Influence of Ambient Humidity on PDIV and Endurance of Inverter-fed Motor Insulation

This work aims to report the influence of ambient humidity on partial discharge inception voltage (PDIV) and lifetime (endurance) of the insulation for inverter-fed motors. The PDIV on polyimide film and rotor bar insulated by NOMEX at sinusoidal voltages with 50 Hz frequency and the endurance tests of inverter-fed motor turn insulation under repetitive unipolar impulsive voltages with 10 ns rise time and 200 ns voltage on-time were performed at four relative humidity (RH), i.e. 40%, 60%, 80%, 95%, controlling the ambient temperature at 50 °C. Experimental results show that both the PDIV and endurance decrease significantly with increasing RH. Accordingly, the influence of ambient humidity on the test results should be carefully considered when performing PDIV and endurance tests on the insulation of low-voltage and high-voltage inverter-fed motors according to IEC standards.