Estimating the Impact of Pulse Voltage Stress Caused by Modern Power Electronics Technology on Machine Winding Insulation Material

Modern electric drives are generally driven by voltage source inverters. With the aim of reducing size and losses, switching speed of modern power electronic devices is steadily increasing. At the same time, it can be observed that operation under repetitive fast voltage transitions is reducing reliability and lifetime of motor insulation due to the additional stress. Available data for allowable voltage pulse stress in insulation material is usually limited to voltage pulses having rise time below 300ns and dv/dt below several kV/µs. With the introduction of wide bandgap power electronic devices, dv/dt will be significantly increased leaving the question about the impact on resulting insulation life time. In this paper insulation life time tests are presented under operating conditions similar to medium voltage SiC technology. Reversible and irreversible effects within the material are identified and their connection to switching speed and pulse voltage magnitude shown.