Open Ct Detection Feature - ABB Relion 670 Series Technical Reference Manual

Section 5
Differential protection
5.1.2.4
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Figure 59: Direct fiber optical connection between two IEDs with LDOM over
longer distances.
If communication is lost on the primary channel, switchover to the secondary channel
is made after a settable time delay RedChSwTime. Return of the primary channel will
cause a switchback after another settable time delay RedChRturnTime.
For a three-, four- or five-terminals line in a master-master configuration, a loss of one
communication channel will not cause the line differential protection to be
unserviceable. Instead it will automatically revert to a partial master-slave mode with
the two IEDs that have an unserviceable communication link between them, will serve
as slaves.
For more details about the remote communication see section
communication" and the application manual.

Open CT detection feature

Line differential protection has a built-in, advanced open CT detection feature.
The open CT circuit condition creates unexpected operations for Line differential
protection under the normal load conditions. It is also possible to damage secondary
equipment due to high voltage produced from open CT circuit outputs. Therefore, it is
always a requirement from security and reliability points of view to have open CT
detection function to block Line differential protection function in case of open CT
conditions and at the same time, produce the alarm signal to the operational personal to
make quick remedy actions to correct the open CT condition.
The built-in open CT feature can be enabled or disabled by a setting parameter
OpenCTEnable (Disabled/Enabled). When enabled, this feature prevents mal-
operation when a loaded main CT connected to Line differential protection is by
Telecom. Network
Telecom. Network
Primary Channel
Hot Standby Channel
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Technical reference manual