S-Transform Assisted CUSUM Based Protection Strategy for Transmission Lines Possessing UPFC

The different operating modes of unified power flow controller (UPFC) affect the voltage, current and hence the measured impedance at the relay location both during steady-state and transient conditions. As a result, the conventional distance relay based on fixed impedance setting finds difficulty in protecting the UPFC compensated transmission line (TL). In this paper, the effect of UPFC on distance protection is studied explicitly and a Fortescue and Stockwell transform based fault detection and classification scheme is proposed. The functioning of the proposed technique is evaluated by simulating data for different fault cases on a 400 kV two-bus and double circuited UPFC installed power system through EMTDC/PSCAD software. The fast and accurate results for the proposed scheme clearly justify the efficacy of the proposed relaying technique for UPFC compensated line.