Online Monitoring for Underground Power Cable Insulation Based on Common-Mode Signal Injection

Online monitoring for underground power cable insulation will lead to early alarms of insulation faults in distribution grids, which has become an urgent need in the industry. However, the existing approaches require complicated monitoring devices, and cannot provide an estimation of insulation ageing severity. A novel online monitoring method for underground power cable insulation based on common-mode (CM) signal injection is proposed in this article. A CM monitoring signal injection device is designed by modifying the secondary side of current transformer in the system, with no need of extra injection voltage source. A monitoring scheme based on CM leakage current measurement at selected monitoring frequencies is proposed and an ageing feature extraction method based on principle component analysis (PCA) is developed which provides an estimation of the insulation ageing severity. Simulations and experiments are conducted, which proves the effectiveness of the proposed device and method under different system operating conditions with different parameters.