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REA Bulletin 61-16

Guide for Economic Evaluation of Distribution Transformers

REA Bulletin 61-16 Guide for Economic Evaluation of Distribution Transformers

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Date Published:

Aug 1983


Evaluate power transformer losses to compare and evaluate different transformers based on economic considerations.


Since the oil crisis of 1974, there has been a steady escalation of fuel prices not just for oil, but also for gas, coal and nuclear fuels. The rising fuel prices have resulted in steadily escalating costs for electricity that have prompted the electrical industry to look for ways of reducing costs. One way is to reduce system losses as much as possible. A very effective method to reduce distribution system losses is to evaluate transformer losses and consider the costs in your purchase decisions. Lower loss transformers may cost more initially but the cumulative effect of the reduction of losses in many individual transformers can result in a significant reduction in system energy losses for which no revenue is received and, therefore, in the total cost of system kilowatt hours. Other significant savings can be in the reduction in magnitude of the system peak, with a resultant savings in the demand cost for kilowatt generating capacity.

Since there is now an acute awareness of the possible savings to be made by evaluating and buying the most economical transformers, the "Guide for Economic Evaluation of Distribution Transformers" (The Guide), has been issued to provide a quiCk and easy way to make economic comparisons of manufacturers' trans formers.

The Guide gives three different methods. However, the second method, which utilizes calculation sheets and tables, is recommended because it is routine, can be done fairly quickly and is sufficiently accurate for comparison purposes. To do transformer evaluations, there is a great deal of system data required, which may not be available or is difficult to obtain. Every reasonable effort should be made to obtain data which applies specifically to your system. It is essential to do a meaningful transformer evaluation. However, there is a table, included in the guideline, of data obtained by Edison Electric Institute, that gives the range of system data for utilities all across the country. The data in the table should not be used except as a last resort.

By using this guide and your system data, you can obtain transformers which will be economical for your system. To ensure that you obtain transformers with losses equal to, or less than what you are paying for, incoming transformers should either be tested periodically for losses, or the manufacturer should be told to supply factory core and copper loss test data for each transformer supplied.