Partial Discharge Inception Characteristics of Twisted Pairs Under Single Voltage Pulses Generated by Silicon-Carbide Devices

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Partial discharge (PD) is a major cause of degradation of motor winding insulation. It is a challenge to the successful electrification of all types of ground, sea, and aerial vehicles. However, the mechanism of PD under pulsewidth modulated voltages is not fully understood. This article studies PD inception characteristics in twisted pairs under single voltage pulses with reduced voltage overshoot, aiming to study the PD inception characteristics and mechanism without the influences of memory effects and voltage overshoot. The tests are conducted with a lab-designed 10-kV silicon carbide (SiC) device-based voltage pulse generator. The generator can produce voltage pulses with variable rise/fall times and pulse widths to emulate the output voltages of both silicon (Si) and SiC device-based power electronics converters. The voltage overshoot in this study has been limited to less than 5%. In addition, single voltage pulses are utilized as the excitation to remove charge memory effects. PD inception voltages, PD current magnitudes, and PD time delays of twisted pair samples are measured under various test conditions. It is found that the partial discharge inception voltage (PDIV) of the test sample decreases with reduced voltage rise time and increased voltage pulsewidth. Based on the test results, the impacts of voltage rise/fall times and pulse widths on PD behavior are explained using the extended volume-time theory. The relationships between PDIV, voltage rise/fall time, and pulsewidth are presented through empirical equations. Test results and analysis provide insights on the impacts of emerging wide bandgap devices in applications on motor winding insulations.