Electro Mechanical System
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Transcript Electro Mechanical System
Delta-Delta Connection
Three single-phase transformers connected delta-delta
H1 terminal of each transformer is connected to the H2 of the
next transformer. X1 terminal of each transformer is connected
to the X2 of the next transformer
Primary and secondary voltages and currents are inphase.
Lecture 11
Electro Mechanical System
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Delta-Wye Connection
Three single-phase transformers connected delta-wye.
H1 terminal of each transformer is connected to the H2 of the
next transformer the X2 terminals of all transformers are
connected together to form a neutral terminal.
Delta-wye connection produces a 30° phase shift between the
primary and secondary voltages and currents.
Lecture 11
Electro Mechanical System
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Wye-Delta Connection
Connection are identical to those in delta-wye
The primary and secondary connections are interchanged.
The H2 terminals of all transformers are connected together to
form a neutral terminal.
The X1 terminal of each transformer is connected to the X2
terminal of the next transformer.
Connection results in a 30° phase shift between the
primary and secondary voltages and currents.
Wye-wye Connection
In wye-wye, special precautions have to he taken to
prevent severe distortion of the line-to-neutral
voltages, when load becomes unbalance.
One way to prevent is to connect the neutral of the
primary to the neutral of the source, usually by ground.
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Electro Mechanical System
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Wye-wye Connection
Another way is to provide each transformer with a third winding,
called tertiary winding.
The tertiary windings of the three transformers are connected
in delta.
They often provide the substation service voltage where the
transformers are installed.
There is no phase shift between the line voltages of a wye-wye
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Open-Delta Connection
It is possible to transform the voltage of a 3-phase
system using only 2 transformers.
Identical to a delta-delta connection, less one transformer.
Limited use due to a 86.6% reduction in the installed power
capability.
Two 50 kVA transformers could carry 100 kVA, but
limited to 86.6 kVA in an open-delta connection.
Used in emergency conditions.
Used in metering of power system voltages.
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Three-phase Transformers
One 3-phase transformer may replace a
transformer bank of three single-phase units.
The magnetic core has three flux-carrying legs.
Two yokes, bottom and top, couple the flux of
the three legs.
The sum of the three fluxes equals zero.
Each leg contains the primary and secondary
windings of one of the phases.
The windings are connected delta or wye,
internal to the transformer tank.
Only six terminals are brought out of the tank.
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Step-up & step-down
autotransformers
When a small change in voltage is required in
3-phase, it is economical to use 3 single phase
transformers to create wye-connected
autotransformer
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Home Work & Assignment
Home Work
Page 245, Example 12.1
Page 247, Example 12.2
Page 249, Example 12.3
Page 251, Example 12.4
Page 259, Example 12.7
Assignment 4
Page 259, Problems: 12-2, 12-4, 12-6, 12-8,
12-10
Due Date: Tuesday 1st March, 2011
Lecture 11
Electro Mechanical System
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