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One of the benefits of the “re-trip” function is that it can used to avoid accidental tripping
of an adjacent CB or an upstream CB. This is particularly requisite during maintenance and
testing of the system.
2.20.3 Backup feature
As cited above, “re-trip” issues a further trip signal so that the CB receives an instruction to
trip again. If “re-trip” cannot remove the fault, CBF will issue a “back-trip” command. Back-
tripping is used as a last resort to remove the fault.
Figure 2.20-1 Timing chart for re-trip and back trip during CBF operation
Figure 2.20-1 is a sequence diagram for the CBF function; the overall sequence illustrated
shows a target CB failing to remove a fault with the consequence that back tripping of the
adjacent CB(s) is required following operation of the CBF protection to finally clear the fault.
The CBF function is initiated via a signal from other protection functions.
If the target CB is tripped normally on receipt of a trip signal so that the fault is removed,
both OCCBF and EFCBF will reset before the time settings of timer #1 and timer #2 have
elapsed.
Following the issue of the first trip signal, if either OCCBF or EFCBF were to continue
to operate and if timer #1 were to time out according to the timer setting value [TCBF1-RE], a
“re-trip” command would be issued to the target CB. If the target CB were to open to clear the
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