Impact of Rise Time and Frequency on Motor Winding Insulation Lifetime Under High Frequency, High Slew Rate Bipolar Square Wave Voltages

Emerging power electronic drives and converters, especially wide bandgap (WBG) technology-based devices, are expected to operate at high voltages and switching frequencies, potentially reaching up to several hundred kHz. These operating conditions pose significant challenges to the reliability of insulation systems in motor windings, which are critical to the longevity and safe operation of electrical machines. This study investigates the impact of high-frequency square wave voltage pulses on the lifetime of motor winding insulation by conducting lifetime tests on twisted pair magnet wire commonly used in electrical machines. The experiments were conducted in the frequency range of 100 kHz to 300 kHz, with rise times of 50 ns and 400 ns (slew rate ranging from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2.4 \text{kV} / \mu$</tex> s to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$19.2 \text{kV} / \mu \mathrm{s}$</tex>), to simulate the conditions typical in modern power electronics and inverter-driven systems. The results show that fast rise times and high switching frequencies influence turn-to-turn insulation's aging and breakdown characteristics. The findings highlight the importance of switching frequency and rise time in determining the reliability of insulation systems, offering critical data to enhance the design and performance of electrical machines in the context of high-frequency operation.