Properties of indices for voltage stability assessment

The paper deals with evaluation of a power system from the view-point of voltage stability. It is concerned with the indices which are proposed as voltage collapse proximity indicators. In the existing papers, many such indices can be found. In the paper, the so-called line stability indices, defined using the static approach to the study of voltage stability, are taken into account. If the line stability indices are close to 1, a line can be considered to be critical. After the considered indices are described, investigations of correlation of values of the mentioned indices and results of a single-contingency analysis for a power system are presented. The investigations shows, that not always when the branch stability indices are large the outage of the branch is critical, and the outage of a branch can be critical, though values of branch stability indices are low.