Secondary redundant
channel
IEC05000289 V1 EN-US
Figure 39: Direct fibre 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-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 remote
communication and the application manual.
6.1.7.4 Open CT detection feature
GUID-5B7ACC4D-4EC9-40F1-B18D-561F13945FE3 v1
Line differential protection has a built-in, advanced open CT detection feature.
A sudden inadvertently opened CT circuit may cause an unexpected and unwanted
operation of the Line differential protection under normal load conditions. Damage
of secondary equipment may occur due to high voltage from open CT circuit
outputs. It is always an advantage, from the point of view of security and
reliability, to have the open CT detection function to block the line differential
protection function in case of an open CT condition, and produce an alarm signal to
the operational personnel to quickly correct the open CT condition.
The built-in open CT feature can be enabled or disabled by the setting parameter
OpenCTEnable (Off/On). When enabled, this feature tries to prevent mal-operation
when a loaded main CT connected to line differential protection is by mistake open
circuited on the secondary side. Note that this feature can only detect interruption
of one CT phase current at a time. If two or even all three-phase currents of one set
of CTs are accidentally interrupted at precisely the same time, this feature cannot
operate. Line differential protection generates a trip signal if the false differential
current is sufficiently high. An open CT circuit is typically detected in 12–14 ms,
Section 6 1MRK 505 394-UEN A
Differential protection
104 Line differential protection RED650 2.2 IEC
Technical manual
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