Transformer Mania

Bubbles

Got a call the electric all of a sudden quit working in a building. Showed up and started looking around. It was 277/480 Delta setup 3 wire in a 480-240V Step Down Transformer (75kVa) I do believe. We got 82 volts on A, 218V on B, and 324V on C. Perplexing....as we scratched out heads. As it turns out 22min later....we found out someone hooked up the primary and secondary in reverse?? i'm guessing someone changed transformers and mixed up the X's and H's. Not sure how. One set is really big and one is really small (250MCM AL parallels and 4/0Cu). Anyone know why those type of readings would happen?? Not really a transformer expert here. But I do know the differnce between a primary and secondary. In essence didn't they make it a step up transformer and shouldnt the Voltage go up??

Magnettica

If they had a 480/277 VAC set up, how could it have possibly worked without the 4th wire - the neutral? To get 277 volts to ground the transformer has to be wired in parallel, a Wye connection. Only a Delta set up (480/240) is wired in series.

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Bubbles

It was delta series

JohnJ0906

I'm not sure about this
Is the building service 480/277v 3 ph?
Is the transformer 480 v, or 480/277 on the primary side? I would be a bit surprised to see a 480/277.
What is the secondary? 240v? 208v? 208/120?

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John from Baltimore
"One Day at a Time"
All replies based on the 2008 NEC

Bubbles

sorry...on a couple forums talking about different transformers. Its a delta delta 480 2:1 ratio trans. Line volts=phase volts Neutral to L1 or L3 120V Neutral to L2=208V (high leg)
everything else is same

Bkessler

bubbles is to overqualified to work in california, try acting when you move or maybe Governor.

nap

stay down for the count bubbles...stay down for the count.


You seem to be terribly mixed up.

A center tapped delta is a 4 wire system.

You got that voltage measuring to what? How exactly was the transformer wired; both the primary and the secondary?
those two wire sizes are quite close to being the same size. Somewhere to the tune of about .070" difference depending on what wire type you are using.

Some information that is not all confused would help in figuring out what was going on.
I would have to do a bit of calculating (and it's too late for that tonight) but your wire size doesn;t sound correct either.

Magnettica

We got 82 volts on A, 218V on B, and 324V on C

To ground?

What about phase-to-phase?

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Bubbles

phase to phase was just as bad. Readings were all over the place. Once we flipped the line load around everything downstream went back to normal. it was 3 wire

Bubbles

Ahh...I now have a new friend to add to my list BKessler or "Mr. Perfect" from now on. I noticed you really don't post anything too electric related on your post. It's all jibberish for the most part and has nothing to do with solving anything. You probably pick on retarted people as well to help your weak ego I presume. Everyone go look at BKesslers posts. Who cares now if it was 3 or 4 wire. If your getting 80-300ishVolts on any leg to anything it really doesn't matter does it BKessler? It was a year ago and someone hooked up reverse and we fixed. Phase to Phase and Phase to ground on load side of trans was all whacked out. Why is that Mr. Perfect? What was your score on the master electrician test? Once again, if you don't proofread your stuff on here it's like sharks going for the kill. Didn't you have that happen once magnettica?

Yours truly, your buddy , your pal

JohnJ0906

Bubbles, you didn't exactly give enough info.
delta/delta 2:1?

That could be a 240v 3 wire grounded leg, or a 240/120v high leg. If you want help, you have to give info.

The questions and comments were legit.

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John from Baltimore
"One Day at a Time"
All replies based on the 2008 NEC

Bubbles

240/120v high leg sir. But seriously, does it really matter? The readings jumped minute to minute. one minute 82V Phase to ground next min 128V. It would constantly change. Have any answers BKessler?

Magnettica

Sure, that's happened before -- it sucks while you're going through it -- but in the end all criticism is good criticism because it can make you a better electrician. What is good here in New Jersey may seem ridiculous in Texas, or wherever. When it comes to transformers, though, in America an open-delta used for light 3-phase applications is the same here as it is in Oklahoma, Vermont, or Washington State. No electrician I ever knew knows everything so don't be afraid to ask if you don't know about something because how else are you going to learn?


Btw, I don't believe bklesser was trying to be a hard guy. I think he was being facetious, as in, ha-ha. You know, funny like a clown. I'm here to amuse you?

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nap

if your secondary is a 3 wire, it is not a center tapped delta.

there is no 3 phase 3 wire with 120 voltage available in typical use. I understand the Navy uses such a system but not typical anywhere else.

On top of everything else, if a transformer is hooked up correctly other than X and H reversed, you would be spouting 960 volts from the secondary phase to phase.

There is more than that happening to get what you experienced.

Granted, it works now but you seem to be wanting an answer as to why it was what it was. There are those here trying to help you but you need to work with us so we have enough info to give you an answer. So far, we don't have the complete picture.

mickeyco

You're not using a Chinese multi-meter are you?

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Bubbles

I think it was 0.00048 megasiemans. Put a hold on all this. This was a favor I did for a friend 1-2yrs ago for free. Within minutes of weird readings we took off cover of transformer and saw the secondary and primary were reversed. Switched it back and everything was on the money and everything worked fine so we left. Let me go back there this week and take pics and get facts then repost. I really didn't commit it to memory since we fixed it and never got around to figure out why the strange readings.

Stay tuned

Magnettica

A teacher once told me that in order to fix something you have to know in order how the thing works in the first place. He was an HVAC specialist teaching control wiring for heating and air conditioning. It was probably the best advice I ever got.

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Bkessler

Yes it was a poor attempt at humor, since the question was over my head, I thought bubbles solved the problem just liike that. Oh well I can eat crow. Sorry bubbles bad joke.