Analysis of cable failure modes and cable joint failure detection via sheath circulating current

Power cables are preferred in urban areas for power transmission and distribution because of their high reliability, environmental friendliness and the visual invisibility. Whilst the volume of underground power cable has been growing steadily, the voltage level of the power cables have also increased significantly in recent years. The increasing volume of high voltage power cables brings about technical challenges to the power system operators and maintenance engineers. One of these challenges is the application of appropriate condition monitoring techniques to detect incipient cable faults and to reduce unplanned outages. This paper aims to analyse the causes, modes and mechanisms, among cable joint failures, and to propose an applicable sheath circulating current monitoring technique with the associated criteria for fault diagnosis. Two joint faults, flooded link box and joint insulation breakdown, are analysed in detail. Finally, a set of criteria is proposed for cable joint fault diagnosis based on the simulation of an 110kV underground power cable system of length 1.5km.