Re: Primary Heating

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

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Peter,

On 7 Mar 2002, at 13:42, Tesla list wrote:

> Original poster: "Peter Lawrence by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <Peter.Lawrence-at-Sun-dot-com>
> 
> 
> Are you suggesting that the current flow in a thick primary conductor is not
> uniform across the cross section of the conductor, and that this
non-uniformity
> would be different for inner turns verses outer turns? Wouldn't this have
to be
> something other than skin effect since inner and outer are both operating at
> the same frequency? Are you suggesting that the inner facing surface of a 
> spiral has different magnetic coupling hence voltage and current than the
> outer facing surface of the same portion of that spiral conductor, since
it is
> geometrically closer to the center.
> 
> -Peter Lawrence.

Proximity effect closely related to skin effect and causes the ESR 
of, for example, a single layer solenoid to be considerably higher 
than skin effect alone would predict. The effect is well known and is 
formally treated in technical papers dealing with the design of high 
frequency switching transformers and chokes. Just as the magentic 
field generated by a single conductor can have an impact on its 
resistance at different frequencies, so too can a bunch of wires 
interact with each other. I think that if the observed effect cannot 
be explained by differences in cooling rates for different portions 
of the coil, then Bert's explanation is the most likely. 
 
Regards,
Malcolm

> 
> >Original poster: "Paul Nicholson by way of Terry Fritz
<twftesla-at-qwest-dot-net>" 
> <paul-at-abelian.demon.co.uk>
> >
> >Hi All,
> >
> >David Rieben wrote:
> >> I definitely have a good, solid low resistance ground connection
> >> fron the inner primary turn
> >
> >Fair enough - had to be eliminated.
> >
> >Bert wrote:
> >> Perhaps "current bunching" on the innermost turns (due to proximity
> >> effect?) so that these turns develop higher Joule heating? 
> >
> >Well that sounds like the next best explanation.  I suppose I'm going
> >to have to write that program to plot the magnetic field. As a quick
> >look we can use acmi to show the distribution of self-induction
> >across the primary.  If this is divided by the area of each turn,
> >we end up with a set of numbers proportional to the B field strength
> >in the region of each turn [*]. Eg for a 12 turn primary, 5" inner, 
> >12" outer, see
> > http://www.abelian.demon.co.uk/tmp/flat-pri-B.gif
> >
> >Is that enough of a concentration in the center?  If the inner field
> >were say 5 times the outer field, does that mean the proximity loss
> >is 5 times higher in the inner turns?  It would only make a difference
> >to the heating of the inner turns if the proximity loss was 
> >significant (equal or greater than) compared with the straight line
> >AC resistance (ordinary skin-effect) loss.  I've no idea how to work
> >that out.
> >
> >rheidlebaugh wrote:
> >> MY 4 PARRALEL DOUBLE STRAPED WITH 1" WIDE STRAPS 30 KV CAPACITORS
> >> ONLY PRODUCE SLOW CURRENT INPUT OF A SIGN WAVE WHEN MY SG FIRES.
> >
> >Caps key stuck?  You seem very sure that your primary fails to obey
> >elementary circuit theory.  I wonder why?  Hmm, on second thoughts,
> >perhaps I'd better not ask.
> >
> >[*] I've just thought, dividing by the area enclosed by each turn
> >just gives the average field within the given turn, so the actual
> >difference between inner and outer parts of the field may be a lot
> >higher than shown in the graph.  I'll just have find time to do
> >that program.
> >--
> >Paul Nicholson
> >--
> >
> >
> >
> 
> 
> 
>