In my earlier Video titled "Power Angle curve of Synchronous Generator" it was seen that Generator becomes unstable after Load Angle becomes more than 90 Degree.
Suppose there is Transient and Load Angle crosses 90 Degree momentarily, Question is whether Generator will return back to Stability. For finding out that Equal Area Criteria is used. Using Equal Area Criteria, Critical Clearing Time is found. Fault should be cleared before Critical Clearing Time.
At Steady State suppose Load Angle is delta 0. Fault occurs and Electrical Output Power becomes Zero. Rotor accelerates and Load Angle becomes delta 1. At Load Angle delta 1, fault clears and Electrical Output Power restores. Since Angular Velocity of Rotor is still greater than Angular Velocity of Stator, Load Angle keeps on increasing till Load Angle becomes delta 2.
Between Load Angle delta 0 and delta 1, Rotor accelerate and Area under Power Angle Curve is called Area of Acceleration. Between Load Angle delta 1 and delta 2 there is deceleration. Area under Power Angle Curve is called Area of Deceleration.
Using Swing Equation it can be proved that both Areas are equal.
Thus Energy stored during Acceleration is released during Deceleration.
Негізгі бет Transient Stability in Synchronous Generator Equal Area Criterion
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