Series Compensated Transmission Line Protection based on Mutual Impedance Scheme

Abstract

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.