Dependability is directly proportional, while security is
inversely proportional, to the number of operational copies of
a given protection function. Today, we predominately deploy
one BF function per breaker with external BFI signaling and
physical lockout relays. The observed performance in terms of
the frequency of unwarranted BF operations is a reflection of
this practice. A scheme with multiple BF function elements
for a given breaker, with each initiated from all the associated
zone relays, would potentially multiply the probability of BF
misoperation. This danger can be alleviated in a number of
ways, while integrating the BF function as explained later.
Most importantly, the danger can be alleviated by not having
all zone relays initiate all operational copies of the BF
function.