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Distribution Transformers

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A distribution transformer provides the final voltage transformation in the electric power distribution system by reducing the high voltage of electric current from a power line to a lower voltage for use in a building. The Department of Energy (DOE) has regulated the energy efficiency level of low-voltage dry-type distribution transformers since 2007, and liquid-immersed and medium-voltage dry-type distribution transformers since 2010. A distribution transformer designed and constructed to be mounted on a utility pole is referred to as a pole-mount transformer. A distribution transformer designed and constructed to be located at ground level or underground, mounted on a concrete pad, and locked in a steel case is referred to as a pad-mount transformer.

Beginning in 2016, newly amended energy efficiency standards for distribution transformers will save up to $12.9 billion in total costs to consumers — ultimately saving families and businesses money while also reducing energy consumption. The new distribution transformer standards will also save 3.63 quadrillion British thermal units of energy for equipment sold over the 30-year period of 2016 to 2045.

The new amendments to the existing efficiency standards would further decrease electrical losses by about 8 percent for liquid-immersed transformers, 13 percent for medium-voltage dry-type transformers, and 18 percent for low-voltage dry-type transformers. In addition, about 264.7 million metric tons of carbon dioxide emissions will be avoided, equivalent to the annual greenhouse gas emissions of about 51.75 million automobiles.

The distribution transformers final rule was the DOE's first "negotiated rulemaking," conducted under the Federal Advisory Committee Act and the Negotiated Rulemaking Act, and is viewed as an alternative to traditional procedures for drafting proposed regulations.

The Standards and Test Procedures for this product are related to Rulemaking for Liquid-Immersed and Medium-Voltage Dry-type Distribution Transformers Energy Conservation Standard and Rulemaking for Low-Voltage Dry-Type Distribution Transformers Energy Conservation Standard.


Recent Updates | Standards | Test Procedures | Waiver, Exception, and Exemption Information | Statutory Authority | Historical Information | Contact Information


Recent Updates

DOE published a final rule regarding amended energy efficiency standards for liquid-immersed, medium-voltage dry-type, and low-voltage dry-type distribution transformers. 78 FR 23335 (April 18, 2013). For more information, please see the rulemaking webpages: liquid-immersed and medium-Voltage Dry-type and low-voltage dry-type.


Standards for Distribution Transformers

The following content summarizes the energy conservation standards for distribution transformers. The text is not an official reproduction of the Code of Federal Regulations and should not be used for legal research or citation.

Current Standard

Distribution transformers covered by this standard are defined in the Code of Federal Regulations, 10 CFR 431.192. The three types of distribution transformers covered by the standard: low-voltage dry-type, liquid-immersed, and medium-voltage, dry-type distribution transformers. The full standard can be found in the Code of Federal Regulations, 10 CFR 431.196. This information is also in the Electronic Code of Federal Regulations.

The efficiency of a low-voltage dry-type distribution transformer manufactured on or after January 1, 2007, shall be no less than that required for their kVA rating in the table below. Low-voltage dry-type distribution transformers with kVA ratings not appearing in the table shall have their minimum efficiency level determined by linear interpolation of the kVA and efficiency values immediately above and below that kVA rating.

Table 1. Energy Conservation Standards for Low-Voltage Dry-Type Distribution Transformers
Single phase Three phase
kVa Efficiency (%)1 kVa Efficiency (%)1
15 97.7 15 97.0
25 98.0 30 97.5
37.5 98.2 45 97.7
50 98.3 75 98.0
75 98.5 112.5 98.2
100 98.6 150 98.3
167 98.7 225 98.5
250 98.8 300 98.6
333 98.9 500 98.7


750 98.8


1000 98.9

1 Efficiencies are determined at the following reference conditions: (1) for no-load losses, at the temperature of 20°C, and (2) for load-losses, at the temperature of 75°C and 35 percent of nameplate load. (Source: Table 4–2 of National Electrical Manufacturers Association (NEMA) Standard TP–1–2002, "Guide for Determining Energy Efficiency for Distribution Transformers.")

The efficiency of a liquid-immersed distribution transformer manufactured on or after January 1, 2010, shall be no less than that required for their kVA rating in the table below. Liquid-immersed distribution transformers with kVA ratings not appearing in the table shall have their minimum efficiency level determined by linear interpolation of the kVA and efficiency values immediately above and below that kVA rating.

