Re: Wire Length (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

Moderated and approved by: Gerry Reynolds <greynolds@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Sun, 24 Dec 2006 08:48:20 -0700
From: resonance <resonance@xxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Wire Length (fwd)




Perhaps this failure mode in the last turn is being caused by the sudden 
loss of inter-electrode capacitance, very similar to the suddenly high 
potential rise above the last turn in a classic vertical secondary inductor. 
This causes the sudden potential rise and the corona off the last turn in an 
inductor that does not have adequate electrostatic field control such as a 
toroid.

This same fault mode is the same reason flyback manufacturers always slowly 
diminish the number of turns in their outmost windings, usually down to 85% 
less windings in the last layer and 50% less windings in the adjacent lower 
layer.

Dr. Resonance



>
> Bart, All,
>
> There doesn't seem to be a coding error involved with this Cint
> problem.  Removing the interpolation (ie running the internal
> capacitance extraction at the same resolution - 91 segments - as
> the network model) doesn't help.   What does make a difference,
> and accounts for the discrepancy between the two programs,
> is the precise manner in which the disc of the secondary is
> segmented within the model, especially in the region near the
> grounded rim where dQ/dx and dI/dx are very high.
>
> It's a matter of taking the approximately smooth and continuous
> charge distribution across the disc and representing it by
> a matrix of finite size.  That means chopping the disc into
> a set of concentric rings and we have some free choice over
> where to set the boundaries between the rings.   Normally,
> with a large enough number of rings, variation in the placement
> of ring boundaries doesn't make much difference to the final
> results, and that gives us confidence that the model is stable
> and reliable.    Difficulties usually only arise when looking
> at the overtones (in which the in-coil wavelength spans fewer
> segments so is more sensitive to segmentation, especially at
> the ends).
>
> For some reason, in the rim-grounded flat coil, there's a
> lot going on in the outer few turns and this is stressing
> the model.  With various slight changes in segmentation, I can
> vary Fres from 460kHz to 500kHz, which is not much good at all.
> The only prediction then is 480kHz +/-5%.
>
> I'll try to put in the primary and center load.  Perhaps that
> will settle things down in the model... one wonders if the
> electrical stresses in the coil will appear in the same place,
> perhaps for the same reason.
>
> When rim-grounded flat coils fail, do they fail in the outer
> few turns?
>
> --
> Paul Nicholson
> --
>
>
>
>