The procedure is intended to provide a direct evaluation of the composite insulation system of either a power or distribution, liquid immersed transformer. The purpose is to establish a uniform method for investigating the effect of operating temperature on the life expectancy of liquid-immersed power and distribution transformers. Revision Standard - Superseded. A test procedure is established to provide a uniform method for investigating the effect of operating temperature on the life expectancy of liquid-immersed transformers. The test proce-dures are intended to provide data for the selection of a limiting hottest-spot temperature for rating purposes, provide data which may serve as the basis for a guide for loading, and permit the com-parative evaluation of a proposed insulation system with reference to a system that has proven to be acceptable in service.