Technical
-> Three Phase Vector Groups
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Three Phase Vector Groups
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 Three
phase supply systems consist of three independent sinusoidal
voltage waveforms with a phase angle between each phase of
120°, as shown in Fig.
These three voltages have been drawn relative to a common
voltage reference (or neutral) point.
The three voltages may be supplied through a 3 wire system
(most common) or with the inclusion of a neutral point via
a 4 wire system.
These two systems (3 wire and 4 wire) form the basis of the
vector group configuration that can be specified for a three
phase transformer.
| The DELTA group comes from the connection of three coils
connected between the lines of a 3 wire system |
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| The STAR or WYE group comes from the connection of three
coils from the three lines to the common neutral (or star)
point. |
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By far the most common vector configuration of three phase
transformers we manufacture is the DYN11 vector group. The
first letter “D” refers to the primary configuration
being a Delta connection the “Y” refers to the
secondary configuration being a star connection. The letter
“N” following the “Y” indicates that
the neutral point which has been connected as a common point
on the secondary is actually brought out as an accessible
terminal. Finally there is a number that indicates the phase
difference between the primary line voltages and the secondary
line voltages. This number relates to the numbers on the dial
of a clock and each one represents 30° of the 360°
in a full circle. Numbers 1 to 5 on the clock occur when the
secondary voltage leads the primary voltage while 7 to 11
the phase angle lags
Different clock positions for phase angle shift between primary
and secondary are generated by different connections between
the start and finish leads of the windings of the coils. For
example in the DYN11 vector group the start leads of the secondary
coils are joined together to form the neutral point. To produce
the DYN5 vector group the finish leads of the secondaries
would be joined to form the neutral.
Other common configurations are YY0, DD0, YD1
| It should be noted that it is not possible to generate
a zero phase shift between primary and secondary with
a combination of delta and star windings. For this a more
complex vector group the Zig-Zag or inter-connected star
configuration is used. In this format half of each secondary
is wound on a different leg of the transformer. The secondaries
are then interconnected. An example would be DZN0, here
the lead angle of one leg is used to balance the lag angle
of the other leg |
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Voltage
/ Current / Power Relationships
Delta Tap Connections
When a transformer is supplied with a delta winding for a
single voltage the interconnections between the coils are
made as standard linking up to the terminals. However when
the delta windings are wound with the option for taps each
individual tap is connected to its own terminal and the delta
connections are made with movable link wires. As standard
the delta links will be supplied connected for the nominal
rated voltage. When connecting the incoming leads to a tap
the delta connection link wires also have to be moved to the
tap
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