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

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.

Standards: Final Rule, Federal Register, 71 FR 58190 (Oct. 12, 2007)
Technical Support Document
Technical Support Document Appendices
Docket No. EERE-2006-STD-0099 contains all notices, public comments, public meeting transcripts, and supporting documents.

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

Amended Standard

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.

Final Rule: Standards, Federal Register, 78 FR 23335 (April 18, 2013)
Technical Support Document
Government Regulatory Impact Model (GRIM)
Docket No. EERE-2010-BT-STD-0048 and EERE-2010-BT-STD-0051

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:

OIRA Compare Document

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.

Final Rule: Test Procedures, Federal Register, 71 FR 24972 (April 27, 2006)
Docket No. EERE-2006-STD-0090 contains all notices, public comments, public meeting transcripts, and supporting documents.

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

Energy Conservation Standards for Certain Consumer Products and Commercial and Industrial Equipment: Correction, Federal Register, 70 FR 61698 (Oct. 25, 2005)
Energy Conservation Standards for Certain Consumer Products and Commercial and Industrial Equipment: Final Rule, Federal Register, 70 FR 60407 (Oct. 18, 2005)
Docket No. EERE-2005-0002 contains all notices, public comments, public meeting transcripts, and supporting documents.

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