Analog And Binary Signal Transfer For Line Differential Protection; Communication Channels For Line Differential Protection - Hitachi 670 Series Application Manual

1MRK505382-UEN Rev. K
Section 4
4.1

Communication channels for line differential protection

The line differential protection function uses 64 kbit/s or 2 Mbit/s communication channels to
exchange telegrams between the line differential protection IEDs. These telegrams contain current
sample values, time information, trip signals, block signals, alarm signals and 8/192 binary signals,
which can be used for any purpose. Each IED can have a maximum of four communication channels.
On a two terminal line there is a need for one communication channel provided that there is only one
CT at each line end (see Figure 13).
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IEC05000437 V2 EN-US
Figure 13:
In case of 1½ breaker arrangements or ring buses, a line end has two CTs (see Figure 14).
IEC05000438 V2 EN-US
Figure 14:
Current values from two CTs in double breakers, ring main or 1½ breaker system ends with dual
breaker arrangements need to be sent to the remote end. As a 64 kbit/s LDCM only has capacity for
one three-phase current (duplex), this implies that two communication channels are needed at both
ends, and this is also the normal solution.
To reduce the number of communication channels needed, it is also possible to sum up the two local
currents before sending by using a software in the IED. However, this is not recommended as it
reduces information about bias currents. Bias current is considered the greatest phase current at any
line end, and it is common for all three phases. When sending full information from both local CTs to
the remote end, the principle works, but when the two local currents are summed up before sending,
information on real phase currents from the two local CTs will not be available at the remote line end.
Communication set-up, 670/650 series
Application Guide
Analog and binary signal transfer for
line differential protection
Two-terminal line
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Two-terminal line with 1½ breaker
In Figure 14, both local CTs on the left side are treated as separate ends by the line
differential protection function.
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Analog and binary signal transfer for line differential protection

Protected zone
Protected zone
Section 4
M12022-69 v7
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