Relaying scheme for STATCOM compensated transmission line

Static Synchronous Compensator (STATCOM) is a high speed controllable reactive power compensator used to improve the voltage profile. STATCOM can inject/draw the reactive power by shifting the phase of its voltage relative to the bus voltage. The challenges in the presence of STATCOM have been reported in the existing literatures such as under/over-reaching of distance relays etc. In this study, a directional based internal fault detection scheme (based on superimposed energy) is presented. Along with fault injected superimposed components, there are STATCOM injected superimposed components also. However, it is found that STATCOM injected superimposed components are smaller than that of fault injected components. A relay detects forward fault if superimposed energy is negative and it detects reverse fault if superimposed energy is positive. For internal fault, both the relays detect forward fault whereas for external fault, one of the relays detects reverse fault. The developed criterion is independent of the dynamics and degree of compensation, and is adaptive to the system changes. The criterion works accurately for different types of fault and different locations of the STATCOM. Further, the scheme is fast enough to detect the fault within one cycle.