Power Lines

Thanks for that explanation, Ty. I always thought induction was the greater danger with our steel cables, just never understood the particulars. Being mechanical, I don't have as much understanding for that KillerWart stuff.

What would you surmise is going on with lines shocking you in threatening weather? I've always thought that was generated static, but it's kind've contradictory when humidity is high and moisture is imminent. Or is it another inductance situation caused by crossing the lines of force between the ground and the air?

Just curious.

The idea of two single conductors (our lines) passing thru the lines of flux surrounding a power line and producing any induced voltage that the human body could detect is not plausible. Just not enough conductors, the flux field density is low and the rate at which the lines cut the flux lines is too slow. This theory would have you getting zapped when you unroll your lines near a high voltage power line.

Secondly, the typical high voltage system 138KV (138,000 VAC ) can't jump much more than 10" in average environmental conditions. So that isn't going to be a biggie.

The biggest problem I see would be wandering around while flying and contacting the power lines. This will get ya!

Follow the AMA guidelines. Minimum of 50ft.

Oh, by the way, I believe the mandated clearance from the KV lines you mention is at least 16 ft according to OSHA. Clearances vary with voltage, but personnel clearances are on the order of 6 ft below 50KV, and increase with higher voltages. This is because of the observed tendency to arc in spite of not touching. That distance is certainly not the same as the arc potential, but even at a quarter of that distance, it's much greater than you imply.

Another thing - before we continue too far down this road, are you suggesting that some CL Elite Genius has written chapter and verse, dissertation, and has been subjected to peer review on said subject ("This topic comes up often.")?

For subject lines, I tried "Power Lines", "High Tension Power Lines", and "High Voltage Power Lines", with the "and" mode checked. If you can think of another subject to try, have at it.

The CL Site in Richmond, B.C., has the circles close to a serious looking set of power lines. Close enough to make me nervous, but they have been flying there for at least a couple of decades with no problems. Maybe Chris Cox or Keith Varley could chime in with some actual dimensions? Steve

While we are on the subject, I've heard, at least third hand, about an incident where a combat ship, dragging its lines, struck a high tension line (encircled it), inducing a short that caused a transformer to explode. Apparently this happened at a Nats many years ago? I'm sure someone can relate the specifics.

I'm certainly not saying it did not happen, but I do remember my Electrical Power classes, and I also have a good idea how much (should I say how little?) energy it takes to vaporize .015" stranded steel wire.

In the power classes, Professor Donald Crosno frequently referred to "crowbarring" a power source (and the term is used, even for small power supplies). One day someone asked what would REALLY happen if we threw a crowbar across the power lines, and without raising an eyebrow, he calmly answered "it would clear the fault."

Extraordinary things occur, certainly, but it seems to me that a large high tension power line would surely "clear the fault" for a .015" steel wire short. And think of how much energy would be required to heat up a transformer enough to explode. More likely, somehow the transformer developed some massive internal short, which was the REAL crowbar..

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"The only relevant test of the validity of a hypothesis is comparison of prediction with experience." -Milton Friedman

I personally witnessed just such an accident, except the transformer didn't blow up, but the power line blew in half - we all saw the line fall. Took out half the power on that side of the Navy Base - including the Navy Exchange, Cafeteria, and Bowling Alley. The base had about 20,000 personnel at the time, so I don't think it was a small incident.

See my story in the first thong thread - all true:
http://www.clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=show_thread&om=11629&forum=DCForumID1&omm=15&viewmode=threaded

If your talking about getting shocked while flying during an impending thunderstorm, think about your statement regarding static and humidity. Given your theory, it should never lightning during a thunderstorm (oxymoron??). It is indeed static causing the problem.

>
>Oh, by the way, I believe the mandated clearance from the KV
>lines you mention is at least 16 ft according to OSHA.
>Clearances vary with voltage, but personnel clearances are
>on the order of 6 ft below 50KV, and increase with higher
>voltages. This is because of the observed tendency to arc
>in spite of not touching. That distance is certainly not
>the same as the arc potential, but even at a quarter of that
>distance, it's much greater than you imply.

