PD characteristics in an air-filled void at room temperature under superimposed sinusoidal voltages

Partial discharge in an artificial air-filled void under superimposed sinusoidal voltages is investigated at room temperature in order to clarify the effect of voltage superposition. The applied voltage waveform is composed of a 60 Hz fundamental sinusoidal wave and a high frequency sinusoidal wave of 300 Hz to 1.2 kHz. It was found that PD started when the peak value of the superimposed voltage reached the PD inception voltage under 60 Hz sinusoidal voltage. Also, PD occurrence frequency increased remarkably when the peak value of the high frequency component exceeded a critical value, which is smaller than the PD inception voltage under 60 Hz sinusoidal voltage. PD characteristics under such conditions were discussed as the effect of the residual voltage, caused by the surface charge deposited in the void by the preceding PD. The obtained experimental results suggest that the superposition of high frequency component accelerates the degradation of the solid insulator containing void defects.