Distance protection for HVDC transmission lines based on MMC modulation strategy

Abstract

In case of permanent pole-to-ground line faults bipolar High-Voltage Direct Current (HVDC) transmission systems can be kept in operation as asymmetrical monopoles. However, power transmission is limited to half of the system's rated power during that time. To reestablish bipolar operation maintenance measures are needed, which can only be performed, if the fault location is known. Within this paper, a new distance protection concept for HVDC systems based on full-bridge modular multi-level converter (MMC) modulation strategy is introduced. An enhanced converter control is used to evoke an alternating current (AC) component on the faulted pole enabling the evaluation of a reactive line loop impedance component. By that, the distance to the fault location can be estimated. The developed concept is applied in a PSCAD model and different fault scenarios are investigated. As the results indicate, the developed concept can successfully be used to localize HVDC transmission system faults, before the faulted line segment is isolated from the rest of the system. Thereby, the proposed technique does not require a communication infrastructure or high sampling frequencies.