I don't see how you can refute known facts. I have firsthand experience designing high voltage dielectric testing equipment. A most shocking endeavor.

>
>Another thing - before we continue too far down this road,
>are you suggesting that some CL Elite Genius has written
>chapter and verse, dissertation, and has been subjected to
>peer review on said subject ("This topic comes up often.")?

I would suggest that some person with knowledge of the subject of high voltage power transmission lines was consulted prior to the AMA recommending a 50ft min. safety zone. I'm sure the lawyers wouldn't allow a SWAG for an issue with these potential legal liabilities.

Interesting reading re: power transmission lines http://www.calpoly.edu/~dhafemei/background2.html
Note when you read this that the average magnetic field strength below a power line is about 1/5 that of the earth's magnetic field strength.

By the way Tom, what got you so energized (pun intended)? I wasn't attacking anyone nor were my comments directed at any individual. Just trying to sort out fact from fiction.

I wasn't so particularly energized, really - at least not by you on this thread (hint, hint). It's just that I'm leery after the bellcrank issue, and my rhetoric gets carried away sometimes.

As far as static during humid conditions, it does not occur on ground level. Static electricity becomes an issue in human environments when relative humidities drop below 30% - that's not rainy or even pre-rainy weather. That's why I asked the question. Moisture inhibits static generation. The effect at higher altitudes that results in opposing charges high enough to develop lightning, seems not to be an explanation for what's happening at ground level (or something around a few dozen feet). I would like an explanation, but I don't think that's it. Perhaps it's the potential target offered by the point discharge geometry of the small cables? Maybe what I'm trying to say is that it can't be static from friction of the lines moving through the air.

Also, please see the literature I referenced in one of the other posts. The clearances recommended by OSHA and various lineman standards are distances that vary directly with voltage levels. It's not a question of touch. (Crane clearances are much more concerned with touching, but inductance is still a concern.) Perhaps dielectrics are dealing with static charges, but not power lines. The article I referenced makes a direct statement that inductance is causing an electric current to flow in equipment no closer than 13 feet. Admittedly, it was a much higher KV than what you referenced, but 13 feet is another whole magnitude.

I have also seen training exercises and lineman standards that deal with clearances in over ten feet - specifically because arcing may occur. Maybe those instances were very large KV's, but I'm not sure they have much bigger - in regular use, anyway.

Your theory discounts ground strikes during a storm but they do happen. So the idea of only accumulating charges during low humidity conditions on earth is not valid during thunderstorm activity.

Edit - The only times that I've been zapped are right before a thunderstorm.. I've never had it happen in low humidity or high humidity conditions without thunderstorm conditions.

No, of course lightning strikes the ground - and anything else that might be a convenient discharge point (people?). I'm just saying that you can't rub your feet along the carpet, and develop static from friction in those conditions. So, I don't think it's friction of the lines through the air that's developing the charge. It may be that there's such a charge difference developing between the atmosphere and the ground, that the lines are picking up minute discharges since you and your plane form a ground path.

It does admit, in your referenced article, that no one knows the exact mechanism.

Thanks for your patience. I've got to go to bed.

I lost a good friend to powerlines, so it hits close to home.

This is still confusing, though. I assume that you mean Dick is right about the induction and arcing, but I keep finding contradictory material.

Here's an example of tingling felt when climbing a ladder. The gist of the story is that everyone violated the OSHA standard. Yet, the important point seems to me that a noticeable (if not harmful) current was generated at more than 13 feet away from a 230KV line. Yes, I know that a lot more metal was in play, and 230KV is a lot more than even Dick cited:

http://www.hanford.gov/lessons/sitell/ll99/199955.htm

However, the question remains in my mind about the circumstance of steel cables in motion. The movement means that a significant amount of field is crossed. In the case above, everything was stationary, and nothing was probably as good a conductor as our steel cables. There seems no reason to justify a moving distance vs. voltage safety standard if actual touching is the issue.

If you were dealing with the field of a strong magnet or just a coil of wire carrying a constant direct current, you'd have to physically move a conductor through the field to induce a current in it.

