I have found that although X-ray transformers are neat and fun for the typical high voltage experimenter, they are NOT really suitable as a SG Tesla coil power supply transformer. As Jim says, corona starts becoming a real issue once you surpass the 30 kV threshold. If one were to try to throttle down the input to a >100 kV rated X-ray transformer to reduce the output voltage to a more ‘Tesla coil friendly’ 25 kV or less, via a variac, then the output current will likely not be sufficient to fully charge the primary capacitor within a reasonable BPS time frame or even at the mains frequency. Plus it would take a hella voltage rating of the primary capacitor to take advantage of the full rated voltage output of an X-ray transformer. Also, X-ray transformers are rated at their nameplate outputs with a limited duty cycle, too, since most X-ray exposures require only a small fraction of a second of energizing of the X-ray tube head. Most utility power transformers are rated at a full 100% duty cycle. Assuming adequate input ballasting, backwards wired, single phase, 120/240 secondary volt pole transformers, with primary voltages in the 10 kV to 20 kV range (14.4 kV probably the most popular voltage choice amongst coilers) are the tried and true workhorse for power supplies for large SG driven coil systems.
David
Sent from my iPhone
> On Oct 12, 2018, at 3:39 PM, Yurtle Turtle via Tesla <tesla@xxxxxxxxxx> wrote:
>
> This would increase the creepage distance, if it were only a little more rigid.
> http://bometals.com/products/waterproofing/pvc-waterstops/
>
>
>
> On Friday, October 12, 2018, 4:29:06 PM EDT, jimlux <jimlux@xxxxxxxxxxxxx> wrote:
>
> On 10/12/18 11:32 AM, Yurtle Turtle via Tesla wrote:
>> I'd think primary turn to turn surface tracking along the primary supports would occur.
>> On Friday, October 12, 2018, 11:03:03 AM EDT, jimlux <jimlux@xxxxxxxxxxxxx> wrote:
>>
>>
>> Every few years, someone comes up with an inexpensive surplus X-ray
>> transformer (100kV kinds of voltages) - Life is really hard above around
>> 30-40 kV - corona is a big issue, as is plain old breakdown.
>>
>> Remember the rule of thumb is that you want 1" of clearance between
>> conductors per 10-15 kV - 30kV equipment tends be big and bulky.
>>
>> Also consider the minimum conductor radius for no corona. Breakdown
>> field in air is about 70kV/inch. The field at the surface of a
>> conducting sphere V/radius, so a 1" diameter sphere at 35kV is right at
>> the breakdown - and a bit of surface roughness is all it takes.
>> Cylinders work pretty much like spheres -it's the smallest radius of
>> curvature that's important.
>>
>>
>
> If your primary supports have long enough creepage distance, that won't
> happen. A rule of thumb is that distance along an insulating surface
> shuold be > 3 *free air spark distance.
>
> So if your primary turns were 1/2" diameter tubing spaced 1" apart
> (center to center), your supports should be >1.5" along the support. So
> 1/2" height pegs on 1" centers would work.
>
>
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