A high-speed protection scheme for the DC transmission line of a MMC-HVDC grid

Abstract

High Voltage Direct Current (HVDC) grids based on Voltage-Source Converters (VSC) are flexible and can absorb large amounts of renewable energy. However, since the magnitude of fault current increases quickly, and it cannot be controlled after DC transmission line fault, the DC transmission line protection should operate very fast after the fault event. Otherwise, the DC circuit breakers will not be able to interrupt such a large fault current, which may cause permanent damage to the devices in the converter station. Based on the analysis of the feature of fault-induced travelling waves after DC transmission line fault, this paper proposes single-ended initial travelling wave based protection scheme. Based on the analysis of the feature of lightning disturbance, this paper also proposes fast identification scheme for lighting disturbance, in order to increase the reliability of the protection and maintain the high operation speed at the same time. A protection device prototype has been designed and implemented. Abundant tests have been conducted to verify the performance of the prototype device. The operation time of the protection is less than 1.2ms.