However, keep in mind that that there are three phases of alternating current, generating magnetic fields which are peaking and collapsing 60 times a second, which will induce current in a conductor which is physically fixed. After all, that's how a transformer works, right?

I don't think motion effects are really significant for control lines, ladders, or other conductors near conventional HVAC power lines.

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"It isn't a calamity to die with dreams unfulfilled, but it is a calamity not to dream." -Benjamin E. Mays

Better watch those acronyms, Larry. HVAC is Heating, Ventilating and Air Conditioning.

You're right about the motion. I was thinking that might have some additional effect, but it's certainly trivial in comparison to the 60 Hz already present in the power lines.

What about the straight inductance just from conductor and voltage effects (and 60Hz AC) and what of the arcing distances?

The point of 60 hertz (cycle) is also valid. You can induce current by either moving the conductor in a fixed field (DC voltage) or move the field and keep the conductor stationary(AC). So my point earlier was that the collapsing field around the power lines would induce a current in your lines just by their being in proximity to the lines. Adding 50 - 60 mph to the speed of the lines isn't even of consequence in the big picture.

Edit - Tom, I see we were both posting at the same time. Read this regarding high voltage safety. It's a Gov. document page 14 has what you want. http://www.wapa.gov/rm/psmmCHAP-14.pdf

Well this certainly nails it as far as arc length, as you say. However, is it possible that the document concerns working on switchgear, and not line work? As said before, the OSHA clearances are way over these. Might that be because line work involves a bucket or heavy steel cage and the proximity of that metal makes induction more important? Still confused because OSHA is in feet, but arc length is in inches.

When I was a kid flying in a school yard my friend Ken let this airplane go on purpose. The combat wing flew about a 1/2 mile and hit power lines. It got tangled up and was flying round and around with the handle in up on the wires. We had followed it. when we got there the plane had just hit the curb. Ken reached up to pull the lines down. when he touched the we heard a big POP and he said OOOOH - HOT! The wires had shorted out and burnt off. There was a power man down the street and he came running over asking Ken if he was alright. He was luckily. What a moron!

This is one question whose answers should never deal with Minimum Margins. That's on a par with playing chicken with nitro glycerine!

We have some legitimate expert answers here. Should we listen to them?
You bet your life!

Well I don't think anyone is suggesting that we argue this point so that we can get as close as possible to power lines.

I have 2 questions I'm trying to understand:

1. There seems to be some difference of opinion of whether 50 ft or 300 ft CL clearance is the more appropriate standard for the AMA.
2. I would like an explanation for why flying CL in overcast, near-rainy weather causes shocks, when it seems that is the point of least static electricity generation.

One guy in our area made a serious attempt to use the Kevlar lines. He gave up and donated them to me. Actually just a trick to make me wreck one of my planes.

They work great as a "stooge" release, still use them today.

I was just going to give up but I guess I understand where Brett comes from sometimes.

I would say that it would contradict the laws of physics.

Let's consider this. The voltage induced by AC power lines in the flying lines will start at zero and increase to some peak value (too small to feel…. But you don’t have to buy this right now) and then decrease to zero. Just like a transformer right? Its’ AC voltage .

Static charges usually accumulate on the surface of an object and will only dissipate when a path is provided for them to return to whence they came. If no path is provided then the charge will continue to increase until it reaches some potential (voltage) adequate to jump a gap creating its’ own path (a spark).

So lets assume its’ induced voltage and we put the grounding line from our flying lines to our wrist as described in another post. Now our body is in the circuit from the flying lines to the ground and our body completes a circuit for current flow. So then wouldn’t it seem plausible that each time the voltage in the power lines goes up and down and the current goes up and down and the magnetic flux lines move back and forth cutting our flying lines and the induced voltage goes up and down it produces a current that passes through our body. If its’ as large as you maintain then WE SHOULD LIGHT UP LIKE A LIGHT BULB ALL THE TIME . This is not the type of jolt people are describing in their posts.

So if I assume it to be static jolts then same grounding line will keep the static charge from accumulating on the lines by allowing it to be dissipated through our body to ground before the voltage reaches a level that we can feel.

I stand my “espoused theory”.

My closing and final thoughts .

