A Time-Domain Pilot Protection for AC Transmission Lines Connecting BESSs Based on Sequence Matching Index

Abstract

Battery energy storage station (BESS) possesses flexible operating states and complex fault characteristics. With the continuous increase in its installed capacity and number, the risk of maloperation of traditional relay protection significantly increases. To mitigate this risk, this paper presents a time-domain pilot protection that accommodates BESS’s operating states and fault characteristics. Firstly, the issue of the traditional current differential protection (CDP) caused by the integration of BESS is analyzed. Subsequently, the fundamental principle of the Jaro distance is introduced, and the criteria for calculating the number of matching points and transpositions are redesigned accordingly. The Jaro distance is utilized to evaluate the matching degree of current sampling sequences between BESS side and grid side, thereby accurately identifying internal and external faults. Additionally, by introducing delayed operating current sequences in the process of calculating the number of matching points, the security issue caused by current transformer (CT) saturation is resolved. Finally, PSCAD/EMTDC simulations and digital-physical co-simulation (DPCS) testing validate the proposed protection’s significant advantage. The results indicate that proposed protection algorithm offers gratifying performance in dependability, security and selectivity, and outperforms several emerging pilot protections.