A New Out-of-Step Relay with Rate of Change of Apparent Resistance Augmentation

A new concept in out-of-step protective relaying that has several advantages over conventional out-of-step relaying is developed. The technique involves augmenting apparent impedance or apparent resistance based control with computed rate of change of apparent impedance or resistance. By use of appropriate control laws plus adaptive features, a relay which can be set closer to stability limits is obtained.