Synchrophasors-based transmission line protection in the presence of STATCOM

Abstract

The distance relay using the transmission line impedance measurement identifies the type and location of the fault. However, any other factors that cause the failure of the measured impedance, makes the relay detect the fault in incorrect location or do not detect the fault at all. One of these factors is the fault resistance which directly increases the measured impedance by the relay. Another factor that indirectly alters the impedance of the transmission line is static synchronous compensator (STATCOM). When a fault happens, current injection by the STATCOM changes the measured signals by the relay and thus makes the calculated impedance incorrect. In this paper, a method is provided based on the combination of distance and differential protection. Firstly, from the current data of buses, faulted transmission line is detected. Then using the presented algorithm, the fault location is calculated on the transmission line. The basis of the algorithm is on the active power calculation of the buses. Fault resistance is calculated from the active powers and its effect will be deducted from calculated impedance by the algorithm. Furthermore, with choosing data of appropriate bus, STATCOM effect is eliminated, and fault location will be obtained.