Study of functioning of relay protection system under regular check conditions

Abstract

An analytical model of the operation of the relay protection of power systems is presented, which takes into account such types of failures as unwanted operation, failure to operate, as well as defects dangerous from the point of view of unwanted operation and failure to operate. Operability checks of relay protection of power systems are conducted with a constant period. The listed events can be divided into two groups: random and regular ones. The presence of random and regular components of events of recovery of relay protection of power systems can be correctly taken into account in the framework of the apparatus of the theory of Markov processes. The model is based on the description of the process of operation of relay protection of power transmission line by a semi-Markov process. The functioning of the system in time is presented in the form of cycles. The cycle of the functioning of the system consists of a subset, where the system is functioning and verifi ed, and a subset, in which it is restored. The model is implemented in a graph with 9 states. Probabilities of events describe the process of changing states on a discrete set of states of relay protection of the power system. The probability of a change of states is the initial characteristic of a semi-Markov process. This model has enabled to obtain the dependence of operation and reliability parameters on the frequency of regular checks. It is established that the frequency of regular checks with the exponential distribution law overstates the value of the unavailability factor, since the time of the onset of a periodic check is greater than the mathematical expectation of a given value of the periodic check under a random distribution law. With a signifi cant time between checks, or in absence of periodic checks, the unavailability factor tends to a value that does not depend on the way of setting the time between periodic checks.