3.3 Commissioning
409
7UT613/63x Manual
C53000-G1176-C160-2
– If the differential current is in the size of the restraint current (approximately twice
the test current), you may assume a polarity reversal of the single-phase current
transformer. Check the polarity again and compare it with the setting in address
711 EARTH IX1 AT if the auxiliary single-phase input IX1 is under test (cf. also
subsection 2.1.4 under margin heading „Current Transformer Data for single-
phase Auxiliary Current Inputs“), or accordingly the parameters for the actual
input under test.
– If there is a differential current which does not correspond to twice the test cur-
rent, the matching factor for the 1-phase input may be incorrect. Check the set-
tings relevant for current matching. These are mainly the data of the protected
object and its current transformers (Subsection 2.1.4):
– for power transformers addresses 313, 323 etc. (dependent on the tested wind-
ing), under margin heading „Object Data with Transformers“ and
– in all cases addresses 712, 713 or 722, 723 etc. (depending on the used 1-
phase input), under margin heading „Current Transformer Data for Single-phase
Auxiliary Current Inputs“.
• In all cases (whether or not the starpoint current is available)
:
Check the differential currents I
Diff L1
, I
Diff L2
, I
Diff L3
.
– The differential currents must be low, at least one scale less than the test current.
If considerable differential currents occur, re-check the settings for the starpoints:
– Starpoint conditioning of a transformer: addresses 313 STARPNT SIDE 1, 323
STARPNT SIDE 2, etc. (depending on the tested winding) (Section 2.1.4, margin
heading „Object Data with Transformers“), as well as
– the assignment of the starpoint current transformer to the 1-phase current input
under test: address 251, 252, etc. depending on the input under test, see Sub-
section 2.1.4 under margin heading „Assignment of Auxiliary 1-phase Measuring
Locations“.
– Countercheck: The restraint currents of the differential protection I
RestL1
, I
Rest L2
,
I
Rest L3
are equally small. If all tests have been successful until now, this should
be ensured.
• Finally, switch off the test source and the protected object (shut down the genera-
tor).
• If parameter settings have been changed for the tests, reset them to the values nec-
essary for operation.
Please keep in mind that the previous tests must be repeated for each earthed side.
3.3.10 Current Tests for Busbar Protection
General For single-phase busbar protection with one device per phase or with summation
transformers, the same checks have to be performed as described in Subsection
Symmetrical Current Tests on the Protected Object. Please observe the following
four remarks:
• Checks are often performed with operational currents or primary testing devices.
Please take note of all warnings you can find in the said section and be aware of
the fact that you will require a backup protection at the supplying point.
• Checks have to be performed for every current path, beginning with the supplying
feeder.
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