A study of the effect of temperature on cavity partial discharges in polyethylene insulation

Abstract

This paper examines cavity partial discharge (PD) mechanisms in polyethylene insulation material as a function of temperature. Experimental PD measurements were carried out in accordance with the IEC 60270 standard. A test voltage of 11 kV ac and frequency of 50 Hz was used. The test temperatures studied were 15°C, 40°C, 50°C, 60°C, 70°C, 80°C and 90°C. Test specimens with a cavity diameter of 2.5 mm were assembled using three 1.5 mm thick polyethylene sheets sandwiched between two flat brass electrodes. Partial discharge parameters such as the charge magnitude, inception voltage and PD phase resolved pattern (PDPRP) were measured and analysed at varying temperatures. Results showed that Partial Discharge Inception Voltage (PDIV) increased linearly with temperature for the entire test range. PD charge magnitude initially decreased with temperature from 15°C to 60°C and then increased from 60°C to 90°C. The evolution of PDPRP with temperature was characterised by a turtle-like pattern at ambient temperature, which transitioned into a rabbit ear PDPRP as the temperature increased to 90°C. The findings are interpreted using the mean free path effect on ionisation probability as well as the residual charge dynamics in the cavity as a function of temperature.