Power Transformer noise

[gw544931]

We have installed a 225KVA transformer in a room approximately 8' x 10'. The building is wood frame construction, the room is insulated and the transformer is on cork/rubber vibration dampers. All covers are tight armature bolts have been relieved. The humm from this transformer can be felt 50 feet away down the hall, with the door closed. Any ideas on how to quiet it?

 

[Pierre C Belarge]

Teach it the words...:wink: I know, pretty lame.:grin:



Have you checked the balance on the load side of the transformer?

Also, check the primary and secondary voltage readings.

 

[brian john]

Try loosening the covers and if that does not work (which I doubt it will on a unit this size) contact the manufacture ASAP, you may have a defective transformer.

 

[charlietuna]

The ability for a transformer to create noise is called "magneticostriction" and there isn't much you can do for it . Move the transformer away from the people or possibly install soundproofing materials and additional sound screens inside the room without interfearing with the ability to cool the transformer.

 

[winnie]

I second checking the voltages. If the core is heavily saturated, the noise will be much louder. So you want to make sure that the primary taps are correctly set to get proper saturation.

-Jon

 

[TOOL_5150]

What actually makes the hum sound? Lets say it was just the transformer, no guards - just what it needs to operate, would it still hum?

~Matt

 

[mxslick]

Matt,

Yep it will still hum. The core laminations can be loose, the windings insulating form can be loose on the core pieces, and the coils themselves will generate some noise.

I second the call to have it checked by the mfgr, it is possibly defective if it is that loud.

 

[broadgage]

What actually makes the hum sound? Lets say it was just the transformer, no guards - just what it needs to operate, would it still hum?

~Matt

Yes it will still hum, but often less loudly.
Part of the noise from a transformer is vibration from the case or guards. Sometimes the noise can be reduced by removing covers or guards, and refixing with rubber washers or similar.

Oil filled transformers are usually much less loud, but are less used these days on account of the fire risk.

I would agree that the manufacturer should be consulted, since exxcessive noise can be caused by improper assembly or transit damage.

 

[slect]

mxslick is right.. the noise is caused from the insulation on the core wires either breaking, or loosening up. The louder the noise the worse it is.. I have a friend that works in a plant that makes transformers for a defense contractor.. their transformers are built with extreme specs and they operate with almost no noise whatsoever. If its new, return it..

 

[LarryFine]

Could also be the conduits, conducting sound out of the room. Is there flex in the connections?

 

[masterinbama]

The original post states this is in a wooden structure. Is this transformer sitting on a wooden floor? I had one in a wooden building once and i had to actually add a solid rubber mat with a 4 concrete pad poured over it to dampen the noise. According to my brother who is an aircraft structures engineer. It seemed the transformer was resonating at the structures natural frequency, and the mass of the concrete and rubber changed that frequency.

 

[Besoeker]

The original post states this is in a wooden structure. Is this transformer sitting on a wooden floor? I had one in a wooden building once and i had to actually add a solid rubber mat with a 4 concrete pad poured over it to dampen the noise. According to my brother who is an aircraft structures engineer. It seemed the transformer was resonating at the structures natural frequency, and the mass of the concrete and rubber changed that frequency.

I think that could be at least part of the problem.
Without the acoustic properties of wood, conventional stringed instruments wouldn't work.

 

[Besoeker]

Oil filled transformers are usually much less loud, but are less used these days on account of the fire risk.

Quieter, yes. The fire risk has been largely mitigated by the use of synthetic fluids such as Midel and Dow Corning 561 for example.
That said, I would't want an ONAN in a wooden building for various reasons other than fire risk.
Maybe cast resin would be the way to go.

I would agree that the manufacturer should be consulted, since exxcessive noise can be caused by improper assembly or transit damage.

But how do you quantify excessive noise?
It generally isn't a big issue for me as we normally supply to industrial sites.
The only customer spec. I have seen addresses it as a limit rather than expected levels.
Noise level : (Table 1, Curve a of BS 5969 :80 db(A)
80 db(A) is quite loud. Even for an old duffer like me.
I'm sure my hearing isn't as acute as it once was - my sweet wife tells me that it is selective....:wink:

 

[charlietuna]

I believe it has to do with the quality of the metal in the cores--we have had the same manufactured transformers much louder than others--same load--tapped off the same bus duct?? Same with operating temperatures!

 

[HCC]

check the primary voltage rating of the trans. what is the actual primary voltage feeding the trans. are you over exiting the trans?

 

[charlietuna]

Have you ever run into a sound battening system that looks like a quilted canvas material?? They also use in air handling rooms. They system is attached to the entire surface of the room including the door(s). This being frame construction - much of the noise is being transmitted via the structure. Some transformers-same spec-same manufacturer-same size-same load can be noisier than another too, and i believe it's actually the grade of metal the core happens to have--(my$.02)....

 

[beanland]

Isolation Dampers

Isolation Dampers

(1) Transformer hum is caused by magnetostriction. This is caused by flux in the core. Flux in the core is caused by the excitation of the core. If the voltage is high (wrong tap) the flux will be high and the noise worse. Change the primary tap to the highest value you can tolerate to keep the flux as loww as possible.

(2) The sound is low frequency. 240Hz, 480Hz typically. Rubber mats do not attenuate or isolate at such low frequencies. You need spring isolators tuned to isolate the transformer vibration at low frequencies. The isolators need to have soft springs (low k) but sufficient number to support the weight.

(3) The addition of a floating concrete pad between the transformer and the floor can reduce sound transmission. You still need spring isolators between the transformer and pad and the pad and the structure.