ment of the measured current inputs of the device against the measuring locations (current transformer sets)
of the power plant (section 2.1.4 Power System Data 1 under margin heading “Assignment of 3-phase Meas-
uring Locations”
NOTE
If the time overcurrent protection is assigned to a side of the main protected object, the current values are
set referred to the rated current of that side Ι/Ι
NS
. In other cases, current values are set in amps.
At address 3001 PHASE O/C, phase overcurrent protection may be switched to ON or OFF. The option Block
relay allows to operate the protection but the trip output relay is blocked.
Address 3008A MANUAL CLOSE determines which phase current stage is to be activated instantaneously with
a detected manual close. Settings I>> instant. and I> instant. can be set independently from the
selected type characteristics; Ip instant. is only available if one of the inverse time stages is configured.
This setting can only be made with DIGSI under Additional Settings.
If time overcurrent protection is applied on the feeding side of a transformer, select the higher stage Ι>>,
which does not pick up by the inrush current or set the manual close feature to Inactive.
In address 3002 InRushRest. Ph inrush restraint (restraint with 2nd harmonic) is enabled or disabled for all
phase current stages of time overcurrent protection (except stage Ι>>). Set ON if one time overcurrent protec-
tion stage is to operate at the supply side of a transformer. Otherwise, retain setting OFF. If you intend to set a
very small pickup value for any reason, consider that the inrush restraint function cannot operate below 10 %
nominal current (lower limit of harmonic filtering).
High-set Stages I>> Pickup
The I>> stage (address 2011 or 2012) combined with the I> stage or the Ip stage, results in a two-stage
characteristic. If one stage is not required, the pickup value has to be set to ∞. Stage I>> always operates with
a defined delay.
If time overcurrent protection is used on the supply side of a transformer, a series reactor, a motor or starpoint
of a generator, this stage can also be used for current grading. Setting instructs the device to pick up on faults
only inside the protected object but not for traversing fault currents.
Example:
Transformer used in the infeed of a bus supply with the following data:
Transformer
YNd5
35 MVA
110 kV/20 kV
u
SC
= 15 %
Current Transformer 200 A/5 A on the 110-kV side
The time overcurrent protection is assigned to the 110 kV side (= feeding side).
The maximum possible three-phase fault current on the 20 kV side, assuming an impressed voltage source on
the 110 kV side, is:
[ueb-3polkurzschlussstrom-021026-rei, 1, en_GB]
Assuming a safety margin of 20 %, the following primary setting value results:
Setting valueI>> = 1.2 · 1224.7 A = 1470 A
For settings with secondary values the currents will be converted for the secondary side of the current trans-
formers.
Secondary setting value:
Functions
2.4 Time Overcurrent Protection for Phase and Residual Currents
SIPROTEC 4, 7UT6x, Manual 147
C53000-G1176-C230-5, Edition 09.2016
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