RELATIONSHIP BETWEEN VOLTAGE INSTABILITY AND MULTIPLE LOAD FLOW SOLUTIONS IN ELECTRIC POWER SYSTEMS.

There have been observed several voltage instability phenomena in electric power systems where receiving end voltages oscillate remarkably or get much lower than the nominal values. Those phenomena tend to occur in heavy loaded conditions and seem to be related to the multiple load flow solution problem for the following reasons. It has been confirmed analytically and by simulations that the multiple load flow solutions are likely to appear under the heavy-loaded conditions, and that the individual solutions of the solution pair have different features from each other, from the standpoint of stability, although they are close to each other. This paper proposes a sequence of criteria which are applied to the individual members of a solution pair of the load flow to see their difference in behavior. The relationship between the voltage instability and closely-located solution pair is analyzed from various viewpoints for power systems in different types and sizes. A discussion of the paper is appended.