On-line incipient faults detection in underground cables based on single-end sheath currents

Incipient faults in underground cables would repeatedly occur until they evolve into permanent faults. Detection of incipient faults can determine the status of cable insulation and provide an early warning before the breakdown of underground cables. The characteristics of traveling waves of incipient faults are analyzed in the modal domain, and the theoretical analysis shows that the sum of sheath currents can be used to detect incipient faults. Both the over-current and the wavelet transform modulus maximum of the sum of single-end sheath currents are examined to detect an incipient fault. After an incipient fault is detected, the faulty phase is selected according to the root-mean-squares of three phases. A cable system model is built in PSCAD/EMTDC, and simulation results show that the detection algorithm can accurately detect incipient faults under different fault conditions.