Lecture_11 Equal Area Criterion Equal area criterion is one of the methods method to analyse the stability of power system. In this method, the t fault clearing time is considered as it plays important role on transient stability. When fault occurs in the system, in that case, if the fault is cleared much faster, that is much very quickly,, then the system may remain stable. Whereas, if more time me is taken to clear the fault then the disturbance, that is the accelerating power or decelerating dec power, will be remaining for a much longer period of time. And the system become unstable under such situation. Take an example, where a synchronous machine is connected to an infinite bus, through a transformer and a transmission line as shown in fig, as follows. Critical Clearing Angle How to find Critical Clearing Angle a. From Equal area criterion b. From Swing equation Case of Two Parallel Lines a. Equal area criterion applied to the opening of one of the two lines in parallel b. Equal area criterion applied to Short circuit at one end of line and disconnected at δC c. Equal area criterion applied to Short circuit at middle of one line and line is disconnected at δC ****