Significance of Space Charge Accumulation DC Endurance of XLPE under Varying Insulation Thickness

Abstract

High voltage endurance is a fundamental characteristic of dielectrics. Ideally, the structure of dielectric, electrode design and type of employed electric field has no effect on internal breakdown endurance. On the other hand, experimentally estimated breakdown strengths are quite different under high voltage for the material given. This paper demonstrates space charge dynamics utilizing PEA (pulse electro-acoustic) system under high dc electric voltages to investigate the dependence of varying XLPE thickness on dielectric breakdown. As XLPE is employed for insulation of HVDC cables so it is mandatory to examine the space charge effects under high dc fields for varying insulation thickness. Generally, the influence of space charge leading to breakdown at high stresses is not considered for various bulk insulation thicknesses. However, we demonstrate the long time space charge profiles under high dc electric stresses for various thicknesses ranging from 0.07mm to 0.2mm. We examined that the time dependent internal field and space charge exhibit decreasing pattern with increasing thickness up to 0.1mm and then increasing pattern up to 0.2mm. Space charge measurements under high dc applied electric fields also depict a correspondence with short time dc breakdown test results. This observed phenomenon could find its importance in designing XLPE (material) insulation for HVDC transmission systems.