Effect of TCSC on distance relay tripping characteristic

Distance relays are widely used as the main protection for transmission lines, though they can provide the back-up protection. They operate based on impedance measurement at the relaying point, which is affected by several factors, including the pre-fault line loading condition and short circuit levels at the line ends. The introduction of flexible AC transmission system (FACTS) devices imposes further changes on the apparent impedance measured at the relaying point. The paper studies the effect of one type of FACTS device, the thyristor controlled series capacitor (TCSC), on the apparent impedance measured by the distance relay. In addition to the TCSC control parameter, its installation point affects the apparent impedance. The paper shows the variation of the tripping characteristic of the distance relay for different installation points and control parameter of the TCSC.