Study on sensitivity characteristic of capacitive coupler for PD detection in HV cable joint

Abstract

The capacitive coupler is an attractive tool for on‐site partial discharge (PD) detection in a cable joint. To study its sensitivity characteristic, PDs in a 110‐kV prefabricated joint containing two artificial defects were detected successively using capacitive couplers with six different electrode widths installed at the same position of the cable. For the quantification of sensor sensitivity, the sensitivity factor is defined as the ratio of capacitive coupler output voltage amplitude to apparent charge that was determined through a conventional PD‐measuring circuit according to IEC 60270. As random variables, the sensitivity factors were displayed in the probability distribution plots for each capacitive coupler to visually compare their sensitivity levels. The results demonstrate an almost monotonically increasing dependence of sensitivity on the coupling electrode width, which agrees with the qualitative analysis based on the amplitude–frequency characteristic of the capacitive coupler. Besides, there is an obvious distinction in sensitivity factors between two distinct defects, indicating that the capacitive coupler is more suitable for PD trend analysis rather than apparent charge quantification. In addition, the insensitivity of the capacitive coupler to certain defect types may explain the cause of some undetectable dead zones in on‐site PD measurement. This study provides experimental support for the geometrical optimization of capacitive couplers. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.