Re: Acmi k x turns

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Paul Nicholson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>

Antonio wrote:

> Acmi...k is absolutely independent on the number of primary
> or secondary turns.  I was expecting little variation, but
> not total invariance.  Is this right?

You correctly describe the behaviour of acmi, but the program
may not be representative of nature.

acmi breaks each winding into around 300 small elements, each of
which is an arc of a planar circular filament.  The program then
sums the individual EMF contributions from all 300x300 pairs of
elements, by assuming that for small element length, the EMF
induced is proportional to the length (ie B field is uniform
over the length of an element).

Increasing the density of turns without altering the overall
dimensions thus has the effect of increasing both M and L in
the exactly the same proportion. 

This is also true of the Neumann integral for which the above
summation is a discrete approximation. 

Both the above statements assume that the density of turns
is increased uniformly along the coil, so that the EMF 
induced from another coil's field rises by the same factor as
the EMF induced from the coil's own field.  This would not
be the case if turns were added to only some parts of the
coil.

We'd expect to see some departure from this idealised behaviour
for coils of few turns, or where the wire size is not small
compared to the coil dimensions.  Fortunately, the method
seems to do OK for typical TC primary coils.
--
Paul Nicholson
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