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Investigations on DC Breakdown in Solids under Needle tip-Plane Electrode Configuration

Electrical treeing is considered to be one of the most important physical evidence of insulation damage in HV cables, caused due to the high field enhancement at the tip of these defects in the insulation. In this paper, breakdown experiments are conducted using needle-tip electrode configuration under stepped DC stress profile. Further, the authors present an estimation of electric field and space charge distributions in needle tip-plane system based on FEM. Nonlinear conduction is incorporated in the computation by using a semi-empirical equation of field and temperature-dependent conductivity. The results show the interesting aspects of nonlinear conductivity on the electric field and space charge distribution. Further, the effect of temperature dependence on field distribution at the needle-tip is also presented. Furthermore, from the breakdown experiments, the electric field at the tip is estimated for different tip radii and the results give a reasonable and realistic estimate of breakdown tip-field, using the proposed model.