Phase-resolved analysis of discharges in air, liquid and solid insulating materials

This paper describes the experimental results on the discharges in air, liquid and solid insulating materials. The electrode used for producing discharges was needle plane system. Under AC voltage discharges in air in the form of corona was developed. Discharge in liquid insulating material was produced in silicone oil with viscosity of 1000 cs. The discharge associated with the streamer in the oil. For solid insulating material, discharge associated with electrical treeing was investigated in low density polyethylene (LDPE). The discharges were measured using a personal-based discharge measurement system which able to measure the magnitude, frequency and the phase of discharge occurrence. The phase-resolved analysis of the discharges revealed that for corona, discharges were concentrated around the peak of applied voltage at negative half cycle. For silicone oil similar results were obtained while for electrical treeing in LDPE, the discharges were spread before the zero cross of the applied voltage up to the peak at both positive and negative half cycles. The discharge magnitude for all sources seemly strongly depends on the instantaneous of the applied voltage. The phase-resolved analysis indicated that for corona only several discharges took place in every half cycle which is concentrated around the peak of applied voltage. This similar trend was observed for discharges in oil. This indicated that the PD occurrence in air and oil are strongly affected by the applied voltage. However, for electrical treeing it was observed that the discharge occurrence was strongly affected by the time derivative of the applied voltage (dv/dt). This was clarified under triangular and rectangular voltages application