Coil Efficiency (was megavolt)

["Greg Leyh" <lod-at-pacbell-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

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


>>
>>  [1/2 * Cp * Vp^2] * 75%  =  1/2 * Cs * Vs^2
>>
>
> This equation could be re written to:
> 
> Vs = Vp x SQRT(Cp/Cs) x SQRT(0.75)
> 
> Which can be equivalent to:
> 
> Vs = Vp x SQRT(Ls/Lp) x SQRT(0.75)
> 
> Which is:
> 
> Vs = 0.866 x SQRT (Ls/Lp)
> 
> "i" usually estimate the secondary voltage as:
> 
> Vs = 0.5 x SQRT (Ls/Lp)
> 
> For most small coils, I am fairly confident that "the factor" is 0.5 to 0.6
> 
> If your are fairly confident that the factor is "around" 0.87 for your
> "really big" coils, (that the rest of us can only dream of ;-)) it would
> provide an interesting comparison of the efficiencies of large coils vs.
> smaller coils...


I am not confident of the exact efficiency values by any means,
but I would expect a TC to be easily above 70% efficient.

A 'factor' of 0.87 implies an efficiency of 75%  (0.87 * 0.87)
A 'factor' of 0.60 implies an efficiency of 36%  (0.60 * 0.60)
A 'factor' of 0.50 implies an efficiency of 25%  (0.50 * 0.50)

My rotary drops about 1300V at 2800A.  Since the primary is a
26kVDC system, the rotary loss is about 1300/26000 or about 5%.
There are no other obviously dissipative components (warm to the 
touch, at least) in the coil system.  So I can't imagine how more 
than 20% of the coil's throughput could be dissipated as heat.  
I'm sure that the stationary electrodes would glow red, if they 
were radiating any more than a kilowatt or two.  The throughput
with the new primary configuration is only 28kVA.

Empirical evidence seems to hint that the smaller coils are more 
efficient than larger ones.  I suspect that this has to do with 
the squared/cubed scaling laws -- A coil that's twice as big has
to fill *eight* times the volume with magnetic flux..
-- 


-GL
www.lod-dot-org