Potato chips, laminations and eddy currents (fwd)

---------- Forwarded message ----------
Date: Wed, 29 Apr 1998 09:04:41 -0700
From: Eric Davidson <edavidson-at-icva.gov>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Potato chips, laminations and eddy currents

Hello everyone!

I've been following this lamination thing for a couple days now, and
thought I'd add my 2 cents worth. The purpose of using a laminated core
is: The laminations can be insulated from one another, which prevents
(reduces) the flow of eddy currents in the core. Eddy currents represent
wasted power which is converted to heat. The direction of flow of the
eddy currents is perpendicular to the lines of flux in the core and is
not the result of the 'shorted turn' effect. The 'shorted turn' effect
would make the existence of toroidal transformers with spiral wound
cores very impractical if not impossible, which is not the case.  A
laminated core does not appreciably effect the losses due to
hysteresis.  Hysteresis is a phenomenon associated with the composition
of the core material.  The amount of hysteretic loss is proportional to
frequency, flux density, cross sectional area etc.  The laminations only
need a thin layer of varnish or the like to insulate them, since the
voltage driving the eddy currents is not very large, and is in no way
directly associated with the voltages in the windings. The core itself,
however, must be adequately insulated from the windings.  There are also
some logistical assembly perks to using laminations too, but they are
secondary (NoPunIntended) to the electrical reasons. I hope this helps.

Eric Davidson