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In this article, the aging and degradation of resin-rich mica-based insulation, used in Type II machine turn insulation, is studied to determine the characteristics of converters that affect insulation failure. Dissection of failed turn insulation specimens from voltage endurance tests and findings from simplified two-cavity specimens are studied at various stages of aging which are then related to the rise time, switching frequency, and overshoot of the converter supply. The experimental observations and the simulation studies show that the aging and life of turn insulation are found to be strongly associated with the discharge rate and the surface erosion of the insulation. The overlap and interface play a significant role in the failure of taped turn insulation.