Monitoring of MV Cable Screens, Cable Joints and Earthing Systems Using Cable Screen Current Measurements

Abstract

The paper presents the possibility of using cable screen earthing current measurements for MV, single-core cable line monitoring. Cable screen earthing current measurement allows the condition of cable screen connections, degradation of earthing systems, and the earthing system integrity to be observed, which allows a condition based maintenance (CBM) strategy to be introduced for cable screens and earthing systems in MV networks. CBM allows the workload and failure rate to be reduced. Analysis of the condition of the cable screen and earthing system is carried out based on the cable screen earthing current trends and rapid changes of the current. The proposed system is integrated with a state of the art advanced metering infrastructure (AMI) and uses AMI data to calculate currents flowing through cable segments of the analyzed feeder. Additionally, a system which counts thermo-mechanical stresses associated with high current incidents in cable screens is proposed. The stresses are assessed using data from conventional protection relays and the ratio of currents in the cable core and cable screens. The stresses can be used as an indicator of the cable joint condition. The presented phenomena are studied carefully in PowerFactory software. Theoretical considerations are confirmed using measurements taken in the real MV cable line. Finally, the results of a SWOT analysis are presented and future research activities are outlined.