This test procedure for the thermal evaluation of insulation systems of dry-type power and distribution transformers, including both open-wound technology and solid-cast / encapsulated technology is to be used for determining the temperature classification of the insulation systems. The purpose of this test procedure is to establish a uniform method for the following: a) Providing data for the selection of the temperature classification of the insulation system; b) Providing data that may be used as a basis for a loading guide; c) Comparative evaluation of different insulation systems. Revision Standard - Superseded. A uniform method is established for determining the temperature classification for the insulation systems for open-wound, solid-cast and resin-encapsulated power and distribution transformers by testing rather than by chemical composition. These insulation systems are intended for use in transformers covered by IEEE Std C57.12.01(TM) and IEEE Std C57.12.91(TM) as they apply to dry-type transformers whose highest voltages exceed nominal 600 V.