When near high tension power lines, particularly after a good rain, the lines themselves emit a buzzing noise. A similar noise can be heard coming out of the electric meters attached to my apartment.
I've heard before that this is supposedly from the 60Hz AC current that's running through the lines — namely, that the buzz is the same 60Hz which is in the lines.
I'm skeptical of this though for a couple of reasons:
- I don't see any reason the change in electricity would somehow be audible.
- The noise subjectively sounds relatively high pitch. 60Hz would sound extremely low pitched — it's near the base of human hearing of 20Hz (typical).
What is the actual cause of that buzzing?
EDIT: I just spent some time playing with a tone generator and the noise I hear from these things sounds closest to 120Hz using a square or triangle wave. (Oddly, not a sine wave, as I would have expected) Perhaps that helps?
Best Answer
The humming you hear around all things electrical is 120hz, because an imperfect 60hz sine wave has strong harmonics at 120Hz which you will likely hear over 60Hz because of the frequencies our ears pick up best.
The humming you hear from power supplies, transformers, power meters, high-voltage distribution boxes (which have coils and such inside), etc etc is because the magnetic field in transformer coils is a physical force acting upon ferrous metals (this is how speakers work). Even though you might see a coil consisting of varnished wire that is glued down or epoxied really tight, the magnetic force is still tugging on these wires ever so slightly to great vibration. It doesn't have to be the coil wire itself either, it could be any metal object around the coil. The force is there and it's pushing and pulling on that metal back and forth at 120 times a second.
For high-voltage lines outside on poles, it's a different story. That is, if you aren't around any transformers like you see in those big distribution plots. What you are hearing is not corona discharge (as that is mostly silent unless when you get total breakdown you will hear and see arcing). After rain, or when moisture levels in the air raise you get condensation developing on the ceramic insulators that hold up the cables. You will notice these are shaped oddly like little half-domes so as to make it harder for a stream of water to make a connection between the live line and ground (or another phase). They aren't perfect though, and when rain or moisture develops on them, it can create shorter little paths for the current to travel. What you are hearing is tiny little bursts of water boiling off the insulators.