EXAMPLE
Overcurrent-protection stage: 110-kV overhead line, 150 mm
2
cross-section
Maximum transmittable power
P
max
= 120 MVA
Correspondingly
I
max
= 630 A
Current transformer = 600 A/5 A
Settings in primary and secondary values result in the setting values:
[foocp005-030311-01.tif, 2, en_US]
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 low-voltage side of the transformer. The following
conditions 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 setting, 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 if the current threshold is briefly exceeded, that this will not lead to the
pickup of the stage and starts fault logging or 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 trigger if
the current threshold is exceeded.
For all short-circuit protection applications, this value is 0.00 s and is considered as a default.
Parameter: Time dial
•
Default setting (_:691:101) Time dial = 1.00
With the Time dial parameter, you displace the characteristic curve in the time direction.
The set value for the Time dial parameter is derived from the time-grading schedule that has been prepared
for the electrical power system.
Where no time grading and therefore no displacement of the characteristic curve is required, leave the param-
eter Time dial at 1 (default setting).
Parameter: Reset
•
Default setting (_:691:131) Reset = disk emulation
With the Reset parameter, you define whether the stage drops out according to the dropout characteristic
curve (in accordance with the behavior of a disk emulation = rotor disk) or instantaneously.
Protection and Automation Functions
6.3 Overcurrent Protection, Phases
SIPROTEC 5, Overcurrent Protection, Manual 345
C53000-G5040-C017-8, Edition 07.2017
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