Saeed Khazaei - Amirkabir University of Technology Tehran, Iran
Shahram Montaser Kouhsari - Amirkabir University of Technology Tehran, Iran
Mehdi Zareian Jahromi - Amirkabir University of Technology Tehran, Iran

Power system stability is a complex problem that has challenged power system engineers for many years. This paper studies transient stability assessment using direct methods by Extended Equal Area Criterion (EEAC) and Transient Energy Function (TEF), and suggestes a Stability Factor (SF) for transient stability margin. Firstly, the proposed method calculates the critical kinetic energies for all machines in a power system. After it, when fault occurs, the system is separated into two bunches: the Severely Disturbed Group (SDG), and the Less Disturbed Group (LDG). Then the stability margin of system is rapidly judged. The proposed method has been tested to IEEE 9bus test system and the obtained results show usefulness of this method.

Transient stability; direct methods; energy function; critical machines