In general, pole transformers shouldn't need any protection. They are built much more ruggedly than NSTs with typical BIL ratings of around 100 KV. That being said, I did add a simple RC low pass filter to my 10 KVA pole transformer just for a little extra insurance. It was very simple to build and I already had two extra 40 KV doorknob capacitors laying around. I also have a safety gap.
I have only heard of two instances of someone damaging a pole transformer and it wasn't from Tesla coil use. They had attached a large transformer to the output to be able to draw very long arcs. The high voltage caused by the resonant rise killed the secondary coil.
Steve White
Cedar Rapids, Iowa
----- Original Message -----
From: "Tedd Dillard" <tedd.dillard@xxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Tuesday, March 16, 2021 9:41:24 PM
Subject: Re: [TCML] Safety gaps
Gary this all very interesting and also the result of much work on your
part.
What can you say about protection for pole transformers?
Teddy
On Tue, Mar 16, 2021, 8:25 PM Gary Lau <glau1024@xxxxxxxxx> wrote:
> A Terry filter contains three independent circuits and you can choose to
> use any or all. I have a web page detailing the how's and why's of
> protection circuits - http://www.laushaus.com/tesla/protection.htm
>
> 1) A 3-terminal safety gap. This is the cheapest of the 3 parts and by
> far, is the most important. But to be useful, the gap width must be set to
> just wider than the NST open-circuit voltage sparking voltage. If you set
> it to where it stops firing when you're running your coil, you've
> accomplished nothing.
>
> 2) An R-C low-pass filter. This filters out VHF transients resulting from
> some seldom-discussed spark gap behaviors. Read my web page above for
> details. Since the components for an R-C filter are pretty cheap, no
> reason not to use it.
>
> 3) MOV voltage limiters. The MOV's must be carefully chosen to have a
> clamping voltage well in excess of the peak cap-charging voltage, but not
> so high as to never conduct, even in the face of an over-voltage
> (uncontrolled resonant rise) event. If you're going to skimp, this is
> probably the place to do it.
>
> Further questions and discussion - very welcome!
>
> Regards, Gary Lau
> MA, USA
>
> On Tue, Mar 16, 2021 at 7:18 PM Adam James <adamjamesarmy60@xxxxxxxxx>
> wrote:
>
> > Hello all,
> > Is there anything better than a simple safety gap, but less than a
> > terryfilter for SG coils?
> > AJ
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