Incipient Fault Detection of Medium-Voltage Distribution Cable Systems Using Time-Frequency Analysis of Grounding Wire Currents

Incipient cable faults pose a significant risk to the normal operation of power grids. Addressing the issue of detecting incipient faults in underground cables is particularly difficult due to their hidden external characteristics that are not easily observable. Furthermore, these faults occur randomly, with short durations, which further complicates their detection. This paper firstly establishes a cable field-circuit equivalent model that considers multi-conductor electromagnetic coupling for incipient faulty scenarios. The mathematical relationship between the grounding wire currents (GWCs) and fault conditions is then theoretically deduced specifically. A novel method is developed to detect incipient faults in three-core cables by analyzing the time-frequency characteristics of GWC frequency components considering the time-varying fault resistance. The simulation results demonstrate the effectiveness and robustness of the proposed method, showing little impact from fault initial conditions, disturbances, and distributed generations (DGs). Finally, the method is verified in an actual 10 kV distribution network.