A Novel Distributed Equivalent Circuit Model for Single-Core Cables

The number of cables used for urban power supply increases rapidly. The sheath current in these cables, which is generated via induction, produces a current loss. When the situation is serious, the ground lead and the middle connector of the cable will be burned. In this paper, the existing single-core cable equivalent circuit model is used to calculate the sheath current of a 3-phase cable under the condition of non-transposition and cross connection. By comparing the calculated results with the simulation and the experimental results, it is found that the current distribution law for the sheath, which was obtained using the existing model, differs substantially from both the simulation and actual measurements. The error reason of the existing model is revealed, and it is found that the magnitude and phase of the current in the metal sheath of the cable varies with the position under the combined effect of distributed capacitances in the cable and the core-current flux, especially for a 3-phase cross connection, each section of the cable does not meet Kirchhoff’s laws, but the sheath electric current in the existing models are considered equal everywhere. Therefore, a novel cable equivalent model is proposed in this paper, which is based on a distributed circuit, and an equation to calculate the sheath current is derived. The model presented in this paper corrects the problems of the existing model, which can be applied to power system, subway, high-speed rail, and any application of single-core cables.