Current trajectory coefficient based time domain line protection for battery storage energy stations

On account of distinctive fault signatures, the extensive integration of large-scale battery energy storage stations (BESSs) results in severe performance degradation of relaying protection. Firstly, the performance problems of classic current differential protection and recently proposed cosine similarity coefficient-based pilot protection are illustrated. Subsequently, the trajectories of two current pairs in two-dimensional space, i.e., fault path current and current on BESS-side, fault path current and current on grid-side, are described and relationship of these three currents is analyzed. On this basis, this paper presents current trajectory coefficient-based time domain protection algorithm for transmission lines connecting BESSs. It describes the basic principle of protection algorithm and designs the operating and restraining regions of two current trajectories. The authors widely assessed the performance of proposed protection algorithm under internal fault by varying fault location, type, resistance and operating state of BESS. Furthermore, the security of proposed protection algorithm was also tested under various nonideal conditions, including severe current transformer (CT) saturation, CT measurement error and outliers. The results indicate that proposed protection algorithm offers gratifying performance in operating speed, dependability, security and selectivity, and outperforms current differential protection and recently proposed pilot protection. •Performance problems of classic and recently proposed pilot protection are illustrated in the presence of BESSs.•The trajectories of two current pairs in two-dimensional spaceare analyzed.•Protection algorithm based on current trajectory coefficient is presented, which is applicable to fault signatures of BESSs.•The proposed protection algorithm offers gratifying robustness against various nonideal conditions.•Proposed protection algorithm exhibits excellent performance in operating speed, dependability, security and selectivity.