Thermal endurance of Class H insulation

A COMPREHENSIVE MOTOR test program was undertaken to determine the thermal endurance of Class H insulated motors at several different temperatures. A scattering of thermal life and points was obtained over a sufficiently wide temperature range to permit extrapolation of life expectancy to lower temperatures. A comparison was obtained between the behavior of Class B insulation and Class H insulation under the same test conditions. The fundamental concept followed in this test program is that appreciable decrease in the humidified insulation resistance of windings is a criterion of minimum motor insulation life.