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Electronic Theory and Principle Discussion of electrical theory, law, etc.

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  #11  
Old 10-25-2009
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I guess it is like lightning hitting a plane. There is so much difference in potential there that the electricity can flow into the helicopter for as long as it takes to equalize the charge.
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  #12  
Old 10-25-2009
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Quote:
Originally Posted by Zero82z View Post
The power lines are at a very high potential, whereas the chopper is not. The arc is created because the potential difference between the two is enough to ionize the air and cause it to conduct electricity between them. Then he clamps a wire onto the power line which equalizes the potential between the line and the helicopter. That allows the man to work on the lines, because now that he's at the same potential as they are, no electricity will flow from the power lines to him.

If he didn't equalize the potential first, he would be at a much lower potential than the power lines, so the second he touched them, it would cause a flow of electricity which would kill him.
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ADDING:

The helicopter also produces a strong static electrical field of its own,
this is a very big deal when a Navy or Marine choper lowers equipment or personal on to a ship at sea.
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  #13  
Old 10-25-2009
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I=C\frac{du}{dt}, Helicopter has a much larger capacitance than a bird, so it get more current on contact.
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Old 10-25-2009
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Also, birds get fried all the time on high tension lines.

There's just nothing left to worry about after.
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Old 10-25-2009
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I can attest to that.

Where we live out in the country there are some big high voltage wires coming from in the woods in a corn field across the street. Big birds just get zapped and burnt, and fall to the ground. All the little birds just disappear.
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Old 10-25-2009
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Oh, so you are saying that at a certain transmission voltage birds are not able to land on the transmission lines without being barbecued?
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Old 10-25-2009
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Quote:
Originally Posted by Per Hansson View Post
Oh, so you are saying that at a certain transmission voltage birds are not able to land on the transmission lines without being barbecued?
Yup. I would imagine the EMF would dissuade most animals from going near the high voltage lines like the ones in the video. The local transmission lines in the US are something like 4 or 13kV but I think it varies. Those are the ones feeding each neighborhood where is it is then jumped down to 120/240V for each house. I know the high voltage lines are uninsulated, but I'm not sure about the local transmission lines. I doubt any animals would want to be on even a 4kV uninsulated wire. The 120/240V going to each house is insulated though.
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Old 10-25-2009
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The smaller lines that branch off of the transformer station down the road are insulated and birds love to sit on those because they get a bit warm.
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Old 10-25-2009
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Quote:
Originally Posted by Per Hansson View Post
Oh, so you are saying that at a certain transmission voltage birds are not able to land on the transmission lines without being barbecued?
Sounds like the big birds get cooked, and the small ones vaporized (either that or their body fluid flash boil and blow them to little gory bits...).
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Old 10-25-2009
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Quote:
Originally Posted by shinji2k View Post
Yup. I would imagine the EMF would dissuade most animals from going near the high voltage lines like the ones in the video. The local transmission lines in the US are something like 4 or 13kV but I think it varies. Those are the ones feeding each neighborhood where is it is then jumped down to 120/240V for each house. I know the high voltage lines are uninsulated, but I'm not sure about the local transmission lines. I doubt any animals would want to be on even a 4kV uninsulated wire. The 120/240V going to each house is insulated though.
The local transmission lines in my area are insulated. I imagine the 500KV lines are uninsulated, because at those voltages insulation light enough for the wires to support wouldn't make a significant difference, while insulation that would make a difference would be *far* too heavy for the wires to support.
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