Configuration Of Output Signals; Open Ct Detection - ABB RED650 Applications Manual

1MRK 505 393-UEN B
6.1.2.7
6.1.2.8
Line differential protection RED650 2.2 IEC
Application manual

Configuration of output signals

There are a number of signals available from the LDCM that can be connected to
the virtual binary inputs (SMBI) and used internally in the configuration. The
signals appear only in the Signal Matrix Tool (SMT) where they can be mapped to
the desired virtual input.
The signal name is found in the Object Properties window by clicking on the input
signal number in SMT. Connect the signals to the virtual inputs as desired (see
Figure 37
SMBI
IEC06000638 V2 EN-US
Figure 37: Example of LDCM signals in SMT(example showing 670 device)l

Open CT detection

Line differential protection has a built-in, advanced open CT detection feature. This
feature can block the unwanted operation created by the Line differential protection
function in case of an open CT secondary circuit under a normal load condition.
However, there is no guarantee that the Open CT algorithm prevents an unwanted
disconnection of the protected circuit. The Open CT can be detected in
approximately 14 ± 2 ms, and the differential protection might by that time in some
cases have already issued a trip command. Nevertheless, the information on an
open CT as the reason for trip is still very important. An alarm signal can also be
issued to the substation operational personnel to make remedy action once the open
CT condition is detected. The open CT algorithm is active under normal load
conditions and a little above, i.e. in the range of load current from app. 10 % to
app. 150 % rated load. Under normal conditions load is considered to be well
described by the bias current. The Open CT detection algorithm is based on the
principle that in the phase with an open CT, the current will suddenly drop to zero,
while in the other two phases the currents continue as before. The Open CT at each
end is enabled 60 seconds after the currents at that end are higher than 3 % rated
current of the protected line circuit. An open CT can only be declared if in the
phase where an open CT is suspected, exceeds 10 % of the rated current. The Open
Section 6
Differential protection
IEC06000638-2-en.vsd
GUID-DB3841A9-5B55-490E-8A2D-EBF0CB263378 v7
M12022-93 v4
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