Mandated Changes in VTI’s UDS

Energy Efficient Transformers Required by Federal Regulation after January 1, 2007

With the passage of the 2005 Energy Policy Act (Public Law 109-58, signed on August 8, 2005) all low voltage, dry type distribution transformers manufactured after January 1, 2007 must meet the requirements of NEMA TP-1 standard for energy efficient transformers.


The U.S. Environmental Protection Agency introduced a voluntary program in 1992 to identify and promote more efficient products to reduce gas emissions. In order to reduce consumption of electricity in 1995 and 1996 the program was expanded in conjunction with the Department of Energy to include home heating and cooling products and all kinds of appliances at home and in industry, creating what has become known as Energy Star Products. In 1996 the National Electrical Manufactures Association (NEMA) developed a standard for "low voltage dry type energy efficient distribution" transformers (TP-1-1996). Over the past few years several states have recommended or required the use of the TP-1 transformers. In August of 2005 as part of the national Energy Policy Act, Public Law 109-58 was signed requiring that all dry type and distribution transformers manufactured after January 1, 2007 meet the revised NEMA standard TP-1-2002.

The low voltage dry type transformers are those having an input voltage of 600 volts or less, are air cooled and do not use oil as a coolant. These transformers must meet the Class 1 efficiency levels of NEMA standard TP-1-2002 with a 35% load and a temperature of 75° centigrade. Qualifying transformers must meet the efficiency requirements in the tables below.

Class 1 Efficiency Levels Required to Meet NEMA Standard TP-1-2002
Single Phase Transformers   Three Phase Transformers
KVA Rating Efficiency Level (%)   KVA Rating Efficiency Level (%)
Source: NEMA. 2002. Guide to Determining Energy Efficiency for Distribution Transformers. NEMA Standard TP-1-2002. Arlington, Va: National Electrical Manufacturers Association.
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

In general the NEMA TP-1 transformers will be available with the same options or modifications that have been available in the past, such as: copper windings, 150° C or 80° C temperature rise, special primary and secondary voltages and more.

While these transformers will be more efficient they will also be more expensive. Early pricing indicates that the increase in transformer cost will be in the range of 20 to 30 percent depending on the size and the material specified.

The cost benefit of using the energy efficient or Energy Star transformer will vary based on several factors. In a study done by the EPA the 24 hour average loading on distribution transformers is about 35% of full load and this is the bench mark that was used to establish the efficiency levels for the NEMA TP-1 standard. At this loading the Energy Star transformer losses are about 30% lower than the standard 150° rise transformer we have been using. However in applications where the average loading of the transformer is running at a higher percentage of full load, say 80%, the losses may be only around 15% lower. In the EPA study they estimated a 3 to 5 year payback when using the 35% average loading and a average electricity cost of $.075 per kilowatt hour. However, each application will be different and a cost benefit analysis will have to be made based on: the size of the transformer, percentage of full load and the efficiency at that load level and the cost per kilowatt hour.

Considering the life cycle cost, the payback period should only improve since over the 20 to 25 year life of a distribution transformer the cost of energy will certainly increase. However the outcome of the cost benefit analysis may be a moot point since the energy efficient transformer is all that will be available after January 1, 2007.

VTI · P.O. Box 9086 · 24 McMillan Way · Newark, DE 19714 · USA
Phone: (302) 738 0500 · Fax: (302) 738 6594

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