Analysis of Induced Voltages on the Sheath of Double-Circuit Underground Power Lines - Part I: Without Phases Transposition

This paper introduces mathematical formulations for calculating induced voltages on the sheath of non-transposed double-circuit underground transmission lines, emphasizing four formations of three-phase power lines. For these formations, sectionalized and continuous cross-bonding techniques were employed to evaluate and reduce induced voltages on sheath. Our study centers on two critical aspects: first, calculating induced voltages on the sheath of underground lines and, subsequently, computing current imbalance in an underground sub-transmission system. The results indicate that the induced voltages and currents on the sheath generated by the four formations are distinct in each phase, uncontrolled, and have high values. The induced voltages achieved values up to 287.88 V when utilizing the flat formation with continuous cross-bonding, leading to high losses on the sheath and decreasing the current rating. This comparative study emphasizes the importance of carefully evaluating the method of bonding the sheaths, the types of formations used, and the necessity of phases transposition to ensure the safe and efficient operation of double-circuit underground transmission lines.