Measuring cable sheath currents to detect defects in cable sheath connections

This paper presents a method for detecting different types of defects in the cable sheaths interconnected in a cross bonding configuration of a HV cable system installed in flat or trefoil layout using the sheath currents as input data. Three different defects have been analyzed: electric continuity loss of earth connection, short-circuit between sectionalized metal sheaths of a cable joint and link-box flooding. The sheath current has been calculated by two different approaches, one on the basis of theoretical equations, programed in MATLAB® and the other on the basis of ATP software simulating the cable system model. The results obtained using both methods have achieved a good agreement between them. A simple criterion by the means of a easy normalized code of four discrete levels 0, 1, 2 and 3 has been developed to distinguish the magnitude level of change of sheath currents in case of the indicated defect existence in order to trigger alarm.