Evaluation of dynamic voltage stability of a power system

Voltage stability is one of the major factors that dictates the maximum loadability of a power system. This paper investigates the dynamic aspect of voltage stability problem of a simple power system by considering the dynamic effects of both fast-acting and slow-acting devices. A comprehensive computer program in Matlab/Simulink environment is developed for this purpose. The effects of slow acting devices, such as on load tap changers, over exciter limiters, etc. on long-term voltage stability is vigorously tested. It is observed that, for some disturbances, the system may not face any voltage instability problem in short-term but it may suffer from voltage instability problem in long-term because of the activation of generator over exciter limiter. It was also observed that both the short-term and long-term voltage stability limits can be improved by providing adequate reactive power support at load buses.