2. 1. Dot convention
2. Vector group
3. What is vector group?
4. Why we need vector group?
5. Symbol designation
6. Experiment for determining the vector group of a
transformer
7. MATLAB simulation
8. Examples for vector group
3. Dot convention is a type of polarity marking for transformer
windings showing which end of the winding is which, relative
to the other windings.
We want to do an experiment to determine the dot
convention of the transformer to know the right connection
with a specified vector group.
Component:
1. 2 coils.
2. 3 voltmeter.
3. 2 Ammeter.
4. power supply.
4. Procedures:
1. We would connect the 2 coils in series with each other.
2. we would connect a 2 voltmeter, one for each coil to
measure the voltage .
3. we would connect a voltmeter between the terminal of
the first coil and another terminal of the second coil.
4. Also we would put an ammeter because at a specified
connection the volt will be small and the current will be
high.
5. we would notice the reading of the 3 voltmeter, if the
voltmeter between the 2 coils show a voltage that equal
the summation of the readings of the 2 coils , then the 2
voltage is in the same direction, and the dot convention is
as shown in figure 6.
6. If the voltmeter between the 2 coils show a voltage that
equal the difference between the readings of the 2 coils ,
then the 2 voltage is in the different direction , and the dot
convention is as shown in figure 5.
5.
6. Vector group is the international electrotechnical
commission (IEC) method of categorizing the high
voltage (HV) windings and low voltage (LV) winding
configurations of three phase transformers. The vector
group designation indicates the windings
configurations and the difference in phase angle
between them.
7. The phase windings of a polyphase transformer can
be connected internally in different configurations,
depending on what characteristics are needed from
the transformer.
In a three-phase power system, it may be necessary to
connect a three-wire system to a four-wire system, or
vice versa. Because of this, transformers are
manufactured with a variety of winding configurations
to meet these requirements.
Different combinations of winding connections will
result in different phase angles between the voltages
on the windings. Transformers connected in parallel
must have the same vector group; mismatching
phase angles will result in circulating current and other
system disturbances.
8. The vector group provides a simple way of indicating
how the connections of a transformer are arranged
The vector group is indicated by a code consisting of
two or three letters, followed by one or two numeric
digits.
- Letters: indicates windings configurations (Y-D-Z)
- Numeric digits: indicates multiples of 30 degrees lag
for low voltage winding using the high voltage
as the reference
There is no technical difference between the one
vector groups (i.e. Yd1) or another vector group (i.e.
Yd11) in terms of performance. The only factor
affecting the choice between one or the other is
system phasing, i.e. whether parts of the network fed
from the transformer need to operate in parallel with
another source. It also matters if you have an auxiliary
transformer connected to generator terminals.
9. As shown in figure:
- Capital letter is for high voltage.
- Small letter is for low voltage.
- First letter is for primary winding.
- Second letter is for secondary winding.
10. 1. Connect the transformer and the load to be star-
delta connection.
2. Change the rearrangement of the phases
connected.
3. Notice the phase shift between the line voltage in
the star and the line voltage in the delta.
12. 1. we should connect the transformer to be star with the
load to be delta.
2. The phase A in the star should be connected to the
phase a in the delta then this terminal will be
connected to the ground of the oscilloscope.
3. The phase B in the star should be connected to the
channel 1 in the oscilloscope and the phase b in the
delta should be connected to the channel 2 in the
oscilloscope.
4. Then we will notice the phase shift between the 2
voltages VAB and Vab.
5. If we reverse the connection between the supply and
the terminals of the transformer the phase shift will be
reversed then the vector group will be phased with 360
degree, because then we reversed the dot
convention.
