Some Aspects of Stress Distribution and Effect of Voids Having Different Gases in MV Power Cables

Abstract

Partial discharge (PD) may have long time delay from days to years depending on the size and other characteristics of voids under electric stress. Voids may be formed due to expansion and contraction of the cables. Enlargement of voids is due to chemical reaction by discharge byproducts and continuous bombardment of particles ( ). The variation in distribution of stress in the void is influenced by the factors like the size of the void, number of voids along the field distribution, the void orientation, the position of the void and the insulation thickness. The influence of discharge inception voltage on the shape and the location of the void are studied. Field variation inside the cavity, the influence of nearby cavities and the comparison of the various shapes of voids in single and three core cables are studied. The variations in temperature distribution of various gases are studied. Among the various gases, oxygen and nitrogen plays a bigger role during PD activity. Oxygen causes uniform erosion in cavity surface by consuming itself in a closed cavity leaving nitrogen, moisture and other gases to initiate the PD. This will result in faster PD activity than the other gases. These observations are done in COMSOL multiphysics software which uses Finite Element Method (FEM) to solve partial differential equations. Keywords - Partial discharge (PD); Finite element method (FEM); COMSOL multiphysics software; Electric field stress; Voids.