Siemens 6MD85, Manual

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The settings in primary and secondary values result in the following setting values which include a safety
margin of 10 %:
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If short-circuit currents exceed 2365 A (primary) or 19.7 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 and line impedance have different angles, you have to use complex numbers to calculate the
Threshold
.
Parameter:
I0 elimination
•
Default setting
(_:661:120) I0 elimination
=
no
This parameter is not visible in the basic stage.
The I0 elimination in phase currents for overcurrent-protection applications can be used in a transformer. This
increases the sensitivity for the 2-phase short circuit on the transformer low-voltage side. The following condi-
tions must be fulfilled:
•
The transformer neutral point current I
Y
is measured and is available for the protection function group.
•
The parameter
Method of measurement
is set to
fundamental comp.
.
With the
I0 elimination
parameter, you can switch the I0 elimination function on or off.
Parameter:
Pickup delay
•
Default setting
(_:661:102) Pickup delay
=
0.00 s
This parameter is not visible in the basic stage.
For special applications, it is desirable that a short exceeding of the current threshold does not lead to the
pickup of the stage and start fault logging and recording. If this stage is used as a thermal overload function,
that is considered a special application.
When using the
Pickup delay
parameter, a time interval is defined during which a pickup is not triggered
if the current threshold is exceeded.
For all short-circuit protection applications, this value is 0.00 s as a default.
Parameter:
Dropout delay
•
Default setting
(_:661:101) Dropout delay
=
0.00 s
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
•
Default setting
(_:661:4) Dropout ratio
=
0.95
Protection and Automation Functions
7.4 Overcurrent Protection, Phases
608 SIPROTEC 5, High-Voltage Bay Controller, Manual
C53000-G5040-C015-9, Edition 11.2017