# OAK RIDGE NATIONAL LABORATORY

10C." •• " 

# _A_,.•• 

# :*-

IIANAGED AND OPERATED BY LOCKHEED IIARTIN ENERGY RESEARCH CORPORAnOH FORTHEUtfTED STATES DEPARTMENT OfENERGY 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

### EnergyDivision

DETERMINATION ANALYSIS OFENERGY CONSERVATION STANDARDS FORDISTRIBUTIONTRANSFORMERS



### P.R. Barnes 

### J. W. Van Dyke 

### B. W. McConnell S.Das

Published: July 1996



### Prepared for the Office ofBuildingTechnology 

# u.s. DEPARTMENT OFENERGY

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·6847EXECUTIVESUMMARY 

# DT<NL

..**~g47** 

# :Ju L.y) j

### ~

# q",

Subtitle C, Sect. 124 ofthe Energy Policy Act of 1992, Pub. 

### L. 102-486, Oct. 24, 1992, contains an amendment to Sect. 346 ofthe Energy Policy and Conservation Act (42 U.S.C. Sect. 6317) requiring that the U.S. Department ofEnergy (DOE) assess the feasibility ofenergy conservation standards for distribution transformers. The objective ofthis 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 perspective. Distribution transformers are used to deliver electric power as part ofthe electrical distribution system. Electrical energy is delivered to consumers by utility powertransmission 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 ofpowerover long distances. The high-transmission voltages require lower currents, which reduce line losses, conductormaterial, and costs. Once the electrical power has reached the distribution system, it is transformed to lowerprimary 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 ofelectrical power components from the generating sources to theultimate 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 ofconcerns about an oil spill orpossible fire hazard. Electric utilities own about 90% ofall liquid-immersedtransformers. 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 orplant voltage (typically 480Vac) 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 orbuilding 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 theUnited States (Barnes etal. 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 ofimproved materials and manufacturing methods. Following the energy price shocks ofthe 1970s, some utilities began to use purchasing formulae that factored the effect oftransformer 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 ofthe nonutility distribution transformers are purchased on the lowest first-cost basis without evaluating the cost ofthe energy consumed by the units. These "nonevaluated" transformers may have -50% more losses than utility transformers. The maximum efficiencies ofliquid-immersed distribution

xviiTable 1. Characteristics ofdistribution transformers typically used intheUnited 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 contributorto 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 ofthe lack ofeconomic 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 ofthe annual energy lost in the delivery ofelectricity (Barnes et al. 1995). Nonutility liquid and dry-type transformers, although fewer in number, are less efficient and are estimated to consume an additional 80billion kWh ofelectric energy on the customer side ofthe electric meter. New transformers purchased annually can be expected to consume -4.6billion 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 ofenergy 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

95.001950 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 RoutineMaintenance, ORNL·68041R I

. Marcin Marietta Energy Systems, Oak Ridge Nat!. Lab. Also, transfonner manufacturers' data.

xviiiwhich 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. Forexample, Canadarecently 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 ofall types that provide significantenergy savings compared with the typical units purchased in 1994. Ifenergy-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 pertransformer 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 ofmaterials and the use oflower-loss materials. For example, operating at a lower flux density by reducing volts pertum will reduce core losses but require more turns ofthe 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 transformerrequires the use oflow-loss materials (i.e., high-silicon steel or amorphous metal for the core and increased amounts ofcopper or aluminum for the windings) configured in an optimal manner. The materials selected andthe configuration define

. the cost ofthe transformer materials and the laborrequired to assemble the system (i.e., the

transformer cost). Dry-type transformer technology can provide transformers that offerlower 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 ofdry-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 ofthese advantages, but dry units will continue to be used in low-voltage, high-temperature-rise applications.

. 

