Consideration of Hidden Failures in Security Analysis

Many analyses of major system disturbances have shown that protection malfunctions play a key role in catastrophic power system failures. The malfunctions are often due to hidden failures that remain unrevealed until they are exposed by abnormal system conditions. Such hidden failures can transform a benign outage on an apparently secure power system into a major incident. This paper argues that security analysis should consider the possibility of hidden failures. A technique to identify the most dangerous double contingencies that might be caused by hidden failures is presented. Double contingencies are ranked on the basis of a risk index that combines their probability and a measure of their consequences. The most important of these contingencies should be added to the list of contingencies processed by security analysis programs. Test results on a 57-bus and a 162 bus systems illustrate these concepts and demonstrate the benefits of the proposed approach.