So I know a bird can stand on a power line without being electrocuted because there is no current going to the ground. However, I know that curents will pass to different electric potentials. My question is, if a bird has only one foot on the wire instead of two, would this open the current and allow the energy to build up inside the body due to it having a lower potential energy?
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I would like to add to this question. See Why does energy flow between a high voltage transmission line and linemen approaching it on a helicopter?. This explains why a current flows between a helicopter and a power line. So why doesn't it happen to a bird? – mmesser314 Jan 05 '24 at 03:26
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@mmesser314, the high tension line will run 250 kV, 500 kV, or higher. You will get a spark when the high tension rod is touched to the power line as the helicopter equalizes voltage with the line. I'm sure that the same effect happens to birds, but the highest tension line that they land on is in the range of 12 kV, so any spark will be MUCH smaller and probably not noticeable. – David White Jan 08 '24 at 03:04
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1@David White Why don't birds land on the 250 kV lines? – Albertus Magnus Jan 08 '24 at 03:54
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1I found an answer here. Do birds know how to avoid high voltage power lines? – mmesser314 Jan 08 '24 at 04:14
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You are confusing charge redistribution (things like static shocks) with continuous current flows in closed loop circuits.
If a bird stands on two feet with each foot on a different line, there is a potential and continuous current will flow zapping the bird. This is scenario is equivalent to a closed loop circuit.
If the bird stands on only one line, all feet can only touch the same potential so it makes no difference between one foot or two. There is no potential difference in the circuit so it doesn't matter whether it is one foot or two. This is like replacing the voltage source in a simple circuit with a 0V source (aka a piece of wire). It makes no difference whether you attach lots of wire loops to this 0V source or a bunch of dead end wires to it.
That said, to bring the floating potential of the bird's body to be the same as that of the line, there is still a momentary charge equalization between the line and the free space capacitance of the bird's body. For extremely high voltages lines, this charge equalization involves enough energy to cause harm, akin to a very strong static discharge. If I recall correctly, these high voltage lines start at 100kV, well beyond the 30kV voltage of your strongest static shock. Again, one or two feet does not matter here.
At these extremely high voltages, you can actually see the air around the lines glow in the dark as they ionize the air. So yeah, it's going to do something to a bird that touches it, and even do something to a bird before it makes physical contact with the line.
DKNguyen
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1Excellent post! I have always wanted to see that "glow" around the power lines. When I was a kid, we would go around some during the day, and you could hear them. I think we could here little discharges here and there. – Albertus Magnus Jan 08 '24 at 04:05
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1Suppose a bird approaches and there is a momentary discharge while the line is at +250 kV. Half a cycle later, there will be another with the line at -250 kV. This is why the arc to the helicopter doesn't stop. – mmesser314 Jan 08 '24 at 04:07
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@mmesser314 True. I've never thought about that but for AC, the charge equalization would persist. For DC lines it would just be once. – DKNguyen Jan 08 '24 at 05:07
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When a bird stands on a power line, it can do so without being electrocuted because the power line and the bird's body are at the same electrical potential. The bird's body acts as a conductor, allowing the current to flow through it without any buildup of energy or potential difference. Whether the bird has one foot or two on the wire doesn't affect the situation, as long as it's only touching a single power line. The principle of equipotentiality ensures that there is no voltage difference across the bird's body.
DrDark
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If there is no potential difference across the bird's body, then the bird is not conducting and it can sit without harm. If however, a potential difference is developed, there will be a voltage drop across the bird and it will experience a shock. – Albertus Magnus Jan 05 '24 at 00:46
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That bird becomes a poor capacitor, as a small amount of charge no doubt builds up on its body. However, this amount of charge is very small. – David White Jan 06 '24 at 02:18
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even a small amount of current flow (tens of milliamps) through a bird will kill it. Now when a bird stands on a power line with two feet, there is no current flow up one leg and down the other because the wire is a far better conductor of electricity than a bird is. this means there is essentially zero potential difference between the bird's feet, zero current flow, and it does not get electrocuted.
If the bird is big enough to touch two wires at different voltages, it will get fried like a ball of bacon.
niels nielsen
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I don't know about that, most birds do not have enough saturated fat to pass as bacon! – Albertus Magnus Jan 08 '24 at 04:02