Consideration of excitation control for transient stability assessment

Direct transient stability margin (TSM) prediction using the `extended´ equal-area criterion method is able to provide fast dynamic security assessment when used with the classical generator model. However, the latter model is found to be too crude for many practical engineering applications. The TSM prediction has previously been successfully extended to accommodate the use of the two-axis generator model, i.e., the constant E´q model, which is more acceptable by the utilities for both planning and operation purposes. In this paper, the TSM prediction technique is further developed by incorporating the effect of excitation control on the transient energy of a multi-machine power system during the first swing. The models used are: the generator represented by the two-axis model and the exciter and regulator represented by (i) one gain, one time constant and one limiter, and (ii) one PI control term, one time constant and one limiter. The proposed method has been tested on a typical three-machine power system, and very promising results have been obtained. The simulation results show that the method can provide reliable, accurate and fast information about the TSM of a multi-machine power system with excitation control realistically considered