current returning to a different source

[Rick Christopherson]

As for 20 KV per inch required to ionize air - ...

Actually, the 20kV/in. is toward the low end of the spread. Some sources put it as high as 80kV/in. at STP.

I am going to preempt your next thought: While it is true that once ionization occurs, a spark can be maintained at lower voltages. However, this is not applicable for AC voltages because the voltage goes to zero twice per cycle. At each zero crossing, the ionization path is broken and has to reestablish itself.

As for the impedance of the air, again, I know very little. .... If the air was an "extremely good conductor" like a copper wire, then shouldn't the spark be near ambient temperature?

You didn't put very much thought into this statement, did you? When is the last time you saw a #12 wire get hot with only 60mA? You are supposed to be trying to convince me that the current is lower, not higher...oops :smile:

I am guessing there are some flaws in the "122,000 volts" and "conductor".

A 5 minute Google search would have negated your guessing.

Regardless, this point applies to both the capacitor explanation and your explanation of the helicopter phenomenon.

No it doesn't apply to both, because your capacitor assumption precludes this amount of current flow.

In your explanation of the helicopter phenomenon, what level of current do you suspect is flowing between wire and copter?

I don't know the exact amount at this time, but I do know it is too high to support the capacitance supposition.

 

[ELA]

How about 3 x 10^6V/M for dielectric breakdown of air?
Or about 76Kv/in. I thought there was a rule of thumb about 20K/0.25 in?
Of course it varies a lot with other factors.

As far as the 60 ma current in the arc. I thought that was capacitive current and thus limited by capacitive reactance?

 

[crossman]

You didn't put very much thought into this statement, did you? When is the last time you saw a #12 wire get hot with only 60mA? You are supposed to be trying to convince me that the current is lower, not higher...oops :smile:

First, I put plenty of thought into it. Second, you missed the point entirely. I am saying that the arc from probe to wire is quite hot. For 60mA to cause heat, there must be some resistance that it is traveling through. 60mA does not cause much heat in a #12 wire. 60mA does not cause much heat in any good conductor. A 60mA spark through air is causing considerable heat. Hence, the air is not a good conductor. Unless I am wrong and the arc is not hot. Perhaps this is the case?

I don't know the exact amount at this time, but I do know it is too high to support the capacitance supposition.

How about an educated guess? 600 mA? 6 amps? 60 amps? 600 amps? 6000 amps?

 

[zog]

For what it is worth I can draw an arc to an ungrounded piece of metal (And maintain it) through about 4-6"" of air with my 100kV Hipot (AC), current stays around a few mA. Where is the path for current? I can see the arc, see it on the ammeter on the hipot.

However, if I try to draw the same arc to ground, the hipot trips off line (Exceeds 1A).

 

[Rick Christopherson]

Rick, I don't think you have the credentials to tell anyone else how to solve a problem, and I see no evidence that you understand AC Circuits.

Yup. You caught me. I'm really just a fake. I actually only have a liberal arts degree in hamburger management. I just thought it would be fun to see how long I could string you experts on before you figured it out. Hey, 31 pages for my first posting on this forum can't be too bad.

On the other hand, if I was such an idiot, then why are you still discussing this after 2 weeks and 31 pages? Someone that is a sharp as you think you are, should have been able to quell this heresy in a matter of minutes, right?

When I see people, whose only recourse in an argument is to levy personal attacks as the sole method of making their point, it tells me that they are the ones that don't have the technical wherewithal to levy a proper argument and are stepping beyond their knowledge base. To date, you have added no substance to this discussion outside of personal attacks.

I respect Crossman because he has stated that much of this is beyond is knowledge base, but he is nevertheless willing to learn. I have absolute contempt for someone like yourself that pretends to know more than they do, but hides their deficiencies behind mockery and ridicule.

I registered for this forum using my full name, so my credentials are out there for everyone to see. Why are you hiding behind a moniker? You profile says you are an "Electronics Engineer". Is that a full EE degree, or is it like one of those titles they give to the janitors to make them feel better?

 

[jghrist]

For what it is worth I can draw an arc to an ungrounded piece of metal (And maintain it) through about 4-6"" of air with my 100kV Hipot (AC), current stays around a few mA. Where is the path for current? I can see the arc, see it on the ammeter on the hipot.

