Bird on an overhead line - Current flow

cabraham

Sorry but that makes no sense. If zero current flows in the bird, how do they feel any "tingle". Also, a small current does indeed flow since the IR drop over the distance spanned by the bird's feet is non-zero due to cable resistance. It just happens that the bird resistance is so high compared to that of the cable, the fraction of the current in the bird is very small.

Also, voltage is not "the driving force" that makes current flow. The term "electromotive force" was coined in the early days before Lorentz force was known and understood. Voltage is indeed energy per charge, i.e. joule/coulomb, but Lorentz force is what moves charges. I don't mean to nit pick but it should be mentioned. Best regards.

Claude

sophiecentaur

There is no explanation for this if you refuse to consider Capacitance. If you do not understand capacitance then look it up - but don't ignore the fact that it exists and accounts for the charges flowing on and off the bird.
I already showed you that you get something in the order of 10μV drop across each cm of the length of a transmission cable so that is nothing to do with the 'tingle'.

cabraham

Capacitance is something I understand very well w/o having to "look it up". I just wasn't sure if that is what the poster I responded to was inferring. I realize 10 uV is very small, not likely to be felt by the bird. I was merely hoping to get clarification.

FWIW, capacitive coupling, or E field if you prefer, would be strongest in between the wires. I'm sure you know that. Standing on top a wire would incur an E field through the bird since the equipotential lines bend and converge on each cable.

I probably read the post i responded to, and further down you offered an explanation which I did not get a chance to read. I wasn't ignoring you. Any way, hopefully this clears things up. BR.

Claude

Windadct

For the very high voltages > 100-200KV - the birds will experience another phenomena - the current due to corona, or ioninizing of the air. The cable is round and has a uniform voltage gradient - the air does not typically ionize, but the bird is not a uniform (smooth) shape - and they will generate corona, thus current ( as well as noise ), this effect is also more pronounced with high humidity and at altitude.
The effect of capacitance would also be in microamps, and I suspect below their level of sensation
Also - I would not refer to the live line suits that linemen use as Faraday - the suits ensure all of the surface is at an equal potential. Faraday cage really applies to Electro-Magnetic radiation and static.

sophiecentaur

You are right that the capacitance would only have an effect of (more like tens of) microamps but this is a lot more than the nanoAmps up one leg and down the other. This simple model assumes a capacitor connected directly to the conductor.
Humans can easily detect 1mA and there are many animals that will detect much less that this. In fact, very low currents can be detected from ungrounded electronic equipment. Objects can be felt to 'vibrate'. I have two touch operated lamps and it is easy to tell when they are powered or not, by the 'feel' of them. This can't be a fault condition because they both exhibit the same thing. You can get the same from microphones and electric guitar pickups.
I couldn't find information about bird sensitivity. They may have evolved a higher sensitivity than humans.