An integrated cable condition diagnosis and fault localization system via sheath current monitoring

This paper presents the research and development of an integrated high voltage (HV) power cable condition monitoring and fault localization system. The system consists of the functionalities of online dielectric loss (DL) monitoring, outer sheath and earthing system condition monitoring, and a rapid fault localization system, all based on monitoring of cable sheath currents. Within the distributed sheath current monitoring system, the DL monitoring is achieved via subtraction of sheath currents at different points of a sheath loop, allowing the relative change in DL among the three cables to be trended. Through modelling and analysis of monitored sheath currents, cable outer sheath and cross-bonding connections can be monitored. This includes alarming of theft of earthing conductors which contributed to a large proportion of HV cable failures. The distributed sheath current monitoring system can also be used to record short circuit current between the instant of cable fault and the moment when the protection system actuate, for rapid fault localization. For each of the three applications, the fundamental research and initial results are provided.