Siemens 7SJ85 - Settings

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In case of short-circuit currents exceeding 1246 A (primary) or 10.39 A (secondary) there is a short-circuit on
the line to be protected. The overcurrent protection can cut off this short circuit immediately.
Note: The amounts in the calculation example are accurate enough for overhead lines. If the source impe-
dance, line impedance and zero-sequence impedance have very different angles, you have use complex
numbers to calculate the Threshold.
Parameter: Dropout delay
•
Recommended setting value (_:751:101) Dropout delay = 0
This parameter is not visible in the basic stage.
Siemens recommends using the default setting 0 since the dropout of a protection stage must be done as fast
as possible.
You can use the Dropout delay parameter ≠ 0 to obtain a uniform dropout behavior if you use it together
with an electromechanical relay. This is required for time grading. The dropout time of the electromechanical
relay must be known for this purpose. Subtract the dropout time of your own device (see Technical Data) and
set the result.
Parameter: Dropout ratio
•
Recommended setting value (_:751:4) Dropout ratio = 0.95
This parameter is not visible in the basic stage.
The recommended set value of 0.95 is appropriate for most applications.
To achieve high-precision measurements, the setting value of the parameter Dropout ratio can be
reduced, for example, to 0.98. If you expect highly fluctuating measurands at the response threshold, you
can increase the setting value of the parameter Dropout ratio. This avoids chattering of the tripping stage.
Settings
Addr.
Parameter C Setting Options Default Setting
General
_:751:1 Definite-T 1:Mode
•
off
•
on
•
test
off
_:751:2 Definite-T 1:Operate &
flt.rec. blocked
•
no
•
yes
no
_:751:26 Definite-T 1:Dynamic
settings
•
no
•
yes
no
_:751:27 Definite-T 1:Blk. w.
inrush curr. detect.
•
no
•
yes
no
_:751:8 Definite-T 1:Method of
measurement
•
fundamental comp.
•
RMS value
fundamental
comp.
_:751:3 Definite-T 1:Threshold 1 A @ 100 Irated 0.010 A to 35.000 A 1.200 A
5 A @ 100 Irated 0.05 A to 175.00 A 6.00 A
1 A @ 50 Irated 0.010 A to 35.000 A 1.200 A
5 A @ 50 Irated 0.05 A to 175.00 A 6.00 A
1 A @ 1.6 Irated 0.001 A to 1.600 A 1.200 A
5 A @ 1.6 Irated 0.002 A to 8.000 A 6.000 A
6.5.4.3
Protection and Automation Functions
6.5 Overcurrent Protection, Ground
386 SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017