High-Speed Circuit Breakers

High-speed circuit breakers have been successfully applied to d-c. railway systems for a number of years, but designs suitable for application on 12,000-volt single-phase systems have not been available until recently. A description of an air circuit breaker design suitable for 12,000-volt applications and having a speed of operation comparable with the d-c. type has been included. The method of applying the magnetic type of mechanism previously used for d-c. breakers to the a-c. type breaker has been described. The theory of the operation of the saturated transformer type of trip circuit used for this purpose has been given. Typical oscillograms of short circuit tests showing the high speed of operation on a-c. circuits are included. The method of obtaining selective operation in connection with railway feeder circuits has also been outlined. The use of this type of breaker on a 12,000-volt single-phase system makes possible the same degree of protection and selective operation as is now being realized on d-c. systems.