Calculated DC resistance‐based pilot protection scheme for bipolar high‐voltage direct current transmission lines

Abstract

The current differential protection for high‐voltage direct current (HVDC) transmission lines has low reliability due to the distributed capacitive current and time delay. This paper proposes a pilot directional protection, which is based on the calculated DC resistance (CDCR) at both ends of DC lines. The characteristics of superimposed components and CDCR are analysed using the superposition theorem. The magnitude of CDCR is equal to the resistance of the converter for a forward internal fault, while it is equal to the sum of the line's DC resistance and the converter's resistance for a reverse fault. CDCR is a useful characteristic to construct the protection scheme as the resistance of DC line is significantly greater than that of the converter. Detailed simulation tests carried out on PSCAD/EMTDC under different fault conditions show that the proposed scheme is able to identify internal and external faults accurately.