Effects of Harmonic Voltage Distortion on Partial Discharge Characteristics on Polymeric Insulation Foil

The partial discharge (PD) characteristics of polymeric insulation foil are investigated under harmonic distorted voltage waveforms. Distorted voltage waveforms can cause intensified aging, leading to preliminary insulation failure, especially when PD are present. The exact mechanism in which way harmonic distortion influences the PD activity and hence the degradation of e.g. polymeric insulation is not yet clear. The contribution presents results of parameter measurements of surface discharges on polyethylen terephtalat (PET) insulation foil. Voltage waveforms with different superimposed harmonic voltages up to 31st order and total harmonic distortions up to 20% but constant peak voltage are utilized to isolate principal influencing factors on the PD activity. The measurements show that the shape of the voltage waveform, expressed by a shape factor, has a significant effect on the apparent charge and repetition rate as well as the phase interval per period in which PD are present. Hereby, the frequency of the superimposed harmonic affects the PD activity more than the total harmonic distortion. The implications of the obtained measurement results are discussed in the context of intensified degradation and hence accelerated aging of polymeric insulation systems.