Why do transformers buzz or hum?

[Mortartube]

The reason that I ask, is that I have a disco lighting effect where the transformer sometimes buzzes. The mounting points all seem tight and secure and the buzzing will often stop if the light is mounted horizontally. Very large national grid transformers also hum sometimes. Is this the windings resonating in a varying magnetic field or any other reason?

Thanks

[mjd]

If it's a "standard" transformer & not a toroidal one then I think that the buzz will be coming from the laminations that make up the core. As current flows through the windings and a corresponding magnetic flux flows around the core then the laminations tend to be forced apart, similar poles repelling one another. If the clamping holding them together is at all loose then they will buzz at twice the frequency of the supply.

[naz_nomad]

mjd ...would I be right in saying that it would buzz more under load ?

[rojash]

Many moons ago, I worked for a hi fi manufacturer. Occasionally we would get a problem with our transformers where the core laminations didn't fit tightly in the former, but there wasn't room to insert another lamination. This would cause the core to buzz at certain frequencies.

Our solution was to pour a very thin cyanoacrylate adhesive into the core.

[mjd]

naz_nomad: yes , the greater the load, the greater the current and the greater the magnetic flux.

[Mortartube]

Thanks for that rojash. It can be really loud and annoying, so I tend not to use the lighting effect in question now, as when palying a nice quiet first dance at a wedding for instance, it sounds loke an angry wasp has got caught inside my light. I'll try to give that a go.

[rojash]

Make sure you use the thinnest glue you can get, as the solution relies on capillary action to get it between the individual laminations

[Mortartube]

Okay, will do. Anything to stop that annoying buzz.

Thanks again.