New IEEE Standard - Superseded. A uniform method is established for determining the temperature classification of solidcast and resin-encapsulated power and distribution transformer insulation systems by testing rather than by chemical composition. These insulation systems are intended for use in transformers covered by IEEE Std C57.12.01-1989 and IEEE Std C57.12.91-1995 as they apply to solidcast and resin-encapsulated transformers whose highest voltages exceed nominal 600 V.