David,
My horn safety gap uses 1/4 inch brass rods. I initially set the gap with just the pole transformer connected. I gradually opened the gap until it just stopped arcing. When I then ran the full tesla coil with that setting, I got excessive firing of the safety gap. I opened the gap just a little more, maybe 2 or 3 mm, until it just very occasionally fires. I have read that this is a no-no but the safety gap was just firing excessively. My capacitor bank (45 nF) is no where near the resonant value with the transformer according to JAVATC so I shouldn't be experiencing excessive over-voltage. As best as I can tell, my RSG seems to be firing consistently at 4 times per cycle (240 bps). I have had no trouble with safety gap quenching when it does fire.
Steve
----- Original Message -----
From: "David Rieben" <drieben@xxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Thursday, May 10, 2018 5:46:29 AM
Subject: Re: [TCML] Safety Gap: 2-pole or 3-pole?
Steve,
Since a pole transformer essentially has only two HV outputs (without the third center tapped ground, as with most NSTs), I would figure that a two-pole gap should suffice.
Out of curiosity, is your safety gap set so that it occasionally fires during coil operation and assuming that it does occasionally fire, do you have issues with the gap quenching once it does fire? I have personally always had trouble with the formed power arc quenching once the safety gap fires, due to the level of power being processed by a pole pig. That is why I opt for a properly rated MOV distribution arrester to act as my ‘safety gap’. I use a 27 kV rated arrester directly across my RSG and a 21 kV rated one across the HV output bushings of my 14.4 kV pole pig.
David
Sent from my iPhone
> On May 8, 2018, at 11:07 PM, Steve White <steve.white1@xxxxxxxxx> wrote:
>
> My current pole transformer safety gap is a horn gap and has 2 poles: one pole for each of the 2 HV leads. The other type that I have seen, used mainly on NSTs, uses 3 poles: 2 poles for the HV leads with the 3rd pole being ground located between the 2 HV terminals. Is there any advantage in using one or the other for pole transformers?
>
> Steve
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