Enhanced selectivity and fault detection for distance protection in meshed grids by evaluating local 50‐hz‐phasors

Abstract

AbstractDue to different operating conditions distance protection units measure varying short‐circuit impedances (impedance uncertainty) and with that varying fault locations for one and the same short circuit. Therefore, it is necessary to reduce the reach of the respective time zones to avoid unwanted relay operation. This, however, may lead to an undesirable long fault clearance time. For the first time zone an optimal uncertainty minimizing strategy is presented based on pre‐fault power measured at the relay. For back‐up protection a method is proposed that minimizes the impedance uncertainty with the help of symmetrical components. As a result of meshed grids, the problem is often to detect short circuits in higher time zones on the whole. To cope with that problem a simple method is discussed, which allows an optimal distinction between load and fault states.