A Modified Ratio Braking Differential Current Protection Criterion for Energy Storage Station

In current engineering practice, short circuit current of the energy storage is affected by the pre-fault charging and discharging state, and its active component is consistent with the pre-fault state. Therefore, when energy storage encounters an access line fault in the charging state, the phase difference between the short circuit current of it and that of the system on the other side of the line may be greater than 90°, which brings the risk of current differential protection refusal. In this paper, a modified ratio braking current differential criterion is proposed, which can effectively reduce the phase difference between the fault phase currents on the two sides of access line, avoid current differential protection refusal and improve the protection sensitivity. By simulation, this modified criterion is verified.

I. Introduction

In current engineering practice, when a fault occurs on the access line, energy storage needs to change control mode to satisfy the fault crossing requirements specified by the national standard [1]. In addition to this, during the relay protection action time, the control strategy of the energy storage will try to ensure that its charging and discharging state remains stable. Therefore, influenced by the pre-fault charging and discharging states, the direction of the active component of the short circuit current supplied by the energy storage remains consistent with that before the fault. When the energy storage encounters a fault on the access line in the charging state, the phase difference between the short circuit currents of fault phases on both sides of the access line may be greater than 90°, and the conventional ratio-braking current differential protection has the risk of refusing to act.