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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => AC Power and Grounding => Topic started by: Mike Sokol on February 14, 2014, 09:04:34 AM
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Here's another thing you might not be aware of, but certainly a possibility for any spring outside gigs you may have coming up. (remember spring?) If a large surface is anywhere under high-tension power lines, there can be significant voltage and moderate current induced from inductive coupling. I've heard this complaint numerous times from RV owners who park their camper under high-tension lines overhead, then feel painful shocks when they touch the side of the RV and the ground at the same time. This is also a big problem for farmers who often lease the right of way on their land to power companies. They have to temporarily "ground" any irrigation pipes they're taking off the truck, especially if they're parallel to the power lines overhead. And my PoCo buddies warn me that parking their truck under a high-voltage line will zap them when stepping out of the truck.
Here's a great paper on the subject written by Bonneville Power.
http://www.bpa.gov/news/pubs/GeneralPublications/lusi-Living-and-working-safely-around-high-voltage-power-lines.pdf (http://www.bpa.gov/news/pubs/GeneralPublications/lusi-Living-and-working-safely-around-high-voltage-power-lines.pdf)
I've talked to the author of this paper, and they tell me there can be "significant voltage" on something as large as a semi-trailer or RV parked under lines. When I asked how much voltage, they told that a car's spark plug attached between the vehicle bumper and a ground stake would continuously spark. Yikes, that's got to be a few thousand volts. But not to worry, they said the induced current was less than 5 mA, so it's not deadly. Still, that's like grabbing onto an electric fence charger and holding on.
So if your stage is located anywhere under high-tension power lines, I would REALLY be sure it's grounded via an 8-ft ground rod and properly bonded to your generator neutral/ground.
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And you can do this: http://www.larkinweb.co.uk/miscellany/fluorescent_tubes_under_power_lines.html
Steve.
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I wonder if the anti-static straps we used to hang from cars would help dissipate the charge from campers?
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This is an old story but I was once called by a lawyer who wanted me to be an expert witness for him. His client was suing the power company because he claimed that the voltage in the drop down to his house from the pole power transformer, arced over to his aluminum ladder and threw him to the ground injuring him.
I explained to the lawyer how many volts it takes for the voltage to arc across the tiny speak plug gap (tens of thousandths of an inch), and then how much less voltage is in the power drop. So his client had to be so close to to the power drop wire that it was more likely he actually touched it.
For some reason I did not get hired for that particular expert testimony. I guess my explanation of the facts did not support his case. ;D
JR
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For some reason I did not get hired for that particular expert testimony. I guess my explanation of the facts did not support his case.
It would have been fun to go along with his story until you got to court, then tell the truth. Especially if they were paying for you to be an expert witness.
Steve.
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I wonder if the anti-static straps we used to hang from cars would help dissipate the charge from campers?
I've proposed this exact experiment to Fluke and First Energy (my local power company). Fluke will send me a high-voltage probe for measurements, and First Energy has a section of 500,000 volt power lines close to my house with easy road access I can play with. Now don't worry about me climbing up and measuring the power line directly (I'm not qualified or stupid enough to try that). But driving a ground stake next to an RV and measuring the voltage between it and the bumper of the RV should prove interesting. I'll also see if I can find a high-voltage/high-ohm resistor and do a current calculation at the same time. And yes, I'll HAVE to try the spark plug demonstration and take a video if it actually works.
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A couple of months ago, The Columbian (the local newspaper in Vancouver, WA) had a writeup about BPA's high-voltage lab at their Ross Complex Facility just north of Vancouver.
http://www.columbian.com/news/2013/dec/09/high-voltage-bpa-lab-a-rare-asset-ross-complex/
P.S. -- Mike, I hate dirty URLs. So I fixed it for you:
http://www.bpa.gov/news/pubs/GeneralPublications/lusi-Living-and-working-safely-around-high-voltage-power-lines.pdf
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A couple of months ago, The Columbian (the local newspaper in Vancouver, WA) had a writeup about BPA's high-voltage lab at their Ross Complex Facility just north of Vancouver.
http://www.columbian.com/news/2013/dec/09/high-voltage-bpa-lab-a-rare-asset-ross-complex/
Gosh, I need a lab like this.
P.S. -- Mike, I hate dirty URLs. So I fixed it for you:
http://www.bpa.gov/news/pubs/GeneralPublications/lusi-Living-and-working-safely-around-high-voltage-power-lines.pdf
Thanks, I've corrected it in the intro to this thread as well. Guess I was just a little lazy....
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Yes, I've experienced this on a couple of occasions. Once we were camped in a spot down in the Mojave Triangle (somewhere east of Barstow, CA) with a beautiful view that just happened to be under a cross-country transmission line. At one point I walked up to my parked motorcycle and pulled a pretty good arc off my finger. I'm guessing that, in this case, I was floating on my rubber-soled shoes and the bike was grounded through its kick stand. I moved away from the lines before fueling from a gas can, and made sure to touch the bike and the can before opening either.
