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Section 6
Differential protection
By a parameter setting it is possible to provide self-rest or latched trip output contacts from
the IED. However it shall be noted that the latching is electrical (that is, if DC supply to the IED
is lost the output contacts will reset).
However, sometimes due to a large number of required trip output contacts (that is, single
pole operated circuit breakers and/or main and backup trip coils), a separate trip repeat relay
unit is applied for the tripping of the circuit breakers in the station. In that case the tripping
arrangement can be done in different ways.
Trip arrangement with one-phase version
When one-phase version of the IED is used it is typically required to have three IEDs (that is,
one per phase). Thus, when busbar protection in one IED operates the trip commands will be
given to all bays but internal circuit breaker failure function will be started in the same phase
only. In order to secure internal breaker failure starting in all three phases it is advisable to do
the following. Connect a zone, say Zone A, trip signal from one IED to the external trip input of
the Zone A in the other two IEDs. Thus all three IEDs will then issue trip in Zone A and start
internally circuit breaker failure protection in all three phases.
Note that:
•
similar arrangements shall be done for the other zones
•
this have to be done between all three IEDs (that is, three times)
Such a scheme can be arranged in one of the following ways:
•
by wiring between three IEDs
•
by using GOOSE messages when IEC 61850-8-1 is used
•
by using LDCM communication module.
Note that in this case the external trip signal from other two IEDs shall be arranged via pulse
timer in configuration in order to avoid locking of the trip signal between three IED. Such
arrangement via GOOSE is given in Figure 52:
110
1MRK 505 370-UEN D
SEMOD130408-6 v4
Busbar protection REB670
Application manual
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