Degradation of turn insulation subjected to fast repetitive voltage pulses

The paper describes the failure mechanisms of medium voltage inter-turn insulation as a consequence of space charge formation and partial discharge (PD) activity. In order to investigate the failure behavior, models of turn insulation are prepared with magnetic wires having polyimide and nano-filled coating. The ageing of such model bar samples is done under sinusoidal (60 Hz), fast repetitive unipolar voltage pulses and high frequency waveforms. The ageing tests are performed in the presence of PD activity. To establish the residual strength of bar samples, DC breakdown voltages are determined before and after the ageing. Experimental results reveal that the evaluation and analysis of such model study will be helpful for both motor and wire manufacturers to minimize ageing and to improve motor performance under medium voltage inverter-fed drive applications