Ratio of zero-sequence impedance and positive-sequence impedance of the source impedance at the
beginning of the line: Z
P0
/Z
P1
= 2
Current transformer = 600 A/5 A
Resulting in the following values for the line impedance Z
L
and the source impedance Z
P
:
[fo_OCP002_030311, 1, en_US]
[fo_OCP003_030311, 1, en_US]
The 3-phase short-circuit current at the end of the line is I
sc end
:
[fo_ocpph4_030311, 1, en_US]
The settings in primary and secondary values result in the following setting values which include a safety
margin of 10 %:
[foocp004-030311-01.tif, 2, en_US]
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.
Protection and Automation Functions
6.3 Overcurrent Protection, Phases
334 SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
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