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The phenomena of surface charging of insulating materials have been of great concern in many areas, such as electrical, aerospace, and medical systems. The main effect of surface charge accumulation is that it modifies the electric field present in the nearby region, which impacts system performance. Corona discharges or the ionization of surrounding medium at sharp edges often occur in high-voltage systems, resulting in insulator surface charging. A lot of research has been done on the DC corona charging of insulators, but understanding the AC corona charging of insulators is still a challenge. Additionally, the decrease in pressure significantly increases the discharge activities at higher altitudes. Therefore, it is important to examine the surface charging of insulators in low pressure conditions. The present study analyzes the surface charge distribution on a polymeric insulator exposed to AC discharge at low pressure. The interaction of charges originating from different sources was also investigated. In this regard, the three types of electrodes, namely singlel-needle, two-needle, and three-needle were considered. It is observed that the decrease in pressure increases the discharge activities. In the case of AC corona charging, the deposition of negative charges is observed to be dominant. The accumulation of charge depends on various factors such as electrode configuration, tip radius of the electrode, pressure, type of source, etc. It is found that the increasing number of needles with decreasing pressure enhances the uniformity of the charge distribution on the insulator sample surface. The noted increase in the discharge in low pressure is explained through the current pulses and the discharge images.
Saini et al. (Thu,) studied this question.