Computer Modelling of Electrophysical Phenomena in High Voltage Insulation

Doctoral thesis, 2004

Different kinds of dielectrics are used for high voltage insulation. In most of the cases, they are combined into complex insulating systems forming macro- and micro-scale composite structures. Presence of interfaces in a composition leads to specific phenomena when subjected to high electric fields, first of all to the accumulation and polarization of charges on the interfaces and to electrical discharges in the gas phase having the lowest dielectric strength among other materials. This thesis focuses on developing computational approaches for simulations and analysis of these processes. Computer modelling of dielectric relaxation, effective dielectric properties and local characteristics (distributions of electric fields and power losses) of the composites is performed for binary mixtures with regular and stochastic structures using experimentally obtained frequency dependent properties of the constituents as input parameters. The model is verified by comparing the computed results with the experimental data. The developed procedure is then applied to analyze interfacial charges, fields and losses in a water-treed polymeric insulation of a high voltage cable. The computational model of electrical discharges in gases utilizes the drift-diffusive approximation. Simulations are performed for two different arrangements, where the air gap is comprised by metallic electrodes and by electrodes covered with solid dielectric layers. In the first case, conditions of propagation of positive and negative streamers in low background fields are examined. In the second case, the developed procedure is used to study dynamics of discharges in a hybrid air-dielectric insulation and for analysis of processes determining its performance. The results of the simulations are compared with available experimental data. Further, the elaborated computer model is applied to examine a possibility of generating homogeneous plasmas by means of high-frequency discharges in helium under different conditions. Microscopic and integral properties of such plasmas determining their usability in technological applications are analysed.