Transformers

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Transformers
Purpose to change alternating (AC) voltage to
a bigger (or smaller) value
changing flux in secondary induces emf
input AC voltage in the primary produces a flux
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Principle of Transformer Action
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Principle of Transformer Action

• Principal of Transformer Action
• Principle of electromagnetic induction.
• Ideal t?o ?inding transformer
• ?inding resistances are negligible
  
• Fluxes confined to magnetic core
• Core lose negligible
• Core has constant permeability
• V1 I1 MMF N1Ie
• Core flux f follo?s, Ie very closely.
• Ie f sinusoidal
• f fmax sin?t

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Principle of Transformer Action
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Transformers

• Nothing comes for free, however!
• Increase in voltage comes at the cost of current.
• Output power cannot exceed input power!
• power in power out

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Transformers Sample Problem

• A transformer has 330 primary turns and 1240
  secondary turns. The input voltage is 120 V and
  the output current is 15.0 A. What is the output
  voltage and input current?

step-up transformer
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Ideal Transformer on an inductive load
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• The exciting current leads the flux by hysteretic
  angle,

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Transformer on LOAD
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• Equivalent circuit referred to the LT side of a
  250/2500 single phase transformer is shown in
  fig. The load impedance connected to HT is
  380j230?. For a primary voltage of 250V, compute
• the secondary terminal voltage
• primary current and power factor
• Power output and efficiency

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Equivalent circuit referred to the LT side of a
250/2500 single phase transformer is shown in
fig. The load impedance connected to HT is
380j230?. For a primary voltage of 250V,
compute

• the secondary terminal voltage
• primary current and power factor
• Power output and efficiency

• Z'L (380j230) (N1 / N2)2
• (380j230) (250/2500)2
• 3.8j2.3
• Total impedance in the primary
  
• Secondary terminal voltage I2ZL

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• Im V1/jXm 250?0/250?90 1?-90 0-j1
• I'e Ic Im 0.5 (0-j1) 0.5-j1
• I'1 I'1 Ie 40- j300.5- j1 51?-37.4
• b) Primary current I1 51A
• Primary p.f cos?1 cos37.4 0.794
  lagging
• (c) Load p.f
• cos?2 380/ (38022302 ) 0.855
• Power Output V2I2cos?2 222050.855
• 9500 Watts
• Power Output I'12RL 5023.8 9500 Watt
• Core Loss ,PC v12 / RC Ic2 RC 0.520.2 500
  Watts
• Power Input V1I1cos?1 250510.794 10123.5

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