 

75 238 827 270 872 333 887 

100 292 1025 335 1136 385 1138 

167 439 1589 530 1841 515 1942 

15 108 277 133 267 156 260 

30 173 502 206 500 260 478 

LiquidImmersed, 

Thre e-Phase 

45 218 700 259 706 316 696 

75 316 1098 374 1118 442 1128 

112 .5 439 1565 501 1619 551 1686 

150 573 1944 627 2045 650 2177 

225 934 2608 1005 2770 1121 3003 

300 1141 3428 1195 3528 1380 3964 

500 1760 5597 1848 5766 2055 6333 

3.9 TECHNOLOGY ASSESSMENT 

A transformer is a device constructed with two primary components: a magnetically 

permeable core, and a conductor of a low-resistance material wound around that core. A 

distribution transformer's primary function is to change alternating current from one voltage 

(primary) to a different voltage (secondary). It accomplishes this through an alternating magnetic 

field or "flux" created by the primary winding in the core, which induces the desired voltage in 

the secondary winding. The change in voltage is determined by the "turns ratio," or relative 

number of times the primary and secondary windings are wound around the core. If there are 

twice as many secondary turns as primary turns, the transformer is a step-up transformer, with a 

secondary voltage that would be double the primary voltage. Conversely, if the primary has 

twice as many turns as the secondary, the transformer is called a step-down transformer, with the 

secondary voltage half as much as the primary voltage. Distribution transformers are always 

step-down transformers. 

Transformer losses are generally small, in the vicinity of a few percent or less of the total 

3-33 

 EE-RM/STD-00-550 COMMENT 196
power handled by the transformer. There are two main kinds of losses in transformers: no-load 

(core) losses and load (winding) losses. Higher transformer efficiencies are achieved by reducing 

the losses associated with these two assemblies: the core and the windings. 

3.9.1 Distribution Transformer Types 

In general, there are two primary types of distribution transformer: liquid-immersed and 

dry-type. Liquid-immersed transformers typically use oil as both a coolant (removing heat from 

the core and coil assembly) and a dielectric medium (preventing electrical arcing across the 

windings). Liquid-immersed transformers are typically used only outdoors because of concerns 

over oil spills or fire if the oil temperature reaches the flash-point level. In recent decades, new 

insulating liquid insulators (e.g., silicone fluid) have been developed which have a higher flashpoint temperature than mineral oil, and transformers with these liquids can be used for indoor 

applications. However, high initial costs for these low-flammable, liquid-immersed 

transformers, relative to the cost of dry-type units, prevents widespread market adoption. 

Dry-type transformers are air-cooled, fire-resistant devices that do not use oil or other 

liquid insulating/cooling media. Because air is the basic medium used for insulating and cooling 

and it is inferior to oil in these functions, all dry-type transformers are larger than liquidimmersed units for the same voltage and/or kVA capacity. As a result, when operating at the 

same flux and current densities, the core and coil assembly is larger and hence incurs higher 

losses. Due to the physics of their construction (including the ability of these units to transfer 

heat), dry-type units have higher losses than liquid-immersed units. However, dry-type 

transformers are an important part of the transformer market because they can offer safety, 

environmental, and application advantages. 

3.9.2 Transformer Efficiency Levels 

There are two main types of losses in transformers: no-load (core) losses and load 

(winding) losses. Core losses are virtually constant, occurring continuously in the core material 

to keep the transformer energized and ready to provide power at the secondary terminals. Core 

losses are present even if the load on the transformer is zero. Winding losses occur in the 

primary and secondary windings around the core, and increase as the square of the load applied 

to the transformer. Winding losses result primarily from the electrical resistance of the winding 

material. 

Figure 3.9.1 depicts the change in core and coil losses with transformer loading on a 75 

kVA dry-type transformer, built with copper windings and an 80 degree temperature rise. This 

illustration clearly shows the exponential growth of the winding losses, in relation to the square 

of the load applied to the transformer. 

3-34 

 EE-RM/STD-00-550 COMMENT 196
Figure 3.9.1 Transformer Losses Vary with Load (75 kVA Dry-Type) 

The equation used to calculate the percent efficiency of a transformer at any loading point 

is given as follows (IEEE, C57.12.00): 

Eq. 3.2 

where: 

P

EEload = percent efficiency at a given per unit load, 


load = per unit load,


kVA = kVA rating of transformer,


NL = no load loss (Watts),


LL = load loss (Watts), and


T = temperature correction factor.


