Department of Electrical and Computer Engineering

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Department of Electrical and Computer Engineering

• EE20A - Electromechanical Energy Conversion
• Transformers

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Principle of Operation

• Ferromagnetic, laminated core
• Primary and Secondary Windings

• Alternating Voltage level conversion

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Principle of Operation

• Alternating Voltage sets up varying flux in core
• Varying flux links with windings on secondary
  side
• Flux linkage results in voltage source

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Non-Ideal Transformer

• Leakage losses in windings

• Hysteresis Eddy Current Losses in Transformer
  Core

• Resistive Losses in primary and secondary
  windings

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Equivalent Circuit
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Points to Remember

• when going to the HV side, impedances go up
• when going to the LV side impedances go down
• any side can be treated as the primary, all the
  must be done is that the turns ratio should be
  adjusted to suit

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Open Circuit Test

• Measure Voc , Ioc and Poc
• Calculate Zoc and qoc
• Io Ioc cos qoc
• Im Ioc sin qoc
• Ro Voc / Io
• Xm Voc / Im
• Poc Voc x Ioc x cos qoc

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Open Circuit Test
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Short Circuit Test

• Measure Vsc , Isc and Psc
• Calculate Zsc and qsc
• Rs Zsccos qsc
• Xs Zscsin qsc
• Psc Vsc x Isc x cos qsc

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Short Circuit Test
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Summary
p.f _at_ qL
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Turns Ratio

• a ( N1 / N2 ) Coil Turns Ratio
• E1 N1 Voltage Turn Ratio
• E2 N2
• I1 N2 Ampere Turn Ratio
• I2 N1

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Summary

• Power out V2 I2 cos qL
• IIN INL I1
• INL IO jIm PHASE DIFFERENCE 90 DEG
• -j Lagging p.f.
• 4. N1I1 - N2I2 0

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Summary

• 
  Equivalent Losses
• 
  Stored Energy
• 7. V2 E2
• 8. E2 E1 N2
• N1

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Summary
9. E1 V1 I1 RS jXS 10. ?
Output Power x 100
Input Power Input Power losses
x 100 Input Power
Output Power x 100 Output
Power Losses
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Summary

• ? V2 I2 cos qL x 100
• V2 I2 cos qL IO2RO
  I12RS
• Efficiency ()
• Regulation () (VNL2 VFL2 ) X 100
• 
  VFL2