The maximum 3-phase short-circuit current I"
sc
flowing through is (at a source voltage of 1.1 V
N
):
[foglchik-170309-01.tif, 1, en_US]
With a safety margin of 10 %, the following setting value results:
[foglnste-170309-01.tif, 1, en_US]
If short-circuit currents exceed 1496 A (primary) or 12.5 A (secondary), there is a short circuit on the line to be
protected. It can be disconnected immediately.
i
i
NOTE
The calculation was performed with absolute values, which is accurate enough for overhead lines. A
complex calculation is required only if the source impedance and the line impedance have extremely
different angles.
Parameter:
Dropout ratio
•
Recommended setting value
(_:3901:4) Dropout ratio
=
0.90
The recommended setting value of
0.90
is sufficient for many applications. To obtain high-precision measure-
ments, the
Dropout ratio
can be reduced. If you expect highly fluctuating measurands at the pickup
threshold, you can increase the setting value of the parameter
Dropout ratio
. This avoids chattering of the
tripping stage.
Release Procedure via Protection Interface
This stage can be applied only if the device is equipped with a protection interface.
7.11.5
Protection and Automation Functions
7.11 Instantaneous High-Current Tripping
770
SIPROTEC 5, High-Voltage Bay Controller, Manual
C53000-G5040-C015-9, Edition 11.2017
Summary of Contents for 6MD85
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