current returning to a different source

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Rick Christopherson said:
No, it is not a capacitor to ground. If the helicopter acted as a capacitor to ground, the wire would do the same thing, and the line would be constantly discharging to ground on its own, and would be very inefficient in transmitting power. This is why the higher voltage lines are strung at greater heights above the ground.

Watch that video that the other posted linked to. It is exactly what I am referring to.
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There is a complete path regarding the service helicopter and HV lines... but there is no second arc as you seem to imply there would be. This is a simple matter of electron density and available electrons. The charge that flows through the electrode is returned to the line via the air itself. The HV lines act as a really long electrode and the paths through air are comparable to infinite tap conductors along that electrode. The electron density of this current flow is way less than the level necessary for visible-to-the-eye arcing.
 
Smart $ said:
There is a complete path regarding the service helicopter and HV lines... but there is no second arc as you seem to imply there would be.
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I never said nor implied there would be a second arc. As a matter of fact, if there was a second arc, that would actually disprove what I was saying.
Smart $ said:
The charge that flows through the electrode is returned to the line via the air itself.
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Why would the charge return to the line? It left the line because there was a voltage difference. For it to return to the line would mean it had to go from a low potential to a high potential, which is counter to electron movement.
Smart $ said:
The HV lines act as a really long electrode and the paths through air are comparable to infinite tap conductors along that electrode. The electron density of this current flow is way less than the level necessary for visible-to-the-eye arcing.
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Given that these power lines can be hundreds of miles long, if you could simply bleed charge from one line to another, then by the time you got to the end of the line, there would be a huge amount of power lost.

Go look at the video. In it you will see that the helicopter is above the power line, so the power line is closer to the ground than the helicopter is. It is also outside of the grouping of phase conductors, so the helicopter is farther away from the other lines than the lines are themselves.
 
Rick Christopherson said:
I never said nor implied there would be a second arc. As a matter of fact, if there was a second arc, that would actually disprove what I was saying...
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Your second sentence demonstrates implication by exclusion, prior to making the statement of course.

Go look at the video. In it you will see that the helicopter is above the power line, so the power line is closer to the ground than the helicopter is.
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The helicopter is above the line to be accessed because 1) the spinning rotors are wider than the workers platform (watch at the very beginning and note where the reddish rotor tips are with respect to the worker) , and 2) it has to be at that level for the worker to get on the line.

It is also outside of the grouping of phase conductors, so the helicopter is farther away from the other lines than the lines are themselves.
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Proximity counts. Note the length of the cable suspension insulators (closest view at 2:43). Note the distance between phase conductors is at least twice that distance (or would that be greater than 1.73 ? :wink: ).

So how do you suppose the workers access the center phase?
 
Rick Christopherson said:
No, it is not a capacitor to ground. If the helicopter acted as a capacitor to ground, the wire would do the same thing, and the line would be constantly discharging to ground on its own, and would be very inefficient in transmitting power. This is why the higher voltage lines are strung at greater heights above the ground.

Watch that video that the other posted linked to. It is exactly what I am referring to.
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Certainly there is line to ground capacitance distributed along the length of the transmission line. That is one of the factors determining the characteristic impedance of the line. Any two conductors separated by an insulating material form a capacitor. And, there is capacitance between the helicopter and ground. I would refer you to a text on the matter, but I don't want another scolding.
 
Its my time to talk crazy to the extreme. And your use to hearing that from me.

I agree with Rattus about the capacitor plate and in the real world it would be equal to something like a .0001 uf cap. because of the high air resistance to the other conductors and earth.

Picture this, look at the old electrical flow analogy the way we compare it to water in a circle pipe and a pump.

We know for sure that a voltage as high as we are talking here 500 kv will jumper several feet through the air this is what makes the spark or arc.



Now imagine our water pipe analogy and say the flow is cut off with a water valve. Now drill a hole into the side of the pipe on the outlet side of the pump and attach a container to it since the container is empty it would fill with water. But with the choper the electrical potential flows to the choper untill it equalizes to the same potential as the conductors and then disapates the electricity through the air to earth in the microamp range just like the conductors are doing.

Please don't confuse this theory by bringing up anything about the air in the container.:D

In my opinion Rick has a point and is right in his theory.

Like Rick I think no matter how high the resistance is so much electrical flow makes it back to its source.
I know we don't have the tools to measure this with and is not even worth considering in the real world.

Roger can I still pool with you all ? :D
 
ronaldrc said:
...But with the choper the electrical potential flows to the choper untill it equalizes to the same potential as the conductors and then disapates the electricity through the air to earth in the microamp range just like the conductors are doing.
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Actually, you are about half way there. This is AC, so for the positive half cycle, the line is delivering charge to the helicopter, but for the negative half cycle, the helicopter is returning the charge back to the line. Because the voltage is so high, it takes longer for this charge transfer to equalize than it takes for the 60 Hz signal to reverse. This is why there is a continuous AC current flowing through the electrode.

