Advanced Monitoring Technique for Leakage Current and Partial Discharge in Inverter-Fed Motor Insulation

The increasing use of Inverter-Fed Motors (IFMs) in industrial, traction, and power applications has significantly changed the electrical stress conditions experienced by motor insulation systems. Pulse-width modulated (PWM) inverter supplies generate fast voltage transients with high dv/dt, repetitive switching events, and voltage reflections, resulting in increased leakage currents and Partial Discharge (PD) activity. These effects accelerate insulation degradation and can lead to sudden motor failures. Conventional leakage current and PD measurement techniques, developed for sinusoidal excitation, are often ineffective in IFM environments due to limited bandwidth, high-frequency noise, and the need for direct access to high-voltage terminals. This paper presents a novel, non-intrusive insulation monitoring technique that enables simultaneous measurement of high-frequency leakage current and PD activity in inverter-fed motors. The method employs a specially designed high-bandwidth sensing device installed on the motor grounding return path, providing a safe, installation-friendly, and universally applicable solution without requiring access to high-voltage terminals or internal motor components. The sensing device is optimized for wideband transient detection, allowing accurate capture of nanosecond-scale PD pulses and fast leakage current transients associated with inverter switching. Comprehensive experimental validation is presented, including sensitivity verification, calibration, laboratory testing using capacitance-based insulation models, and motorette testing representative of practical IFM insulation systems. Comparative studies with conventional capacitive PD measurement techniques show strong correlation in