Re: [TCML] Advice needed: DRSSTC Primary winding

[Grant Visser <freeekyg@xxxxxxxxx>]

Hi Finn,

Thank you very much for your answer. The corona buildup you describe is the
one issue that hadn't even crossed my mind although I must admit to having
considered filling that airgap with mineral oil .... more for insulation and
heat dissipation but would surely also get rid of the corona problem?

Hmmm probably not the most practical idea though .... lol


2009/3/25 Finn Hammer <f-h@xxxx>

> Grant,
>
> I will advise you against using an internal primary winding, although *I*
> do it all the time....
> The reason is, that the voltage gradient between primary coil and secondary
> is going to be of a character that will invariably lead to corona on the
> primary coil.
> You cannot solve a corona problem by adding insulation material, it will
> make it worse.
> The only solution to a corona problem is either field control or potting,
> ie. removing all air in the intervening space.
>
> A couple of years ago I wrote a .lua script for FEMM, which draw the
> geometry of an internal primary, for subsequent finite element treatment to
> solve the complex electrical field between windings.
> It was later rewritten by Russian coiler, Father Dest, and it became very
> good.
>
> Using this script it was possible to produce a series of FEMM models of
> internal primary愀, and it was shown that if you want to control the corona,
> substantial amounts of potting material had to be used.
> I never pursued the problem, although there still is a bucket of potting
> material in my store purchased at that time.
> In coils designed to run at low duty cycles, internal primary's are a
> possibility, because it takes some time before the corona *get's at* the
> plastic, but for ordinary coils, running flat out for minutes on end, It is
> not practical.
>
> Cheers, Finn Hammer
>
> Grant Visser skrev:
>
>> Hi all,
>>
>> I am building a small DRSSTC (3.5" x 15.8" Secondary - 1600) and was
>> wondering if I could put the Primary winding "inside" the Secondary, and
>> if
>> so, how the design parameters should be adjusted?
>>
>> The former for the 2ndary is plexiglass as is the former I'd like to use
>> for
>> the primary (1.9"). I do have commercial nomex transformer insulation
>> which
>> I could use for additional insulation between the two coils. ie  secondary
>> winding/plexiglass/nomex/airgap/primary winding/plexi/... etc.
>>
>> IF this "could" work ... how would I need to change the design parameters
>> of
>> the primary? I was going to use 6 turns of 3mm copper tubing ...
>>
>> How would this affect the desired coupling co-efficient and overall energy
>> transfer?
>>
>> Any words of wisdom greatly appreciated :-)
>>
>> Grant
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>
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