Digital relaying scheme for protection of shunt-compensated transmission lines

The role of shunt Flexible AC transmission System (FACTS) devices is to improve voltage profile. However, in the presence of Shunt FACTS Devices (SFDs), protection schemes may incorrectly operate as SFDs inject reactive power in the line. This study presents an Imaginary component of Virtual Fault Impedance (IVFI) based improved relaying for the transmission line in the presence of SFD which is immune to large variations in source impedance. During normal operation or during an external fault, the magnitude of IVFI is very large, on the other hand, during an internal fault, the magnitude of IVFI is either zero or very small. The proposed scheme can be used to detect the internal fault and to classify fault type and it is applicable to uncompensated transmission lines also. The EMTDC/PSCAD simulations are carried out to investigate the performance of the proposed scheme. The scheme is found to be selective, robust, and accurate for all possible faulty conditions, for different types of SFDs with different compensation levels and for high resistance faults.