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2.20.4 Scheme logic
CBF function can issue a trip signal in each phase. The trip signal will be generated where
OCCBF1 or EFCBF1 element is being operated and signals ‘GEN.TRIP-*’† are generated
constantly. In other words, the circuit breaker has not been opened successfully with the
GEN.TRIP-* so that the fault has not been cleared yet; therefore, CBF trip command is
required separately.
†Note: The IED issues GEN.TRIP signals in trip circuit function (TRC), which is
discussed in Chapter
Relay application: Trip circuit
.
When wishing to issue the CBF trip command without the GEN.TRIP-* commands, the
IED can issue it with external signals come from other relay devices. The user should inject
the external signals at PLC connection points ‘EXT.CBF1_START*’.
On the other hand, when wishing to issue the CBF trip command without the operation
of OCCBF1 or EFCBF1 element, the IED can also issue it with external signals using PLC
connection points ‘SUB.CBF1*’. This technique will be achieved when the user programs to
inject a ‘CB close (closed) state signal’ at the ‘SUB.CBF1*’ points. It is useful if the CBF
function cannot determine the conditions of breaker failures, when OCCBF1 or EFCBF1
element fails to detect small fault currents.
800001EBB0 EXT.CBF1_START-A
810001EBB1 EXT.CBF1_START-B
830001EBB3 EXT.CBF1_START
820001EBB2 EXT.CBF1_START-C
Figure 2.20-2 Elements logic in CBF1
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