Humming Transformers

Usually its either the laminations moving or the conductors moving (or both!) due to the current and induced magnetic field.

John.

Just last week there was a similar Question with a posted Answer from the original poster.....check past threads.

Or maybe they hum 'cos they've forgotten the words?

I think it is the air gaps in the laminations, . In our lab in gtroup projects we built smaa transformers. Those who added more laminations were able to reduce hum a great deal

In ferrite core SMPS transformers there is no air gap.That is it is not laminated core, its a solid core .But still we are getting humming sound problem.

Balu

Basically the root cause of the problem is the 50Hz frequent cycle which can be very destructive in terms of loosening bolt and screw threads, vibrating unsupported conductors and metalwork etc.

The noise in transformers is more prominent when laminated steel cores are used as the individual steel sheets are susceptible to vibration.

Transformer hum is caused by a phenomenon known as magnetostriction.The 50/60 Hz AC supply connected to the Transformer creates molecular vibrations caused due to cyclic expansion and contraction of the metal core generating the vibrations and resultant humming sound.

The second possible reason is vibrations due to loose fastening of the laminations of the core. This is why CRT( Dry Type Transformers) hum less.

The third is poor insulation of the winding due manufacturing defect or deterioration of insulation due to ageing of transformer or Poor maintenance . This humming cause failure of transformer .

I have faced the humming sound problem in SMPS transformers. After our analysis we found that it's a varnishing problem. That is the transformers are dipped in a varnish for 4 to 5 sec. we suspect this that varnish might have not covered all the air gaps in the insulation between the winding completely. so we increased the dipping time in the varnish to >2 minutes. After that we found that humming sound reduced greatly(almost zero hum).

But after 2 lots again we are observing some slight hum sound.

So, i would like to know that you have mentioned poor insulation of winding. Is it insulation between the windings(primary and secondary) or insulation of coil(copper wire)?

The core starting to get loose due to long service and carries to much load on their rated capacity. Also the fastener on secondary windings is loose. Need to pull out for service.

Rubbish! All transformers will hum to some extent, if only due to the current pulling and pushing the wiring apart, but usually due to a slightly loose lamination.

It shouldn't need pulling out of service, unless the noise is significant.

John.

You are right. In fact I have used a US made hair clipper which uses this property to move the blades at the mains frequency.

Unfortunately for me trying to use it at 50 hertz in India in stead of the 60 hertz (US) power through a transformer was a bad experience. The whole unit started oscillating & my hand became numb. Had to abandon it.

Pmshah, I use a couple of those type of 'magnetic motors' (I call them) one is for a hair clipper, but it has an adjustment in the side that you can set the armature movement for different voltages and frequency...

Its just a plastic screww that limits the movement of the armature, so its easy to adjust it....

John.

I've found that in testing transformers(QA), humming is dependent upon the core. When Core loss(no-load loss) testing, the more current pulled, the more the transformer hums. When I get a transformer with a bad core-high saturation-it will scream. We test cores at half of the secondary. So, ie. 120v (120/240)...if I get a high core loss, I will run it up to 115% half of the secondary-132v and sometimes the transformer will pull 80+amps. You can actually feel it at approx. 10 feet. Computer monitors go nuts from the magnetostriction. HUMMING IS DUE TO A BAD CORE.

Which in my experience quality of the core is relative to how a worker "feels" that day...

Justin,

I think you are dealing with the repair of transformer and you are right, not just by theory but on actual. Especially step down distribution transformer 13.8Kv to 220volts. Good luck.

willy

I want to also say that a BAD core isn't the only reason a transformer "HUMS"...however, the common humming tone, is generally associated with bad cores. I can give 100's of specific examples of why a transformer(note:these are all step-down transformers from about 3.3-500kVa)will "HUM". But the common "HUMMING" is a result of a BAD core.

adding to magnetic saturation in the core, when the core windings are loosened/not built properly(there are many ways this can be accomplished)the material cannot absorb a stronger magnetic field...also, take a look at a hysteresis curve it will show the dependence of the core(flux density) upon the magnetic field...

There is absolutely no reason why this should ever be a problem...the only reason you'll find it being a problem in the field is if a quality aspect was overlooked to get the product shipped and out the door.

I have cheap 2.1 desktop speakers with a small external 220V transformer, and with speakers off I can listen to the transformer hum if I get close. In fact it vibrates, and so if I leave it on a ceramic floor the noise resonates to even louder sound. when I turn the speakers on this hum is audible on the speakers themselves, with a constant volume, regardless of speaker volume setting. Any possible fixes?

How it possible to use the desktop speakers to listen the humming of the transformers?

can u help me to try the things you are saying using the speaker so i can prevent the humming of 150 and 288kva transformer