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## Transformers

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### Transformers. 2. Objectives. Describe the components of an ideal transformer. ... Transformers are designated to be most efficient when operated at full rated ... – PowerPoint PPT presentation

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Title: Transformers

1
Chapter 14
• Transformers

2
Objectives
• Describe the components of an ideal transformer.
• Explain the relationship among the voltages,
currents, and turns ratio in a transformer.
• Calculate the voltage, current, and power in a
transformer.

3
Objectives
• Solve problems involving transformer losses and
demonstrate the effect they have on efficiency.
• Show how to connect single-phase transformers to
produce three-phase transformers.
• Apply special transformers such as
autotransformers, current transformers, and
potential transformers.

4
14-1 Introduction
5
14-2 The Ideal Transformer
• V1 / V2 N1 / N2
• a NHS / NLS
• V Vrated f / frated

6
Simple transformer.
7
Transformer using high side and low side
designation.
8
14-3 Transformer Power Losses
• Copper Loss
• Core Loss
• Hysteresis Loss
• Eddy Current Loss

9
Copper Loss
• I2R power loss in the copper wire in the
transformer windings.
• Proportional to the square of the winding
current.
• Minimal when the transformer is operating with no
• Maximum copper loss occurs at rated load.

10
Core Loss
• Hysteresis Loss
• Frictional loss caused by the constant change in
magnetic field polarity in the core.
• Increases with an increasing voltage or frequency
applied to the transformer windings.
• Eddy Current Loss
• I2R loss in the core material caused by
circulating induced currents in the core.
• Proportional to the square of the voltage and the
square of the frequency applied to the
transformer windings.
• Minimized by laminating the core.

11
14-4 Transformer Efficiency
• ? Pout / Pin
• Pin Pout Plosses
• Plosses Pcu Pcore

12
14-5 Effect of Power Factor on Transformer
Performance
• P V I cos ? V I x P.F.

13
14-6 Impedance Reflection
• RL(HS) a2 RL(LS)

14
Impedance reflection.
15
14-7 Impedance Matching Transformers
• ZHS a2 ZLS

16
14-8 Transformer Construction
• Shell
• Large
• Leakage flux
• E-Core
• Compact
• Leakage flux reduced

17
Cores types, (a) shell and (b) E-core.
18
14-9 Three-Phase Transformers
• Wye-to-Wye
• Wye-to-Delta
• Delta-to-Wye
• Delta-to-Delta

19
Three-phase transformer wye and delta connection
possibilities.
20
14-10 Autotransformers
• When wired as an autotransformer, the maximum
current capacity of any winding of a transformer
is the same as when it is used as a conventional
transformer.
• The voltages, currents, and turns ratio still
conform to the equations given.
• Although the autotransformer can deliver more
apparent power (S, in volt-amperes) than the
transformer alone, the transformer itself cannot
safely deliver more apparent power than its
rating.
• Because autotransformers can be connected in
several different ways, rather than attempt to
memorize the equations used to analyze each, it
is easier to gain a fundamental understanding of
how a basic autotransformer operates and then
develop the governing equations as needed.

21
Autotransformer (boost connection).
22
Autotransformer voltages and currents.
23
Autotransformer buck configuration.
24
Variable autotransformer.
25
14-11 Instrument Transformers
• Potential Transformer
• Current Transformer

26
Potential transformer and current transformer
application.
27
14-12 Useful Transformer Tips
• The core losses in a transformer are determined
by the applied voltage and frequency. Winding
currents have no bearing on core loss. Reducing
the load on a transformer will not reduce its
core loss.
• The copper losses in a transformer are
proportional to the squares of the winding
currents and the square of the frequency. The
applied voltage has no bearing on the copper
loss.
• The maximum current that can be carried safely by
a transformer winding is determined only by the
wire gauge of the windings. The dimensions of
the core and applied voltage have no bearing on
maximum current capacity. Operating a
transformer at a reduced voltage will not change
its maximum current capability.
• The real power (watts) that can be delivered
safely by a transformer is the volt-amp rating of
a transformer times the power factor of the load
it is powering. For example, a 1-kVA transformer
can deliver only 700 watts to a 0.7-power-factor