TRANSFORMERS

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TRANSFORMERS

• MARK LEAKEY
• KOK WAI, WONG
• WAN HAZLIN ZAINI

Reference http//www.osha.gov/SLTC/etools/electr
ic_power/images/transformer2.jpg
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DEFINITION

• Device used to transfer energy from primary
  winding to secondary winding by electromagnetic
  induction.
• Based on Faradays Law of induction

Where- e EMF (V) FB Magnetic flux (Wb)
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TRANSFORMER USES

• Impedance matching
• Electrical Isolation
• AC power transmission
• STEP-UP Transformer
• STEP-DOWN Transformer

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HISTORY

• 1831 Michael Faraday invented the Induction
  Ring.
• 1881 Lucien Gaulard and John Gibbs exhibited a
  device called secondary generator.
• 1885 William Stanley developed the fist
  commercially used practical device while working
  for Westinghouse Electric Company in US.

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INDUCTION THEORY

• Transformers behaviour is based on Faradays Law
  of Induction

Where- e EMF (V) N No of turns of wire FB
Magnetic flux (Wb)
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INDUCTION THEORY
Reference http//www.tpub.com/doeelecscience/elec
trical20science2_files/image1053.jpg
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POWER GENERATION AND TRANSMISSION
POWER STATION
400/132 KV
132/11 KV
SMALL INDUSTRY
132/33 KV
LARGE INDUSTRY
11 KV/240 V
RESIDENTIAL
Reference http//www.nationalgrid.com/uk/img/im_
generation.gif
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TRANSFORMER MODELS

• Ideal Transformer

Np No of windings on the primary Ns No of
windings on the secondary ip Current into the
primary is Current out from the secondary Vp
Voltage across the primary Vs Voltage across
the secondary
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Primary and Secondary Relationship

• VP NP a iS
• VS NS iP
• Note a lt 1 Step up transformer
• a gt 1 Step down transformer
• Voltage and current angles are NOT affected
  hence, ?P ?S ?

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LOSSES

• Transformers have losses and these losses must
  come into consideration.
• Copper losses (I2 R)
• Leakage Flux losses
• Core losses
• Eddy currents
• Hysteresis losses

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REAL TRANSFORMER LOSSES

• Copper losses (I2 R)
• Leakage Flux losses
• Core losses
• Eddy currents
• Hysteresis losses

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EQUIVALENT CIRCUIT
Approximate Transformer Model referred to the
primary side
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TYPES

• Auto-Transformer
• Used to change a desirable voltage by only a
  small amount. For example 120/132 V

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TYPES
Three Phase Transformers

• Three phase transformers
• can be constructed in two
• different ways i.e. -
• A three phase bank consists of three single phase
  transformers.
• Three windings wrapped around a common core.

Reference Electric Machinery and Power System
Fundamentals, Stephen J. Chapman
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THREE PHASE TRANSFORMER CONNECTIONS

Delta wye (? Y)
Delta delta (? ?)
Wye delta (Y- ?)
Wye wye (Y Y)
Reference Electric Machinery and Power System
Fundamentals, Stephen J. Chapman
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TYPES

• Two types of special purpose transformers used in
  power systems for taking measurements.
• Potential Transformer
• Current Transformer

Reference Electric Machinery and Power System
Fundamentals, Stephen J. Chapman
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EFFICIENCY

• Efficiency (?) is the ratio of the power out to
  the power in of a transformer.
• ? in an Ideal transformer, no power losses
• PIN VPIP cos ?P
• POUT VSIS cos ?S
• PIN POUT VPIP cos ?P VSIS cos ?S
• SOUT SIN VPIP VSIS
• ?Ideal 100

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Efficiency for a single phase real transformer

• As mentioned previously, losses occur in a real
  transformer and these losses must be taken into
  count.
• Hence, ?Real POUT x 100
• PIN
• POUT x 100
• POUT PLOSS
• VSIS cos ?S_________
• VSIS cos ?S i2R (VP/a)2
• RC

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VOLTAGE REGULATION

• Voltage regulation (VR) is the ability of a
  system to provide near constant voltage over a
  wide range of load conditions. Also it compares
  the VO at no load to VO at full load.

• An Ideal transformer has a voltage regulation,
  
• VR 0

Reference http//en.wikipedia.org/wiki/Voltage_r
egulation