Time Coordination of Distance Protections Using Probabilistic Fault Trees With Time Dependencies

Distance protection of the electrical power system is analyzed in the paper. Electrical power transmission lines are divided into sections equipped with protective relaying system. Numerical protection relays use specialized digital signal processors as the computational hardware, together with the associated software tools. The input analogue signals are converted into a digital representation and processed according to the appropriate mathematical algorithms. The distance protection is based on local and remote relays. Hazard is the event: remote circuit breaker tripping provided the local circuit breaker can be opened. Coordination of operation of protection relays in time domain is an important and difficult problem. Incorrect values of time delays of protective relays can cause the hazard. In the paper, the time settings are performed using probabilistic fault trees with time dependencies (PFTTD). PFTTD is built for the above mentioned hazard. PFTTD are used in selection of time delays of primary (local) and backup (remote) protections. Results of computations of hazard probabilities as a function of time delay are given.