Hello all! I wrote before talking about repairing my 25kva 14400/7620V. Quick rundown Incase you missed last email chain... it’s a new transformer had an issue at shipping which is how I ended up with it... it was running fine till I ran a .125mF 100kv pulse cap in series with a Jacobs ladder... it just stopped and kept drawing 50 amps. At full arc it was ballasted to about 80-90 amps. With no arc it pulled nothing until the damage now it sits there at 50 amps with no arc output. So I pulled the core and found a small burn spot on the outside HV winding I pulled the paper and found it was just a dot the size of a ball point pen. I fixed that easily... tested and still pulling 50 amps... I don’t know if this is the proper way but obviously there is two HV windings I checked resistance on both windings separately.
Here is a link to 10 photos showing all of my measurements can anyone make any sense of these? Also is there any good testing I can do with an oscilloscope and a signal generator?
https://flic.kr/s/aHsmyTD8z8
Sent from my iPad
> On Jan 6, 2019, at 10:14 PM, Bert Hickman <bert@xxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hi Tyler,
>
> If you've removed the dent and substantially increased the clearance distance between the affected winding and the case, the mineral oil itself should provide sufficient insulation.
>
> However, it you'd like to provide additional insurance to make the fix bulletproof, you could slip in a curled piece of 1/16" - 3/32" thick flexible natural LDPE sheet against the metal case opposite the location of the fault. You can simply curl a 6" wide strip around the inside of your transformer case so that it snugly lines the interior of the metal case. LDPE is compatible with mineral oil over the long haul, so it should last for the lifetime of the transformer. Old time coilers will remember times when HV Tesla Coil capacitors were constructed using LDPE sheet under oil as the dielectric material.
>
> Something like the following material:
> https://www.usplastic.com/catalog/item.aspx?itemid=23655&catid=705
>
> Good luck,
>
> Bert
>
> Tyler LaVite wrote:
>> Does anyone know what type of tape that is used on a transformer core to hold the nonexistent paper on the core? The tape they use to tape the seams?
>> Sent from my iPhone
>>> On Jan 4, 2019, at 7:07 PM, David Speck <Dave@xxxxxxxxxxxxxxxx> wrote:
>>>
>>> Tyler,
>>>
>>> Good to hear that the fix looks to be relatively simple.
>>>
>>> I would think that you will have to re-center the core inside the tank. At the voltages involved, a few layers of varnish are not going to provide adequate insulation. Distance from the can and lots of oil are what you will need to prevent further breakdown.
>>>
>>> Dave
>>>
>>>> On 1/4/2019 7:54 PM, Tyler LaVite wrote:
>>>> Guess what guys! I pulled apart my transformer tonight and found a tiny burn mark on the outer wrap of HV side. I opened the paper it was right next to the end and there is one tiny little dot on one wrap of wire. What I found out happened was when this transformer got its bushing hit by a fork lift it shifted the core and it was sitting on the tank and it burned a small dot through the paper and was grounding onto the can. A good couple of coats of electrical varnish should fix it right up... man I’m so happy good end to a Friday!
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