Another time, also in the So Cal desert, a few of us decided to climb a transmission tower (we were younger then -- no further explanation shall be provided). It was cold and dry and I was wearing insulated gloves. When I was about abeam the first set of wires my bare wrist touched the tower. I got a good little tickle and decided it was time to turn around.
On the mode of coupling, are you sure it is inductive and not capacitive? We should be able to come up with an experiment to determine this.
One more aside, don't piss off the power company in the process of doing measurements. Although you're just minding your own business in their electromagnetic field, it could be construed as stealing power, especially when that spark plug video goes viral.
--Frank
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On the mode of coupling, are you sure it is inductive and not capacitive? We should be able to come up with an experiment to determine this.
My sparky buddies say it's capacitive. My EE buddies say it's inductive. I'm thinking testing for leading vs lagging currents to know for sure, but my gut says inductive.
One more aside, don't piss off the power company in the process of doing measurements. Although you're just minding your own business in their electromagnetic field, it could be construed as stealing power, especially when that spark plug video goes viral.
I have my local PoCo's blessing to try this. Unofficially, of course....
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One more aside, don't piss off the power company in the process of doing measurements. Although you're just minding your own business in their electromagnetic field, it could be construed as stealing power, especially when that spark plug video goes viral.
If they want to put an electromagnetic field into the public domain, that's their problem.
My grandfather once told me about a farmer who had a barn very close to a high power BBC transmitter. He lit his barn with tuned circuits and small, low voltage bulbs.
Steve.
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He lit his barn with tuned circuits and small, low voltage bulbs.
Tuned circuits? Hmmmmm, that an interesting idea.... Is it possible that this coupling effect is essentially a big radio wave? If so, then it's a combination of magnetic and electric fields, just like a radio station broadcasting at 60 Hz.
From Wikipedia
The electromagnetic waves that compose electromagnetic radiation can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. This diagram shows a plane linearly polarized EMR wave propagating from left to right. The electric field is in a vertical plane and the magnetic field in a horizontal plane. The two types of fields in EMR waves are always in phase with each other with a fixed ratio of electric to magnetic field intensity.
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I'll bet somebody at the power company knows exactly. It is their business to keep the majority of energy inside the wires, loss is loss.
JR
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I'll bet somebody at the power company knows exactly. It is their business to keep the majority of energy inside the wires, loss is loss.
JR
If only I could call up Tesla and ask him. I do know that one of the advantages promoted for the new DC smart grid is less losses than AC transmitted over long distance due to power factor issues. More fun stuff to study...
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There is a story around here about a guy with a barn near one of those lines who was found to have a few terns of wire around the barn and a lot of power available to him. Perhaps it is true.
Frank
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There is a story around here about a guy with a barn near one of those lines who was found to have a few terns of wire around the barn and a lot of power available to him. Perhaps it is true.
Frank
I know that the power companies don't like buildings directly under their high-tension lines. And if you read the pdf link from Bonneville Power I referenced at the beginning of this thread they'll talk about grounding metal buildings under power lines and that holding an irrigation pipe in your hands (like a big horizontal antenna) can cause painful shocks. That why they recommend that farm workers drive a ground stake and clamp a ground wire to bundles of irrigation pipes. They also make mention of adding ground stakes to wire fences running under high tension lines.
But nothing that I've read really discusses just how much amperage and voltage is induced in these cases, perhaps because they're worried about low-life individuals stealing "free" power. Even if a stage or RV under a line had 1,000 volts at 5 mA induced from this effect, that's only 5 watts of power. And 10,000 volts at 5 mA would still only be 50 watts of "free power" which hardly seems worth all the trouble.
I'm really interested in this subject mostly from the human shock perspective. I do know that 10,000 volts at 5 mA is probably what a lawn-mower magneto delivers to a spark plug. As a young kid (maybe 10 years old) I tried to stop a running lawn mower engine by pulling off the spark plug wire with my bare hand. That was a BIG shock that slammed me to the ground.
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If only I could call up Tesla and ask him. I do know that one of the advantages promoted for the new DC smart grid is less losses than AC transmitted over long distance due to power factor issues. More fun stuff to study...
For the record Tesla was pursuing wireless transmission of energy.
High voltage DC is used for contact points and power transfer between major different grids. AC is just too convenient for conversion up and down between different voltage levels to reduce IR losses.
The heat loss in the transformers is what those saboteurs used to knock out a power sub-station by shooting holes in the transformer oil tanks so the transformers would overheat.
JR
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Stealing power is done with large coils. Both large in area and lots of turns. The power transfer is inductive.
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But if you work near a transmission line, and drive one of the new electric cars, perhaps a coil built into the roof and parking under the line would save you the energy cost of driving to work each day? Just thinking outside the box....
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Partial quote...
So if your stage is located anywhere under high-tension power lines, I would REALLY be sure it's grounded via an 8-ft ground rod and properly bonded to your generator neutral/ground.
