Transformer Humming?

The reason is that the transformer is connected to a AC source, and it wants to hum the frequency to your ears.

Manufacturers try to make that sound as low as possible with bonding the core as solid as possible and also the windings.

Different techniques are used:

One is immersing it in a liquid that hardens e.g. after baking in an oven, as is the case with shellack.

The slightest vibration of one of the parts may cause some humming.

Vibrators like in some hair cutters and trimmers are a practical application of controlled vibration of the core, by splitting it.

it is because of INDUCTION...changing one potential to another causes induction or sometimes referred as electromagnetism..electrons tries to escape causing vibration in the air which is audible to the human ear..

I think when current passes throgh the winding magnetic field is creating. Also core is getting magnetised. Transformer core is sliced to reduce eddy current losses. At the positive peak of current flow, core is getting magnetised to the peak level. Then because of the magnetic forces core is getting compressed itself. After the peak point current is reducing and reaches zero point. At that point core have no magnetism. That is when current is reducing, core is also getting released. Next half cycle core is magnetising in the opposite direction but again it is getting compressed. On the way that the sine wave reaches zero point from negetive peak again core is getting released.

This compression and relaxation of core makes the humming noise.

Some material feeders are working based on this principle for getting constant feeding due to the vibration.

You will need to study the phenomenon of Magnetostriction.

Here is a good link : http://www.federalpacific.com/university/transnoise/chapter2.html/

Changing currents and magnetic fields have been mentioned, but the word you want to explore is magnetostriction. Google has 152,000 hits for this link.

Here's Federal Pacific's explanation, pretty good, ranking near the top.

The abstract of a 1963 IEEE paper by J.E. Thompson, titled, Magnetostriction and transformer noise, reads, "In practice, the noise output of a transformer core is due mainly to magnetostriction. Compressive stresses in core sheets need to be avoided. The importance of sheet flatness is emphasized, and well oriented material is desirable. Two laboratory methods of producing a low-magnetostriction material are discussed." An illustration from the paper shows measurements for two materials with different grain sizes. That's one of many factors that affect the magnetostrictive noise level created in a transformer.

Guest, do not listen to those guys.

Your transformer is humming because it is happy to be working for you. Continue to treat it well, and the happiness (as well as the work) will continue.

Can't believe no one used "it hums because it does not know the words"

Someone did :)

"If you don't have any thing useful to say don't post,OK ?"

Gee, I'd never get to say anything!

Besides, it's only humming because it isn't able to whistle.

Hello,

I followed the link posted by kvsridhar....very nice, indeed..and I found this line at the first page :

Transformer "humming" has been known to soothe people (which makes it a sound) but generally it is thought to be a nuisance (which makes it a noise).

And Guest, I guess the same applies to certain comments made in this forum... while you may find them completely useless, some may actually find it fun...

Now, I'm sure you did not find my comment useful, but I certainly had fun making it..

How true ! Now i know why i can sleep like a child when power is on... the pole-mounted transformer (the lowest bidder got the order of course, i am sure he hasn't even used silicon steel) is 20 feet from my bedroom window. No power, i wake up.

i also think i now know why i couldn't sleep in USA ! The 120Hz is not so soothing

Because it doesn't have lips. It knows the words, it just can't sing.

Grow up! Geez, these people are here on their own time, they are entitled to crack a joke once in a while, especially since the question was answered pretty thoroughly half a dozen posts back.

You don't like how we answer questions, then get lost, nobody has a gun to your head to be here.

I just don't know if it is useful.

Who knows by the way?

To purify your post there is always a Off- topic possibility.

Just join the club of the frustrated guess what'ers

1. Primo: a transformer does NOT need to hum at all. There are more advanced means to create humming sounds.

2. Secundo: a transformer needs to transform or is made for a transformation of an electric property, being voltage, current or impedance.

Oh, I forgot- or to be the title of a movie.

3. Tertio: transformers are made in various sizes, models and shapes, using different components for the (electro)- magnetic part (and also for the windings part). Some that can HUM and others like ferrite cores that CANNOT HUM.

4. Quattro: If you want ferrite core transformers to hum, you need to wind the wires very loose, so that they can take the complete humming partiture.

5. Cinquo: While HUMMING is only possible at lower frequencies, they can start to whistle when applied with AC supplies at higher frequencies. Also in low frequency circuits with a lot of harmonics they can produce strange noises, not exactly specified as HUM.

6. Sexy: (?) The bad ones stop producing sound when no tension (fm French) is applied. Just like women. I hope Your Excellency accepts my comment.

There is also a way of not reading it. But now you read here, you have been challenged to read the foregoing text too. We are all afraid now. Especially since your comments in particular have contributed a lot to this topic. D.

There are plenty of other sites available for those without a sense of humour....

Its because of internal technical losses. Go and research about core losses, compare the design of transformer with high and low losses. Another cause maybe the overload or temperatures of the enviroment where the transformer is positioned