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Re: Balancing L/C Sizes



Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-uswest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Michael,

On 1 May 01, at 11:33, Tesla list wrote:

> Original poster: "Michael Rhodes by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <rhodes-at-fnrf.science.cmu.ac.th>
> 
> For the groups' information in case it hasn't been posted here
> is the relationship of frequency to skin depth.
> 
> In a copper wire at 100C, this depth (in centimeters) is 7.5/sqr(f)
> where f is the frequency in Hz.  Don't know what it is at other
> temperatures, perhaps someone out their can let  us know.  The
> following is a table of frequencies appropriate for TC work.
> 
> Table 1-Skin-effect penetration depth
> Frequency(kHz)    Depth(cm X 10-3)   AWG gauge
> 50                          33.5                         27
> 100                        23.7                         31
> 200                        16.8                         33
> 300                        13.7                         35
> 400                        11.9                         36
> 500                        10.6                         38
> 750                        8.7                           39
> 
> So if you take the radius (not diameter) of #22 AWG wire (.032cm) that
> would suggest a frequency of 55kHz before the skin effect is totally
> negligible?  If I have time I'll try to write a program that
> correlates the frequency with the cross sectional area that the
> electrons will travel per gauge of wire.  That would reflect the
> current handling capability and loses.
> 
> 
> Found this information at
> http://www.ednmag-dot-com/ednmag/reg/1999/012199/02df1.htm
> while researching for losses in magnets.
> 
> Would be interested in any comments on this.
> 
> -- Michael

I've used a similar relationship 66/SQRT(f) mm. Both are dependent on 
the resistivity of the conductor which varies for various forms 
copper e.g. annealed, work hardened etc. Skin effect is very much 
alive and well at all frequencies down to (but excluding) 0Hz. For 
example, it matters in choosing a suitable conductor size for 60Hz 
currents of whatever magnitude. Too much cross-sectional area and 
more copper than necessary is being included although it is generally 
true that the larger the wire, the lower its resistance at any 
frequency. So copper utilization is a cost issue.

Regards,
malcolm