Electric fields in multi-layer dielectrics under high DC stresses in plane-parallel geometry

Abstract

Joints are Achilles heel of underground cables. Since there are multiple layers of insulation (XLPE, rubber), which encompass the cylindrical conductor, breakdown may occur at joints due to prolonged electrical and thermal stress. Unlike in ac cables conductance is not uniform in dc case, owing to temperature effects. Also the case of multiple layers of insulation makes the mathematical analysis of electric fields considerably difficult, but essential. The purpose of this work is to analyse electric fields in multi-layer dielectrics under high DC stresses in plane-parallel geometry, which forms a basis, for mathematically more complex cases like cylindrical geometry or practical cable joints (rubber joint) in industry. Using finite difference method the variation of electric fields and temperature fields with position and the interaction of them at different voltage levels has been investigated. The Poisson's equation, current continuity equation and heat flux continuity equation were solved simultaneously using the finite difference method. The parallel plane geometry consisting of layers of XLPE and rubber is taken and analysed as a first step.