A technique for establishing winter loading guidelines for 15, 25, and 50 kVA pole and pad mounted distribution transformers based on the direct measurement of winding and oil temperatures

Abstract

Outdoor winter seasonal conditions have been achieved with a 10 ft × 10 ft × 7 ft environmental chamber having a temperature range of 165 - 0°F. The loading back technique was used in the chamber to test and establish winter loading guidelines for thirteen distribution transformers of 15, 25, and 50 kVA pole top and pad mount design. Temperatures were logged every two minutes from eight thermocouples placed within the transformers. Direct measurements were made with carefully insulated and grounded thermocouples placed within the high voltage and low voltage windings. Recommended winter loading guidelines may be achieved from these data for the operation of such transformers on the utility distribution system.