1. Stay away from power ines (even the ones to your house) while flying. AMA say 50ft.....prudent people would double that.

2. The danger of flying near power lines is accidental contact. This can lead to injury or death. If you wander while flying, increase your safety zone.

3. Any jolts you feel while flying are probably static discharges. (Induce voltages are typically in the magnitude of less than .001 volts.) Static discharge straps connected to the lines and you will help this problem. I think this can be a dangerous practice. The static generating capabilities can be magnified by an approaching storm. Lightning can and does strike well in advance of the storm. Treat the jolts as an early warning system. Pack it up, go home and live to fly another day.

Just MHO

Under fair-weather conditions, the fair-weather electric field is directed vertically and runs about 100 volts/meter (V/m), with the ground negatively charged and the "sky" positively charged). Our lines are about 20 m long, so they span a 2000 V potential, which is insufficient for any noticeable effect (note: you can't measure this with any volt meters you might have -- the mesurement requires very specialized equipment called field mills).

Under a thunderstorm, however, things get wild. Typically, near the surface the field is reversed and the field strength is about 50,000 V/m. This isn't much exceeded because everything (EVERYTHING: trees, grass, people, hair, control lines) begins to exhibit corona discharge, which prevents the electric field from intensifying. Now your lines can conceiveably span as much as 1,000,000 V at the top of a wing-over and *will* exhibit corona discharge. This corona current *can* be neasured with a sensitive ammeter (I've measured 50-100 microAmperes at my house from my ham radio antennas). Corona discharge *will* generate a voltage potential between you and the lines because an electric current is now acting to move electric charge across space by the corona process. Thus, you and your lines may develop a significant voltage difference compared to the ground. If you happen to hold the handle lightly, without contact with the lines -- or have a handle that insulates you from the lines -- the potential can become large enough to jump the gap and generate a shock. If you're in contact with the lines all the time (assume a metal handle) you could get a shock through your feet.

It is extremely dangerous to play with thunderstorms: Lightning strikes are the second largest weather killer (floods are number 1). And, only about 30% of the peole struck are killed outright. The rest usually suffer some permanent disability and almost all exhibit permanently altered mental states. Use the "30-30" lightning safety rule: When you see lightning, count the time until you hear thunder. If this time is 30 seconds or less, seek proper shelter. If you can't see the lightning, just hearing the thunder is a good back-up rule. Wait 30 minutes or more after hearing the last thunder before leaving shelter.

What about big arcs? If our lines actually contact a high voltage, low-impedance source (big voltage, lots of available current), they will immediately and explosively vaporize. But, they will leave an ionized trail that will sustain the arc until the current is otherwise interrupted. And these arcs can become *huge*. Check out <http://www.wiseguysynth.com/larry/day.htm> for an example. Once the arc is struck, it can stretch a long, long way before it extinguishes, even with relatively "low" voltages.

What about true fair-weather "bites?" The act of dragging an object through the air can also lead to physical charge separation (like rubbing a cat with a peice of wool), which leads to voltage build-ups and arcs (irrtating the cat because they blame it on you). So, moving your airplane and lines through the air is enough to build up significant voltages on the airplane-line system by physical cahrge separation. Check out high-performance aircraft: they often have "static wicks," which are used to drain off static charge in flight. This is why aircraft are physically grounded with a clip and a wire prior to fueling operations. There is a remote possibility that the airplane will retain a static charge that could ignite fuel vapors. If it hadn't happened at least once in the past, you can bet it wouldn't be a standard procedure.

Sorry to be so long-winded about this, but as someone who has "chased" this stuff, and played with high-powered ham radio gear, I've learned a very heathy respect for lightning as well as the realtively puny voltages we can generate. The last thing I want to see is someone hurt or killed because of a lack of understanding.

Kim Elmore (National Severe Storms Laboratory)

As an engineer, I am reluctant to disprove with calculations effects that I can feel, or effects that others can report. Unlike some that will go unmentioned, I would rather assume that there's something I just haven't considered, or that there are other variables that are beyond my capability to define.

An engineer is merely a scientist with thumbs..

