Re: Inter-turn arcing

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

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

Hi,

>At 03:24 PM 7/21/2002 +0100, you wrote: 
>
>Re: flat spiral or inverted-conical primaries- does the voltage on the outer 
>turns present problems with inter-turn arcing -as it would appear the 
>volts/turn on the outer -i.e.. longer- turns would be greater than the 
>volts/turn on the inner -i.e.. shorter- turns
>
>due to increased inductive reactance and resistance in the added wire?

Yes, this "autotransformer action" suggests that the unused turns at the
outside of a primary do indeed see high voltages.

>
>In view of this might it be appropriate to space the outer turns further 
>apart than the inner turns, maybe even use a reversed parabolic type of 
>primary -with the wires becoming progressively more closely pitched towards 
>the middle -by "reversed" I am thinking of a normal parabolic dish where the 
>extremities of curve have been turned around so that they are now at the 
>centre to give the profile of a funnel- or trumpet- shaped cone.

I have never had any problems with it.  My big coil's primary has many
unused turns close together but it has never arced at the outside.

http://hot-streamer-dot-com/TeslaCoils/MyCoils/BigCoil/primary.jpg

The current in this unused portion is very low but the magnetic induction
should cause the voltage to be high at the edge.  It is rather surprising
it does not arc.

>
>I have not so far encountered primary inter-turn arcing although I would be 
>interested to know how common it is and what can be done about it for future 
>reference -as well as any opinions on the advantages or otherwise of wider 
>pitching of outer turns or funnel-shaped profiles to prevent inter-turn 
>arcing on Tesla coil primaries.
>

If it's not a problem don't fix it :-))  But it is curious "why" it is not
a problem...  I'll try to take some measurements this afternoon...

Cheers,

	Terry