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#177524 05/05/08 08:48 PM
Joined: May 2008
Posts: 13
dura101 Offline OP
Hello All, just writing to get some input from others. I have a 75kVA 3 phase transformer and it is pretty loud. I looked to make sure the that the shipping bolts were out, that it was on rubber mounts, and that all the wires going in were in flex. Besides doing that I don't think that there is anything I could do except change a transformer. That would cost a bunch and it's in a room that nobody works near anyway. Is loud transformer noise a sign of an imminent failure? or Will the transformer continue to work for a long time and just be loud? Any suggestions?


Joined: Dec 2005
Posts: 866
Likes: 4
First Question, Oil or open transformer ?

Second Q , Is it a continuous noise or occasional noise ?

Third Q , How tight are the bolts clamping the iron laminations ?

Loose lamination packs do create noise.
also other loose mountings in the TX tank or mounting frame.

Fourth Q , Check the loading, overload or unbalanced loads can create extra noise.

Fifth Q , Harmonics on the powerlines can change the pitch of the noise.

Regards, Raymond

Last edited by RODALCO; 05/05/08 10:24 PM. Reason: typo's

The product of rotation, excitation and flux produces electricty.
Joined: Jan 2005
Posts: 5,316
Cat Servant
I think it's not a problem with the transformer, as much as one of acoustics. Given the right conditions, the right-angled hard surfaces we tend to make our electric rooms of can actually act as an amplifier.

I'd consider placing some softer, acoustic material on three opposing sides of the area - say, the ceiling, and two adjacent walls. This might interrupt the way the sound waves can reinforce each other.

Joined: May 2008
Posts: 13
dura101 Offline OP
Thanks for the responses so far.

-It is an open dry transformer.

-It is a continuous noise (same loud noise whether it is light or heavy loaded)

-I never de-energized and opened it up to check tightness of bolts.

-At the time that I did a load test it was not overloaded. The current was a bit different on each phase but minimal because of the size of the transformer.

It is definitely a humming transformer. I know that they all make sound but this one is a buzzer.

Joined: Mar 2005
Posts: 1,213
How old is it? I've seen a lot of transformers get loud as the resin hardens up over time. It's not a danger or anything, just the nature of the beast, considering that transformer is essentially a giant 75,000 Watts speaker coil, and if it gets a little room to vibrate, it will. It's a wonder they don't all hum as loud as a jet engine.

It's it's too disruptive, replacing it is about all you can do.

Joined: Sep 2005
Posts: 120
Zog Offline
How old is it is the key question. Have it tested by a real testing company, they gets these calls all the time. A DAR and PI test will be key info for evaluating the condition of the insulation. They will also inspect all connections, grounding, and other things that can "Rattle" at that B flat note.

MV/HV Testing Specialist, "BKRMAN"
Zog #177780 05/12/08 12:42 AM
Joined: Oct 2000
Posts: 2,722
Broom Pusher and
Room Acoustics affect the sound emitted from a Transformer greatly.
Square shaped rooms are the worst (equal length walls on all four sides). Rectangular shaped rooms are a bit better; and rooms with one "iregular" shaped wall are best.

Hollow wall cavity, framed with steel studs, are easilly vibrated by Transformers. Dampening the walls surrounding a Transformer is an effective way to reduce the transmitted vibrations. Dampen with typical Building Insulation or Sound Battings.

Other things which add to the noise are:

* Reflective Flooring Materials - such as hard VCT, or sealed - bare Concrete floors,

* Setting a Transformer in a corner, where one side of the Transformer is less than 6 feet from one wall, and the front is also less than 6 feet from another wall,

* Non-Flexible Conduit connections to the Transformer,

* Transformers set back - to - back (one facing forward on one side of a hollow wall, another facing backwards on the opposite side of the same wall),

* Setting Transformers against, or near Concrete walls (Tilt-Up Panels),

* Not isolating the frame from floors via dampening materials,

* Loose core laminations, mounting hardware, covers and/or enclosure sections.

The loading of a Transformer does not affect the output sound, nor do Harmonics.
A Transformer will "hum" the same level at idle, as it would at full load / 25% load / 50% load / 75% load.

If everything is tight, the Transformer is connected with flexible whips, and the legs are isolated, then you will need to correct the room's acoustics.


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Joined: May 2008
Posts: 13
dura101 Offline OP
Thanks everyone!

Joined: Mar 2004
Posts: 947
twh Offline
Try re-levelling it. I'm not sure if levelling it helps, or if its the jarring of picking up and dropping the corners when you try to adjust the way it sits.

Think of it another way: How embarrassing would it be to buy a new transformer and have someone bump the old transformer while moving the new transformer into place, and have the old transformer quit buzzing? You would never get another service call without being told to take Joe, the fork lift driver to give you a hand.

Joined: Mar 2005
Posts: 1,213
Originally Posted by Scott35
The loading of a Transformer does not affect the output sound, nor do Harmonics.
But harmonics do affect the output sound, they add harmony at each frequency laugh

It's wierd to hear a 400Hz transformer humming, I'll tell you that much.

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