Siemens SIPROTEC 7UT613 series Manual page 130

2 Functions
Starpoint Condi-
tioning
130
Note
When delivered from factory, the differential protection is switched OFF. The reason
is that the protection must not be in operation unless at least the connection group (of
a transformer) and the matching factors have been set before. Without proper set-
tings, the device may show unexpected reactions (incl. tripping)!
If there is a current transformer in the starpoint connection of an earthed transformer
winding, i. e. between starpoint and earth electrode, the starpoint current may be
taken into consideration for calculations of the differential protection. The earth-fault
sensitivity is thus ensured.
If a starpoint is earthed but the earth current is not available, the zero sequence
current is eliminated automatically in order to avoid a faulty reaction by the differential
protection in case of an external earth fault; the following parameters are then omitted.
Equally, the parameters are not available for sides of the protected object that are not
earthed. The device has been informed about the earthing conditions during setting of
the object properties (section „General Power System Data" under margin heading
„Object Data with Transformers", addresses 313, 323, 333, 343 and/or 353 and
section „Topology of the Protected Object" under margin heading Assignment of
Further „1-phase Measuring Locations").
The conclusion is: If the starpoint of a side of the protected power transformer is
earthed and the starpoint current is fed to the device (via a further 1-phase current
input) you can, nevertheless, leave the default setting for inclusion of the earth current
unchanged in address 1211DIFFw.IE1-MEAS for side 1 on „Yes".
This parameter can only be altered with DIGSI under Additional Settings. The same
considerations apply to any other or additional earthed sides:
• 1212 DIFFw.IE2-MEAS for side 2 if earthed,
• 1213 DIFFw.IE3-MEAS for side 3 if earthed,
• 1214 DIFFw.IE4-MEAS for side 4 if earthed,
• 1215 DIFFw.IE5-MEAS for side 5 if earthed.
During setting YES the corresponding earth current will be considered by the differen-
tial protection.
In auto-transformers the earth current flowing in the winding can be considered even
if a complete three-phase CT set has been installed as illustrated in figure 2-6, where
instead of measuring location Z3 also the three phase currents can be connected to a
three-phase measuring input of the device. The device then calculates the sum of the
three currents and uses it as earth current. Set address 1216 DIFFw.IE3phMEAS to
YES. It is required to assign the respective three-phase measuring location to one side
and to declare it as earth winding (the side of the auto-connected winding facing the
earth electrode). This parameter can only be altered in DIGSI at Display Additional
Settings.
7UT613/63x Manual
C53000-G1176-C160-2