Fault diagnosis of 3/2 connection

In substations of power system, 3/2 connections are used commonly whose protective relay configurations are complex. There is lots of information when a fault occurs, especially when protective relays and circuit breakers fail to work. How to determine the fault component is particularly intricate. According to above features of 3/2 breaker schemes, this paper put forwards a new fault diagnosis method based on fuzzy Petri nets and associated tree. Markov state-space method is used to calculate the reliability of protective relaying system. This paper defines and corrects the action reality of the main protection, backup protection and breaker failure protection. The concept of group is introduced to define the associated tree, which is used to describe the topology of the 3/2 connection. The associated tree is created to identify every possible fault primary component according to breaker-primary component association. Depending on the relationship of protective relays, a fault diagnosis model based on fuzzy Petri nets is established to determine the faulty components and the fault type quickly and accurately. Finally, by forward and backward reasoning, the malfunctioned circuit breakers and protective relays, even the missing and/or false alarms can be identified. The simulation results given in this paper illustrate that this fault diagnosis method can make a rapid diagnosis and give an accurate evaluation about the 3/2 breaker scheme faults.