Impact of Thickness on Space Charge and Breakdown Field of XLPE Insulation

Abstract

The dependence of the breakdown field strength on thickness of dielectric is of important concern for solid insulation material. In this paper, a theoretical model incorporating experimental test results is presented which relates thickness versus breakdown strength. The breakdown field strength of XLPE samples thickness ranging from 50um to 200um is experimentally calculated for both AC and DC stresses. For AC stresses the results show that breakdown strength decreases with the increase in sample thickness. The phenomena of breakdown strength for various thicknesses under AC stress are completely different from applied DC stresses. For DC stresses the breakdown field strength increases with the increase in sample thickness ranging from50um to 100um and then breakdown strength show decreasing pattern with the increasing thickness ranging from 100um to 200um. The breakdown scatter diagram for DC field show that the DC breakdown strength increases with increase in thickness up to 100um and further increase in thickness does not show much affect on breakdown strength. It is concluded that the space charge formation resulting in enhancement of local electric field in insulation bulk of XLPE may be the reason behind this phenomenon. Furthermore, analysis of space charge formation utilizing PEA (pulse electro-acoustic) system under high dc electric voltages has been done also to relate impact of local electric field of varying thickness (50um -200um) on breakdown of XLPE insulation. In order to confirm the effect of space charge on the breakdown field strength, this paper builds a new model to explain the phenomenon and conclude the expected results.