# Eddy current loss help please

## Main Question or Discussion Point

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) =

$\frac{d∅}{dt}$ = 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 = $\frac{1}{\sqrt{2}}$ω∅m = $\sqrt{2}$∏f∅m = $\sqrt{2}$∏f(ABm)

Eddy current Power Losses = $\frac{Es2}{Rs}$
= $\frac{2*∏2*f2*A2*Bm2}{Rs}$

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

$\frac{d∅}{dt}$ = 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)

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.

jim hardy