Strategy for Switchover between the Ground Return and the Metallic Return Operation Modes of MTDC Systems

Abstract

For a multi-terminal HVDC (MTDC) system in the bipolar configuration with earth electrodes, the switchover between the ground return operation mode and the metallic return operation mode is under researched. An optimal strategy for switchover needs to be selected to minimize the interrupting capacities of the metallic return transfer breaker (MRTB) and the ground return transfer switch (GRTS) so as to reduce capital costs. To select an optimal strategy for switchover between the two operation modes of MTDC systems, the paper not only develops location selection schemes and switching sequences of MRTB and GRTS but also proposes a concise and feasible method to address the maximums of the interrupting current functions of MRTB and GRTS under every scheme and sequence using the random number calculation method. In the paper, based on a three-terminal HVDC system, numerical examples using MATLAB have proved the effectiveness of the proposed method of selecting an optimal strategy for switchover between the two operation modes.