Estimation Method of Metallic Sheath Current of High-Voltage Power Cables Based on Field Data

Sheath current is a critical indicator for defect diagnosis in the metallic sheath grounding system of high-voltage single-core shielded power cables. In practical engineering, the absence of precise cable electric and structural parameters and layout details makes it difficult to accurately calculate defect-free sheath current values using theoretical formulas, potentially leading to misjudgment. This paper proposes a data-driven functional methodology for estimating the normal sheath current. The approach estimates the normal sheath current of a target cable section using field-measured sheath current data from a reference cable section, based on the similarity between the two sections and the relationship between sheath current and key factors. A sheath current calculation model is established using multi-conductor transmission line theory and two-port electrical network theory to analyze the influence factors on sheath current. Through simulations under trefoil, flat, and right-angle layout formation, fitting functions are derived to describe the relationship between sheath current and key factors, including ground resistance, length unbalance rate, average minor section length, and load current. Based on these fitting functions, an estimation formula is proposed to account for differences between the target and reference sections in terms of influencing factors. This method enables the determination of normal sheath current without prior knowledge of inductance, induced potential, or other electrical parameters of the power cable. As a result, it improves the accuracy of defect diagnosis in cable sheath systems.