ABB Relion 670 series, Applications Manual

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RED
670
RED
670
64 kbit/s
Protected zone
en05000437.vsd
IEC05000437 V1 EN-US
Figure 50: Two-terminal line
In case of 1½ breaker arrangements or ring buses, a line end has two CTs, as shown in
Figure 51 .
RED
670
64 kbit/s
Protected zone
64 kbit/s
RED
670
en05000438.vsd
IEC05000438 V1 EN-US
Figure 51: Two-terminal line with 1½ breaker
Observe that in Figure 51 , each of the two local CTs on the left side is treated as
a separate end by the differential protection.
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 51 )
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 "" .
6.3.2.6 Configuration of analog signals
M12022-86 v5
Currents from the local end enter the IED as analog values via the Analog input modules. These
currents are converted to digital values and then forwarded to the line differential protection
function in the local IED. From there, they are transmitted to remote IEDs via a Line differential
communication module (LDCM). Currents coming from a remote IED are received as digital
values via local IED's LDCM, and they are then forwarded to the protection function in the local
IED.
LDLPSCH acts as the interface to and from the protection function.
Section 6 1MRK 505 343-UEN B
Differential protection
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Application manual