For the purposes of examining a complex bus arrangement,
this example looks at a double/transfer-bus single-breaker
arrangement. In this bus configuration, each circuit can be
connected to either bus. This can make BF tripping complex
because the BF relay must know which breakers are connected
to the same bus as the failed breaker in order to backup trip
the correct breakers. For bus configurations like this, the bus
protection relay must also have this information in order to
make up the proper bus differential zones. Because of this
commonality, BF protection is often combined with the bus
protection system for this bus configuration.