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Re: Propagation velocity in long helical coils.

Hi Terry and all,

As you can read my mathcad files thats going to be helpful.  I suggest you
start with the zero internal C version as thats the one I have the equations
for.   Also I have not included ground reflections or top load mag
reflections. The ground reflections may be important for end effects at
least thats what Malcolms measurements indicate.  When you or Malcolm has
some comparative L measurements on the ground and isolated we will know more
about it.  You will also need inverse FFT.  As in many of these types of
problems you solve the transformed equation then convert back to get the
answer you wanted. One more thing I assume you have complex FFT routines
i.e. unless its a symmetric bipolar coil you need the sin and cos terms. Or
I can add the ground reflection for symetry that probaly best but a bit more
work on the equations and we need those measurments as a check on the
reflection equation.

Could Malcolm get hold of Wheeler's paper for his L formula so we can check
its got no inapprorate assumptions ie it is valid for short coils.

I will need to tidy up the work sheet and put it in an algoritmic form.  Can
I assume the resusltant programme will be freely distibuted?   I am looking
forward to seeing the current profile of a short coil.  Do we have any
volinters for some anamated graphic output rotines.

Ultimatly we need the transiant solution so we can watch the current and
voltage profiles build.  That may require an FFT for each element of the
current and voltage profile.  Or we could build a finite element simulation.
Thinking about that it would have the mega advantage of showing how the I
and V build and it may be possible to patch it into microsim.  Even a 100
element one would be good and  the distibuted coupling to the primary would
be a relatively simple. So which one do you want the equations for ?

Need to do the sums on the computation time for the simulation.  You have
the self C and current flow in and out and voltage across each element then
the mL and C to every other element. Just 5 equations per element So 3N +
2N**2 calculations per run cycle. Say 50 run cycles per coil cycle (depends
on the integration and diff algorithms).  So for one cycle and 100 elements
its one million equations. Say 10 million floating point operations.   How
does this compare to the self C program.  Both  would be a nice cross check
and the maths one normally provides more insight.  I think ground
reflections are simple for both due to symmetry.

Regards Bob

-----Original Message-----


>Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
>
>Hi Bob,
>
> Let me know what needs to be done and I'll get to it.  I wrote an FFT
>thing in school once that worked and Bert sent me some info tonight too on
>FFTs.
>
>At 07:06 PM 05/16/2000 -0400, you wrote:
>>Hi Terry,
>>
>>I can now include end effects because I have solved the boundary problem
but
>>I don't have an equation for the end C (except  Med).  However the method
>>could be included in your program but it would need FFT routines.  It
would
>>have the advantage I think of accurately predicting the output voltage and
>>coil profile voltage (for long coil).  The later would be useful for flash
>>over prediction at the lower end.  It is also valid for shorter coils
until
>>internal self C starts to produce errors. i.e. insight into current
>>profiles.
>>This method could have internal C added then it would be valid for very
>>short coils.
>>
>snip...
>
>