Power Swing Detection and Out-of-Step Prediction Using the Equal Area Criterion

Abstract

During the operating conditions, the modern interconnected power systems are more subjected sudden changes, such as faults, network changes due to line trip outs, and disconnection of a large load or of a generating plant. Such disturbances create power swing among the other generators which forces the remaining generators to adjust and settle to new stable conditions. In some cases, the swings are so large that some generators run out of step and lose synchronism. During stable power swing, if the measured impedance becomes very small and enters the distance relay zones, it can lead to an undesired trip of the distance relay. So, fast and proper detection of power swing and fault is very important for distance protection. It is also very important to distinguish between stable and unstable power swings. So, many different methods are used for detection. This paper presents a new approach based on equal area criterion to detect system stability. The fundamentals and its application to detect fault and power swing are discussed in this paper. With the help of MATLAB/SIMULINK simulations technique, we can also distinguish stable and unstable power swing correctly, which is very useful for setting of out of step blocking (OSB) and out of step tripping (OST) functions.
Keywords: Distance protection, stable and unstable power swing, loss of synchronism, equal area criterion