Table 2. Energy Conservation Standards for Liquid-Immersed Distribution Transformers
Single phase Three phase
kVa Efficiency (%) kVa Efficiency (%)
10 98.62 15 98.36
15 98.76 30 98.62
25 98.91 45 98.76
37.5 99.01 75 98.91
50 99.08 112.5 99.01
75 99.17 150 99.08
100 99.23 225 99.17
167 99.25 300 99.23
250 99.32 500 99.25
333 99.36 750 99.32
500 99.42 1000 99.36
667 99.46 1500 99.42
833 99.49 2000 99.46


2500 99.49

Note: All efficiency values are at 50 percent of nameplate-rated load, determined according to the DOE Test-Procedure. 10 CFR Part 431, Subpart K, Appendix A.

The efficiency of a medium-voltage dry-type distribution transformer manufactured on or after January 1, 2010, shall be no less than that required for their kVA and BIL rating in the table below. Medium-voltage dry-type distribution transformers with kVA ratings not appearing in the table shall have their minimum efficiency level determined by linear interpolation of the kVA and efficiency values immediately above and below that kVA rating.

Table 3: Energy Conservation Standards for Medium-Voltage Dry-Type Distribution Transformers
Single phase Three phase
BIL kVa 20–45 kV efficiency (%) 46–95 kV efficiency (%) 96 kV efficiency (%) BIL kVa 20–45 kV efficiency (%) 46–95 kV efficiency (%) 96 kV efficiency (%)
15 98.10 97.86
15 97.50 97.18
25 98.33 98.12
30 97.90 97.63
37.5 98.49 98.30
45 98.10 97.86
50 98.60 98.42
75 98.33 98.12
75 98.73 98.57 98.53 112.5 98.49 98.30
100 98.82 98.67 98.63 150 98.60 98.42
167 98.96 98.83 98.80 225 98.73 98.57 98.53
250 99.07 98.95 98.91 300 98.82 98.67 98.63
333 99.14 99.03 98.99 500 98.96 98.83 98.80
500 99.22 99.12 99.09 750 99.07 98.95 98.91
667 99.27 99.18 99.15 1000 99.14 99.03 98.99
833 99.31 99.23 99.20 1500 99.22 99.12 99.09




2500 99.31 99.23 99.20




2500 99.31 99.23 99.20

Note: BIL means basic impulse insulation level.
Note: All efficiency values are at 50 percent of nameplate rated load, determined according to the DOE Test Procedure. 10 CFR Part 431, Subpart K, Appendix A.

For further guidance or to submit questions related to the implementation of this standard, visit the Guidance and Frequently Asked Questions page.

Amended Standard

Distribution transformers covered by this standard are defined in the Code of Federal Regulations, 10 CFR 431.192. The three types of distribution transformers covered by the standard: low-voltage dry-type, liquid-immersed, and medium-voltage, dry-type distribution transformers. The full standard can be found in the Code of Federal Regulations, 10 CFR 431.196. This information is also in the Electronic Code of Federal Regulations.

The efficiency of a low-voltage dry-type distribution transformer manufactured on or after January 1, 2016, shall be no less than that required for their kVA rating in the table below. Low-voltage dry-type distribution transformers with kVA ratings not appearing in the table shall have their minimum efficiency level determined by linear interpolation of the kVA and efficiency values immediately above and below that kVA rating.

Table 4: Amended Energy Conservation Standards for Low-Voltage Dry-Type Distribution Transformers
Single phase Three phase
kVa Efficiency (%) kVa Efficiency (%)
15 97.70 15 97.89
25 98.00 30 98.23
37.5 98.20 45 98.40
50 98.30 75 98.60
75 98.50 112.5 98.74
100 98.6 150 98.83
167 98.70 225 98.94
250 98.80 300 99.02
333 98.90 500 99.14


750 99.23


1000 99.28

Note: All efficiency values are at 35 percent of nameplate-rated load, determined according to the DOE Test Method for Measuring the Energy Consumption of Distribution Transformers under Appendix A to Subpart K of 10 CFR part 431.

The efficiency of a liquid-immersed distribution transformer manufactured on or after January 1, 2016, shall be no less than that required for their kVA rating in the table below. Liquid-immersed distribution transformers with kVA ratings not appearing in the table shall have their minimum efficiency level determined by linear interpolation of the kVA and efficiency values immediately above and below that kVA rating.

Table 5: Amended Energy Conservation Standards for Liquid-Immersed Distribution Transformers
Single phase Three phase
kVa Efficiency (%) kVa Efficiency (%)
10 98.70 15 98.65
15 98.82 30 98.83
25 98.95 45 98.92
37.5 99.05 75 99.03
50 99.11 112.5 99.11
75 99.19 150 99.16
100 99.25 225 99.23
167 99.33 300 99.27
250 99.39 500 99.35
333 99.43 750 99.40
500 99.49 1000 99.43
667 99.52 1500 99.48
883 99.55 2000 99.51


2500 99.53

Note: All efficiency values are at 50 percent of nameplate-rated load, determined according to the DOE Test Method for Measuring the Energy Consumption of Distribution Transformers under Appendix A to Subpart K of 10 CFR part 431.

