Tettex TTR 2795, Operating Instructions Manual

Page: 42 / 111

38 Setting Up Tests
If a three-phase transformer is being tested, the best way of performing the measurement is in semi-automatic mode:
- set the
HV Config
and
LV Config
according to the nameplate of the transformer.
- Set the Ph Displacement to ??
In this mode the TTR will determine the phase displacement (clock-number) of the transformer. It will also double
check if the vectorgroup and the phase deviation (clock-number) fit together. E.g. Dyn fits together with clock-number
1,3,5,7,9 &11. If the detected phase deviation (clock-number) is 0, 2,4,6,8 or 10, the TTR will give an error message,
while the vectorgroup and phase deviation (clock-number) don’t fit together.
The Automatic determination is not working for all types of transformers and it should certainly not be used with Zig-
zag windings without a neutral, as it cannot distinguish between a Delta (D) winding and a Zig-zag (Z) winding without
neutral. If “
Auto 3 Ph
” is selected, the automatic phase displacement determination (semi-automatic mode) is also
automatically selected.
The automatic determination system is intended as an aid, for instance where the
boilerplate can’t be read. Using automatic determination system will extend the testing time
by around 1 minute.
It is not guaranteed to detect correctly in all cases. In the event of the transformer failing to
detect the correct configuration, please generate a debug report on the printer (see section
“OPTIONS”) and send it via fax or e-mail (see contact infos in support section). This will
allow us to further improve the determination procedure and make it even more reliable. If
the configuration system fails to correctly determine the transformer configuration, it will be
necessary to set the configuration manually.
If the configuration for the transformer is manually entered, it is still possible to have the phase displacement
determined automatically. In this case set the displacement to “
Auto
”. To ensure the correct results are obtained, the
user must ensure that the ‘H’ and ‘X’ leads are correctly connected to the system, otherwise a phase displacement
will be introduced which the software cannot compensate for.
When testing a single-phase transformer or a CT, the “
HV Config
” should be set to “
Single
” - in this case it is not
necessary to enter a phase displacement.
7.3 Setting Test Voltage
It is important to select the appropriate test voltage for the system - too high a voltage and there is the danger of
saturating the core of a small transformer, too low a voltage and there is the danger of not magnetizing the core
properly. Ordinarily, the highest test voltage possible should be used for the transformer. The voltage chosen for the
test will depend on the transformer. In most cases, it is adequate to set the test voltage to “
Auto
” - this selects the
test voltage based on the current drawn by the transformer. The system chooses the highest voltage it can without
going into over-current. This is not infallible as different test configurations can draw different amounts of current. If
the system repeatedly fails the test with an “
Over Current
” error, note the voltage selected by the system for
testing and retry the test with the next voltage down. Even if a specific test voltage is selected, the system performs a
pre-check and if it cannot achieve the selected voltage without risking overloading itself, it will use a lower voltage for
the test.
If Automatic voltage setting is selected, the system will use automatic selection each time a test is run irrespective of
the voltage determined on the last test performed.
7.4 Setting up an Untapped Transformer
To set up an untapped transformer, the parameters set depend on whether the deviation from the boilerplate ratio is
to be determined. If no check against the boilerplate ratings is to be performed, the “
Max Deviation
” should be set
to 0. The “
Total Taps
” should be set to 1 indicating there is only a main output on the transformer.
When the test is run, the system will perform its integrity checks, determine the test voltage, configuration and
displacement if required and will then run the test on the transformer.