A Model for Assessing the Magnitude and Distribution of Sheath Currents in Medium and High-Voltage Cable Lines

Abstract

In this article, the authors discuss a simulation model to study the effect of cross-bonding of metallic sheaths, and/or nonmagnetic armors, of single-core medium-and high-voltage cables in the same circuit. In single-core cables, the resistive losses due to the induced circulating currents in cable sheaths or armors cause an increase of the cable temperature, which therefore reduces its ampacity. This is a serious issue affecting the distribution and transmission lines. In addition, the risk of electric shock due to induced voltages may be present if a person is in contact with the armor/sheath at its unbounded end. For these reasons, special bonding techniques of metal sheaths are employed to reduce these currents. The simulation model to assess the magnitude and distribution of induced armor/sheath currents of medium-and high-voltage cables that is herein proposed may be used to optimize the cross-bonding configuration of single-core cables employed in high-current industrial applications or in transmission/distribution power grids. The model has been experimentally validated by means of actual data from a high-voltage underground line and field measurements performed by Prysmian Electronics.