Mounting and Commissioning
3.3 Commissioning
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
425
For the external fault, the percentages of the operational measured values are (on the device: Measurement
→ I-Diff, I-Rest) to be read out:
3I0-1 Calculated zero sequence current of side 1
3I0-2 calculated zero sequence current of side 2 or measured earth current I
EE2
(depending on
configuration)
I0-Diff calculated differential current
I0-Rest calculated restraint (stabilizing) current
Both zero component currents 3I0-1 and 3I0-2 must be equal and correspond to the injected current. The
differential current I0-Diff is almost zero. The restraint (stabilising) current I0-Stab is twice the flowing cur-
rent. If the differential and the restraint current are equal, the polarity of one CT must be wrong. Minor deviations
are caused by CT errors.
If there are deviations, connection error are normally assumed. If necessary modify the wiring, or in Power
System Data 1, the allocation of the CT starpoint for the phase CTs or the earth CT I
EE2
. For the phase CTs,
keep in mind that they are also used by other protection functions, such as the differential current protection.
Feedback effects should be examined. If the differential current protection has already been checked, and the
CTs of side 1 and 2 are used for the earth current differential protection, the above errors can be excluded. If
the I
EE2
input is used, a wrong polarity of the connections is not uncommon. Check the connection and/or the
starpoint allocation in Power System Data 1 (address 214 GRD TERM. IEE2). The default setting assumes
that terminal 7 is looking towards the protected object. If there are deviations in the measured values, the mea-
sured quantities are probably not properly matched. Check the parameter settings of the protected object and
of the CTs in Power System Data 1. The default setting assumes that terminal 7 is looking towards the protected
object.
If there are deviations in the measured values, the measured quantities are probably not properly matched.
Check the parameter settings of the protected object and of the CTs in Power System Data 1.
Proceed as follows:
• Shut down and earth generator
• Check and correct connections, if necessary, or modify settings in Power System Data 1
• Repeat measurement
If the earth current differential protection is used on a transformer, a comparative test is performed (see Figure
3-26). The measured value 3I0-1 is allocated to side 1 and 3I0-2 to the earth currrent I
EE2
. The test method
is similar to the one described above. For the test current, it is essential to ensure that on the generator side
the continuously admissible unbalanced load current is not exceeded. With a wye-delta connection, the single-
phase fault is modeled on the generator side as a phase to phase fault.
Figure 3-28 Testing the earth current differential protection on the transformer
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