New modified first zone algorithm for transmission lines with series compensators

Increase in transmittable power, improvement in system stability, reduction in transmission losses, enhancement in voltage control and more flexible power flow control are the factors which promote the use of series compensator on transmission lines. However the presence of series compensator on the line affects the distance protection of the line in the form of under-reach or over-reach of the distance relay. In this paper, a new algorithm for first zone distance protection of series compensated lines with considering the effect of shunt capacitance of the line is presented. The algorithm detects whether the fault is in zone 1 of distance relay for series compensated transmission lines by comparing two specific impedances with three appropriate regions and then trip signal is decided by applying suitable logic.