Transient stability analysis with equal-area criterion for out of step detection using phasor measurement units

The electrical power systems function as a huge interconnected network dispersed over a large area. A balance exist between generated and consumed power, any disturbance to this balance in the system caused due to change in load as well as faults and their clearance often results in electromechanical oscillations. As a result there is variation in power flow between two areas. This phenomenon is referred as Power Swing. This paper presents a transmission line protection scheme that uses measured values of the currents and voltages of the three phases of two buses (equivalent to PMU data). The measured data is transformed from time domain into phasor domain using Discrete Fourier Transform to predict whether the swing is a stable or an unstable one. The performance of the method has been tested on a simulated system using PSCAD and MATLAB software. The proposed scheme can be used for the detection of out of step condition using equal-area criterion with different types of faults at different locations and different models of transmission lines.