Power-system small-signal stability and maximum loadability

This paper presents an efficient method for power-system maximum loadability assessment considering small-signal stability. Conventional methods are based on accurate load-flow solutions and calculation of all the system eigenvalues. The proposed method uses appropriate equivalents to reduce the computation time of the load-flow solution and also applies a special approach to find only the worst-damped modes. Hence, the computation time is reduced considerably with respect to conventional methods. The approach uses the REI (Radial Equivalent Independent) equivalent of the network for a quick load-flow solution of the different operating points rather than detailed computation of a sequence of exact power-flow cases. Meanwhile, instead of calculating all the eigenvalues, only the worst-damped ones are evaluated using the S-Matrix method. The algorithm also considers practical aspects of the power systems, so that it does not perform the calculation for cases where the maximum loadability is more than the maximum units generation. Since the distance between any operating-point loading of a power system and its permissible maximum loading without small-signal instability is evaluated in this method, it is expected that further developments in this respect will lead to the possible implementation of on-line small-signal stability assessment packages on an energy management system in the near future.