The influence of repetitive square wave voltage duty cycle on partial discharge statistics and insulation endurance

The influence of voltage duty cycle on partial discharge (PD) characteristics and endurance of inverter-fed motor insulation were investigated through tests performed on single-contact crossed enameled wires under bipolar repetitive square wave voltages with different duty cycles. The PD patterns, amplitude, repetition rate and lifetime obtained show that short duty cycles, i.e., lower than 50 µs, at 10 kHz frequency, can induce asymmetric PD patterns and reduce the probability of PD inception at falling flanks of impulsive voltages. Moreover, the endurance tests indicate that the duty cycle of the repetitive square wave voltage can affect the insulation endurance significantly. Accordingly, when performing PD inception voltage and endurance tests on insulation of inverter-fed motors, the influence of duty cycle on PD statistics and endurance should be carefully considered.