However, if I try to draw the same arc to ground, the hipot trips off line (Exceeds 1A).

Seems like you could do some experimentation with your hipot to put to rest some of the helicopter arguments. You could create a simplified situation where the dimensions of the hipot terminal, the ungrounded piece of metal, and a nearby ground plane were such that the capacitance could be calculated. Then you could determine experimentally if the arc current was anywhere close to the calculated capacitor current.

What happens to the current if you replace the arc with a solid metallic connection from the hipot to the ungrounded piece of metal.

Does the current depend on the mass of the ungrounded piece of metal?

 

[zog]

I could do all that if I didnt have a job.

I did play around wih the arc distance to see if current changed, it didnt, even when I touch the metal to the probe, maybe current chaged a little, but not more than a few microamps, hard to tell the leakage current was bouncing aroud a little bit anyways.

I will try the different mass experiment next time I set up the hipot.

P.S. i use the term "Play with my 100kV hipot" loosely, I dont condone this at all. 100kV hipots are not toys.

 

[crossman]

Gentlemen:

I would like to submit the following for your approval. I am proposing this as the simplest model of the helicopter/powerline.

Diagram 1: On the far right is the powerline closest to the helicopter. On the far feft is the other powerlines and ground. I feel it is acceptable to model the overall capacitance from the line on the right to everything else which has an electrostatic field connected to the line on the right. Although there are several capacitances, I am modeling it with one capacitor.

The wires charge and discharge based on the capacitance and the source voltage and frequency.

Diagram 2: The helicopter moves into the electrostatic field. Yes, the helicopter is not actually between the wires, however it is no doubt inside the electrostatic field as shown in Smart$'s wonderful drawings. There is no doubt that the helicopter is affected by both the positive side and negative side of the field.

In effect, the helicopter is a moving plate inside a larger capacitor. This can be looked at as two capacitors. We cannot ignore the effects on the copter of both the positive and negative sides of the field. It is not only the right hand wire that affects the helicopter. The left hand wire affects it too. Any electron movement in the helicopter must be attributed to both the positive and negative side of the electrostatic field. This is important to understand.

Diagram 3: AS the helicopter approaches the right powerline, the resistance of the air becomes low enough to begin shorting out the capacitor between the copter and right hand wire. Again, the right side of the helicopter and the right hand wire form a capacitor. The arc forms because we are shorting out a charged capacitor from one side to the other, and the arc is completing the path of the capacitance from the left wire to the right wire.

Diagram 4: The helicopter/probe touches the right hand wire and the helicopter/right hand wire capacitor is effectively shorted out and no longer plays a role. The helicopter/right hand wire is the right hand plate of the overall capacitance.

That's the way I see it, in its simplicity.

 

[crossman]

I could do all that if I didnt have a job.

I did play around wih the arc distance to see if current changed, it didnt, even when I touch the metal to the probe, maybe current chaged a little, but not more than a few microamps, hard to tell the leakage current was bouncing aroud a little bit anyways.

I will try the different mass experiment next time I set up the hipot.

Jghrist is right. You have the perfect instrument to test all this.

I do have a couple questions... Is one terminal of the high voltage tester connected to the earth? Could you draw a diagram of what you did? And, how did you isolate the metal from ground?

Dang, I wish I had one of those.

 

[Rick Christopherson]

I could do all that if I didnt have a job.

I couldn't agree more. Some have criticized me because I said I was not willing to go through the math. If I didn't have anything better to do with my time, I would do this. Like you, I am willing to expend only a limited amount of time on this issue.

I did play around wih the arc distance to see if current changed, it didnt, even when I touch the metal to the probe, maybe current chaged a little, but not more than a few microamps, hard to tell the leakage current was bouncing aroud a little bit anyways.

I am not sure from your previous postings if you agree with my hypothesis or not, but this statement actually agrees with my latest statement regarding conductivity of ionized air.

I apologize if I am using your information to make a point that opposes your position, but if you can change the length of the arc without changing the current flowing through the arc, then this supports the "high conductivity" aspect of ionized air I stated earlier. If the conductivity was low (high resistivity), then changing the arc length would have significantly changed the resistance of the ionized path, and therefore, changed the current flow.

I will try the different mass experiment next time I set up the hipot.

It would be interesting to see what effects are achieved with 1). a conductive path, 2). a low capacitive path (physical capacitor), and 3). no apparent path with a large separation of components.

