Siemens SIPROTEC 4 7UT6 Series Manual Download

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•

Switch on test current.

•

If the starpoint current is available:
Read out the differential and restraint currents I-Diff; I-Rest under Measurement → Percent Values →
Differential and Restraint Currents.
–

The differential current of the restricted earth fault protection

Diff REF

must be low, at least one scale

less than the test current.

–

The stabilisaing current

Stab REF

corresponds to twice the test current.

–

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

X1 is under test (see also Section

2.1.4 Power System Data 1

under margin heading “Current Trans-

former 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 current, the matching
factor for the 1-phase input may be incorrect. Check the settings relevant for current matching.
These are mainly the data of the protected object and its current transformers (Section

2.1.4 Power

System Data 1

–

for power transformers addresses 313, 323 etc. (dependent on the tested winding), 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

Diff L1

Diff L2

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 Power System Data 1

, 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 Section

2.1.4 Power System Data 1

under

margin heading “Assignment of Auxiliary 1-phase Measuring Locations”.

–

Countercheck: The restraint currents of the differential protection

RestL1

RestL2

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 generator).

•

If parameter settings have been changed for the tests, reset them to the values necessary for operation.

Keep in mind that the previous tests must be repeated for each earthed side.

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 protec-
tion at the supplying point.

Siemens SIPROTEC 4 7UT6 Series, Manual

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