Application benefits of modern microprocessor distance protection for AC electrified railways

Distance relays have provided reliable and secure protection for AC electrified railway circuits. This paper examines microprocessor distance relays which offer the flexibility of shaped impedance characteristics, for increased fault arc resistance coverage and load avoidance. Microprocessor relays offer applications flexibility through many ancillary features. In addition, each distance relay can include comprehensive self-monitoring, with any factor affecting availability communicated to the operator. Such failures would traditionally have remained unnoticed until inception of a fault, or until maintenance testing. Simple function testing can now replace comprehensive periodic testing. Traction circuit measurements can be polled on demand, either locally, or remotely via serial communications. Measurements are also appended to fault records, allowing fault diagnosis, and the establishment of condition-based maintenance regimes for circuit breakers