Motor Winding Insulation Degradation Under Repetitive Voltage Pulses

Variable speed drives (VSDs) are widely utilized to control motors such as pumps, compressors, fans, etc. However, the endurance of motor winding insulation under repetitive voltage pulse excitation is weakened, resulting in premature failure and shortening the expected operating life. This article reviews the literature of investigations spanning the last two decades on the problem. Researchers have focused on different aspects to explain this from a particular angle. The precise mechanism is complicated as a number of interacting factors contribute to premature insulation failure. Insulation degradation in motors can be attributed to thermal, mechanical, chemical, and electrical stress. It seems that space charge accumulation and partial discharge (PD) are the two main influences; the former can exacerbate the electric stress distribution whilst the latter promotes insulation deterioration.