Visit this article to see the updated DOE standards as of 2024.
One important factor in the economic operation of electrical transformers is energy efficiency. In this article, we will explore DOE 2010, and 2016 standards, transformer efficiency ratings prior to DOE, and the future of efficiency regulation.
What is Transformer Energy Efficiency
A transformer’s energy efficiency is the ratio of the useful power output to the total power input. The closer the total input power is to the useful output power, the more efficient the transformer. Since transformers have no moving parts, only a small amount of energy is lost during the transformation in the form of heat. For context, modern gasoline engines have a thermal efficiency of about 20% to 40% when powering a car. Transformers operate at 98% plus efficiency.
(Learn about transformers cooling classes)
What are DOE Efficiency Standards for Transformers
DOE Efficiency Standards are a set of efficiency levels created by The Department of Energy (DOE) that transformer manufacturers are required to meet in order to sell their transformers.
History of DOE Efficiency Standards
On the whole, transformers are quite efficient, so transformer efficiency wasn’t always regulated. However, the Department of Energy (DOE) began regulating efficiency standards for low voltage dry-type transformers (600 volts and below) in 2007 and added regulations for larger dry-type and liquid-filled distribution transformers in 2010. Both dry-type and liquid-filled transformer efficiency regulations were updated again in the newly amended efficiency standards for distribution transformers on January 1st, 2016.
DOE Efficiency Standards for Transformers
Below are the minimum efficiency levels for distribution transformers under both DOE 2010 and 2016.
Liquid Filled
Efficiency values are at 50% of nameplate-rated load at a reference temperature of 55 deg. C
Low Voltage Dry-Type (600 volts and below)
Efficiency values are at 35% of nameplate-rated load at a reference temperature of 75 deg. C
There was no change in efficiency requirement for single-phase low voltage dry-types between 2007 and 2010.
Medium Voltage Dry-Type (601 volts and above)
Efficiency values are at 50% of nameplate-rated load at a reference temperature of 75 deg. C
Efficiency values are at 50% of nameplate-rated load at a reference temperature of 75 deg. C
What kinds of transformers are exempt from DOE efficiency standards?
While DOE standards apply to most distribution transformers there are several types of transformers that these standards do not apply to.
Below is a list of transformers that are exempt from DOE efficiency standards.
- Autotransformer
- Drive (isolation) transformer
- Grounding transformer
- Machine-tool (control) transformer
- Non-ventilated transformer
- Rectifier transformer
- Regulating transformer
- Sealed transformer
- Special-impedance transformer
- Testing transformer
- Transformer with tap range of 20 percent or more
- Uninterruptible power supply transformer
- Welding transformer
Transformer Efficiency Pre-2010 Regulation
Although there were not any governmental efficiency regulations for distribution transformers prior to 2010, transformers have always been extremely efficient machines. We reviewed our database of over (110) 3-phase padmount transformers built between 1990 and 2009 and found the following average efficiency levels for these kVA ranges. When compared to today’s efficiency standards, we see a modest average increase in efficiency of only 0.4%.
Manufacturers represented in this sample include ABB, GE, Howard Industries, WEG, ERMCO, Cooper EATON, Balteau Standard, Westinghouse, McGraw Edison, and others. Raw data can be provided upon request.
There seems to be little to no correlation between manufacturing date, and efficiency pre DOE 2010. For example, one transformer manufactured in the 1970s by McGraw Edison had a tested efficiency of 99.13 compared to a transformer manufactured by Cooper in 2006 of the same kVA, which had a tested efficiency of 99.14. An additional sample set was selected of transformers manufactured prior to 1990. Five 1000 kVA units manufactured between 1970 and 1989 were selected at random with an average efficiency of 99.04 (higher than the average of all 10 units selected between 1990 and 2009)
The highest efficiency unit tested was a 2000 kVA padmount manufactured by ABB in 2002, with a tested efficiency of 99.54, which actually exceeds the DOE 2016 requirement.
