Partial discharges under moderately distorted voltage: a preliminary study

This study compares the number of partial discharges (PDs) per cycle N_NS, caused by a nonsinusoidal voltage, with the number of partial discharges per cycle N_S caused by a sinusoidal voltage with the same rms value as the sinusoidal one. The results are based on two theoretical models that account for peak, inception and residual voltages, a time-constant characteristic to the cavity´s geometry and deterioration as well as the voltage waveform. The obtained results indicate that for practical situations at power system busses with randomly varying harmonics, where the voltage distortion is low, THD≤5%, the expected partial discharge ratio is in the range 1 < N_NS / N_S ≤1 .05.