Positive sequence phasor estimation-based pilot relaying scheme for shunt-compensated line

Abstract

Although the shunt Flexible AC Transmission System (FACTS) devices improve voltage profile, Shunt FACTS Devices (SFDs) may mal-operate the protection schemes due to reactive power injection. This study presents a phasor estimation-based pilot relaying for the SFD-compensated line. For a loaded line, the phase difference between the shunt FACTS device voltage and current is close to −90° as it injects the reactive power. However, it also draws small active power to meet the losses which deviates the working angle of SFD towards positive direction by some angle. Hence, the working angle of SFD depends on active and reactive power. During normal operation, this working angle can be estimated at both the relay locations. However, it is not possible to estimate exact working angle of shunt FACTS device at both the relay locations during an internal fault. The analysis reveals that estimated phase angle will largely tend towards positive direction during an internal fault. This criterion has been used to distinguish internal and external faults. The proposed relaying is robust against all real conditions and fast enough to detect a fault within desired time limits. Furthermore, the scheme is unaffected by the dynamics of SFD.