1991 Volume 111 Issue 3 Pages 267-276
In order to monitor the voltage stability of an electric power system, various voltage stability indices have so far been proposed. However, they behave quite differently from index to index, and hence, none of them can be an almighty index being effective for a wide variety of voltage instability situations. Therefore, the development of an effective monitoring scheme by the combination of several powerful indices has become one of major topics in power system engineers. In the authors' opinion, minimum requirements for such a scheme should be: (1) to indicate a system-wide stability margin, (2) to show loading margins at critical buses, (3) to provide correct results and (4) fast computation time. It is also desirable that constitunent indices should change linearly with respect to load level and should be continuous even when the reactive power output of a generator reaches the upper limit.
This paper proposes an effective monitoring scheme using three indices that satisfy all the above requirements. First, based on an examination of multiple load flow solutions, we have developed a method to find important buses associated with voltage collapse. Then, a new index is proposed which can indicate loading margins to these buses. It is shown that the new index, combined with two of the conventional indices, enables successful monitoring. The linearity and continuity are realized by a normalization operation on these indices. The effectiveness of the proposed approach has been verified through numerical simulations on the IEEE 30, 57, 118 bus test systems.