Aging characterization of medium voltage groundwall insulation intended for PWM applications

The paper describes an investigation into aging of medium voltage mica-based groundwall insulation when subjected to high frequency AC and steep-front pulse voltages. The test conditions adopted in this study involve 60 Hz, 3 kHz and 4 kHz AC frequencies, nanosecond rise time pulses with repetition rates up to 2000 pps, and at temperatures of 20 and 155 degC. The experimental data of time-to-failure in the accelerated life tests are presented by Weibull distributions. The parameters of the life model are developed that link the failure time to the amplitude and temperature of the applied voltages. The test method and the data processing adopted in this study are useful to characterize groundwall insulation in terms of improved vacuum pressure impregnation (VPI) and for applications at higher temperatures and frequencies