With the increase in the number of Static Synchronous Compensator (STATCOM) type FACTS devices in transmission lines, operation of distance relays in transmission lines are affected. It is very important that the distance relays do not maloperate under system fault conditions, as this will result in the loss of stability or the security of the system, which defeats the main objective of installing a STATCOM. As STATCOM type FACTS devices has fast response and their functional characteristics and control system introduce dynamic changes during fault conditions in a transmission line it is important that distance relays perform correctly irrespective of such dynamic changes introduced during fault. In this dissertation, the measured impedance at the relaying point is calculated and the analytical and simulation results of the application of distance relay for the protection of transmission line incorporating Static Synchronous Compensator (STATCOM) are presented. A detailed model of STATCOM and its control is proposed and integrated into the transmission system for the purposes of accurately simulating the fault transient.
An apparent impedance calculation procedure for transmission line incorporating STATCOM based on the power frequency sequence circuits has been explored. The simulation results show the impact of STATCOM on the distance protection relay during the different fault condition; the influence of location of STATCOM, the setting of STATCOM control parameters and the operation mode of STATCOM are studied as well. The results are presented in relation to a typical 138kV transmission system employing STATCOM. Followed by a review of the effects of a STATCOM connected at the midpoint of a transmission line on the performance of distance protection relays.