Underground/Submarine Cable Protection Using a Negative-Sequence Directional Comparison Scheme

Protective relaying requirements for underground and submarine cables are different from those for overhead lines. This paper analyzes the application of directional comparison schemes to protect two 34.5 kV submarine cables. These cables are 24-km long and connect Cozumel Island to Mexico’s mainland network. The paper discusses cable modeling using symmetrical components and analyzes the performance of a negative-sequence directional element during cable fault conditions. INTRODUCTION Traditionally, current-differential relays have protected cables in transmission and distribution applications. These applications also require directional overcurrent or distance relays to provide protection when the communications channel is out-of-service. This paper proposes an alternative solution for unbalanced fault protection. The solution is based on negative-sequence directional relays in a directional comparison scheme. This solution provides excellent fault resistance coverage and does not require additional backup protection. The paper also analyzes the performance of the directional relay in cable applications when the cable admittance is not negligible. UNDERGROUND AND SUBMARINE CABLE PROTECTION Power cables are the most reliable means of connecting different equipment in an electric system [1]. They can be used as transmission or distribution links. We expect more power cable applications in electric systems because of advances in cross-linked polyethylene (XLPE) cable technology, environmental restrictions, and right-of-way availability. Power cables require protection for overload and short-circuit current conditions. Power cable protection applications must consider different cable impedance characteristics and configurations.