((I'm also an engineer - hell, I thought I was going to get to drive a train, but NOOOOOOO!))

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"Is that your final answer?" -Regis Philbin

Ahh... and I like some others, prefer to explore the possibilities without ignoring physical laws. I don't ascribe to dancing around the fire and reading the bones for my answers nor do urban legends mean much to me. Our possible causes were well defined (static or induced voltage). Without belaboring the point, I think I made a valid point (and would be happy to share my calculations and assumptions with anyone interested) that you can't induce a voltage in our lines under our flying conditions that the human body can detect. That leaves ionization or static. I can't think of any other processes in our flying environment that would generate voltages in our lines. I'm open for additional suggestions.

If we are flashing our credentials.... I have a B.S. in Physics and have held various process, design, plant engineering positions in my career.

You seem to enjoy dogging me and usually have comments that are a attempts to discredit me or my ideas. I'll make you a deal. Get versed in the subject matter and terminology and we can have some meaningful exchanges. I kept it simple just for you.

No one was dogging you. I am sorry you interpreted my professed humbleness as an excuse to "flash credentials." Mine means nothing in this context, and I certainly wasn't specific about degrees or positions - just describing a way of looking at things.

Perhaps a famous joke can illustrate:

An Engineer and Scientist were put in a room some distance away from a beautiful girl. An announcement was made that the Scientist and Engineer could try to cut their distance to the girl in half at each sound of a bell. Upon reaching the girl, she would grant their heart's desire (trying to keep it clean). Upon striking the first bell, the Engineer lunged forward as fast as he could at half the distance, panting in preparation for the next step.

The Scientist, meanwhile, stood in his original position and never moved. The experiment controller asked him why? "Because cutting the distance in half each time means that I will never reach the girl. I will always have another half distance remaining. So, there's no point in trying." The Engineer said instead, "That may be, but I think I can get it close enough to work."

No dogging intended - at least in seriousness.

There are 3 mechanisms electrical energy can get into control lines and hurt you.

1) Conduction - You get physically ( touch it or start and arc) close enough to establish a current path from the conductor though your body. This is the most dangerous.

2) Electromagnetic Induction - A large magnetic field with a conductor cutting through it. Or a stationary conductor with a changing magnetic field. In our case the conductor is the control lines, and the field is generated by the power lines. The strengths of the magnetic fields, and the speeds of the conductor ( control lines) are too low for this to be a large factor.

3) Electrostatic effects. This is the rubbing of the feet on the carpet, or placing a di elecrtic object in a strong elecrtic field. In out case it is rubbing the control lines the charged air molecules. The air molecules are charge from the Electric (potential difference) field near a thunderstorm. In this case the speed of our airplanes has an effect. Dry air holds more charge, and an approaching thunderstorm carries a great deal of charge in its clouds. If this static charge gets too high, it will arc through your body producing the painful tingling sensation we all feel. I have attempted to calculate how much charge can be built up, but am not getting anywhere. Can be fatal near bad weather.

I have a few questions from above.
1) What is the strength of the electric field near a power line?
2) Does the Electric field near a power line cause increased electrostatic (capacitive coupling) effects?

One other observation about electrostatics. The field is much higher near a sharp point. That is why lightening rods are sharp, and why uoy are told to get low during an elecrtical storm. An erect human can change the magnitude of the electric field 10x or so from open field measurements. What about a model airplane at the end of a 60 foot conductor? If would be much larger than 10x, more like 100x.

Just a question as to why electrostatic discharges (shocks and tingles) could be worse near power distrbution towers.

Dave Siegler

About teh eletrostatic coupling, I'll guess it's minimal..Our control systems probably have only a few picofarads of capacitance (but much more indiuctance -- on the order of microhenries). The capacitive coupling effects are miniscule, at best. And, the fact that the electric field is AC minimizes any charge build-up. Most electric fields around thunderstorms switch polarities at periods of maybe 20 min to an hour and so are effectively DC, not AC.

The biggest danger from power lines is physical contact (as has been noted by others). After that, all bets -- especially on survival -- are off.

Kim Elmore

I was just attempting to get a number to see if there was enough electrostatic coupling be anything other than painful.

