CM
6.3.3.2
External initiation of BF Protection
Protective Relays
P742/3
P
eripheral
Unit
Trip A, B, C
P3752ENa
Trip Command
FIGURE 10: EXTERNAL INITIATION OF BF PROTECTION
To test the retrip:
As shown in the Figure 10, we initiate the opto inputs “External Trip A,B,C” and apply a
current twice the I< threshold.
Check that the PU issue a retrip order after the settable time tBF3.
IMPORTANT: THE TIME INDICATED ON THE PU LCD IS THE DURATION OF THE
OPERATION OF THIS PU TRIP COMMAND.
The fast reset retrip order is equal to the fault clearance time + 13ms – tBF3 pick-up time.
For example, if tBF3 = 50ms and the fault is cleared after 60ms, the PU displayed value will
be 23ms.
To test the backtrip:
Do the same tests as for retrip however apply a faulty current for more than tBF4 and check
that the backtrip signal is sent to the CU.
Check that PU2 and PU3 connected to the bus-section 1 are tripped by the CU.
Note: If the I>BB or IN>BB are enabled in menu “Busbar Trip Confirm” in
Peripheral Unit, the CB fail trip command issued by the Central Unit
will be confirmed by a measured phase currents or neutral currents
greater than I>BB (Phase) or IN>BB (Earth).
For example: PU2 and PU3 will operate only if the phase currents > I>BB else the local trip
will be not confirmed.
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