As equation 3.2 shows, the efficiency of a transformer is not a static value, but rather will 

vary depending on the per unit load (Pload) applied to the transformer. Using the losses plotted in 

Figure 3.9.1, the Department used equation 3.2 to calculate the efficiency of this 75 kVA drytype transformer at each loading point from 0 to 100 percent of nameplate load. The results are 

shown in Figure 3.9.2, which clearly indicates that the efficiency of a transformer is not static, 

but rather varies depending on the load applied. The apex, or highest point on the efficiency 

curve, occurs at the loading point where core losses are equal to winding losses. 

3-35 

 EE-RM/STD-00-550 COMMENT 196
Figure 3.9.2 Transformer Efficiency Varies with Load 

Consequently, any discussion of transformer efficiency must include an assumed loading 

point. The loading points used in the Department’s analysis of distribution transformers are 

discussed in the energy use and end-use load characterization section of this TSD (Chapter 6). 

3.9.3 Transformer Losses 

This section discusses methods to reduce transformer losses that have been developed 

over the nearly 120 years of technology evolution, starting in 1885 with William Stanley. The 

physical principles of distribution transformer operation are discussed in detail in Chapter 2 of 

1 the Determination Analysis of Energy Conservation Standards for Distribution Transformers. 

This section summarizes some of the main technological methods for reducing transformer 

losses.38 

Core losses occur in the core material of the distribution transformer, and are present 

whenever the transformer is energized—i.e., available to provide or providing load. Core losses 

are chiefly made up of two components: hysteresis and eddy current losses. Hysteresis losses are 

caused by the magnetic lag or reluctance of the core molecules to reorient themselves with the 60 

Hz alternating magnetic field applied by the primary winding. Eddy current losses are actual 

currents induced in the core by the magnetic field, in the same manner that the field induces 

current in the secondary winding. However, these currents cannot leave the core, and simply 

circulate within each lamination, eventually becoming heat. In both instances, hysteresis and 

eddy current losses create heat in the core material. 

Measures to reduce core losses include utilizing thinner cold-rolled oriented laminated 

steel (e.g., M2 or M3) or amorphous material (e.g., Metglas®). However, these measures 

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increase the manufacturing cost. In the case of amorphous material, due to a lower maximum 

core flux density, larger cores must be built, which increases the winding losses. 

Winding losses occur in both the primary and secondary windings when a transformer is 

under load. These losses, the result of electrical resistance in both windings, vary with the square 

of the load applied to the transformer. As loading increases, winding losses increase and are 

typically much more significant than core losses at levels higher than 50 percent of the nameplate 

loading point. 

Methods of reducing winding losses tend to cause an increase in no-load losses. One 

method is to increase the cross-sectional area of the conductor (decreasing current density in the 

winding material), but that means the core has to be made larger to accommodate the larger 

volume of the conductor, increasing core losses. Transposition of a multi-strand conductor can 

also help reduce winding losses. 

Table 3.9.1 was prepared by ORNL.1 This table summarizes the methods of making a 

transformer more efficient by reducing the number of watts lost in the core (no-load) and 

winding (load). However, as previously discussed, measures taken to reduce losses in one area 

typically increase losses in another. This table presents those inter-relational issues, as well as 

the overall impacts on transformer manufacturing costs. 

Table 3.9.1 Options and Impacts of Increasing Transformer Efficiency 

No-load 

losses 

Load 

losses 

Cost 

impact 

To decrease no-load losses 

Use lower -loss co re ma terials Lower No change* Higher 

De creas e flux de nsity by: 

 (a) Increasing core cross-sectional area (CSA) 

 (b) Decreasing volts per turn 

Lower 

Lower 

Higher 

Higher 

Higher 

Higher 

Decrease flux path length by decreasing conductor CSA Lower Higher Lower 

To decrease load losses 

Use lower-loss conductor material No change Lower Higher 

Decrease current density by increasing conductor CSA Higher Lower Higher 

De creas e curr ent pa th length b y: 

 (a) Decreasing core CSA 

 (b) Increasing volts per turn 

Higher 

Higher 

Lower 

Lower 

Lower 

Lower 

*Amorphous-core materials would result in higher load losses. 

The methods shown in Table 3.9.1 for making a transformer more efficient are discussed 

in the screening analysis (Chapter 4) and the engineering analysis (Chapter 5). The Department’s 

analysis of the relationship between cost and efficiency for distribution transformers is presented 

in Chapter 5. 

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REFERENCES


1. ORNL, 1996. Determination Analysis of Energy Conservation Standards for Distribution 

Transformers, P.R. Barnes, J.W. Van Dyke, B.W. McConnell, S. Das, Oak Ridge National 

Laboratory, Oak Ridge, Tennessee. ORNL-6847. See website: 

http://www.eere.energy.gov/buildings/appliance_standards/commercial/dist_transformers.html 

2. ORNL, 1995. The Feasibility of Replacing or Upgrading Utility Distribution Transformers 

During Routine Maintenance, P.R. Barnes, J.W. Van Dyke, B.W. McConnell, S.M. Cohn, S.L. 

Purucker, Oak Ridge National Laboratory, Oak Ridge, Tennessee, ORNL-6804/R1. See website: 

http://www.eere.energy.gov/buildings/appliance_standards/commercial/dist_transformers.html 

3. IEEE, 2001. IEEE PC57.12.33/D8 Draft Guide for Distribution Transformer Loss Evaluation, 

prepared by the Working Group for the Guide for Distribution Transformer Loss Evaluation of 

the Distribution Sub-committee of the IEEE Transformers Committee, October 2001. 

4. NEMA, 1996. NEMA Standards Publication No. TP 1: Guide for Determining Energy 

Efficiency for Distribution Transformers, National Electrical Manufacturers Association, 

Rosslyn, VA.; NEMA, 2002. NEMA Standards Publication No. TP 1: Guide for Determining 

Energy Efficiency for Distribution Transformers, National Electrical Manufacturers Association, 

Rosslyn, VA. 

5. Efficiency Vermont, Energy Star Three-Phase, Low-Voltage Transformer Incentive 

Application, <http://www.efficiencyvermont.com/Docs/Transformer.pdf>, viewed July 2005. 

6. Dagher, 2003. Fouad Dagher, National Grid, Westborough, Massachusetts, personal 

communication, February 2003; National Grid, Design 2000 Plus Transformers Worksheet, 

<http://www.nationalgridus.com/narragansett/non_html/energy_eff_d2_dry_trans_pif.pdf>, 

viewed July 2005. Energy Advantage New Hampshire Transformers Worksheet, 

<http://www.nationalgridus.com/granitestate/non_html/energyeff_newconst_transformer.pdf>, 

viewed July 2005. 

7. NHSaves, <nhsaves.com>, viewed July 2005. Public Service of New Hampshire, New 

Equipment and Construction Program Worksheet, 

<http://www.psnh.com/SharePDFs/NewEquipTransformerApplication.pdf>, viewed July 2005. 

Unitil Energy Systems, Inc., New Equipment and Construction Program Worksheet, 

<http://services.unitil.com/content/pdf/NCTransformer.pdf>, viewed July 2005. 

8. Northeast Utilities, Energy Efficiency Services for Custom Services and New Construction 

and Major Renovation, personal communication, July 2002. 

9. Seattle City Light, Energy Smart Services, 

<http://www.cityofseattle.net/light/conserve/business/cv5_fi.htm>, viewed July 2005. 

10. Tacoma Power, Transformer Rebates application, 

<http://www.ci.tacoma.wa.us/power/business/Rebate%20Application_Effective_05_10_2005.pd 

f>, viewed July 2005. 

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11. Two Rivers Water and Light, Energy Star Transformer Incentive, 

<http://www.trwaterandlight.com/business_customers/participationrequest.asp?CategoryNumber 

=1&SubcategoryNumber=3>, viewed July 2005. 

12. Haller, 2003. Roy Haller, United Illuminating, New Haven, Connecticut, personal 

communication, February 2003. 

13. Hoffman, 2003. Gregory Hoffman, Oconomowoc Utilities, Oconomowoc, Wisconsin, 

personal communication, February 2003; Voigtlender, 2003. Chris Voigtlender, Waupun 

Utilities, Waupun, Wisconsin, personal communication, February, 2003 

14. Gruen, 2003. William Gruen, Xcel Energy, Minneapolis, Minnesota, personal 

communication, February 2003; Lidbeck, 2003. Kim Lidbeck, Xcel Energy, Minneapolis, 

Minnesota, personal communication, January 2003 

15. Arizona State Legislature, An Act Relating to Appliance and Equipment Energy Efficiency 

Standards, <http://www.azleg.state.az.us/legtext/47leg/1r/laws/0226.htm>, viewed July 2005. 

16. Martin, 2003. Michael Martin, California Energy Commission, Sacramento, California, 

personal communication, February 2003; Holland, 2003. James Holland, California Energy 

Commission, Sacramento, California, personal communication, February 2003 

17. State of Connecticut, Substitute Senate Bill No. 145,

<http://www.cga.ct.gov/2004/act/Pa/2004PA-00085-R00SB-00145-PA.htm>, viewed July 2005. 

18. Maryland State Government. Maryland Energy Efficiency Standards. 

<http://www.energy.state.md.us/eesa/regulations.pdf>, viewed July 2005. 

19. Weitz, 2002. David Weitz, Massachusetts Board of Building Regulations and Standards, 

Boston, Massachusetts, personal communication, September 2002 

20. Massachusetts State Government, An Act Establishing an Minimum Energy Efficiency 

Standard for Certain Products, <http://www.mass.gov/legis/bills/senate/st01/st01821.htm>, 

viewed December 2005. 

