OAK RIDGE 

NATIONAL 

LABORATORY 

10C." •• " _A_,. •• :*-

IIANAGED AND OPERATED BY 

LOCKHEED IIARTIN ENERGY RESEARCH CORPORAnOH 

FOR THE UtfTED STATES 

DEPARTMENT Of ENERGY I 

ORI'l.-27 (3-96) 

,\P 

{' ORNL-6847 

Determination Analysis of 

Energy Conservation 

Standards for Distribution 

Transformers 

P. A. Barnes 

J. W. Van Dyke 

B. W. McConnell 

S. Das 
Energy Division 

DETERMINATION ANALYSIS OF ENERGY CONSERVATION 

STANDARDS FOR DISTRIBUTION TRANSFORMERS 

P.R. Barnes 

J. W. Van Dyke 

B. W. McConnell 

S.Das 

Published: July 1996 

Prepared for the 

Office of Building Technology 

u.s. DEPARTMENT OF ENERGY 

Budget Activity No. EC1401000 

Prepared by 

OAK RIDGE NATIONAL LABORATORY 

P.O. Box 2008 

Oak Ridge, TN 37831 

Managed by 

LOCKHEED MARTIN ENERGY RESEARCH CORPORATION 

for the 

U.S. DEPARTMENT OF ENERGY 

under contract DE-AC05-960R22464 

ORNL·6847 
EXECUTIVE SUMMARY 

DT<NL .. ~g47 

:Ju L.y) j ~ q", 

Subtitle C, Sect. 124 of the Energy Policy Act of 1992, Pub. L. 102-486, Oct. 24, 1992, 

contains an amendment to Sect. 346 of the Energy Policy and Conservation Act (42 U.S.C. 

Sect. 6317) requiring that the U.S. Department of Energy (DOE) assess the feasibility of energy 

conservation standards for distribution transformers. The objective of this study was to determine 

whether energy conservation standards for distribution transformers would have the potential for 

significant energy savings, be technically feasibl~, and be ~conomicall;y justified from a national 

perspecti ve. 

Distribution transformers are used to deliver electric power as part of the electrical 

distribution system. Electrical energy is delivered to consumers by utility power transmission and 

distribution systems. The transmission network delivers power at high voltages (69-765 kV) from 

power plants to local distribution systems. Transmission voltages are used to transmit high levels 

of power over long distances. The high-transmission voltages require lower currents, which 

reduce line losses, conductor material, and costs. Once the electrical power has reached the 

distribution system, it is transformed to lower primary distribution voltages (ranging from 4 to 

35 kV) that are more economical for the short distances within distribution systems. The primary 

distribution voltage is transformed by distribution transformers to lower secondary voltages 

(120-600 Vac) that are suitable for customer equipment. These transformers provide the fmal 

link in the chain of electrical power components from the generating sources to the ultimate 

power-consuming equipment. 

Distribution transformers are very reliable devices with no moving parts and average lives of 

-30 years. There are two basic types: liquid-immersed and dry-type. Liquid-immersed 

transformers typically use oil as a combination coolant and dielectric medium; they are normally 

used outdoors because of concerns about an oil spill or possible fire hazard. Electric utilities own 

about 90% of all liquid-immersed transformers. Dry-type transformers are air-cooled, 

fire-resistant, non-oil devices and thus do not need special oil-spill containment. Recent advances 

in liquid materials offset these traditional "advantages" for dry units. Many commercial and 

industrial (C&I) customers use secondary distribution dry-type transformers within buildings to 

transform the building or plant voltage (typically 480 Vac) to a lower secondary voltage 

(120-240 Vac). Large load center dry-type transformers are also used to transform the primary 

distribution voltage to the plant or building voltage. There are -40 million liquid-immersed 

distribution transformers owned by electric utilities and an additional 4 million non-utility-owned 

liquid-immersed units in the United States (Barnes et al. 1995). Transformer manufacturers 

estimate that -12 million dry-type distribution transformers are used by C&I customers in the 

United States. The definition for distribution transformers as considered in this study can be 

summarized as transformers that are continually energized; these fall within the voltage classes 

and capacities shown in Table 1. 

