2.24 Inverse time operation
2 Protection functions
Technical description
132
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VM259.EN007
Local panel graph
The device will show a graph of the currently used inverse
delay on the local panel display. Up and down keys can be used
for zooming. Also the delays at 20xI
SET
, 4xI
SET
and 2xI
SET
are
shown.
Inverse time setting error signal
If there are any errors in the inverse delay configuration the
appropriate protection stage will use definite time delay.
There is a signal ‗Setting Error‘ available in output matrix,
which indicates three different situations:
1.
Settings are currently changed with VAMPSET or local
panel, and there is temporarily an illegal combination of
curve/delay/points. For example if previous settings were
IEC/NI and then curve family is changed to IEEE, the
setting error will active, because there is no NI type
available for IEEE curves. After changing valid delay type
for IEEE mode (for example MI), the ‗Setting Error‘ signal
will release.
2.
There are errors in formula parameters A…E, and the
device is not able to build the delay curve
3.
There are errors in the programmable curve configuration
and the device is not able to interpolate values between the
given points.
Limitation
The maximum measured secondary phase current is 50xI
n
and
the maximum directly measured earth fault current is 10xI
0n
.
The full scope of inverse delay curves goes up to 20 times the
setting. At high setting the maximum measurement capability
limits the scope of inverse curves according the following table.