Investigation into the dissipated energy under accelerated thermal aging in PVC/B used in low-voltage cables insulation

Due to their excellent insulating characteristics, polymer materials are widely used in electric power transmission and power cables. However, the thermal stress is one of the most severe service constraints that can lead to the reduction of insulating polymers lifetime. In light of this, an experimental study on polymer samples was carried out to investigate the impact of the accelerated thermal aging on the dissipated energy through the insulating material. In this study, polyvinyl chloride (PVC, class B or PVC/B), used as electrical insulation in low-voltage cables, was chosen as the studied material. Accelerated thermal aging on circular shaped samples of PVC/B was performed at two temperatures, 80°C and 120°C, during 3024 hours (126 days). The measurements of the cumulative charge were carried out in order to follow the evaluation of energy at different aging stages and for five AC applied voltage levels ranging from 3 kV to 12 kV. The variation of mechanical characteristics as well as the evolution of dissipated energy were examined and analyzed. The investigation results show a significant increase of the dissipated energy with thermal aging due to material degradation. This increase was clearly observed at 120°C. Furthermore, a good correlation between the mechanical properties and the dissipated energy of the material has been found. Through this paper, the dissipated energy and mechanical properties have commonly proved to be effective to evaluate the aging level of insulating materials, which can be used to assess the conditions of low-voltage cables operating.

I. Introduction

Polyvinyl chloride (PVC) is extensively used as a sleeve material of power cables and as the insulating material for low-voltage applications [1]. In conventional power cables, the voltage is applied between a central metallic conductor and an earthed metallic screen that surrounds it. The two components are separated by the insulation system [2].