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Discussion Starter · #1 · (Edited)
Can a dry type transformer winding be repaired without rewinding the whole transformer. 4 inches of the very outer winding got slightly dented and a little bit of the varnish and tape came off. This transformer is 25kv (7.65kv per phase)
 

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Sub transient reactance X”d worshiper.
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Can high voltage dry type transformer winding be repaired without rewinding the whole transformer if it’s the very outer winding
Only the manufacturer can really answer that question properly.

On thing to have it repaired. Another thing to have it tested. And another thing to put in to service….

Like did it get dented and the varnish is scraped?

Or did it fail.?
 

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Why would you even ask such a question. If you are considering patching an high voltage transformer > 65K volts your crazy.

Just so we understand each other
  • High (HV), Extra- High (EHV) & Ultra-High Voltages (UHV) - 115,000 to 1,100,000 VAC.
  • Medium Voltage (MV) - 2,400 to 69,000 VAC.
  • Low Voltage (LV) - 240 to 600 VAC.
 

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While I agree trying to repair this is not a good idea, you could make a few calls and see if its possible. You may not have to replace the complete xfmr as the coils are separated and maybe all they have to do is repair the bad one.
I would call the manufacturer first. There are xfmr repair replacement shops too. Give these guys a call. If they cannot help you, they can point you in the right direction.
Jenkins Electric | Electrical, Mechanical Repair & Machining I used them for custom xfmr's in the past. They sell and repair.
 

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T&R in South Dakota or SUNBELT SOLOMON SERVICES, Kansas. Used to give better warranties on rebuilds than you could get new. I once had a transformer that I waiting for a rebuild was going to take to long. Talking to my buddy at Sunbelt, Jed found out they had just finished one that would work for my need. Contacted the customer and made a deal. They shipped the rebuilt one and picked up the old one. Everyone was happy except for my 20 man crew that had to disconnect and reconnect in less than a week. This was 115kv to 69 kv. Got yelled at by the big boss for give the guys a 4 day weekend when the job was done. That was ok every one in the shop wanted to work on my projects.
 

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Discussion Starter · #8 ·
Only the manufacturer can really answer that question properly.

On thing to have it repaired. Another thing to have it tested. And another thing to put in to service….

Like did it get dented and the varnish is scraped?

Or did it fail.?
4 inches of the very outer winding got slightly dented and a little bit of the varnish and tape came off. This transformer is 25kv (7.65kv per phase)
 

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Discussion Starter · #9 ·
Why would you even ask such a question. If you are considering patching an high voltage transformer > 65K volts your crazy.

Just so we understand each other
  • High (HV), Extra- High (EHV) & Ultra-High Voltages (UHV) - 115,000 to 1,100,000 VAC.
  • Medium Voltage (MV) - 2,400 to 69,000 VAC.
  • Low Voltage (LV) - 240 to 600 VAC.
Sorry it’s medium voltage 25kv (7.65 kv per phase)
 

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Why would you even ask such a question. If you are considering patching an high voltage transformer > 65K volts your crazy.

Just so we understand each other
  • High (HV), Extra- High (EHV) & Ultra-High Voltages (UHV) - 115,000 to 1,100,000 VAC.
  • Medium Voltage (MV) - 2,400 to 69,000 VAC.
  • Low Voltage (LV) - 240 to 600 VAC.
What many call high voltage is really low voltage. I try to go by context rather than terminology. I bet 90% of electricians call 480/277 high voltage. Being that the OP asked the question, I doubt he works with 5000 volts or above. I commend him for asking because I was in a situation 30 years ago where we needed one on a Saturday night. There was a damaged one on site but we opted to wait until we could get a new one. What is 12 volts considered?
 

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T&R in South Dakota or SUNBELT SOLOMON SERVICES, Kansas. Used to give better warranties on rebuilds than you could get new. I once had a transformer that I waiting for a rebuild was going to take to long. Talking to my buddy at Sunbelt, Jed found out they had just finished one that would work for my need. Contacted the customer and made a deal. They shipped the rebuilt one and picked up the old one. Everyone was happy except for my 20 man crew that had to disconnect and reconnect in less than a week. This was 115kv to 69 kv. Got yelled at by the big boss for give the guys a 4 day weekend when the job was done. That was ok every one in the shop wanted to work on my projects.
I remember the last 13.2/ 13.8kv -480 volt transformer we changed cost more to ship and handle than it was worth to ship, repair, and send back. We had a transfer company move it in and out of place. It was about 7' tall, very heavy but, at the time, it was a stock item.

Ah, there is one on Ebay: Siemens 3 Phase Dry Transformer 3000/4000 KVA 13800-480 Volt DELTA | eBay
 

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I think that’s what is going to end up happening. Hard to tell unless I take off the varnish / tape.
I wouldn’t. I’d see what happens with it you know u are already gonna need a new one buy that one off eBay for a backup

Heroes Get Remembered, but Legends Never Die. Follow Your Heart, Kid, and You'll Never Go Wrong.
 

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The thing with this transformer is even though it's 25KV, the voltage from one coil turn to another is not 25,000 volts. It's a couple hundred at most.

If the bad spot looks like it can handle a few hundred volts to the adjacent windings, it'll be fine.
 

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Only the manufacturer can really answer that question properly.

On thing to have it repaired. Another thing to have it tested. And another thing to put in to service….

Like did it get dented and the varnish is scraped?

Or did it fail.?
BS from someone that doesn’t know how to do it/

It depends on the extent of the damage: if it passes standard transformer tests a little epoxy to clean up the damage is all you need.

Rewinding is usually only done on very large or unusual transformers where lead time is an issue. Removing the varnish or epoxy means heating to 550-650 at for several hours to burn it off. You can’t realistically do a small area.
 

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I think that’s what is going to end up happening. Hard to tell unless I take off the varnish / tape.
It depends on the extent of the damage: if it passes standard transformer tests a little epoxy to clean up the damage is all you need.
Skipping this step has the potential to turn a relatively inexpensive repair into a very expensive repair.
 

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BS from someone that doesn’t know how to do it/

It depends on the extent of the damage: if it passes standard transformer tests a little epoxy to clean up the damage is all you need.

Rewinding is usually only done on very large or unusual transformers where lead time is an issue. Removing the varnish or epoxy means heating to 550-650 at for several hours to burn it off. You can’t realistically do a small area.
So, what part is BS?

Be specific….:

They are pretty general statements. So since your talking from a position of authority.

And let’s see. Once you modify/repair electrical equipment in Canada. It has to haRecertification Documentation. Depending on the provincial AHJ.

caution: bias sarcasm below…
I can go on but you should continue for me. Since you know from a position of authority.
 
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