Transient stability output margin estimation based on the energy function method

In this paper, a new method of estimating the critical generation margin (CGM) in power systems is proposed based on transient stability diagnostics. The proposed method can directly compute the stability limit output for a given fault based on the transient energy function method (TEF). Since CGM can be directly obtained by the limit output using estimated P‐θ curves and is easy to understand, it is more useful than the conventional critical clearing time (CCT) of the energy function method. The proposed method can also estimate CGM as a negative value, which means instability in the present load profile, and so a negative CGM can be directly used as a restriction on generator output. The accuracy and fast solution ability of the proposed method are verified by applying it to a simple 3‐machine model and IEEJ EAST10‐machine standard model. Furthermore, the usefulness of the method for severity ranking of transient stability for various fault cases is discussed by using CGM. 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(3): 10–19, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/ eej.21035