¹C. M. Khan, ²C .K. Chanda and ³S. C. Konar, ¹Global Institute of Management and Technology, India and ^2,3Bengal Engineering and Science University, India

Stability analysis programs are a primary tool used by power system planning and operating engineers to predict the response of the system to various disturbances. Important conclusions and decisions are made based on the results of stability studies. The conventional method of analyzing stability is to calculate the transient behaviour of generators due to a given disturbance. Direct methods of stability analysis identify whether or not the system will remain stable once the disturbance is removed by comparing it with a calculated threshold value. Direct methods not only avoid the time consuming solutions required in the conventional method, but also provide a quantitative measure of the degree of system stability. This additional information makes direct methods very attractive when the relative stability of different plans must be compared or when stability limits must be calculated quickly. Direct methods of transient stability analysis of a multi machine power system, using a function describing the system's transient energy, are discussed. By examining the trajectory of the disturbed system, the following fundamental questions are dealt with: the concept of a controlling unstable equilibrium point (U.E.P), the manner in whichsome generators tend to lose synchronism, and identifying the energydirectly responsible for system separation. Resolving this issue will substantially improve transient stability analysis by direct method.

Transient stability, power system, directs method, transient energy function, energy merging, and Stability limit formulation.