The efficiency of a medium- voltage dry-type distribution transformer manufactured on or after January 1, 2016, shall be no less than that required for their kVA and BIL rating in the table below. Medium-voltage dry-type distribution transformers with kVA ratings not appearing in the table shall have their minimum efficiency level determined by linear interpolation of the kVA and efficiency values immediately above and below that kVA rating.

Table 6: Amended Energy Conservation Standards for Medium-Voltage Dry-Type Distribution Transformers
Single phase Three phase
BIL* kVa 20–45 kV efficiency (%) 46–95 kV efficiency (%) 96 kV efficiency (%) BIL kVa 20–45 kV efficiency (%) 46–95 kV efficiency (%) 96 kV efficiency (%)
15 98.10 97.86 - 15 97.50 97.18 -
25 98.33 98.12 - 30 97.90 97.63 -
37.5 98.49 98.30 - 45 98.10 97.86 -
50 98.60 98.42 - 75 98.33 98.13 -
75 98.73 98.57 98.53 112.5 98.52 98.36 -
100 98.82 98.67 98.63 150 98.65 98.51 -
167 98.96 98.83 98.80 225 98.82 98.69 98.57
250 99.07 98.95 98.91 300 98.93 98.81 98.69
333 99.14 99.03 98.99 500 99.09 98.99 98.89
500 99.22 99.12 99.09 750 99.21 99.12 99.02
667 99.27 99.18 99.15 1000 99.28 99.20 99.11
833 99.31 99.23 99.20 1500 99.37 99.30 99.21




2000 99.43 99.36 99.28




2500 99.47 99.41 99.33

BIL means basic impulse insulation level

Note: All efficiency values are at 50 percent of nameplate rated load, determined according to the DOE Test Method for Measuring the Energy Consumption of Distribution Transformers under Appendix A to Subpart K of 10 CFR part 431.

After a regulatory action has been completed, Executive Order 12866 requires agencies to identify the substantive changes between the draft submitted to Office of Information and Regulatory Affairs (OIRA) for review and the action subsequently announced, and to identify those changes made at the suggestion or recommendation of OIRA. The document below provides more information:

Test Procedure for Distribution Transformers

Current Test Procedure

To determine compliance with DOE standards, manufacturers must follow the test procedures specified at 10 CFR 431.193 and Appendix A for distribution transformers manufactured or distributed in commerce. These are also in the Electronic Code of Federal Regulations.

For further guidance or to submit questions related to the implementation of this test procedure, visit the Guidance and Frequently Asked Questions page.

Waivers, Exceptions, and Exemptions

Waivers

Test procedure waivers have not been issued for distribution transformers. For more information, please see the table below.

For information about obtaining test procedure waivers, see 10 CFR section 431 subpart V.

Exceptions

DOE's Office of Hearings and Appeals has not authorized exception relief for distribution transformers.

For information about obtaining exception relief, see 10 CFR part 1003.

State Exemptions to Federal Preemption

DOE has not exempted any state from this energy conservation standard. States may petition DOE to exempt a state regulation from preemption by the Federal energy conservation standard. States may also petition DOE to withdraw such exemptions. For details, see 10 CFR 431 subpart V or subpart W.

Statutory Authority

The current energy conservation standards for distribution transformers are mandated by Part A–1, the "Certain Industrial Equipment" of Title III of the Energy Policy and Conservation Act (EPCA), as amended. (42 U.S.C. 6311–6317). This equipment is treated as covered equipment under Part A-1. (42 U.S.C. 6317(a)) In addition, the Energy Policy Act of 2005 (EPACT 2005) amended EPCA to set energy conservation standards for low-voltage dry-type distribution transformers. (42 U.S.C. 6295(y))

Historical Information

DOE published a final rule in October 2007 that established energy conservation standards for liquid-immersed and medium-voltage dry-type distribution transformers. 72 FR 58190 (Oct. 12, 2007). During the course of that rulemaking EPACT 2005 amended EPCA to set standards for low-voltage dry-type distribution transformers. (42 U.S.C. 6295(y)) Consequently, DOE removed these transformers from the scope of that rulemaking. 72 FR 58191 (Oct. 12, 2007). Prior to publishing the October 2007 energy conservation standard, DOE published a final rule test procedure for distribution transformers.71 FR 24972 (April 27, 2006).

Previous Standard

Helpful Links and Contact Information

Helpful Links

Find tips and guidance for making your home, workplace, or vehicle more energy efficient visit EnergySavers.gov.

Contact information

For more information related to the regulation of this product, please email:


distribution_transformers@ee.doe.gov