An improved reliability model for redundant protective systems - Markov models

In recent years, a number of reliability models of power system components including protective-system failures have been proposed. These models have concentrated on modeling a single protective device. When this protection fails, it is usually assumed that backup protection will isolate the faulted component with 100 % reliability. In reality, power system components have redundant protection schemes with two or more protective devices operating in parallel. Existing reliability models have not dealt with redundant protective systems adequately. This paper presents an improved reliability model capable of modeling these systems. The proposed Markov model and the equations for a number of important performance indices are derived and illustrated in this paper using the data for a typical transmission system.