current returning to a different source

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Yer right!

Yer right!

ELA said:
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?
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The arc current is indeed limited by capacitive reactance. Short the copter to earth and blooey!
 
Another test that could be done would be to completely disconnect the hi-pot tester from ground and see if that changes the milli-amp reading of the arc to the chunk of metal.
 
crossman said:
Another test that could be done would be to completely disconnect the hi-pot tester from ground and see if that changes the milli-amp reading of the arc to the chunk of metal.
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Not a test that could be done safely, however.

If you did it, the hi-pot would lose it's reference voltage. It would be like disconnecting one secondary lead from a single-phase transformer.
 
crossman said:
Jghrist, I do that all the time. Take a 480 to 120 control xfmr, energize the primary, and do nothing to the secondary. No problem.
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Thats a little different than 100kV, why do you think there are 2 grounds like I mentioned earlier, in case 1 falls off.
 
Rick Christopherson said:
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.:rolleyes:
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Rick, explain to us why there is no arc from a vehicle driving under a xmission line.

Tell us also what we have to accept or dismiss completely. Tell us why there is no in-between.
 
rattus said:
Let me repeat myself:

First, you have no numbers to justify your assumption that line to ground capacitance is neglible especially when you consider the added area of the copter to the equation.
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Actual numbers, no... so you are correct. However, I supplied suppositional numbers in post #232...
Smart $ said:
...e-field strength is inversely proportional to the square of the distance ... so let's say the power line and helicopter are 80' off the ground and the center of the conductive mass of the helicopter is 10' away from the power line. The e-field strength between power line and ground vs helicopter would be (10 ? 80)^2 = 0.0156 or 1.6%...!!!
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I could offer further substantiation, but I feel the issue has been confused enough already... no need to add more to something so elemental.

Additionally, at least I supplied some numbers. I believe you brought what, a formula or two into the discussion?

Second, even if you ignore the line to earth capacitance, you still have the line-copter-line capacitance which can account for the arc current by itself. Surely you con't claim we can ignore that current.
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I believe I'm the one that pointed out the effect other two power lines was missing from the discussion...

...and I do my best to not ignore anything relevant. It would be an outright fabrication if I were to say nothing slips by me :grin:

Clearly, the arc current is capacitive. Claiming otherwise is like jousting with windmills.
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As I wrote earlier, capacitance exists between any two bodies of mass. I have not been the least bit quixotic, from my point of view :wink:
 
Smart $ said:
I believe I'm the one that pointed out the effect other two power lines was missing from the discussion...
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Not that it matters, but I had already made that point.

As I wrote earlier, capacitance exists between any two bodies of mass. I have not been the least bit quixotic, from my point of view :wink:
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You seem to agree that the arc current could flow through stray capacitance.

And, BTW, the field is inversely proportional to the FIRST power of the distance in the vicinity of a long, straight, charged line.

[Sears, "Electricity & Magnetism", Addison-Wesley, 1954]
 
rattus said:
Rick, explain to us why there is no arc from a vehicle driving under a xmission line.

Tell us also what we have to accept or dismiss completely. Tell us why there is no in-between.
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That would depend on how low the lines were and how high the truck is.
 
rattus said:
Not that it matters, but I had already made that point.
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Perhaps ou did and I simply missed it, but it matters not who brought it up first, but rather that it was brought up when it was inappropriately being ignored.

You seem to agree that the arc current could flow through stray capacitance.
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In my mind, there is no such thing as stray capacitance. Capacitance is inherent with all matter. It simply comes down to that which we acknowledge or ignore.

If we were accounting for all local capacitance in this situation, we could justifiably take the capacitance of the air itself into account. But instead, we only consider its dielectric properties and breakdown thereof.

And, BTW, the field is inversely proportional to the FIRST power of the distance in the vicinity of a long, straight, charged line.

[Sears, "Electricity & Magnetism", Addison-Wesley, 1954]
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You are correct. My bad. I had forgotten that we were not discussing a point source.

