Eddy current loss help please

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Hi, I have been trying to understand eddy current loss in transformer cores but seem to have run into a bit of a misunderstanding with one of the books I have read, and I was wondering if someone could just clarify if I have got this all right.

starting with the beginning, if the magnetic flux varies sinusoidal, then the flux at one instant would be;

∅ = ∅msin(ωt) (I have been told this should be done in degrees and not radians?)

value of induced emf in core at any time (t) =

[itex]\frac{d∅}{dt}[/itex] = ω∅mcos(ωt)

Am I correct in saying that from this second equation, ωθm = Em (Max induced EMF in core)?

If Es = rms value of emf induced in core, this = [itex]\frac{1}{\sqrt{2}}[/itex]ω∅m = [itex]\sqrt{2}[/itex]∏f∅m = [itex]\sqrt{2}[/itex]∏f(ABm)

Eddy current Power Losses = [itex]\frac{Es2}{Rs}[/itex]
= [itex]\frac{2*∏2*f2*A2*Bm2}{Rs}[/itex]

The next bit is the section of the notes that seems to confuse me,

Eddy current Power Loss = PE = KE*f2*BM2, where KE = Constant = 2*∏2*A2/Rs.

The book then says 'hence eddy current losses = α (f2*BM2)

Does this mean that KE is the same as α and eddy current power loss is the same as eddy current loss, or are these two different things? As far as I can see they appear the same but I just wanted to make sure from someone who has a bit more experience or knowledge of this.

thanks
 

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  • #2
NascentOxygen
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value of induced emf in core at any time (t) =

[itex]\frac{d∅}{dt}[/itex] = ω∅mcos(ωt)

Am I correct in saying that from this second equation, ωθm = Em (Max induced EMF in core)?
That would be emf induced per turn in the winding around the core, I think.

The book then says 'hence eddy current losses = α (f2*BM2)
Lose the equals sign. I think that should be a simple proportionality:

eddy current losses α (f2*BM2)
 
  • #3
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Eddy current Power Loss = PE = KE*f2*BM2, where KE = Constant = 2*∏2*A2/Rs.
The book then says 'hence eddy current losses = α (f2*BM2)
Both are the same, eddy current losses means the power loss due to eddy current.
 
  • #4
jim hardy
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Try a search on Steinmetz - he figured it out by experiment late 1800's
some old textbooks are showing up online nowadays with first-hand explanation.
 

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