To utilize your analogy, if you rotated that pipe with its attached vessel, so that at one point the vessel is below the pipe, and water would flow into the vessel. When it rotated so the vessel was above the pipe, then water would flow out of the vessel and back into the pipe. Make sense?
 
The distance between phases in a 500Kv line is about 17 feet or greater feet. I have seen live line work done, the size of the helicopter is very small. The helicopter is so small, looks like a toy, compareable to a minivan. This copter manuvered around the line with ease.:D
 
Rick Christopherson said:
...This is AC, so for the positive half cycle, the line is delivering charge to the helicopter, but for the negative half cycle, the helicopter is returning the charge back to the line. Because the voltage is so high, it takes longer for this charge transfer to equalize than it takes for the 60 Hz signal to reverse. This is why there is a continuous AC current flowing through the electrode...
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I agree with this assessment. However, the only problem I have is part of your initial statement in this thread:
Rick Christopherson said:
This is probably going to raise a few hackles, but any time you have a difference in voltage, you will have current flowing. It does not matter if there is a completed circuit or not. The monkey wrench in this statement is that in order to have a difference in voltage, there will generally need to be a common reference point, and in most cases, this will end up being a return current path.
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The part I have underlined and made red is, simply put, a false statement. The voltage between the helicopter and the power line exists prior to any arcing. Voltage, no current. Arcing occurs when the electric field strength exceeds the breakdown voltage of the surrounding air, such that it is ionized. This in principal is the same condition by which lightning occurs.

http://en.wikipedia.org/wiki/Corona_discharge
http://science.howstuffworks.com/lightning2.htm
 
No, the statement is not false. You are confusing this statement with the arcing. The only reason why I chose an example that showed arcing is because it was a visual cue to you and others that current was flowing.

When the technician touches the line with his electrode, current is still flowing through the electrode in the same manner as when it was arcing, but the results are not as dramatic and visible without an ammeter. (By the way, notice that his electrode still arcs when he releases the helicopter to move away.)

The reason why these guys wear a full-body Faraday suit is to prevent a voltage gradient from one part of their body to the next. If we were dealing with lower voltages, this suit would not be required, because the entire body would be able to maintain the same voltage--like a bird landing on a power line. However, you will not find a bird resting on one of these ultra-high voltage lines, because there will be a voltage gradient across the body of the bird and they will be electrocuted. Without the Faraday suit, the technician too would be electrocuted, simply from the voltage difference from one part of his body in contact with the line to another part of his body away from the line.

We all know that under normal circumstances we can grab a live conductor and not get zapped as long as we are not in contact with another voltage potential. However, when you are dealing with these ultra-high voltages, the minor difference in distance from the line will create a voltage gradient. If you touch one of these lines, you will be electrocuted from the inside-out. That is to say, you will have a current flowing inside your body, regardless whether any current is entering or leaving your body from the actual contact.

So yes, current will flow any time you have a difference in voltage. If you still don't believe this, I will pay you $100 to climb the power pole and get within a couple feet of the line without a Faraday suit. (I'll make the check payable to your widow, of course.) :D Disclaimer: I am joking!! Please don't do this!!
 
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Rick Christopherson said:
The monkey wrench in this statement is that in order to have a difference in voltage, there will generally need to be a common reference point, and in most cases, this will end up being a return current path.
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The reason why I chose the ultra-high voltage example is because it is one of the few cases where you can have a sustained voltage difference without that reference device preventing the very same voltage difference in the first place (the "Earth to the Moon" example is another case). As Roger asked in the first reply to my posting, the reason why this won't be applicable to a couple of batteries is because as soon as you connect them together, the voltage difference is gone.

At these high voltages, simply the distance from the conductor is enough to create a voltage gradient. It is this voltage gradient that results in a current flow. The current flow will be sustained, and it will occur regardless of a return path.

The reason why this is so hard to accept is because most people have not encountered situations where a voltage difference can exist when a conductor is present between those voltages. It is not intuitive, but it is real.

Can I drive the bus?
ICONATOR_7935198a01ad5281988588747d401fac.gif
 
Maybe this will help make Rick's point.

Consider that 765 kV line, but forget about the helicopter. At one instant in time, the voltage to ground of the conductor is 765?sqrt(2)?sqrt(3) = 625 kV. This causes an electric field between the conductor and ground, with an intensity measured in volts/meter.

This electric field exerts a force on electrons. Now, let's take a copper wire and place it vertically below the conductor (not touching the conductor or ground). The free electrons in the wire will be pushed towards one end of the wire and start moving that direction.

Now, we reverse the voltage. The electric field reverses and so does the direction of force on the free electrons. They start moving toward the other end.

With the alternating voltage on the line, the free electrons first move one way, then the other, an alternating current.

