Waveform distortion impact of TCSC in FCL mode on transmission line protection

This paper presents the impact of waveform distortion of Thyristor-Controlled Series Capacitor (TCSC) operating as a Fault Current Limiter (FCL) on transmission line distance protection. Although the poor waveform and the high valve stress of TCSC in inductive boost mode is less attractive for steady state operation, it is more desirable for limiting the fault current by increasing the inductance of the line higher than the parallel combination of the capacitor and the reactor. This mode of TCSC operation is accompanied by high current distortion which can seriously affect the commercial distance relay functionality not suitably designed for such circumstances. Simulation results show the extent of waveform distortion. A real relay widely applied in power systems is used for testing. The results indicate poor behavior of the relay when TCSC operates as a FCL.