Modeling of partial discharge activity in spherical cavities within a dielectric material

摘要

The partial discharge (PD) activity in a cavity within a solid dielectric insulation material is known to be dependent on the size, shape, and location of the cavity. These factors have a strong influence on the local electric field distribution, which directly affects PD activity and its characteristic behavior. Forssen [1] made an experimental study of PD activity in cylindrical cavities within a dielectric material and found that there were fewer PD events per cycle for smaller cavity sizes, and when a cavity was bounded by an electrode rather than being entirely surrounded by insulation. In the case of a cavity bounded by an electrode, the measured phase-resolved PD patterns showed an asymmetry between positive and negative discharges. However, the total apparent charge per cycle increased as the cavity diameter increased; this may be associated with the size of avalanche developed during a discharge event [2]. Other researchers have shown that differently shaped cavities in a dielectric material influence the PD phase and charge amplitude distributions in different ways [3]. Spherical, ellipsoidal, cylindrical, and cuboid cavities have been studied. In this work, a model for a spherical cavity within a homogeneous dielectric material was developed using finite element analysis (FEA) software. The model was used to study the influence of different cavity conditions on local electric field distribution and consequent PD activity. The study involved variation of cavity diameter and cavity location within the dielectric material. In addition, experimental measurements were undertaken using epoxy samples containing single spherical cavities of different diameters.