Utility-owned distribution transformer efficiencies steadily improved from the 1950s to the 

1970s with the introduction of improved materials and manufacturing methods. Following the 

energy price shocks of the 1970s, some utilities began to use purchasing formulae that factored 

the effect of transformer efficiency into the purchasing decision. Manufacturers responded by 

tailoring their products to the energy evaluation factors specified by customers, a practice that 

continues to this day. Thus, it is now possible to purchase a relatively high-cost, high-efficiency 

transformer or a unit with a lower first cost and lesser efficiency. Most of the nonutility 

distribution transformers are purchased on the lowest first-cost basis without evaluating the cost 

of the energy consumed by the units. These "nonevaluated" transformers may have -50% more 

losses than utility transformers. The maximum efficiencies of liquid-immersed distribution 

xvii 
Table 1. Characteristics of distribution transformers typically used in the United States 

Transformer 

type 

Liquid-immersed 

Liquid-immersed 

Dry-type 

Dry-type 

Dry-type" 

Phase 

3 

1 

3 

1 and 3 

Primary voltage 

(kV) 

35 and below 

35 and below 

35 and below 

35 and below 

35 and below 

Secondary voltage Capacities 

(V) (kVA) 

600 and below 10-833 

600 and below 15-2500 

600 and below 15-833 

600 and below 15-2500 

600 and below 0.25-<15 

"The smaller dry-type units are included for completeness, but they are a small contributor to the overall energy 

losses and are not likely to be included in an energy efficiency standard. The units below 9 kV A nonnally have primary 

voltages below 600 V. 

transfonners have improved over the past several decades, but nonevaluated dry-type units have 

decreased in efficiency because of the lack of economic incentives. Figure 1 shows efficiencies 

for 75-kVA, liquid and dry-type, three-phase transfonners. 

Distribution transformers used by utilities account for -61 billion kWh of the annual energy 

lost in the delivery of electricity (Barnes et al. 1995). Nonutility liquid and dry-type transformers, 

although fewer in number, are less efficient and are estimated to consume an additional 80 billion 

kWh of electric energy on the customer side of the electric meter. New transformers purchased 

annually can be expected to consume -4.6 billion kWh; thus, the potential for saving energy with 

more efficient transformers could be significant (i.e., -0.9 billion kWh with a 20% reduction in 

losses). 

This report demonstrates the potential for distribution transformers to achieve cost-effective 

national energy savings. A number of energy conservation options were analyzed, the results of 

~ >-

t.) 

z 

w 

(3 

u:: 

u. 

w 

99.50 

MAXIMUM UQUID 

99.00 EFFICIENCY 

98.50 

98.00 

97.50 

97.00 

96.50 

96.00 

95.50 

95.00 

1950 1955 1960 

ORNL-OWG 94-2162R 

~ ~ ~ \ DRY EFFICIENCY 

AT 15% LOAD 

1965 1970 1975 1980 1985 1990 1995 

YEAR 

Fig. 1. Distribution transformer efficiencies over the years for 75-kVA, three-pbase units. Sources: Barnes, 

P. R., el al. 1995. The Feasibility of Replacing or Upgrading Utility Distribution During Routine Maintenance, 

ORNL·68041R I. Marcin Marietta Energy Systems, Oak Ridge Nat!. Lab. Also, transfonner manufacturers' data. 

xviii 
which provide DOE with information for making a determination on proposing a national energy 

conservation policy for distribution transformers. Other countries are also considering energy 

conservation for distribution transformers. For example, Canada recently developed a national 

conservation policy based on maximum loss values for distribution, power, and dry-type 

transformers (Canadian Standards Association 1994). 

TECHNICAL FEASmILITY 

Without regard to cost, it is technically feasible to design and to build distribution 

transformers of all types that provide significant energy savings compared with the typical units 

purchased in 1994. If energy-saving designs are restricted to those that are economically feasible 

using national average energy costs, there is a potential for moderate savings per transformer 

from liquid-immersed units and for more significant savings per transformer from redesigned 

dry-type units. Because utilities routinely evaluate transformers for minimum total owning cost 

(TOC), the technical ability to provide low-loss liquid-immersed transformers is well established. 

In contrast, dry-type transformers are routinely sold on a first-cost basis and have significant 

potential for improved savings. 

The technology used to provide low-loss transformers is based upon changing the 

configuration and, hence, the relative amounts of materials and the use of lower-loss materials. 

