Odd 3 phase bank connection

[HIPotter]

This bank of transformer is scheduled for removal.

Primary is/was a Delta connection
Secondary service is 120/240 3 phase 4 wire

Both outside pots are 75kva, middle pot is 100kva

Here's the deal, left outside pot is 230/460, and other 2 pots are 110/230 per nameplate.

The way it's wired, I don't understand how it gives you that secondary voltage.

Any transformer guru's here?

Hopefully the attachment shows a clear enough picture

HP

[Pootnaigle]

Ummmmmm could the 480 pot just be using half the secondary coil?

[wtdoor67]

The outside pots are very old and the middle also. They used to get them years ago with the secondary wires brought out as you could swap the ends of the coils around as needed without taking off the lids.

The ends of the secondary coils are lettered ACBD. You can see on the left hand pot that A and C are together and B and D are together. That makes the coils of the left hand pot in parallel which would give 230 across them. That way it will work with the other 2 pots.

The right hand pot is of course lettered ACBD like the left pot. However on the right hand pot C and B are tied together putting those coils in series.

Thanks for putting the picture on here. Very nice.

[johnbellamy]

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[T-Man]

I would have splained that the same as door did, but he got r done. Good job and great picture.

If that was Delta tied on top then the left tub would have Let's say for explaining sake, an A and B phase, the center could have a B amd C phase and the right would have a C and A phase.

[rcdallas]

Must be some taps on there lowered or just running high primary voltage if your getting 120/240 with a 110/230 pot.

Oklahoma Cowboy; you get tricky and wire that up when you where tramping around the country? I do remember you quizzing me about a year ago with using a 240/480 pot in a 120/240 bank with paralleling some coils.

[johnbellamy]

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[wtdoor67]

I ran across an irrigation bank once that had a bad pot. It was a Delta/Delta bank and it was 240 volts I knew. However the pots were cutover using the outside bushings. It was the only time I never looked at the labels on a bad pot. I just ordered an ordinary 120/240 pot. Although the pot I ordered would have worked, we decided not to do it and just waited until Monday and made all three regular 120/240 pots.

Always look at the labels on a pot. The existing pots were 240/480 pots and of course paralleled enabling them to be connected delta, thus putting out 240 volt delta. A little squirrely.

[rcdallas]

So with that irrigation bank it must have been a corner grounded 240 bank, eh?

[wtdoor67]

I think it was a straight Delta. Worked around a lot of them. Always used to amuse me. Every spring when the ranchers started messing with their irrigation banks at least one or two electricians would call in and say we had some wild voltage on a straight delta bank. Course you've have to explain that was natural for a straight Delta bank as there's no reference to ground and when you put your volt meter phase to ground you get a crazy reading. It was always alright phase to phase.

[rcdallas]

Make you a deal. I come to Ok, you feed me both food, beer and knowledge and I'll give you a Dallas Cowboy's hat since I know deep down inside you wish you where south of the Red River.

[wtdoor67]

Sooner go to Mexico.

[HIPotter]

Good info and picture, simple and strait forward answer, a good rerferance for all to see. Real life and it jumps off the screen right at ya, thanks for thread, now nobody **** it up by confusin anyone.

Would have been nice to know what the primary voltage was also, name plate info as far as primary, not that it really matters with this one, and before anybody brings up the 4 bushing secondary pots, please post pictures, and start a new thread and please explain what parallal and series mean and then post and discuss till ya can't type. Thanks

OK..makes sense now. Thanks for all the help.

And the primary is 7kv delta.

HP

[Tester]

This bank of transformer is scheduled for removal.

Primary is/was a Delta connection
Secondary service is 120/240 3 phase 4 wire

Both outside pots are 75kva, middle pot is 100kva

Here's the deal, left outside pot is 230/460, and other 2 pots are 110/230 per nameplate.

The way it's wired, I don't understand how it gives you that secondary voltage.

Any transformer guru's here?

Hopefully the attachment shows a clear enough picture

HP

This is how the secondary is hooked up and the voltages that you would have:
The transformer on the left is a 240/480 and the coils are paralleled to give you 240.
The other 2 transformers are 120/240 and their coils are in series.
Opps, I see I put 2 B-phases in the picture, forgot to change the primary letter when I copied the picture over. Should be A - B - C

[dogman]

Good information, Thanks

[rcdallas]

That's something wtdoor talked about awhile back in the past. Ability to use a 240/480 transformer in a 120/240 bank--just parallel the coils.

That diagram shows the wye grounded on the highside...maybe to close in, but I'd float once it's closed in - you'll burn a transformer up.

[Tester]

That's something wtdoor talked about awhile back in the past. Ability to use a 240/480 transformer in a 120/240 bank--just parallel the coils.

That diagram shows the wye grounded on the highside...maybe to close in, but I'd float once it's closed in - you'll burn a transformer up.

I agree that the primary should be floated after all the cutouts are closed.
I was trying to emphasize the secondary connections.

[topgroove]

I agree that the primary should be floated after all the cutouts are closed.
I was trying to emphasize the secondary connections.

Hey Tester welcome aboard bro! I'm glad you joined the forum. We all appreciate your knowedge around here!

This will probebly have a few people scratching their heads. That last bank schematic, if you leave the float grounded after its energized....... I could open one of those cutouts and the customer would never know the difference as long as their load was reasonable.