Basics of Transformers: Negative Signs in EMF Terms

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    Basics Transformers
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SUMMARY

This discussion focuses on the negative signs in the induced EMF terms -N1dΦ/dt and -N2dΦ/dt in transformer circuits. Participants clarify that the negative signs arise from Lenz's Law, which states that the induced EMF opposes the change in magnetic flux. The polarity of the induced EMF is influenced by the winding direction of the coils, and understanding the dot convention is crucial for determining the phase relationship between the primary and secondary coils. The conversation emphasizes that while the signs are important for calculations, the magnitudes and phase relationships are often more critical in practical applications.

PREREQUISITES
  • Understanding of Lenz's Law and its application in electromagnetism.
  • Familiarity with transformer operation and the concept of mutual inductance.
  • Knowledge of Kirchhoff's laws as they apply to electrical circuits.
  • Basic grasp of the dot convention in magnetically coupled circuits.
NEXT STEPS
  • Study the application of Lenz's Law in various electromagnetic scenarios.
  • Learn about the dot convention and its significance in transformer design.
  • Explore the mathematical derivation of induced EMF in transformers using Faraday's Law.
  • Investigate the effects of winding direction on transformer performance and efficiency.
USEFUL FOR

Electrical engineers, physics students, and anyone involved in the design or analysis of transformer circuits will benefit from this discussion.

  • #31
cnh1995 said:
The net flux is the flux set up by the magnetizing current. It is constant as long as the applied voltage (rms) is constant.

If flux is constant , how is EMF induced in the two coils ?
 
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  • #32
Vibhor said:
If flux is constant , how is EMF induced in the two coils ?
RMS value of the flux is constant. Or you can say, the amplitude of the flux waveform is constant.
Merlin3189 said:
I think it would - so long as by constant you mean, varying sinusoidally with constant amplitude.
A literally constant flux does not cause any emfs. EMF is always associated with changing flux.
 
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  • #33
Ok . I will stop here for the time being :wink:

You and @Merlin3189 both have been amazing . Thanks both of you for your time and patience . I really admire the way you both stuck with me in this thread . Some expert members would have been fretting and fuming by now ?:)

You might have also been irritated at times . But the good part is that ,you didn't let me know o0) .

People might have more knowledge than you , but few have finer qualities like patience :smile:

Keep up the good work :thumbup: .
 
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  • #34
cnh1995 said:
This reflected secondary current cancels the secondary mmf.
We have been using this term frequently in this thread, but I think we haven't discussed its another important physical significance.

This reflected secondary current Ip1 is actually the reflection of the load connected to the secondary.
For a resistive load, the product of applied primary voltage and reflected secondary current gives the power supplied by the source, which is dissipated in the secondary.
Hence,
Vp*Ip1=Vs*Isec.

Other than maintaining the core flux constant by cancelling the secondary mmf, the reflected load current in the primary is responsible for supplying power (active and reactive) from the source to the load on the secondary.

And thanks for your kind words!:smile:
 

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