A novel polarity comparison technique for protection of transformer feeder circuits

The paper describes the design and operation of a transient polarity comparison technique for the protection of transformer-feeder circuits. In contrast to conventional directional comparison technique, the proposed technique utilises fault generated transient signals rather than 50 Hz components. By this arrangement, the performance of the relay is not affected by problems using power frequency measurement, such as high impedance faults, power swings and CT saturation. The protection scheme was modelled using RTDS for the performance evaluation. Fault transient signals simulated on typical transformer-feeder circuit via CTs were processed by two relay models installed at both sides of transformer-feeder circuit. The polarities of fault transient signals measured by each relay were compared. The scheme performance was evaluated using different fault conditions encountered in practice. Results show that the proposed scheme is very promising.