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7UT51 v3
18.1.3
Check Matching Factors
Since external matching transformers have been
eliminated and since the digital protection unit 7UT51
offers a number of commissioning aids,
commissioning can be performed quickly and without
external instruments.
Before performance of the actual primary tests, it is
advisable to recheck that the matching factors for the
rated currents of the protected object are correct.
These factors are presented in the operational
annunciation each time the parameterizing process
has been terminated.
Select the operational annunciations either by direct
addressing 5100 or using the PC and WinDIGSI.
The following factors are available:
k CT 1 = current processed by 7UT51
current through the relay terminals
for Side 1 of the protected object and similar for the
other sides:
•
k CT2 =
•
k CT3 = (only 7UT513)
•
ksCT 1 = (only 7UT513)
•
ksCT 2 = (only 7UT513)
•
ksCT 3 = (only 7UT513)
where ksCT are the factors for inputs from the CT in
the star-point connection of a grounded transformer
winding (if used).
When 7UT513 is used, check that LED 14 does not
light. This LED indicates (by default) that combinations
of configuration or function parameters are not
consistent. If this LED is illuminated, look up the cause
of this inconsistence in the operational event log. A
listing of the types of error messages can be found in
Table 13.1.
18.2
Preparation of Primary
Tests
At first commissioning, current checks must be
performed before the protected object is energized for
the first time. This ensures that the differential
protection is operative as a short-circuit protection
during the first excitation of the protected object with
voltage. If current tests are only possible with the
PRIM-2330C
Field Testing and Commissioning
protected object under voltage, it is imperative that a
backup short-circuit protection be available. The trip
circuits of other protection devices such as the
Buchholz protection must remain operative as backup
protection.
The test arrangement varies depending on the
application.
On network power transformers or asynchronous
machines, a low voltage test equipment is preferably
used. A low-voltage current source is used to energize
the protected object, which is completely disconnected
from the network (see Figure 18.1). A short-circuit
bridge, that is capable to carry the test current, is
installed outside of the protected zone and allows the
symmetrical test current to flow.
Figure 18.1
Primary Current Tests Arrangement Example
-
for a Two
Winding Transformer with
-
Low
Voltage Source
On power station unit transformers and synchronous
machines, the checks are performed during the
current tests. The generator itself forms the test
current source. The current is produced by a
three-pole short-circuit bridge that is installed outside
of the protected zone and is capable of carrying rated
current for a short time. The machine is started but not
yet excited. Check that no current transformer is open
or short-circuited. In order to achieve this, read out the
operational measured values (Address Block 5700).
Even when the currents and the measurement
accuracy is still very small, errors can be detected.
18
197
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