Application of TCSC to restore directional overcurrent relay coordination in systems with distributed generation

In this paper a new approach is proposed to mitigate the directional overcurrent relay coordination problem, which arises from connecting distributed generation (DG) in looped power systems. It is based on the implementation of Thyristor Controlled Series Capacitor (TCSC) operating in fault current limiting mode to limit the fault current contribution from DG. Hence, the integrity of relay settings is preserved in emergencies. The original relay coordination is restored if the penetration level of DG is kept at a specified level. By the proposed method, the penetration level of DG is not a limiting factor anymore. The required TCSC inductive impedance beyond the penetration level of DG is indicated.