Pulse width modulation voltage source deadtime effect on partial discharge and lifetime of inverter-fed motor insulation

This paper analyses the impact of square wave pulse voltage deadtime on the partial discharge (PD) and the lifetime of turn-to-turn insulation. A bipolar repetitive pulse voltage with a deadtime of 0-10 mu s is produced using double half-bridge solid-state switches having push-pull technology controlled by a field-programmable gate array. The mechanism of the discharge process at rising and falling edges of the pulse voltage before and after deadtime is analysed in detail. The discharge amplitude and PD probability at the rising/falling edges of the voltage waveform increase as the deadtime increases from 0 to 10 mu s due to the remanent charges. The number of PD and their intensity is higher at the first rising/falling edges of pulse voltage as compared to the second rising/falling edges for all deadtimes 0-10 mu s. As the deadtime increases beyond 2 mu s, the number of PDs increases and concentrates at a specific phase angle of rising/falling edges. These localise discharges degrade the insulation material and reduce its lifetime. This study helps to identify the inverter-fed motor insulation faults due to deadtime. It can provide guidelines to motor insulation designers to determine the limit value of deadtime to compensate PD and ensure the safer operation of such motors.