Manufacturing Costs Associated With DOE Regulation
While the efficiency gained by DOE regulation amounts to a fraction of a percent, the processes and materials required to achieve them in designs that did not already meet them resulted in dramatic increases in production costs between 2015 and 2016.
The primary reason for the increased cost is the use of higher-grade silicon steel, along with more conductor and transformer core material, to achieve the new regulation. Below is a table containing Maddox’s cost for new 3-phase liquid-filled transformers between 2015 and 2016. Numbers have been rounded to the nearest hundred.
In theory, the ideal transformer design should incorporate the highest efficiency possible to lower the cost of power consumption, however, the additional cost involved in such a design may not pay off for some time.
The future of DOE efficiency standards
The DOE is currently proposing new efficiency standards for distribution transformers that would take effect in 2027. The proposed standards would require transformers to be even more efficient (an average of around .16%), which would lead to further energy savings and emissions reductions.
Proposed DOE efficiency standards for 2027
Below are the proposed DOE efficiency standards that apply to any transformer manufactured on or after January 1, 2027.
Liquid Filled
Low Voltage Dry-Type
Medium Voltage Dry-Type
Problems Posed by the New Standards
Several leading transformer manufacturers have sharply criticized the proposed revisions to the DOE efficiency standards. According to these manufacturers, there are several potential problems that the new standards, as currently proposed, would present:
Worsening the Current Supply Chain Crisis
As reported by Bloomberg Law, and the Wall Street Journal, transformer manufacturers are already struggling to keep up with demand stemming from COVID lockdowns, and a global shift away from fossil fuels, which puts more strain on an aging grid. The resulting shortage has stalled housing developments, and commercial construction, and has greatly reduced manufacturers’ ability to respond quickly to natural disasters that wipe out transformers. Transformers that once took weeks to manufacture now take up to two years, or more.
The new DOE standards would also significantly increase the demand for the amorphous steel needed to construct transformer cores. One report estimates that if all amorphous steel was purchased domestically, it would necessitate a 500% increase in production—far beyond what the current number of steel production plants in the U.S. could manage. It is also estimated that the prices for these more efficient transformers would increase 50-125% or more over today's pricing levels. The weight will also increase by 25-50% which will add to transportation costs and cause installation issues. Both the surge in demand for amorphous steel and the surge in the cost of these units would cripple an already unhealthy supply chain and further extend transformer lead times.
Unrealistic Timetable for Implementation
If passed, the new DOE standards would go into effect in 2027, and would require significant expansions of plants, equipment, supply chains, and personnel. Expecting to accomplish such a significant overhaul of manufacturing processes and hiring the additional personnel in an already strained labor market in just three years is unrealistic.
Endangering the National Grid
The factors listed above, in combination with several other potential problems, would pose a major threat to U.S. electrical infrastructure. Without the materials, production, and personnel necessary to adapt to the new changes before they are implemented, the strain on the national grid will be catastrophic as utilities are already scrambling to get transformers. Many U.S. manufacturers anticipate that this would open the U.S.’s electrical grid to overseas transformer manufacturers instead of relying on domestic manufacturers.
Response from Congress
On Apr 3, 2023 sixty-five members of Congress signed a letter in opposition to these new efficiency standards to Jennifer Granholm, the secretary of the Department of Energy. This letter highlighted the long lead times utilities are already facing for distribution transformers and the additional burden that these new standards would place on transformer manufacturers.
On June 1, 2023, a bipartisan coalition of 47 senators also sent a letter to Secretary Granholm, requesting that the DOE halt the implementation of the new standards. The letter cites the short supply of amorphous steel, noting that the proposed DOE standards pose a serious threat to the U.S.’s electrical supply and national security.
Conclusion
If you have any other questions about transformer efficiency or how to size a transformer for your project, drop us a line! We’d love to help you get your next project powered on.
