[SI-LIST] Why does lamination fail to prevent eddy currents at high frequencies?
- From: Steve Rogers <SRogers@xxxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 8 Apr 2002 16:14:06 +0100
Further to my last post...
I have recently read a section in GW Carters book 'Electromagnetics in its
engineering aspects'
This book suggests that the ratio of lamination thickness to skin depth in
the laminations of transformer cores or any laminated core subject to
alternating flux is critical to the loss that will be incurred in the core.
As far as I understand the work, the eddy currents induced in the individual
laminations set up their own flux which opposes the original flux that
caused the eddy currents in the first place. The result of this is that
distribution of flux in each lamination will be such that flux will occupy
mainly the area near the edges of the lamination and not the central portion
of the lamination. The current distribution then follows that of the flux ie
current is crowded toward the edges of the laminations. The eddy currents
thus suffer from skin effect. This is where I get a bit confused...........I
expected the work (GW Carter book) to then show that the eddy current losses
in the core would increase if the skin depth decreased (frequency
increased), or if the lamination thickness decreased. The conclusion however
is the opposite of this. The book gives a curve for a correction factor due
to the effect of eddy current flux. The correction factor suggests reduction
of loss for lamination thickness >> skin depth??
Any comments on this one?
Original post .....
> I have seen a number of simple derivations explaining why it is a good
idea
> > to laminate a conductor which lies in a magnetic field. The idea being
to
> > slice up the material in the direction of the flux and hence break the
path
> > of eddy currents. This is all very well and good, I then find it
mentioned
> > in passing that this technique fails at high frequency but have not yet
> > found a good explanation as to why?
Steve Rogers B.Eng(Hons) AMIEE
RF Design Engineerr
Micromill Electronics Limited
email: srogers@xxxxxxxxxxxxx
Tel : +44 (0) 2392 366600
Fax : +44 (0) 2392 366673
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