Fig. 9 illustrates the simplest application, where each relay
takes care of BF protection for all short-circuit trips that it
initiates. There are no external BFI signals exposed to
spurious initiation. In this configuration, when a relay is
isolated for testing, there are no BFI signals to be concerned
with from the human error point of view. When an individual
relay is out of service or has failed, there is no loss of BF
protection