Novel method of finding the first swing stability margin of a power system from time domain simulation

A novel method of determining the first swing stability margin of a power system is presented by directly analysing the output results of the conventional time domain simulation method. Unlike hybrid methods, the proposed method does not use the concept of the transient energy function method in finding the stability margin. This avoids the computation of pseudo fault-on trajectory or line search and also eliminates the additional computational burden and modelling limitations associated with the transient energy function method. For a stable system, the proposed method determines the stability margin from the decelerating power of the severely disturbed machines when their post-fault angle reaches the peak values. For an unstable situation, the instability margin is determined from the minimum post-fault speed of the unstable machines. The method is very simple to implement and requires only the time response of machine angles and speeds. The proposed method was successfully applied to the CIGRE and Iowa systems for a number of fault conditions