### THE DISTRIBUTION TRANSFORMER MARKET
The total value ofproduct 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 ofthe past decade. The liquid-immersed utility transformer market is expected to grow at an overall growth rate ofnot 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 ofannual capacity sold, the liquid-immersed market (10 kVA-2.5 MVA) will increase from 64,631 MVA (1.14 million units)

xixin 1993 to 99,195 MVA (1.41 million units) by the ye
. 0

.Forthe 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 ofopen-wound and cast-resin, dry-type transformers compared with the total capacity sold 

### in 2030 

### will be 28% (47,361 MVA) and 12% (20,298 MVA) respectively

. The structure ofthe distribution transformer marketcurrently includes various market players and their interactions. Transformerpurchasing 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&Ipurchases ofdry-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 ofwinding 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. Average loss reductions per kilovolt-ampere ofcapacity for cases developed in this study would be between 0.9 and 2.4 W/kVA ofpurchased transformer capacity

.This translates into -8-21 kWh ofelectricity saved annually or 240-630kWh over 30 years (the average life ofa transformer) per kilovolt-ampere oftransformers purchased. It is estimated that in 1993 the total sales ofdistribution transformers were about 93,000MV A. By 2000, sales are projected to be
over 100,000MVA. Savings from conservation would continue to grow with sales ofnew transformers

.Table 2 indicates the initial rate ofprimary energy savings and the cumulative savings after 30 years. A national average powerplant 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 overtheiruseful lives. About 93% ofthese savings could be realized ifdistribution transformers below 10 kVA were excluded from an energy conservation policy. The details ofthe approach used are given in Appendix D.
IMPACTS ON MANUFACTURERS AND USERS Energy-efficient transformers will increase the cost ofproduction to transformer manufacturers because either more material ora better quality ofmaterial will be used. The effect
on manufacturers' revenues will depend on how much ofthe cost increases caused by conservation can be passed through to consumers. Ifless than the actual higherproduction 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 ofthe industry suggests that manufacturers ofdry-type transformers will be more affected than manufacturers ofliquid-im'mersed transformers because a greater number ofdry-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;gycons ervation** **are** expected to 

### b e**m~~ ·**  . .. . .
_ .. .-- ..... . . The energy efficiency

### tr**ansf 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% offull production capability; this available capacity may not be adequate in certain cases to meet any surge in demand for increased supply ofraw materials. There will be a shift in demand



### xx

### r

en Cl 

### « ::::l 

### a Table 2. Energy savings for a conservationcase based on an averageofthe threelowestTOe designs (quads ofprimary 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~

aA quad ofenergy equals 1quadrillion (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 conservationcase based on an average ofthe three lowest total-owning-cost designs. (See Subsect. 4.4.2.)

toward higher performance core materials

. Ifamorphous-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 ofconcern. Itis estimated thatthe capacity utilization level ofthe magnet wire industry would increase from the current level of 80-84% ifenergy efficiency improvements for distribution transformers were accomplished by the use ofcopper alone.


### CONCLUSIONS

A number ofenergy conservation options
·were analyzed. All ofthe conservation options considered for a national policy in this study are economicallyjustified 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 of4.2-13.7**quad~** over the 30-yearperiod from 2000

XXlto 2030, assuming transformer sales grow at a rate of-1 -2% er the period. Ifthe annual sales oftransformer 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 of3.6 to 7.1 quads for the conservation options considered in this study. About 93% ofthese savings could be realized ifdistribution transformer sizes below 10 kVA were excluded from an energy conservation policy. Improved efficiency in dry transformers accounts for the majority ofthese**~** __**-~ ...-------**  . 

## - - 

# -- REFERENCES
Barnes, P. 

### R., et al. 1995. The Feasibility of Replacing or Upgrading Utility Distribution Transformers During RoutineMaintenance, ORNL-68041R1, Martin MariettaEnergy Systems, Oak: Ridge Natl. Lab. Canadian Standards Association 1994. Maximum LossesforDistribution, Power, andDry-Type Transformers, C802-94, Canadian Standards Association, Toronto, Ontario, Canada.

xxii