Analysis of Thermo-Mechanical Aging on Medium Voltage XLPE Cable Insulation

Abstract

Cross-Linked Polyethylene (XLPE) cables are widely used for cables insulation due to its excellent dielectric and mechanical properties. However, its functionality is greatly influenced under the effect of various kinds of stresses such as electrical, thermal and mechanical or a combination of both. During fabrication process and operation of power cables, the high temperature experienced by the insulation can induce mechanical stress in the insulation region. The development of mechanical stresses significantly affects the performance of the power cable and can contribute to aging upon prolonged exposure. The impact of thermo-mechanical stress gets enhanced in the presence of air voids and impurities. With several electrical properties relying on the mechanical conditions of the insulation, the analysis of thermo-mechanical stress is pivotal to study its role in the insulation deterioration due to aging. This paper demonstrates the thermally induced mechanical stress in power cable insulation and its role in the subsequent aging of the insulation. In particular, a 2D thermo-mechanical model is developed using the Finite Element Analysis (FEA) technique on COMSOL Multiphysics. The paper investigates the correlation between electric breakdown strength and the aging time with regards to the increase in the number of the presence of voids in power cable. The study provides thermo-mechanical stress distribution of the cable and the influence of mechanical stress on the cable functionality. The results show variation in the insulation thickness and the dielectric variation in the cable insulation due to thermally induced mechanical stress.