Availability of DTT for the remote breaker needs to be
considered. From this perspective, the configuration illustrated
in Fig. 11 might be preferable because the line relay most
likely already has direct access to the DTT equipment. In this
configuration, there is external routing of the BFI signals, but
the BF protection function is located in a single relay. If the
single relay that provides BF protection is taken out of service
or fails, there is no BF protection on that breaker. However,
this only represents a single contingency because the primary
system for fault interruption (the breaker) is still in service.