Thermal performance of stress grading systems for converter-fed motors

The present paper concentrates on the performance of the stress grading materials as the temperature changes. There have been a number of recent publications on stress grading systems applied to end-windings of stators but little has been published on the effect of temperature on their electrical properties, either in the short term or as a long term aging effect. In particular, the effect these property changes have on the control of electrical stress, when the machine is subjected to converter voltages, has not been published. We describe here a method to categorize the properties of these materials and report on how simple thermal aging can have a dramatic influence on their performance