Partial discharge (PD) measurement is an effective way to diagnose the defects and ageing of insulation system in high-voltage electrical equipment. The variation of applied voltage waveform can contribute to deeper understanding of discharge physical process. In this work, symmetrical trapezoidal-wave voltage was employed to investigate the effect of waveform parameter on PD characteristics, based on the PD activity produced in a spherical-plane asymmetric electrode structure on the stator insulation of electrical machines. The results show that apparent PD charge mainly concentrates around 300-500 pC, and it has little relation with the waveform parameter in the trapezoidal-wave voltage. Maximum PD charge in the negative half cycle of applied voltage is larger than that in the positive half cycle. This is mainly due to the metal-dielectric asymmetrical structure of test cell and space charges deposited on the dielectric surface. With the increase of voltage change ratio dU/dt, average PD charge increases, while time delay caused by the phase shift decreases. With the increase of constant-voltage period, both average PD number and average PD charge exhibit almost exponential increasing trend.

partial discharge  /  trapezoidal wave voltage  /  stator insulation  /  discharge characteristic