However, e-field force lines curve to the nearest countering force. The three power lines are of a closed loop system, likely using earth only as a reference voltage. This suggests the lines combined e-fields are self-countering. However, their arrangement precludes efficient countering of their respective fields. Yet they are also in closer proximity to each other than any one is to ground. I'm still inclined to believe the e-field strength, as it approaches ground, diminishes at a rate less than linear. So how much e-force actually makes it to ground level?
 
I would like to rephrase my previous question concerning an experiment with a "high-pot" tester.

See diagram below. We have a conductive body suspended in the air and perfectly insulated. Both ammeters properly calibrated. Hi-pot enclosure/chassis suspended and perfectly insulated from earth and from the grounded test lead and from the supply. No ground connections to high voltage secondary except through the ammeter. Hi-pot lead is arcing to the conductive body.

Would the meters read substantially the same? Or substantially different?

Rattus?
Rick?
Jghrist?
Smart $?
Zog?
Winnie?
quogueelectric?

test4.jpg
 
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Smart $ said:
However, e-field force lines curve to the nearest countering force. The three power lines are of a closed loop system, likely using earth only as a reference voltage. This suggests the lines combined e-fields are self-countering. However, their arrangement precludes efficient countering of their respective fields. Yet they are also in closer proximity to each other than any one is to ground. I'm still inclined to believe the e-field strength, as it approaches ground, diminishes at a rate less than linear. So how much e-force actually makes it to ground level?
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Then you agree there is SOME capacitance between the copter and ground as well as between phase wires??

Then you must further agree there is SOME current through all these capacitors??
 
rattus said:
Then you agree there is SOME capacitance between the copter and ground as well as between phase wires??
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Yes.

However, because the helicopter is higher than the line, the e-field forces are emanating radially from the line and very likely curving upward and back over the line towards the other two lines. The static charge differential across the helicopter is distributed perpendicularly to the e-field force lines. In other and simpler terms. The electrons of the helicopter are pushed upward and away from the power line (and vice versa on positive half cycle). The premise just stated would preclude ground from having any notable effect on the helicopter. See depiction below.

View attachment 1272

Then you must further agree there is SOME current through all these capacitors??
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No, I mustn't... :wink:

...but I do agree, in part. I disagree with your phraseology. Capacitive currents flow "around" the capacitors, not through them. Curent only flows "through" a capacitor when the dielectric breaks down (which many times means it's no longer a capacitor ;) , but not in this instance).

The helicopter is but one electrode or "plate" in relation to your capacitive premise. On approach to the power line, current flows through it, from one side to the other in an oscillating manner, being in the midst of an AC e-field... but no current flows into or out of it. When arcing occurs, the air dielectric has become conductive and additional current flows to, from, and through the helicopter.
 
crossman said:
Jghrist, I do that all the time. Take a 480 to 120 control xfmr, energize the primary, and do nothing to the secondary. No problem.
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What's the voltage from one terminal of the secondary to a helicopter?;)
 
crossman said:
I would like to rephrase my previous question concerning an experiment with a "high-pot" tester.

See diagram below. We have a conductive body suspended in the air and perfectly insulated. Both ammeters properly calibrated. Hi-pot enclosure/chassis suspended and perfectly insulated from earth and from the grounded test lead and from the supply. No ground connections to high voltage secondary except through the ammeter. Hi-pot lead is arcing to the conductive body.

Would the meters read substantially the same? Or substantially different?

Rattus?
Rick?
Jghrist?
Smart $?
Zog?
Winnie?
quogueelectric?

test4.jpg
Click to expand...
Depends on if the chunk of metal is closer to the earth or to the grounded case of the tester. If closer to the earth, then the currents will be about the same. If the chunk of metal is closer to the tester than to any other grounded objects on the ground side of the milliammeter, then the current in the ground lead will be lower.
 
Smart,

Regardless of phraseology, nit-picking that is, you agree that capacitive current returns either to another line and/or to earth.
 
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