 

[zog]

Jghrist is right. You have the perfect instrument to test all this.

I do have a couple questions... Is one terminal of the high voltage tester connected to the earth? Could you draw a diagram of what you did? And, how did you isolate the metal from ground?

Dang, I wish I had one of those.

There is only 1 high voltage lead, the other side of the hipot is grounded (Twice). The high voltage lead is hanging from our test stand (We test HV breakers in our shop). The metal chunk is being held near the HV lead with a 15' hotstick (The kind linemen use to pull pole fuses).

 

[Rick Christopherson]

In effect, the helicopter is a moving plate inside a larger capacitor. This can be looked at as two capacitors. We cannot ignore the effects on the copter of both the positive and negative sides of the field. It is not only the right hand wire that affects the helicopter. The left hand wire affects it too. Any electron movement in the helicopter must be attributed to both the positive and negative side of the electrostatic field. This is important to understand.

When I asked if a truck driving beneath the power lines would arc to the Earth, this is the argument that I was anticipating. Yes, I was one step ahead of you. :smile:

You either have to accept it completely or dismiss it completely, but you can't have it both ways only when it suits your position.

 

[zog]

I couldn't agree more. Some have criticized me because I said I was not willing to go through the math. If I didn't have anything better to do with my time, I would do this. Like you, I am willing to expend only a limited amount of time on this issue.

I am not sure from your previous postings if you agree with my hypothesis or not, but this statement actually agrees with my latest statement regarding conductivity of ionized air.

I apologize if I am using your information to make a point that opposes your position, but if you can change the length of the arc without changing the current flowing through the arc, then this supports the "high conductivity" aspect of ionized air I stated earlier. If the conductivity was low (high resistivity), then changing the arc length would have significantly changed the resistance of the ionized path, and therefore, changed the current flow.It would be interesting to see what effects are achieved with 1). a conductive path, 2). a low capacitive path (physical capacitor), and 3). no apparent path with a large separation of components.

Rick, if you go back and read my posts (Dont waste your time, I am telling the truth here) you will see I have supported you all along, I was just trying to stay out of this for the same reasons you regret getting in the middle of it.

And here I am getting involved, which I am not going to do, keep up the good work Rick, you are right on this one.

 

[Rick Christopherson]

I was just trying to stay out of this for the same reasons you regret getting in the middle of it.

I laughed so hard at reading this that I scared the dog!!

I respect your position, and that is why I was trying to be careful to not put words in your mouth. :smile:

 

[crossman]

When I asked if a truck driving beneath the power lines would arc to the Earth, this is the argument that I was anticipating. Yes, I was one step ahead of you. :smile:

You either have to accept it completely or dismiss it completely, but you can't have it both ways only when it suits your position.

The way I see it:

The wire is a "pinpoint" for charge and the electrostatic field is very much concentrated near the wire. The earth is not a "pinpoint" for charge. The charges are spread over a wide area. Therefore, the field density is substantially less than near the wire. And there will be much less interaction with a helicopter near the earth as near the wire.

 

[crossman]

I wish I had a highpot tester.

 

[zog]

Lets start a poll

Who in this discussion has ever worked with >50kV power systems?

 

[crossman]

not me, no 50 kV

 

[crossman]

It would be interesting to see what effects are achieved with 1). a conductive path, 2). a low capacitive path (physical capacitor), and 3). no apparent path with a large separation of components.

No doubt about that. I can envision some nice experiments. Only thing is, we need to do them outdoors with blue sky overhead, not all wrapped up in a grounded building.

 

[crossman]

For what it is worth I can draw an arc to an ungrounded piece of metal (And maintain it) through about 4-6"" of air with my 100kV Hipot (AC), current stays around a few mA. Where is the path for current? I can see the arc, see it on the ammeter on the hipot.

Is it possible to put a miili-amp meter in series with the grounded leads as in the diagram?

Here is a test to see where the current is going/coming from.

Metal body suspended in the air and well-insulated. Both ammeters properly calibrated. Hipot enclosure/chassis suspended and insulated from earth and from the grounded test lead and from the supply. No ground connections to high voltage secondary except through the ammeter.

Would the meters read the same? Or different?

Edit: clarify no grounds to high-voltage secondary except through the meter to ground