Proper detection and treatment of power swing to reduce the risk of blackouts

Any sudden load change in a power system, such as a fault, line switching etc. causes the system´s generators to adjust to the new condition. In that case a power swing may occur. This paper describes a zero-setting power-swing detection method that is independent of network parameters. Power swing can be detected up to 10 Hz swing frequency, also during open pole condition and during asymmetrical operation. A blocking logic prevents unselective trips by the distance protection. For unstable power swings a flexible out of step tripping function will be proposed. The coordination of power swing detection, distance protection and out of step protection provides a reliable system protection. The risk of unwanted trips and cascading effects in the power system will be reduced.