For example, operating at a lower flux density by reducing volts per tum will reduce core losses 

but require more turns of the conductor and increase load losses. Similarly, lowering the 

conductor current density will reduce load losses but require more core material or a higher flux 

level, which produces higher no-load losses. Restrictions on weight and volume may reduce the 

selection further. A low-loss transformer requires the use of low-loss materials (i.e., high-silicon 

steel or amorphous metal for the core and increased amounts of copper or aluminum for the 

windings) configured in an optimal manner. The materials selected and the configuration define 

. the cost of the transformer materials and the labor required to assemble the system (i.e., the 

transformer cost). 

Dry-type transformer technology can provide transformers that offer lower losses at 

reasonable costs, but costs are higher for a given efficiency than for liquid-immersed 

transformers. Because air is the .basic cooling and insulating system for dry-type transformers, all 

dry-type transformers will be larger than liquid-immersed units for the same voltage and capacity 

(kilovoltJkilovolt-ampere) rating. When operating at the same flux and current density, more 

material for core and coil implies higher losses and higher costs. These trade-offs are inherent in 

the design of dry-type uni[s, but dry-type transformers have traditionally offered certain 

fire-resistant, environmental, and application advantages for industrial and commercial situations. 

Recent advances in liquid-filled units are reducing some of these advantages, but dry units will 

continue to be used in low-voltage, high-temperature-rise applications. . 

THE DISTRIBUTION TRANSFORMER MARKET 

The total value of product shipments in the distribution transformer market was estimated to 

be -$1.5 billion in 1992, coming from more than 230 companies having annual shipments of 

$100,000 or more. The outlook for the distribution transformer industry is not expected to be 

different from that of the past decade. The liquid-immersed utility transformer market is expected 

to grow at an overall growth rate of not more than 1 % annually. The nonutility, predominantly 

dry-type transformer market growth is estimated to be a little higher (2.5%) than the 

utility-dominant liquid-immersed market. It is estimated that in terms of annual capacity sold, the 

liquid-immersed market (10 kVA-2.5 MVA) will increase from 64,631 MVA (1.14 million units) 

xix 
in 1993 to 99,195 MVA (1.41 million units) by the ye . 0 . For the same years the dry-type 

transformer market (0.25 kVA-2.5 MVA) is forecast to grow from 28,336 MV A (0.779 million 

units) to 70,650 MVA (1.615 million units). The market shares of open-wound and cast-resin, 

dry-type transformers compared with the total capacity sold in 2030 will be 28% (47,361 MV A) 

and 12% (20,298 MVA) respectively. 

The structure of the distribution transformer market currently includes various market players 

and their interactions. Transformer purchasing decision makers play the most important role 

regarding energy efficiency. Electrical contractors or agents (who are not the users paying the 

future electric bills) are currently responsible for most C&I purchases of dry-type transformers. 

Utilities, on the other hand, establish their own loss evaluation criteria in buying their 

transformers. Several criteria such as first cost, TOC, band-of-equivalence, oversizing, and the 

choice of winding material are currently used when transformers are purchased. TOC is the only 

criteria producing minimum overall cost. 

POTENTIAL ENERGY SAVINGS 

Potential energy savings based on cost-effective energy conservation could be significant. 

A verage loss reductions per kilovolt-ampere of capacity for cases developed in this study would 

be between 0.9 and 2.4 W/kVA of purchased transformer capacity. This translates into 

-8-21 kWh of electricity saved annually or 240-630 kWh over 30 years (the average life of a 

transformer) per kilovolt-ampere of transformers purchased. It is estimated that in 1993 the total 

sales of distribution transformers were about 93,000 MV A. By 2000, sales are projected to be 

over 100,000 MV A. Savings from conservation would continue to grow with sales of new 

transformers. Table 2 indicates the initial rate of primary energy savings and the cumulative 

savings after 30 years. A national average power plant heat rate of 1O~000 BtulkWh has been 

assumed to estimate the primary energy savings shown in Table 2. Figure 2 projects the growth in 

cumulative savings for a cost-effective national energy conservation policy. Energy-efficient 

transformers would continue to provide savings over their useful lives. About 93% of these 

savings could be realized if distribution transformers below 10 kV A were excluded from an 

energy conservation policy. The details of the approach used are given in Appendix D. 

