A Model and Computer Simulation of Partial Discharges in High Voltage Liquid Insulation

Under high electric stress, partial discharges may occur in liquid insulations in the form of streamers. The appearance of discharges in the insulation affect the performance of the insulation. This paper reports the experimental results on the characteristics of partial discharges (PD) in liquid insulation under extremely non uniform electric field. Electrode used in the experiment was steel needle-plane arrangement with needle tip radius of curvature of 3 μ m made by Ogura. The discharge pulses were measured using a phase-resolved measurement system. The partial discharges were presented in their magnitude q in pC and phase angle in degree. The experimental results showed that PD took place at both positive and negative half cycles where the negative PD pulse number was higher but with smaller magnitude. PD pulsed took place around the peak of the applied voltage which indicated that PD probability was strongly dependent on the instantaneous applied voltage. In order to obtain more deeply understanding of the streamer discharges in insulating liquid, a computer simulation was done by utilizing an electrical equivalent circuit. The simulated PD patterns were compared to discharge patterns obtained from the experiment. The results indicated that simulated discharge patterns were similar to those obtained from experiment indicating the validity of the proposed model.