Out-of-step protection using the equal area criterion

Abstract

Power systems are interconnected for enhancing the availability of power supply to the customers and for reducing the prices charged to them. A natural consequence of this practice is that the interconnected power systems are likely to swing following faults and other disturbing events. Power swing relays are traditionally used to block distance relays from tripping line circuit breakers if the swing is not likely to cause dynamic instability but open the interconnecting lines if the systems are likely to become unstable. This is achieved by using delay timers but deciding on the delays is a very difficult, complex and judgmental issue. This paper presents a new approach for use in out-of-step relays. The technique is based on the well known equal area criterion. The basis of the protection technique is described in the paper. The technique is able to correctly identify swings that are likely to result in dynamic instability. © 2005 IEEE.