This does not depend on capacitance. The free electrons that were close enough to one end of the wire to get there before the voltage reversed will bunch up on that end - this is the capacitance part. The electrons that don't make it to the other end just jiggle back and forth.

The electric field intensity is very high close to the conductor. High enough to break electrons away from normally stable air molecules. These then start jiggling around as the electric field alternates. Corona!
 
Rick Christopherson said:
I can understand you guys not being too thrilled with the "Earth to the Moon" analogy:smile: , so lets consider something a little more down to Earth.

Have you ever seen utility workers work on ultra-high voltage power lines? They fly to the line with a helicopter and reach out with an electrode to bring the helicopter to the same potential as the power line. This electrode begins to arc a foot or two away, and continues to arc until it makes contact. It is pretty obvious that there is a substantial electron flow in this arc, correct?

Now consider if the helicopter just hovered with the electrode 6 inches away from the line so you could see the arcing. It would continue to arc indefinitely. If you put an ammeter in the middle of the electrode, you would see a substantial AC current flowing through the electrode, yet there is no return circuit.

This isn't contradicting Kirchoff's Law, as a matter of fact, Kirchoff's Law specifically accounts for this.

Yes, the helicopter is acting a a large capacitor, but nevertheless, AC current is flowing between two voltages without a return. If you replaced the ammeter with a light bulb, it would light up.
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Rick:

Are you saying this would work with DC also? (If this current flow isn't just through capacitance, then DC current would also flow from the lines to the helicopter.)

If that is the case, where would all the electrons flowing to the helicopter go?

Would the helicopter get heavier and heavier since it is collecting more and more electrons?

That just doesn't happen.

Steve
 
This is all semantics

Very interesting thread though. To me, this is like a climatologist crashing a plumbers website to argue that there is "water currect" flowing around us continuously without pipes via evaporation. Clouds as storage units etc.

For some reason though, I think the plumbers would just accept this proven theory and go back to work. :roll:

We are a fiesty bunch arent we! :grin:
 
Rick Christopherson said:
The reason why these guys wear a full-body Faraday suit is to prevent a voltage gradient from one part of their body to the next. If we were dealing with lower voltages, this suit would not be required, because the entire body would be able to maintain the same voltage--like a bird landing on a power line. However, you will not find a bird resting on one of these ultra-high voltage lines, because there will be a voltage gradient across the body of the bird and they will be electrocuted. Without the Faraday suit, the technician too would be electrocuted, simply from the voltage difference from one part of his body in contact with the line to another part of his body away from the line.
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Doesn't this tell us that, for there to be a voltage gradient along the body, there must be a difference of potential between the contact end and the non-contact end of the body? Why wouldn't the entire body simply take on the same voltage, just as the Faraday suit does, regardless of voltage?

A voltage gradient requires (or rather, is) a voltage drop along the pathway in question, which requires a current flow caused by a voltage difference. Therefore, the air, earth, capacitance, whatever, must be part of a complete circuit; otherwise, there would be no current to cause such a gradient.

In other words, in the electrical equivalent of the perfect vacuum, there should be no current across the body, because there should be no potential between the contact point and any other part of the body. The entire body should charge up to the voltage of the contact point, like the bird on an MV line.

That's my take on it, anyway.
 
Rick Christopherson said:
No, the statement is not false...

So yes, current will flow any time you have a difference in voltage. If you still don't believe this, I will pay you $100 to climb the power pole and get within a couple feet of the line without a Faraday suit. (I'll make the check payable to your widow, of course.) :D Disclaimer: I am joking!! Please don't do this!!
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I am not in disagreement with the majority of your assessments. The only part I disagree on is the implication you cannot have an electrical potential difference (aka voltage) without current.

In your last example, I do not have to get within a couple feet of a power line for there to be an electrical potential diiference. The difference exists right where I'm at, where the the conductance is near infinitesimally small. The conductance would increase exponentially with a linear decrease in distance from the power line. There would be an abrupt change in conductance if the air between masses became ionized due to a high potential electrical field.

Evaluate the equation E = I ? R, where the value of I is equal to 1/R. For all values of I except 0, the value of E = 1. But I can be a value infinitesimally small... say a current of 1 electron charge transferred between bodies of two masses in 1,000,000 years. Certainly beyond any realistically usefull power, but E is still equal to 1...!!! While this would still conform to your assertion, what happens when I is absolute zero. The truth is, voltage (i.e. electrical potential difference) is still equal to 1 while E is equal to 0.
 
steve66 said:
Would the helicopter get heavier and heavier since it is collecting more and more electrons?
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Why of course. This makes perfect sense, and it is a strange sight to behold. As a matter of fact, while the helicopter is getting so heavy from the excess electrons, and crashes, the utility line is getting more and more holes, so it begins to float away like a balloon.:grin:

Under normal circumstances I wouldn't need to point out that I was being facetious, but given the discussion, it's probably a good idea to make that clear.:grin:
 
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