Series Compensated Transmission Line Protection based on Mutual Impedance Scheme

In conventional distance protection scheme, positive sequence impedance is used to protect a transmission line against short circuit faults. The presence of series compensation increases the load-ability of transmission line and it helps in improving the power system stability. It provides a better voltage profile along the transmission line. The presence of series compensator in the fault path affects reach and directionality of distance relays. Due to the presence of series-compensation, the positive-sequence impedance of the fault path is affected, due to this the distance relay mal-operate. In order to overcome this drawback of distance relay, the concept of mutual impedance-based relaying is proposed as a new protection scheme. Since mutual impedance does not get affected by presence of seriescompensation. In this study, mutual impedance-based distance protection scheme is presented for series-compensated transmission lines. The values of current and voltage at both the ends of the line are used for computing the mutual impedance between the relay and fault point. The proposed scheme can protect the line against single line to ground and double line to ground faults. The protection scheme gives reliable results when it is tested against single- line-to-ground faults and double-line-to-ground faults. The performance of the proposed scheme is studied by computer simulations using MATLAB and its results are compared with conventional distance protection scheme