Partial Discharge and Breakdown Characteristics in Small Air Gap Lengths Under DC 9 Voltage in Needle-Plane Electrode Configuration

The degradation of insulation part of high voltage (HV) power equipment is considered the main problem that happens in such equipment. In this paper, the characteristics of air partial discharge (PD) and breakdown in needle-plane electrode configuration under direct current (DC) voltage have been experimentally investigated to help in the engineering design process of this equipment. In addition, the influence of solid dielectric barrier presence between the two electrodes in small air gaps on the PD and breakdown has been experimentally discussed. Also, the effect of positive and negative polarities of DC voltage on the PD and breakdown under standard atmospheric conditions has been investigated. An epoxy resin material with thickness of 2 mm is used as a solid dielectric barrier. The electrodes are arranged in a vertical position to perform the tests. The breakdown voltage (BDV), PD inception voltage (PDIV) and partial discharge current pulses are measured at different lengths of air gap. The length of air gap is varied from 5 mm to 35 mm with a step of 5 mm. The PD process in the air gap is monitored using an Ultraviolet camera. The above tests have been performed at the normal room temperature and relative humidity in range of 60 to 70%. Furthermore, the effect of air temperature and pressure on the air BDV has been investigated under artificial climate chamber conditions. From the experimental tests, it was concluded that the air gap length, solid dielectric barrier, polarity of DC voltage, air temperature and pressure have a significant influence on the BDV and PDIV.