IMPACTS ON MANUFACTURERS AND USERS 

Energy-efficient transformers will increase the cost of production to transformer 

manufacturers because either more material or a better quality of material will be used. The effect 

on manufacturers' revenues will depend on how much of the cost increases caused by 

conservation can be passed through to consumers. If less than the actual higher production costs 

are passed through, profits will suffer; a pass-through above the increase in production costs will 

increase profits. A manufacturer's production costs will also be determined to some extent by the 

additional investments necessary for retooling to manufacture more-energy-efficient 

transformers. A cursory examination of the industry suggests that manufacturers of dry-type 

transformers will be more affected than manufacturers of liquid-im'mersed transformers because a 

greater number of dry-type transformers are not currently loss evaluated~~ the 

~ liquid-imme~~esItr<l~sformer market is currently more than 90% loss evaluated, the impacts of .-e~e;gyconservation are expected to be m~~ · . .. . . _.. .--..... . . 

The energy efficiency transf rln s also raises issues regarding the production capability of 

raw material suppliers. Most raw material suppliers are domestic and are estimated to be at 80% 

of full production capability; this available capacity may not be adequate in certain cases to meet 

any surge in demand for increased supply of raw materials. There will be a shift in demand 

xx 
r 

en 

Cl 

« 

::::l 

a 

Table 2. Energy savings for a conservation case based on an 

average of the three lowest TOe designs 

(quads of primary energyt 

Annual savings Cumulative savings 

Transformer rate in 2000 2000--2030 

Liquid-immersed 0.0046 2.4 21fr 

Dry-type 0.0108 6.5 73/.: 

Total 0.0154 8.9 /oo~ 

a A quad of energy equals 1 quadrillion (lOIS) Btu. TOe = total owning cost. 

ORNL-DWG 95-1609 

10 ~----------------------------~-------------------------------, 

8 - -- -- - - - --- -- - - -- - - - ------- --- - ---- - -.--- - --

6 - . - - - - -- - - - - - - - - - - - - - - - - - - . - - - - - - - - - - - - - - - - - - --

4 -----._-------- . . --------- - --- - - --------- - ----

2 - -- --- -- -- ----- - --- ----

o ~_4~~~=4_4_4_4_4_4_+_+_+_+_+_+_+_+_+_+_+~~~~~~~~~ 

2000 2003 2006 2009 2012 2015 2018 2021 2024 2027 2030 

YEAR 

Fig. 2. Cumulative primary energy savings from 2000 to 2030 for a conservation case based on an average 

of the three lowest total-owning-cost designs. (See Subsect. 4.4.2.) 

toward higher performance core materials. If amorphous-core technology is to be relied on to 

meet efficiency goals, the higher investments required and the patents associated with the 

technology are important issues of concern. It is estimated that the capacity utilization level of the 

magnet wire industry would increase from the current level of 80-84% if energy efficiency 

improvements for distribution transformers were accomplished by the use of copper alone. 

CONCLUSIONS 

A number of energy conservation options ·were analyzed. All of the conservation options 

considered for a national policy in this study are economically justified based on national average 

electricity costs. These options are also technically feasible, although some retooling may be 

required for the more energy-efficient, dry-type transformer designs. Based on a conservation 

approach similar to the options analyzed, a national energy policy for distribution transformers 

would have the potential for energy savings of 4.2-13.7 quad~ over the 30-year period from 2000 

XXl 
to 2030, assuming transformer sales grow at a rate of -1-2 % er the period. If the annual sales 

of transformer capacity does not grow at the assumed rate of 1-2% but remains constant at the 

19931evel (i.e., a zero growth case), then the savings will be reduced to a range of 3.6 to 

7.1 quads for the conservation options considered in this study. About 93% of these savings could 

be realized if distribution transformer sizes below 10 kVA were excluded from an energy 

conservation policy. Improved efficiency in dry transformers accounts for the majority of these ~ __ 

-~ ...------- . - - --

REFERENCES 

Barnes, P. R., et al. 1995. The Feasibility of Replacing or Upgrading Utility Distribution 

Transformers During Routine Maintenance, ORNL-68041R1, Martin Marietta Energy 

Systems, Oak: Ridge Natl. Lab. 

Canadian Standards Association 1994. Maximum Lossesfor Distribution, Power, and Dry-Type 

Transformers, C802-94, Canadian Standards Association, Toronto, Ontario, Canada. 

xxii