4.5 Link forwarding
GUID-DD3CF47C-A202-4416-954A-EFC0F8BEBCB7 v1
If it is not possible to have a communication link between each station, the solution
has been to set the protection up in a slave-master-slave configuration. This means
that in Figure
24, only IED-B has access to all currents and, therefore, this is the
only place where the differential current is evaluated. If the evaluation results in a
trip, the trip signal will be sent over the two communication links.
IED-A IED-B IED-C
IEC16000077-1-en.vsd
3-end differential protection with two communication links
Ldcm312
Ldcm312
Ldcm313
Ldcm312
IEC16000077 V1 EN-US
Figure 24: Three-end differential protection with two communication links
If the LDCM is in 2Mbit mode, you can send the three local currents as well as the
three remote currents from the other links by configuring the transmitters in IED-B:
1. Ldcm312 transmitter sends the local currents and the three currents received
by Ldcm313.
2. Ldcm313 transmitter sends the three local currents and the three currents
received from Ldcm312.
As a result, six currents are received in IED-A and IED-C. These currents can be
connected to the protection function together with the local three currents.
In order to forward the logic signals (for example, inter-trip or inter-
block) between IED-A and IED-C, the setting LinkForwarded
should be defined. In IED-B, it is set to LDCM313 for Ldcm312
and to LDCM312 for ldcm313.
This setup results in a master-master-master configuration, but without the benefit
of reverting to a slave-master-slave configuration in case of a communication link
interruption. In case of a communication link interruption, all three IEDs would be
blocked.
1MRK 505 382-UEN B Section 4
Analog and binary signal transfer for line differential protection
Communication set-up 670/650 series 2.2 35
Application Guide
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