Analysis of Changes in Dielectric Properties of PVC-Insulated Cables Under Thermal Stresses

Abstract

The world's energy sectors and policymakers have shifted their focus to renewable energy sources, such as Solar PV and Wind, to address global warming and reduce carbon emissions. The problem with the energy transition is integrating distributed generation into existing infrastructure, such as cables installed more than two decades ago. For low-voltage applications, the most widely used cables are PVC cables, which are prone to thermal stress due to their renewable dynamics and intermittent nature. This study characterized the impact of thermal stress above rating and in overloaded conditions, which mimic what will occur under high thermal stress from high current from renewable sources and cyclic loads. The experiment was conducted by preparing PVC sample cables according to standards, subjecting them to a high temperature of 125 °C, and measuring them at baseline temperature in a controlled oven at 35 °C. The aging cycles are at 24, 48, and 52 hours. The experiment aimed to conduct polarization and depolarization current (PDC) analysis, frequency-domain dielectric spectroscopy (100 mHz-1kHz), and mass-loss assessments. The results showed changes in dielectric parameters, FDS measurements, and mass loss. The result showed that thermal stress is a significant cause of insulation degradation: dielectric loss increases, and PDC relaxation features shift with increasing cycle number and mass loss at 52 hours of age. These patterns indicate thermal-induced microstructural changes, including plasticizer loss, chain scission, and increased dipole mobility, in aged PVC insulation. This investigation advances diagnostic techniques to an advanced level and improves distribution line maintenance and preventive capacity through non-destructive methods, enabling early replacement of the oldest assets before catastrophic failure in the networks.