Indoor and outdoor transformer insulation systems

The thermal life studies are presented on a number of transformer insulation systems for equipment up to 500 KVA. Thermal classifications from 105 to 220 C are covered. The data is compiled from transformer models (transformerettes) using IEEE #117 techniques (developed for motorettes) modified for indoor and outdoor transformer conditions as approved by Underwriters´ Laboratories who recognized the classifications following submission of the data. Both copper and aluminum conductors are evaluated. These evaluations apply to both pad mount installations and underground residential distribution systems for both indoor and outdoor exposures.