I was on a hike under a high voltage transmission line a week ago. I couldn’t help but notice a lot of crackling and popping. Where could this be coming from? Were the wires discharging somewhere? To the air perhaps? It sounded horribly inefficient. Aren’t the wires coated to prevent this?
Corona Noise
It’s caused by corona discharge. It’s always present to some degree but can produce audible noise when the field interacts with moisture or air pollutants. At least that’s the way I remember learning it in school. It is inefficient, it creates a line loss, and probably electrical noise as well. The wires are insulated to prevent it, whether it is more prevalent near a bad splice or deteriorating insulation I don’t know.
No, they aren’t. At those voltages, insulators are practically useless at reasonable thicknesses. Effectively insulating such wires would require very thick insulation, adding large amounts of weight, and therefor cost, to the wires and their support structures.
In case you’re disinclined to take my word for it, from Wiki:
Point taken. I was thinking of the insulators at the towers or substations like these We learned to make high voltage splices when I was in school many moons ago and had to learn about the effects of corona discharge. I haven’t had to deal with it much since except in safety courses on arc-flash hazards.
In addition to the point made by Q.E.D., insulation reduces the ability of a conductor to liberate heat to the atmosphere, and therefore would result in it being rated at a lower ampacity that that of an equal size bare conductor.
What is it about moisture that makes the louder noise? I ask because one of my regular biking routes passes under power lines right next to a lake, and the lines there always seem to be crackling really loudly - much more than other power lines in the area.
Does damp air lead to greater losses?
This is the way I understand it. The air surrounding a bare conductor is acting as an insulator for that conductor. The dielectric strength of air is usually given as 3MV/m, if exceeded it causes ionization of the air molecules.
Our townhouse development happens to be very close to a distribution station and the high voltage lines run adjacent to us. There are days when that crackling noise is very noticeable and days when it isn’t. Even on those days, if you listen closely, you can still hear it. I haven’t noticed any distortion of TV or radio signals; maybe because our TV service is cable and we don’t listen to radio more than once or twice a year. (Think hurricane season.)