Implementation of Zero Sequence Current Tests
For these commissioning tests, the zero sequence current must be at least 2 % of the rated relay current for
each phase, i.e. the test current at least 6 %.
This test cannot replace visual inspection of the correct current transformer connections. Therefore, the
inspection of these connections is a prerequisite.
•
Switch on test current.
•
Read out the current magnitudes:
Compare the indicated current magnitudes under Measurement → Secondary → Operational meas-
ured values secondary with the actually flowing values:
–
All phase currents of the tested measuring location correspond to approximately
1
/
3
of the test
current (for 1-phase transformers
1
/
2
),
–
3Ι0 of the tested measuring location corresponds to the test current.
– Phase currents and zero sequence current of the other measuring location are, on transformers,
nearly 0.
– The current at the auxiliary 1-phase current input corresponds to the test current — provided this
current is available and included.
Deviation can practically occur only for the single-phase current (if included) because the connection of
the phase currents had been verified already during the symmetrical tests. In case of deviations:
– Switch off the test source and the protected object (shut down the generator) and earth it.
– Re-check the assignment or the tested 1-phase input (Section 2.1.4 Power System Data 1 under
margin heading “Assignment of Auxiliary 1-phase Measuring Locations”).
– Re-check the settings for the magnitude matching (Section 2.1.4 Power System Data 1 under
margin heading “Current Transformer Data for 1-phase Auxiliary Current Inputs”).
Parameter für die Betragsanpassung überprüfen (Abschnitt 2.1.4 Power System Data 1 unter Rand-
titel “Stromwandlerdaten für 1-phasige Zusatzeingänge”).
– Check the plant connections to the device and the test arrangement and correct them.
– Repeat test and re-check the current magnitudes.
Measuring Differential and Restraint Currents
The differential and restraint currents are referred to the rated currents of the tested side of the main
protected object. If a zero sequence current test does not concern the main protected object but a different
earthed object (e.g. a shunt reactor outside the main object), the base of the referred currents is the rated
current of that 3- phase measuring location to which the 1-phase current input is assigned, i.e. the measuring
location under test. This must be considered when they are compared with the test currents.
Mounting and Commissioning
3.3 Commissioning
382 SIPROTEC 4, 7UT6x, Manual
C53000-G1176-C230-5, Edition 09.2016
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