Incipient Weak Fault Detection in Cross-Bonded Cables Using Multichannel Sheath Currents

In high-voltage cable sheaths, incipient weak faults, such as jacket-damage grounding and high-resistance core–sheath breakdown, release little energy, rarely trigger protection, and can evolve into permanent faults. This study examines whether the topology-induced joint structure of multichannel sheath currents can support fault detection without fault samples. A Mahalanobis-distance-based method is formulated for the three-phase sheath circulating currents measured at a single cross-bonding box. An induction–leakage analysis relates the healthy joint structure to the bonding topology and shows how weak faults disturb it. A normalized pointwise Mahalanobis distance is combined with a threshold calibrated on separate healthy data and a K-consecutive-sample rule; the method requires no signal decomposition, and its per-sample cost is constant. On a PSCAD model of a 110 kV cross-bonded system, all 52 development fault cases are detected with confirmation delays below 6 ms; an independent sixteen-record healthy test is false-alarm-free after an envelope recalibration; boundary-grade faults under joint non-ideal conditions retain nine-fold margins; and per-line calibration extends the criterion to asymmetric and longer geometries. A twenty-seed Monte Carlo campaign shows zero noisy false alarms at all tested signal-to-noise ratios, the observable fault range being set by the disturbance-to-noise energy ratio of the acquisition chain.