Influence on PD parameters due to distorted voltage

In the standard specification of AC dielectric-characteristic measurements of insulating materials, test voltage is prescribed as "approximately sinusoidal" if the highest acceptable deviation of the HV waveform from the correct sinusoidal shape is limited in a ±5% tolerance range of the crest factor value. In the field of Partial Discharge (PD) measurements and their statistical data processing, on which forecasts of long term behavior of components and their reliability are currently carried out, the results of elaborations depend on the voltage waveshape. In this paper, the errors in PD measurements, evaluated at industrial frequencies, due to applied voltages distorted by 3^rd and 5^th harmonics are studied. The analysis is carried out by comparing the main characteristic parameters of PD in the distorted steady-state with those occurring under the sinusoidal steady-state on the basis of the same RMS value of voltages, thus establishing a reference with the usual methods adopted in measuring test voltage as required by prescribed HV test technique. Stochastic and statistical analysis and parameter\´s curves, showing the differences in PD measurements, are obtained as function of harmonic content percent and phase angle.