Why is it that some transformers emit a hummin sound

[LightMage]

Hmm..i got a qns here..why is it that some transformers emit a hummin sound when connected to a AC of 50 hz supply??..also, how do we know what the freq of the hum?seems like there is no link to me..

 

[Integral]

The assumption is that the humming is driven by the input voltage. Thus it would be either at the same frequency as the driving voltage or a higher harmonic.

 

[LightMage]

hmm..the ans is 100 hz..was wondering how can that be??..

 

[BerryBoy]

This is due to bad transformer design...

It used to be that there was a three pronged iron shape and then someone (or a machine) would wrap coils round the outer prongs and then secure a bar of iron over the top (closing a loop of iron).

Now when you pass a magnetic field through the iron, if there was a gap between the the prongs and the top bar, then a magnetic field would pull the bar down and this emmits a noise. This magnetic field will occur twice for one period (one field one way and another in the other direction), this is why you would hear 100Hz.

Does this help?

To make a more efficient transformer, you wrap coils around a torus, this stops the magnetics field escaping; but its tricky to get machines to do this sort of wrapping... Thats just for interest.

Sam