Probabilistic voltage stability indexes

A probabilistic voltage stability index is proposed: the expected voltage instability proximity. To account for the system elements' forced outages, elements are represented by a two-state model. The resulting statespace is truncated by using a practical technique. Voltage stability is assessed for the truncated statespace by using sensitivity parameters that are evaluated from a fast decoupled load-flow contingency analysis exploiting optimal ordering and sparsity techniques. Voltage stability worst scenario is defined, and critical system elements are identified along with the probability of worst scenario to occur. Evaluation and use is demonstrated for a 30-bus system.