Adaptive distance protection for multi-terminal lines connecting converter-interfaced renewable energy sources

Variation in infeed current challenges the distance relay performance significantly for protection of multi-terminal lines. Underreach issue with such a line configuration becomes more prominent for a relay at the substation when connected to renewable sources, due to generation variability and converter control operation. This may result in an incorrect decision by the distance relay, especially with a fixed zone-1 setting. In this paper an adaptive distance relaying method is proposed for such line configurations. The method obtains the remote end data during pre-fault and calculates the fault distance to derive accurate protection decision. Performance of the proposed method is tested for a three-terminal line using PSCAD/EMTDC. Comparative assessment with conventional distance relaying demonstrates the superiority of the proposed method.