Automatic Switching of AC Power in Larger Telephone Exchanges Equipped with Standby Generating Equipment

A concept of switchgear with drawout air circuit breakers used as transfer equipment between commercial utility power and a stand-by power plant is described. The advantages of drawout type air circuit breakers are discussed over the use of commercially available automatic transfer switches. This applies especially to larger exchanges in metropolitan areas. Pictures of actual installations are included to show physical arrangements of transfer breakers and distribution breakers in different combinations. Single line schematics of the equipment shown in the photos are also included. In the second half of the paper the transfer breaker concept is developed further, and the emphasis is on control coordination between the switchgear and the diesel engine or turbine generator system, so that the switchgear and the stand-by power service become a controlled entity with emphasis on ultimate reliability of the AC power in an unattended environment. In conclusion, multi-engine systems are discussed with their special control requirements: Automatic and manual engine generators on common bus, bus systems with tie breakers when used with multiple automatic stand-by sets, as well as multiple units with automatic synchronizing features and their special control considerations. Again, single line diagrams are used to show the systems discussed.