Partial Discharge Characteristics of Tip Defects in Cable Terminations Under AC-Superimposed Switching Impulse Voltage

This study investigates the partial discharge (PD) characteristics of tip defects in cable terminations under switching impulse voltage superimposed on alternating current (AC) voltage. An AC-superimposed switching impulse voltage test platform was established, and the switching-impulse polarity and superposition phase were varied to systematically examine the time-domain characteristics and evolution of the PD. The results show that PD is initiated during switching-impulse superposition when the superimposed voltage reaches the inception condition. During the subsequent AC stage, discharges are mainly concentrated near the zero-crossing point of the first power-frequency cycle, and are primarily governed by the combined effect of residual space charge and the background electric field. Under a positive-polarity switching impulse, the PD intensity exhibits an approximately sinusoidal phase distribution, reaching its maximum at approximately 90° and its minimum at 270°. Under a negative-polarity switching impulse, an inverse sinusoidal distribution is observed. Compared with negative-polarity switching impulses, positive-polarity switching impulses are more conducive to streamer propagation and space-charge accumulation, resulting in more intense discharge activity.