The impact of shunt-FACTS devices on distance relay performance

The paper investigates the performance of distance relays for shunt-flexible ac transmission system (FACTS) compensated transmission lines. Static var compensator (SVC) and static synchronous compensator (STATCOM) are considered as shunt-FACTS devices and the effect of different parameters, e.g. location of FACTS devices and fault along the transmission line, operation mode of FACTS devices, value of fault resistance and type of fault is studied on distance relay performance. Mathematical equations for calculating the impedance at the relaying point are presented for various scenarios and their validity is proved by extensive simulations. It is demonstrated that when the shunt-FACTS devices are located in the fault loop, e.g. they install in the mid-point and the fault occurs at the second half of the transmission line, the impedance seen by distance relay will be miscalculated and consequently, the distance relay will maloperate (under-reach or over-reach). Moreover, maloperation of the distance relay will take place, if the value of fault resistance is non-zero, whether the shunt-FACTS devices are in the fault loop or not. Deviation of measured impedance from its actual value is related to the location of shunt-FACTS device and its mode of operation for reactive power compensation.