Phase-resolved Properties and Simulation of Partial Discharges in High Voltage Liquid Insulation

High voltage equipments play important roles in electric power systems. In order to obtain the equipments work properly it is essential to keep the high voltage insulation system in good condition. High voltage insulations are classified into gas, liquid and solid insulations as well as their composites. Partial discharges may take place in liquid insulation. The appearance of partial discharges may degrade the performance of the insulation. The occurrence of the partial discharge (PD) is also an indication of insulation abnormality. In order to increase the quality of diagnosis of high voltage equipments it is important to deeply understand the partial discharges in each insulation. This paper reports the measurement, analysis and modeling of partial discharges in liquid insulating material. The partial discharges were generated using needle-plane electrode system. Partial discharge measurement was conducted using phase-resolved measurement system which able to measure the PD magnitude (q), phase of PD occurrence (phi) as well as PD number (n). The analysis of the PD data was conducted by utilizing phi-q-n and phi-n pattern. The experimental results showed that for PD pulses were observed at around the peak of both positive and negative applied voltages. The magnitude as well as pulse number are strongly dependent on the instantaneous applied voltage. Based on experimental the results, computer simulation of PD in liquid insulation was conducted. Simulated phase resolved PD patterns were similar to those obtained from experiment.