Studying the Relationship between the Size of Partial Discharge and Values of its True and Apparent Charges

This article is devoted to the subject of interconnection between the size of defective area in insulation and corresponding values of true and apparent charges of partial discharges. The model of partial discharges in a solid сross-linked polyethylene insulation sample with air cavity is presented. The model is based on resistor-capacitor equivalent circuit, with air cavity being shunted by the electric spark discharge resistor. Resistances of insulation and air cavities are taken into consideration as well as time of discharge development delay. The simulation is conducted for different sizes of air cavity under different volume (with the same proportions), height, cross-sectional area. The diagnostic values of true and apparent charges are estimated. The analysis of dependence between the charges and geometric parameters of air cavity is conducted. It is shown that the same value of both true and apparent charges can match air cavities of different size and shape.