Transformer issues

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Jnewell

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I have been called to troubleshoot a couple transformers lately due to humming. I don’t have enough experience to pinpoint the exact cause for them. The first was 112.5 kVA delta 480 to wye 208 and it was carrying A-22a B-19a C-9a and voltage was with 2 volts to ground. The only thing I saw that would mess it up was the imbalance of load. The other was a 225 kVA transformer and we were putting a fluke power logger on it to see if we could find the reason for humming. Same setup as before delta to wye but it was feeding a 400 a panel which is essentially a 200 with a feed through 200 and a separate tap off the transformer to a 200 a panel. It was loaded A-10a B-6a C-4a all within 1v to ground but the power factor was A-99 B-85ish C-71 depending on the active load. Would the pf cause it to start chattering badly? If not what would cause it to with such a low load?
 
Transformer humming is usually a mechanical issue, not electrical. Loose laminations or internal hardware may respond to 60 Hz.
 
It doesn’t know the words...

sorry, I had to.

1 reason, magnetostrsiction.
when the magnetic field changes every cycle the core laminations shrink and expand ever so slightly creating friction, and a hum.
I think the tone is B flat

Another reason,
Something mechanical has come loose. A screw came out and the exterior metal is vibrating rapidly or maybe the core base is vibrating against the case.
Laminations may have separated. Highly doubtful, but...
 
electrofelon said:
I think I would be worried if a transformer DIDNT hum. Perhaps what you mean is this hum has recently gotten louder or worse?
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I agree. Most every largeish transformer I have seen hums. Not real loud all the time, but you can hear it when it is quiet and feel it vibrate.
 
Like they say above, all transformers hum, but we'll assume the hum you are hearing is extra abnoxious.
I don't see an imbalanced load or unbalanced power factors causing a problem either.
Should you actually be able to find a problem, you are likely going to have to fix the transformer or get a new one.
Perhaps a transformer expert like SD Myers or similar companies would be more suited for this work.
 
Some dry transformers have shipping bolts that need to be removed and are often forgotten. Also, consider isolation pads under the unit.
 
Hv&Lv said:
I think the tone is B flat

[/QUOT] Close. It's between B and Bb

______________________________________NOTE___________________________________________FREQUENCY_______________________________________WAVELENGTH (CM)
A#1/Bb1​
58.27​
592.07​
B1​
61.74​
558.84​
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I replaced one last year that was so loud you could not have a conversation outside the electrical room door! One of those factory prefab electrical rooms. Had to cut the welds loose holding it down to the electrical room floor. The new DOE designs are larger, so keep that in mind when replacing it.
 
Yes, very loud humming enough to be annoying beyond 2 closed doors.

So what is the next step in pinpointing the problem if it isn’t a loose mechanical connection? Without shutting it down to laminate the coils?
 
Did the Fluke power logger show any significant amounts of even-order harmonics on either output currents or input voltage? If so that could make the transformer more likely to saturate in one direction.
 
Jnewell said:
Without shutting it down to laminate the coils?
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That isn’t an option. The core laminations are a part of the transformer construction.
I assume this is a dry pack?
Do you know it’s coming from the core? Or could it be coming from something else like the way the transformer is mounted, or the case loose?
I see some that are mounted in a building on a high platform without any cushioning under the transformer where it mounts.
sometimes simply getting the transformer off of a reflective surface will help tremendously.
 
Jnewell said:
Yes, very loud humming enough to be annoying beyond 2 closed doors.

So what is the next step in pinpointing the problem if it isn’t a loose mechanical connection? Without shutting it down to laminate the coils?
Click to expand...

You still didnt say if this was reported to have gotten louder. It may just be a loud transformer. In my experience, generally the older the transformer, the louder it will be. I have seen a bunch that I would not want behind even two closed doors so that isnt necessarily abnormal.
 
synchro said:
Did the Fluke power logger show any significant amounts of even-order harmonics on either output currents or input voltage? If so that could make the transformer more likely to saturate in one direction.
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We haven’t taken it off and synced the info yet, scheduled to go back early next week will post after . Just trying to come up with some ideas/game plan to go further
 
electrofelon said:
You still didnt say if this was reported to have gotten louder. It may just be a loud transformer. In my experience, generally the older the transformer, the louder it will be. I have seen a bunch that I would not want behind even two closed doors so that isnt necessarily abnormal.
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Yes reported louder with small load
 
texie said:
Some dry transformers have shipping bolts that need to be removed and are often forgotten. Also, consider isolation pads under the unit.
Click to expand...
I once had a service call on some transformers that "started" humming supposedly 3 years after being installed at a ski lift at Lake Tahoe (Heavenly). The transformer people had been there twice, I was called because I was a Drives guy. Took me 15 minutes to find the shipping bolts and remove them, problem went away immediately. As to it having "just started" after 3 years? Total BS. The entire place was loud because of all of the high power VFDs running, this was just something someone happened to notice one day while the VFDs were all off at the same time for PM, but they didn't kill power to the station so they would have lights. One of the lift technicians told me he had complained about the transformer noise from day 1, nobody listed to him.
 
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