Application of PDC Testing for Medium-Voltage XLPE Cable Joint Water Ingress Detection

Abstract

This article took 6.6-kV medium-voltage crosslinked polyethylene (XLPE) cables as the test object, conducting field tests of polarization and depolarization currents (PDCs), very-low-frequency (VLF) tan $\delta $ , and time-domain reflectometry (TDR). The correlation between PDC testing and VLF tan $\delta $ and TDR measurements was investigated to enhance the effectiveness of the PDC testing method. PDC test outcomes indicated that polarization currents sometimes exhibit increasing or non monotonic trends over time, referred to as abnormal trends herein. Through in-depth research combining TDR measurement results and relevant theoretical frameworks, it is confirmed that abnormal polarization currents are attributable to water ingress issues in cable joints. Water ingress into the joint induces nonlinear variations in insulation conductivity with the electric field, manifesting as abnormal trends in polarization currents at the joint-insulation interface. These kinds of abnormal polarization currents can serve as an effective diagnostic indicator for identifying cable joint issues. Moreover, VLF tan $\delta $ measurements alone sometimes fail to accurately diagnose water ingress issues in cable joints, necessitating the use of TDR for further diagnosis.