Oh, yes.
I believe it was late Summer 2005, on a request for production at a fair in a neighboring county. The original provider was unable to be there and was a last minute notice.
My friend called me to assist with his rig and off we go.
Upon arrival at the permanent concrete stage platform in front of the grandstands, I cast a wary eye at the HV towers overhead, not very far behind the platform, running parallel to the stage. The droop between the steel towers was at its lowest point in the stage area. Observing the insulators, I was fairly sure it was 138 kV (common in my area). It was a dual 3 phase circuit with lines on both sides of the towers.
I remarked to my friend about the situation and said this could be interesting and my concern about his 30 foot long lighting truss being affected by induction from the high voltage parallel lines. He said lets get moving on assembling the truss to the lifts.
The stage was about 4 feet high and we placed the crank lifts on the ground in front of the stage and attached the truss. We cranked the truss up to 6 feet above the stage level to attach lighting.
I went up on the stage to start the process and proceeded to receive a fairly good wallop on the truss.
That was enough for me. I told the boss we HAVE to get this truss grounded. The electricians working for the county fair were there connecting our cams for our distro and they were summoned to the front of the stage and ended up with #4 copper connected to the lifts and running to a good ground to take care of the issue.
I did not take the time to meter the truss to see what level of voltage was inducted. The rest of the day and evening was uneventful and went well. Yes, the ground conductors remained until the truss was brought back down.
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For the record Tesla was pursuing wireless transmission of energy.
Oh, yeah... 8)
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And you can do this: http://www.larkinweb.co.uk/miscellany/fluorescent_tubes_under_power_lines.html
I have a friend who wanted to do something similar, except rig up a device that would self-climb a wood power pole by pulling on ropes from the bottom. Said device would transport a decorative array of fluorescent tubes up to near the power lines.
My friend never quite dared to rig this up, because he figured the local public power utility would only need one guess to figure out who did it. The irony is that this friend was a past chairman of the board of that utility. :o
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My Ex Father in Law had a pond with High Tension power lines running over part of it. When the water was clear you could see that the area under the lines had no life, not even vegetation.
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My brother has a friend who replaces high tension power lines. One day, miles from anywhere civilised, he found someone living in a shack in the middle of a wood with his own transformer connected to the overhead line. The person he found used to do the same job and knew what he was doing. He had just decided to escape from civilisation and live on his own.
My brother's friend just replaced the lines and re-connected the transformer figuring that no one else will ever stumble upon it so he wasn't doing any harm.
Steve.
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My brother has a friend who replaces high tension power lines. One day, miles from anywhere civilised, he found someone living in a shack in the middle of a wood with his own transformer connected to the overhead line. The person he found used to do the same job and knew what he was doing. He had just decided to escape from civilisation and live on his own.
My brother's friend just replaced the lines and re-connected the transformer figuring that no one else will ever stumble upon it so he wasn't doing any harm.
Steve.
Stealing is stealing... So he probably stole the transformer too.
He is in effect stealing from everybody who does pay their electric bills.
JR
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...figuring that no one else will ever stumble upon it...
Except the next person to inspect or perform work on the line.
On another note, the guy just happened to be able to acquire a transformer capable of dropping the voltage to a usable level? Either had a lot of money saved up or used some "inside sources"... Not many companies who would sell something like that to a single consumer, though I suppose anything is possible.
To clarify, I'm guessing these were medium voltage (1kV to 33kV) not the "high tension" pylons we usually think along the lines of hundreds of kV, since I highly doubt there's a single transformer capable of dropping from 100kV all the way to 208 or 240 in one go.
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Except the next person to inspect or perform work on the line.
Probably won't happen for another ten years
On another note, the guy just happened to be able to acquire a transformer capable of dropping the voltage to a usable level? Either had a lot of money saved up or used some "inside sources"...
Inside sources I think as this used to be his line of work.
To clarify, I'm guessing these were medium voltage (1kV to 33kV) not the "high tension" pylons we usually think along the lines of hundreds of kV, since I highly doubt there's a single transformer capable of dropping from 100kV all the way to 208 or 240 in one go.
Probably from 11,000v to 240v. Definitely not from 132,000v which is the initial distribution voltage here (UK).
I'm just passing on a third hand rendition of the story but don't know the details. I just like the fact that they just re-connected him and left him alone.
Steve.
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I'm just passing on a third hand rendition of the story but don't know the details. I just like the fact that they just re-connected him and left him alone.
Steve.
Sorry I still can't get enthusiastic about an employee who detects theft from his employer and not only looks the other way but helps the thief continue. Disconnecting the unauthorized drop without reporting him to authorities would be less offensive IMO.
I can understand the argument for re-connecting it to keep amateurs away from the dangerous lines, but imagine the drama if he should get hurt while working on that outlaw drop... how do you explain that?
Stealing anything is wrong.
JR