Identification of defects in HV cable sheath based on equivalent impedance spectrum characteristic coding

In recent years, on-line monitoring and condition-based maintenance of HV cable systems have been extensively investigated to prevent cable fault. By analyzing cable sheath current, sheath defects can be identified. A new method of cable sheath defect identification is proposed in this study on the basis of the coding of the equivalent sheath impedance spectrum characteristics. In the proposed method, the sheath defects are identified by calculating the equivalent sheath impedance spectrum on the basis of the detected currents of the on-line sheath monitoring system. The equivalent circuit model of cross-bonded (CB) HV cable for sheath defect identification is constructed. The three-phase circuit model is decoupled to solve each phase independently in accordance with the CB scheme of the cable sheath. The equations of solving the equivalent sheath impedance are deduced. The criteria of sheath defect identification are proposed using the coding of characteristic parameters of the equivalent sheath impedance spectrum. Finally, a simulation model of the HV cable is built in the Simulink software to simulate 12 types of sheath defects. The simulation results have proven the correctness and efficiency of the proposed method.