The spatial distribution and electrical parameters of partial discharges in polyethylene insulation during ageing

The change of discharge parameters obtained from large bandwidth electrical and optical measurements is related to ageing phenomena in polyethylene voids. Discharge-pulse shape, ignition voltage, and spatial distribution were monitored in disc-shaped polyethylene voids for 100 hrs. Optical and electrical results are related to the mechanism of the discharge and the dimensions of the void. Primarily discharge pulse height, discharge pulse width, and discharge repetition rate are important parameters describing the ageing process. These parameters changed drastically during ageing as layers of discharge by-products were deposited on the void surfaces and pits were formed. The creation of pits was linked to the occurrence of a discharge regime with minute pulses of high repetition rate and a decreasing ignition voltage. These minute discharges were therefore regarded as a sign of advanced degradation of the dielectric.<
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