Surely if you fly in a thunderstorm and are part of the discharge path, it is not good.

The practice of discharging the flying lines through your body never set well with me, at some level it is dangerous. The static strap I use to work on static sensitive equipment has a large (1Mohm) impedance in it to protect me from contact with a live circuit. I wondered how much charge can be built up on the wires.

How large is the E field in a thunderstorm and is DC? I am assuming that the data you have is for open field measurements. I'd like to try and swag how much charge can be built up on the lines. Now I just have to find my copy of JD Jackson.

Dave Siegler

>I think somewhere further up, someone provided a guesstimate
>about the feild strength near power lines and it's pretty
>small. Something like 1/5 of the magenetic field strength
>of the Earth's magnetic field.
>
>About teh eletrostatic coupling, I'll guess it's
>minimal..Our control systems probably have only a few
>picofarads of capacitance (but much more indiuctance -- on
>the order of microhenries). The capacitive coupling effects
>are miniscule, at best. And, the fact that the electric
>field is AC minimizes any charge build-up. Most electric
>fields around thunderstorms switch polarities at periods of
>maybe 20 min to an hour and so are effectively DC, not AC.
>
>The biggest danger from power lines is physical contact (as
>has been noted by others). After that, all bets --
>especially on survival -- are off.
>
>Kim Elmore

http://www.calpoly.edu/~dhafemei/background2.html

There are numbers for both E and B fields. You can see how small they are even at close proximity.

Anywhere below cloud base, the upper limit is around 50 kV/m and more typical numbers are probably 1/3 to 1/2 that, so I'd guess 15-25 kV/m. In the cloud itself, magnitudes reach several hundred kV/m (DC), but our instruments tend to saturate at between 200 and 300 kV/m. Keep in mind that the air breaks down, and the Big Spark starts, at around 750 kV/m to 1 MV/m. Also, just for the sake of numbers, peak currents in a cloud-to-ground strike are about 50 kA.

I have no clue about how to compute how much charge might be depoisted on one of our models due to big E-fields. I think we'd have to know the capacitance and then integrate the corona current over time to find the charge deposited. Once we know that, we know the voltage. But I have no feel about what the relevant numbers might be.

I also don't have the foggiest idea about how to compute how much charge one of our models might accumulate in a flight due to mechanical charge separation or what might limit that amount. I'm afraid you're on your own!

Kim Elmore

It might be possible to get some handle (sorry, no pun intended) with a static field meter. I do Electrostatic Discharge (ESD) control in our lab, and there are two instruments which could help. One measures the electric field present near objects; the other can measure the potential due to static charge on an object relative to ground (personal charge monitor). The latter would tell you what you really want to know: what is the potential (in volts) of the airplane relative to ground due to frictional charging while moving through the air (triboelectricity). The only problem is how to make the measurement. You need to charge up the object (airplane) and then touch the test plate on the charge monitor to read the potential in volts. Ah-ha! Connect a wire from the flying lines to the meter at the handle and get a reading in flight. The only problem is that the unit needs a ground, which would literally be a pipe driven into the earth, and the ground wire will want to twist up as you turn in circles. Need to make a commutator arrangement to eliminate this...

Another Ah-ha! Make sure that the pilot is connected to the aircraft via the handle and lines (wire from lines to palm grip). Whenever the pilot touches the test plate on the charge status meter, it will read his potential relative to ground. This puts the capacitance of the pilot into the circuit too, but the potential measured is still relevant to the problem.

Andy

My undergrad Fields class or my E/M design experience does not give me the tools to calculate effectes due to triboelectricity. I have tried to create a simple model and tried to do a first order calculation, but have been unsucessful. Just bored at work.

The ESD meters I have used are real slow, and I don't think they would give an accurate reading for a momentary touch. I am not interested in doing this test in the advancement of science, it might be painful.

On humid days the charge bleeds off the handle and no shocks develop. Grounding the lines by touching them keeps the charge from building up also- either touch a finger to the lines or wrap bare wire around the handle .

Bigiron

Might a fitting condensation of the previous sound, fury and green cheese be: 1) Wires is dangerous! