3-i

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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2

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

3.5 MANUFACTURERS OF DISTRIBUTION TRANSFORMERS . . . . . . . . . . . . . . . . . 3-5

3.5.1 Small Business Impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6

3.5.2 Distribution and Sales Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6

3.5.3 Import Duties on Core Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8

3.6 TOTAL OWNING COST EVALUATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8

3.7 VOLUNTARY PROGRAMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10

3.7.1 National Electrical Manufacturers Association TP 1 Standard . . . . . . . . . . . . 3-10

3.7.2 Energy Star Transformers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-12

3.7.3 Consortium for Energy Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13

3.7.4 Federal Energy Management Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13

3.7.5 Efficiency Vermont . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13

3.7.6 Idaho Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14

3.7.7 National Grid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14

3.7.8 NHSaves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14

3.7.9 Northeast Utilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-15

3.7.10 Seattle City Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-15

3.7.11 Tacoma Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-16

3.7.12 Two Rivers Water and Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-16

3.7.13 United Illuminating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-16

3.7.14 Wisconsin Public Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-17

3.7.15 Xcel Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-17

3.8 REGULATORY PROGRAMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-17

3.8.1 Arizona Efficiency Standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-18

3.8.2 California Efficiency Standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-18

3.8.3 Connecticut Efficiency Standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-18

3.8.4 Maryland Efficiency Standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-18

3.8.5 Massachusetts Efficiency Standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-18

3.8.6 Minnesota Procurement Efficiency Standard . . . . . . . . . . . . . . . . . . . . . . . . . . 3-20

3.8.7 New Jersey Efficiency Standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-20

3.8.8 New York Efficiency Standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-20

3.8.9 Oregon Efficiency Standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-20

3.8.10 Rhode Island Efficiency Standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-20

3.8.11 Washington Efficiency Standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-21

3.8.12 Wisconsin Efficiency Standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-21

3.8.13 Burlington, Vermont Efficiency Standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-21

3.8.14 Proposed State Efficiency Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-21

3.8.15 U.S. National Energy Bill - EPACT 2005 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-22

3.8.16 Canadian Efficiency Standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-22
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3.8.17 Mexican Efficiency Standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-25

3.9 TECHNOLOGY ASSESSMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-30

3.9.1 Distribution Transformer Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-31

3.9.2 Transformer Efficiency Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-31

3.9.3 Transformer Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-33

LIST OF TABLES

Table 3.3.1 Distribution Transformer Product Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2

Table 3.4.1 National Distribution Transformer Shipment Estimates for 2001 . . . . . . . . . . . 3-4

Table 3.7.1 NEMA Efficiency Levels for Liquid-Immersed Distribution Transformers . . 3-11

Table 3.7.2 NEMA Efficiency Levels for Dry-Type Distribution Transformers . . . . . . . . 3-12

Table 3.7.3 Efficiency Vermont Rebate Amounts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13

Table 3.7.4 National Grid Design 2000 Rebate Amounts . . . . . . . . . . . . . . . . . . . . . . . . . 3-14

Table 3.7.5 NHSaves’ New Equipment and Construction Program Rebate Amounts . . . . 3-15

Table 3.7.6 Northeast Utilities Energy Conscious Construction Rebate Amounts . . . . . . . 3-15

Table 3.7.7 Tacoma Power Transformer Rebate Amounts . . . . . . . . . . . . . . . . . . . . . . . . . 3-16

Table 3.7.8 United Illuminating Transformer Rebate Amounts . . . . . . . . . . . . . . . . . . . . . 3-17

Table 3.8.1 Comparison of Massachusetts State Energy Efficiency Standards for MV DryType Distribution Transformers to DOE NOPR TSLs . . . . . . . . . . . . . . . . . . 3-19

Table 3.8.2 Canadian Efficiency Regulations for Dry-Type Transformers . . . . . . . . . . . . 3-25

Table 3.8.3 Characteristics of Regulated Distribution Transformers in Mexico . . . . . . . . 3-26

Table 3.8.4 Minimum Efficiency Levels for Transformers in Mexico . . . . . . . . . . . . . . . . 3-27

Table 3.8.5 Maximum Allowed Losses for Transformers in Mexico . . . . . . . . . . . . . . . . . 3-28

Table 3.8.6 Transitional Standards for Small Manufacturers in Mexico . . . . . . . . . . . . . . 3-29

Table 3.8.7 Transitional Maximum Losses for Small Manufacturers in Mexico . . . . . . . . 3-30

Table 3.9.1 Options and Impacts of Increasing Transformer Efficiency . . . . . . . . . . . . . . 3-34

LIST OF FIGURES

Figure 3.4.1 Liquid-Immersed Distribution Transformer Shipment Estimate, 2001 . . . . . . . 3-3

Figure 3.4.2 MV Dry-Type Distribution Transformer Shipment Estimate, 2001 . . . . . . . . . 3-4

Figure 3.5.1 Market Delivery Channels for Distribution Transformers . . . . . . . . . . . . . . . . . 3-7

Figure 3.9.1 Transformer Losses Vary with Load (75 kVA Dry-Type) . . . . . . . . . . . . . . . . 3-32

Figure 3.9.2 Transformer Efficiency Varies with Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-33
3-1

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 Energy Policy Act (EPACT) of 2005 established the definition of a distribution

transformer 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.

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.
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3.3 PRODUCT CLASSES

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

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

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

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 Phase BIL Rating kVA Range

PC1 Liquid-Immersed Medium Single - 10-833 kVA

PC2 Liquid-Immersed Medium Three - 15-2500 kVA

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

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

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

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

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

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

* Note: PC3 and PC4 were the product classes for low-voltage, dry-type transformers, which were removed from this

rulemaking when EPACT 2005 became law. For consistency with prior Notices and to maintain schedule, the

Department did not renumber the liquid-immersed and medium-voltage, dry-type product 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
3-3

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

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. 

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).

SinglePhase

ThreePhase

Units Shipped

SinglePhase ThreePhase

MVA Shipped

Figure 3.4.1 Liquid-Immersed Distribution Transformer Shipment Estimate, 2001
3-4

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-immersed, medium-voltage, single-phase 977,388 36,633 698.8

Liquid-immersed, medium-voltage, three-phase 79,367 42,887 540.4

Dry-type, medium-voltage, single-phase, 20-45 kV BIL 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 BIL 121 22 0.6

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

Dry-type, medium-voltage, single-phase, >96 kV BIL 20 4 0.1

Dry-type, medium-voltage, three-phase, >96 kV BIL 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

SinglePhase

ThreePhase

Units Shipped

SinglePhase

ThreePhase

MVA Shipped

Figure 3.4.2 MV Dry-Type Distribution Transformer Shipment Estimate, 2001
a

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

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

the ORNL contact database from the Determination Analysis,1

 and participants in DOE’s Distribution Transformers

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

3-5

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.

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
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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

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.
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Used Transformers or 

Repair Shops

Distribution

Transformer 

Manufacturers

Dry-type

• Ventilated

• Cast

Liquid-filled

• Oil

• Silicone

• R-Temp Manufacturers’ 

Representative

Stocking 

Distributor Electrical 

Contractor

Industrial

and 

Commercial

Users

Electric 

(Large User or Custom Order) Utilities

End 

User

Agents for End User 

(A&E or Contractor)

OEMs

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. 

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
3-8

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

replacement.

3.5.3 Import Duties on Core Steel

Import duties are applied to electrical core steels imported as raw material from Japan and

Italy. This duty is levied at the port of entry, and amounts to a 31 percent anti-dumping duty. 

Generally, domestic suppliers are able to offer equivalent specification core steels without the

duty. However, one particular type of steel manufactured by Nippon Steel Corporation in Japan

is patented, and is not available to U.S. transformer manufacturers without the 31 percent duty. 

This electrical steel, known as ZDMH, is a high-permeability, mechanically-scribed electrical

steel, with lower losses than conventional core steels. The mechanical scribing process reduces

the losses, making it the most efficient conventional core steel for wound-core construction. In

the Department’s analysis, this material is used in the liquid-immersed superclass.

Mexico and Canada do not apply this 31 percent import duty to electrical steel, enabling

manufacturers in these neighboring countries to produce transformers with ZDMH at a lower

cost (the steel is not taxed if incorporated into a finished product). Thus, manufacturers in these

countries have a competitive cost advantage of 31 percent on core steel, the most expensive part

of a distribution transformer. The Department considered a dual-price point for this steel in the

ANOPR analysis— a U.S. manufacturer’s price and a Mexican/Canadian manufacturer’s price. 

For the NOPR analysis, the Department modeled a ZDMH core manufactured in Mexico or

Canada and then subsequently imported into the U.S. for transformer assembly (thereby avoiding

the tariff). The Department modeled the ZDMH core in this way for the NOPR because it

received information indicating that this would be the most likely scenario for ZDMH core

manufacturing. The MIA chapter discusses the effect of this scenario on U.S. transformer

manufacturer employment.

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.
3-9

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

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.
3-10

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 is taking effect on January 1, 2007, many of

these programs will cease to exist in 2007. However, at this time, these are the active voluntary

programs working to accelerate the transformation of the market toward more energy-efficient

designs.

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.
3-11

Table 3.7.1 NEMA Efficiency Levels for Liquid-Immersed Distribution Transformers

Liquid-Immersed, Single-Phase Liquid-Immersed, Three-Phase

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

Notes: Temperature: load-loss 85oC, no-load loss 20oC

Efficiency levels at 50 percent of unit nameplate load
3-12

Table 3.7.2 NEMA Efficiency Levels for Dry-Type Distribution Transformers

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

kVA

Min Efficiency (%)

kVA

Min Efficiency (%)

LowVoltage Medium-Voltage LowVoltageMedium-Voltage

<60 kV BIL >60 kV BIL < 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

Notes: Temperature: 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.
3-13

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-Type, Low-Voltage, Three-Phase

kVA Maximum incentive per unit kVA Maximum incentive per unit

15 $250 112.5 $500

30 $275 150 $700

45 $400 225 and higher $1200

75 $450 - -
3-14

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-Type, Low-Voltage, Single-Phase

kVA Maximum incentive per unit kVA Maximum incentive per unit

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
3-15

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-Type, Low-Voltage, Three-Phase

kVA Maximum incentive per unit kVA Maximum incentive per unit

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-Type, Low-Voltage, Three-Phase

kVA Maximum incentive per unit kVA Maximum incentive per unit

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. 
3-16

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 are offered until January 1, 2007, at which point the

NEMA TP 1 standard will be mandated by An Act Relating to Energy Efficiency. The maximum

rebate amounts 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-Type, Low-Voltage, Three-Phase

kVA Maximum incentive per unit kVA Maximum incentive per unit

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.
3-17

Table 3.7.8 United Illuminating Transformer Rebate Amounts

Dry-Type, Low-Voltage

kVA Maximum incentive per unit kVA Maximum incentive per unit

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 will be

the national standard, and will preempt any State efficiency standards when it takes effect on

January 1, 2007. Until that date, however, existing State standards are still in effect. This

section identifies those State-level regulatory programs of which the Department is aware,

including: Arizona, California, Connecticut, Maryland, Massachusetts, Minnesota, New Jersey,

New York, Oregon, Rhode Island, Washington, Wisconsin, and the city of Burlington, Vermont. 

Standards also have been 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.
3-18

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
3-19

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

Dry-Type Distribution Transformers to DOE NOPR TSLs

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

NEMA TP 1-

2002

Massachusetts

Standard

DOE TSL

Corresponding

to Mass.

Standard

NEMA TP 1-

2002

Massachusetts 

Standard

DOE TSL

Corresponding

to Mass.

Standard

#60 kV BIL #60 kV BIL 20-45 kV BIL >60 kV BIL >60 kV BIL 46-95 kV BIL

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

112.5 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
3-20

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.
3-21

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. 
3-22

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). 
3-23

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.
3-24

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.
3-25

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

LowVoltage,

(V)

1.2 kV Class,

% eff. at 

0.35 of

nameplate

BIL 20-150

kV, % eff. at

0.50 of

nameplate

kVA Minimum

LowVoltage,

(V)

1.2 kV

Class, %

eff. at 0.35

nameplate

BIL 20-150

kV, % eff.

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. 
3-26

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.
3-27

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 (%)

Liquid-Immersed,

Single-Phase

5 97.90 97.80 97.70

10 98.25 98.15 98.05

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

Liquid-Immersed,

Three-Phase

15 97.95 97.85 97.75

30 98.25 98.15 98.05

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.
3-28

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

LiquidImmersed,

SinglePhase

5 30 77 38 74 63 55

10 47 131 57 131 83 116

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

LiquidImmersed,

Three-Phase

15 88 226 110 220 135 210

30 137 397 165 400 210 387

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
3-29

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 (%)

Liquid-Immersed,

Single-Phase

5 97.50 97.40 97.30

10 97.75 97.70 97.60

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

Liquid-Immersed,

Three-Phase

15 97.50 97.40 97.30

30 97.80 97.70 97.60

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. 
3-30

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

LiquidImmersed,

SinglePhase

5 36 92 45 88 74 65

10 61 169 71 164 103 143

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

LiquidImmersed,

Three-Phase

15 108 277 133 267 156 260

30 173 502 206 500 260 478

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
3-31

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.
3-32

0

500

1000

1500

2000

2500

3000

0 10 20 30 40 50 60 70 80 90 100

Transformer loading (%)

Transformer losses (watts)

Winding 

losses

Core losses

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

( )

load

load 2

load load

100 P kVA 1000

EE =

P kVA 1000+NL+LL P T 

  × × ×  

  × × × ×  

where:

EEload = percent efficiency at a given per unit load, 

Pload = 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.
3-33

84%

86%

88%

90%

92%

94%

96%

98%

100%

0 10 20 30 40 50 60 70 80 90 100

Transformer Loading (%)

Transformer Efficiency

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

the Determination Analysis of Energy Conservation Standards for Distribution Transformers.

1

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
3-34

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 core materials Lower No change* Higher

Decrease flux density 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

Decrease current path length by: 

 (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.
3-35

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.

REFERENCES
3-36

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.
3-37

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,

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