Detection of Incipient Faults in Distribution Underground Cables

The incipient faults in underground cables are largely caused by voids in cable insulations or defects in splices or other accessories. This type of fault would repeatedly occur and subsequently develop to a permanent fault sooner or later after its first occurrence. Two algorithms are presented to detect and classify the incipient faults in underground cables at the distribution voltage levels. Based on the methodology of wavelet analysis, one algorithm is to detect the fault-induced transients, and therefore identify the incipient faults. Based on the analysis of the superimposed fault current and negative sequence current in the time domain, the other algorithm is particularly suitable to detect the single-line-to-ground (SLG) incipient faults, which are mostly occurring in underground cables. Both methods are designed to be applied in real systems. Hence, to verify the effectiveness and functionalities of the proposed schemes, different fault conditions, various system configurations, and real field cases are examined and other transients caused by permanent fault, capacitor switching, load changing, etc., are studied as well.