Configuration Of Analog Signals - ABB RELION 650 Series Applications Manual

Section 6
Differential protection
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IEC05000437 V1 EN-US
Figure 36: Two-terminal line (example showing 670 device)
In case of 1½ breaker arrangements or ring buses, a line end has two CTs, as shown in
Figure 37.
IEC05000438 V1 EN-US
Figure 37: Two-terminal line with 1½ breaker (example showing 670 device)
In this case, current values from two CTs in the double breakers, ring main or breaker-and-a-
half systems end with dual breaker arrangement need to be sent to the remote end. As a 64
kbit/s channel only has capacity for one three-phase current (duplex), this implies that two
communication channels are needed in both ends, and this is also the normal solution.
Alternatively, but not recommended, it is possible to add together the two local currents
before sending them and in that way reduce the number of communication channels needed.
This is then done in software in the IED, but by doing it this way there is reduced information
about bias currents. The bias current is considered the greatest phase current in any line end
and it is common for all three phases. When sending full information from both local CTs to
the remote end, this principle works, but when the two local currents are added together
before sending the single resulting current on the single communication channel, information
about the real phase currents from the two local CTs are not available in the remote line end.
Whether it is possible to use one communication channel instead of two (as show in Figure 37)
must be decided from case to case. It must be realized that correct information about bias
currents is always available locally, while only distorted information is available in the end that
receives the limited information over only one channel.
For more details about the remote communication, refer to section "".
6.2.2.6

Configuration of analog signals

The currents from the local end enter the IED via the Analog input modules as analog values.
These currents need to be converted to digital values and then forwarded to Line differential
protection in the local IED, as well as being transmitted to a remote IED via an LDCM (Line
Differential Communication Module). The currents from a remote IED are received as digital
values in the local IED via an LDCM and thereafter need to be forwarded to Line differential
protectionn in the local IED.
The function LDLPSCH acts as the interface to and from Line differential protection.
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Observe that in Figure 37, each of the two local CTs on the left side is treated as
a separate end by the differential protection.
Protected zone
64 kbit/s
Protected zone
64 kbit/s
64 kbit/s
1MRK 505 363-UEN A
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en05000437.vsd
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M12022-86 v4
Application manual