Siemens SIPROTEC 7UT613 series Manual page 402

3 Mounting and Commissioning
Measuring Differen-
tial and Restraint
Currents
402
If considerable deviations occur, reversed polarity or swapped phases are expected
on measuring location M2 or the actually tested measuring location.
• Deviation in individual phases indicates reversed polarity in the related phase
current connection or acyclically swapped phases.
• If all phase angles differ by the same value, phase current connections of side 2 are
cyclically swapped or the connection group of the transformer differs from the set
group. In the latter case, re-check the matching parameters (subsection 2.1.4 under
margin heading „Object Data with Transformers" under addresses 314 for side 1,
324 and 325 for side 2, 334 and 335 for side 3, etc. Consider also the assignment
of the measuring location to the sides and the sides to the protected object.
• If all phase angles differ by 180°, the polarity of the complete CT set for measuring
location M2 is incorrect. Check and correct the applicable power system data (cf.
subsection 2.1.4 under margin heading „Current Transformer Data for 3-phase
Measuring Locations"):
Address 511 STRPNT->OBJ M1 for measuring location 1,
address 521 STRPNT->OBJ M2 for measuring location 2, etc.
For 1-phase busbar protection see section 2.1.4 under margin heading „Current
Transformer Data in Single-phase Busbar Protection".
If connection errors are assumed:
• Switch off the test source and the protected object (shut down the generator) and
earth it.
• Re-check the plant connections to the device and the test arrangement and correct
them. Check also the corresponding setting for the CT data.
• Repeat test and re-check the current angles.
All pre-described test must be repeated until every measuring location of the main pro-
tected object has been included in at least one test.
Before the tests with symmetrical currents are terminated, the differential and restraint
currents are examined. Even if the above tests with symmetrical current should to a
large extent have detected connection errors, errors concerning current matching and
vector group can nevertheless not be completely excluded.
The differential and restraint currents are referred to the rated currents of the protected
object. This must be considered when they are compared with the test currents. With
more than 2 sides, the highest rated current of any side of the protected object is the
rated object current.
• Read out the differential and restraint currents under Measured Values → Per-
centage → Measured Values I-diff; I-stab.
In the „WEB Monitor", the differential and restraint currents are displayed as a graph
in a characteristics diagram (figure 3-28).
– The differential currents „Diff L1:", „Diff L2:", „Diff L3:" must be low,
i.e. at least one scale less than the through-flowing test currents.
– The restraint currents „Res. L1:", „Res. L2:", „Res. L3:" correspond to
twice the through-flowing test currents.
7UT613/63x Manual
C53000-G1176-C160-2