Karami - Amirkadir Univ. of Tech.
Askarian Abyaneh - Amirkadir Univ. of Tech.
Jamali - Iran Univ of Science & Tech.

At present the step-by-step transient stability analysis isthe most accurate method for determining the critical clearing time(t,,). However ,this method is very time consuming as it is based on trial and error method. On the other hand, t, con be directly determined by using the transient energy function method, though with less accuracy. This paper presents a new method based on step-by-step and PEBS transient energy function methods in order to determine la,, quickly. The test results on two test system are also presented which confirm the validity of the new method.