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.
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.
