The Impact of Test Voltage Waveform in Determining the Repetitive Partial Discharge Inception Voltage of Type I Turn/Turn Insulation Used in Inverter-Fed Induction Motors

The reliability of induction motors stators realized using Type I insulation systems is ensured only when the partial discharge inception voltage (PDIV) is larger than the operating voltage. The concept of Repetitive PDIV (RPDIV) has been proposed as a replacement of PDIV for tests performed under surges or repetitive square waves. RPDIV estimates exceed the PDIV level. The difference might depend on the surge repetition frequency, possibly providing contradicting results using different high voltage sources. Thus, the industry is concerned about the use of RPDIV in place of PDIV and the possible implications for the quality of the stators. Also, little has been discussed about the randomness of measurements and how to treat data using appropriate statistical tools. In this paper, we shall show results of PDIV and RPDIV tests performed on twisted pairs subjected to AC sinusoidal voltages, surges from a commercial surge generator, and unipolar square waves from a high voltage MOSFET. Tests are performed on ten twisted pairs to derive the distribution of RPDIV estimates and compare the differences using statistical tools. Different types of wire are considered to carry out a comparative analysis.