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Chapter 4 Transformer Connections

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Three single-phase units wired in a delta-to-delta connection can provide power for this ... * * Transformers are classified into connection groups according to ... – PowerPoint PPT presentation

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Title: Chapter 4 Transformer Connections


1
Chapter 4 Transformer 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 Delta
  • Connections Delta Connection with High Leg to
    Ground Three-Phase Transformer Polarity

2
  • The low-voltage winding of a standard
    distribution transformer connected to a
    single-phase circuit is normally made with two
    equal coils. These sections are arranged so that
    they may be connected in series or parallel.

3
  • Transformer polarity may be subtractive or
    additive.

4
  • The polarity of a transformer may be determined
    using a known transformer or with AC voltage.

5
  • A delta connection has the wires from the ends of
    each coil connected end-to-end to form a closed
    loop.

6
  • Studying the current in a delta-connected system
    at both 0 and 90 illustrates the current flow
    in a delta-connected system.

7
  • A wye connection has one end of each coil
    connected together and the other end of each coil
    left open for external connections.

8
  • Studying the current in a wye-connected system at
    both 0 and 90 illustrates the current flow in a
    wye-connected system.

9
  • A 3-phase delta-to-wye connection is often used
    for distribution where a four-wire secondary
    distribution circuit is required.

10
  • Three single-phase transformers may be connected
    in a wye-to-wye connection to form a 3-phase
    transformer.

11
  • A wye-to-delta connection permits single-phase
    and 3-phase loads to be drawn simultaneously from
    the delta-connected secondary at the same
    voltage.

12
  • In a wye-to-delta connection 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.

13
  • In a delta-to-delta connection, the voltage of
    each transformer is equal to the 3-phase line
    voltage and the current in each of the
    transformers is only 57.7 of the line current.

14
  • Grounding one of the midpoints of the windings
    provides 240 V/120 V, single-phase, 3-wire
    service for lighting applications.

15
  • An open delta connection makes 3-phase power
    available anywhere along the distribution line
    with the use of only two transformers rather than
    the usual three.

16
  • A delta connection with a high leg to ground
    provides 240 V, 3-phase power to equipment and
    120 V power for lighting and receptacles.

17
  • The phase sequence on the secondary of a
    three-phase transformer is the same as the phase
    sequence on the primary.

18
  • Transformers are classified into connection
    groups according to their phase shift.

19
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