21. Nelson, 2002. Bruce Nelson, Minnesota Department of Public Service, St. Paul, Minnesota, 

personal communication, September 2002 

22. New Jersey State Government, An Act Concerning Energy Efficiency, 

<http://www.njleg.state.nj.us/2004/Bills/PL05/42_.HTM>, viewed July 2005. 

23. Addario, 2002. John Addario, New York Department of State, Albany, New York, personal 

communication, September 2002; Andrews, 2002. Ray Andrews, New York Department of 

State, Albany, New York, personal communication, September 2002 

24. Stephens, 2002, Charles Stephens, Oregon State Department of Energy, Salem, Oregon, 

personal communication, September 2002. Oregon Department of Energy, Oregon Structural 

Specialty Code (OSSC), <http://egov.oregon.gov/ENERGY/CONS/Codes/cdpub.shtml#Forms>, 

viewed July 2005. 

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25. State of Rhode Island General Assembly, Energy and Consumer Savings Act of 2005, 

<http://www.rilin.state.ri.us/Billtext/BillText05/HouseText05/H5307B.pdf>, viewed July 2005. 

26. Washington State Legislature, An Act Relating to Energy Efficiency, 

<http://www.leg.wa.gov/pub/billinfo/2005-06/Pdf/Bills/Session%20Law%202005/1062-S.SL.pd 

f>, viewed July 2005. 

27. Cibulka, 2002. Richard Cibulka, Wisconsin Department of Administration, Madison, 

Wisconsin, personal communication, September, 2002 

28. Lloyd, 2002. Randall Lloyd, Vermont Dept. of Public Services, Montpelier, Vermont, 

personal communication, September, 2002; Doe, 2002. Loren Doe, Burlington Electric, 

Burlington, Vermont, personal communication, September, 2002. 2005 Vermont Guidelines for 

Energy-Efficient Commercial Construction, <http://www2.iccsafe.org/vermont/>, viewed July 

2005. 

29. Colorado General Assembly, House Bill 05-1162, 

<http://www.leg.state.co.us/Clics2005a/csl.nsf/fsbillcont3/3CB82DB74CD64D8387256F4E0066 

8B61?Open&file=1162_enr.pdf>, viewed July 2005. 

30. Maine State Legislature, Documents for LD 1435, 

<http://www.mainelegislature.org/legis/bills/LD.asp?LD=1435>, viewed July 2005. 

31. State of New Hampshire, SB 205-FN,

<http://www.gencourt.state.nh.us/legislation/2004/SB0105.html>, viewed July 2005. 

32. Pennsylvania State Legislature, HB 2035, 

<http://www2.legis.state.pa.us/WU01/LI/BI/BT/2003/0/HB2035P4640.pdf>, viewed July 2005. 

33. 2005 Vermont Guidelines for Energy-Efficient Commercial Construction, 

<http://www2.iccsafe.org/vermont/>, viewed July 2005. 

34. Delves, Katherine, P.E., Natural Resources Canada, Office of Energy Efficiency, Ottawa, 

Ontario, Canada, personal communication, February 5, 2003. 

35. Gomez, 2001. Jose Antonio Gomez, P.E., Asociacion de Normalizacion y Certificacion 

(ANCE, Association of Standards and Certification). Mexico City, Mexico. personal 

communication, June 17, 2001.; Lara, 2001. Ing. Rene Perez Lara, Dirección General de Gas LP 

y de Instalaciones Eléctricas, Secretaría de Energía. Mexico City, Mexico. Personal 

communication, May, 2001. (Gas and Electric Installations Division, Department of Energy). 

36. Manifestación de Impacto Regulatorio, Proyecto de Norma Oficial Mexicana NOM-002-

SEDE-1997. Secretaría de Energía, Mexico City, Mexico, 1997 (Regulatory Impact Analysis, 

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City, Mexico. 

37. ANFATE, 2001. Asociación Nacional de Fabricantes de Transformadores Eléctricos 

(ANFATE, National Association of Transformer Manufacturers), Mexico City, Mexico. 

Personal communication, June 2001. 3-40 

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38. Energy Efficient Transformers, Barry W. Kennedy, McGraw-Hill Publishing, New York, 

NY. Control of Transformer Losses in Canada, D.A. Wiegand, IEEE Journal, 1994. 

Determination Analysis of Energy Conservation Standards for Distribution Transformers, P.R. 

Barnes, J.W. Van Dyke, B.W. McConnell, S. Das, Oak Ridge National Laboratory, Oak Ridge, 

Tennessee. ORNL-6847. See website: 

http://www.eere.energy.gov/buildings/appliance_standards/commercial/dist_transformers.html 

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