Partial discharge analysis in a needle-plane gap with repetitive step voltage

Partial Discharge (PD) tests are carried out in a needle-plane gap where the plane is covered by an insulating material. The partial discharge activity is studied during application of a periodic negative step voltage, whose duration of the voltage period T₁ and the pause time T₂ between every two consecutive step voltage pulses could be varied separately to influence the decay of deposited surface charges. Compared with the PDs in the needle-plane setup without dielectric, the effect of dielectric placed on the top of ground electrode on the discharge activity is investigated. The results show for the case of the step voltage with the duration of 100 ms and the pause time of 10 s. The PD activity during the first voltage cycle is significantly different from the others. For a lower voltage, the pulse repetition in the virgin curve reaches a saturation level within the charging period; however, for the higher voltages it becomes more linear increasing.