Impact of FACTS devices on distance protection in transmission system

Due to the development in the field of Power Electonics many FACTS devices such as SVC, STATCOM, TCSC, UPSC are introduced in transmission lines. These devices are used to improve the system voltage profile, stability, Powerflow etc. Distance Relays are unique devices used to protect the transmission line from various faults. The reach of the relay is independent of the type of fault. Distance Relays are very sensitive to the apparent impedance seen by the relay and its zones. When a FACTS device say as TCSC is incorporated into the existing transmission line in order to improve the voltage profile, power flow, stability, etc it introduce problems in distance protection scheme in the measurement of the apparent impedance seen by the relay. Due to this significant change in the apparent impedance seen by the relay, it will lead to the mal operation of distance relay. This paper presents about the maloperation of distance protection of transmission line, when it is compensated by a series compensating device such as Thyrister Controlled Seies Capacitor(TCSC).