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PowerPointPresentation
Chapter 4Transformer Connections
Voltage Transformation
Three-Phase Circuits
Delta Connections Wye Connections
Delta-to-Wye Connections Wye-to-Wye
Connections Wye-to-Delta Connections
Delta-to-Delta Connections Open DeltaConnections Delta Connection with High Leg to
Ground Three-Phase Transformer Polarity
7/29/2019 Transformers and power distribution
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Chapter 4Transformer Connections
The low-voltage winding ofa standard distribution
transformer connected to a
single-phase circuit isnormally made with two
equal coils. These sections
are arranged so that they
may be connected in series
or parallel.
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Chapter 4Transformer Connections
Transformer polaritymay be subtractive or
additive.
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Chapter 4Transformer Connections
The polarity of atransformer may be
determined using a
known transformeror with AC voltage.
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Chapter 4Transformer Connections
A delta connection hasthe wires from the ends
of each coil connected
end-to-end to form aclosed loop.
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Chapter 4Transformer Connections
Studying the current ina delta-connected
system at both 0 and
90
illustrates thecurrent flow in a delta-
connected system.
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Chapter 4Transformer Connections
A wye connection hasone end of each coil
connected together
and the other end ofeach coil left open for
external connections.
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Chapter 4Transformer Connections
Studying the current ina wye-connected
system at both 0 and
90
illustrates thecurrent flow in a wye-
connected system.
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Chapter 4Transformer Connections
A 3-phase delta-to-wye connection is
often used for
distribution where afour-wire secondary
distribution circuit is
required.
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Chapter 4Transformer Connections
Three single-phasetransformers may
be connected in a
wye-to-wyeconnection to form
a 3-phase
transformer.
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Chapter 4Transformer Connections
A wye-to-deltaconnection permits
single-phase and 3-
phase loads to be
drawn simultaneouslyfrom the delta-
connected secondary
at the same voltage.
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Chapter 4Transformer Connections
In a wye-to-deltaconnection of three single-
phase transformers, one
unit may be disconnected
from the circuit and
service maintained with
the secondary operating
in open delta connection
at 57.7% of normal bank
capacity.
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Chapter 4Transformer Connections
In a delta-to-deltaconnection, the
voltage of each
transformer is equal to
the 3-phase linevoltage and the
current in each of the
transformers is only
57.7% of the line
current.
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Chapter 4Transformer Connections
Grounding one of themidpoints of the
windings provides 240
V/120 V, single-phase,3-wire service for
lighting applications.
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Chapter 4Transformer Connections
An open deltaconnection makes
3-phase power
available anywhere
along thedistribution line with
the use of only two
transformers rather
than the usual
three.
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Chapter 4Transformer Connections
A deltaconnection with a
high leg to ground
provides 240 V,3-phase power to
equipment and
120 V power for
lighting and
receptacles.
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Chapter 4Transformer Connections
The phasesequence on the
secondary of a
three-phasetransformer is the
same as the
phase sequence
on the primary.
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Chapter 4Transformer Connections
Transformers areclassified into
connection groups
according to theirphase shift.
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Chapter 4Transformer Connections
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Chapter 4Transformer Connections
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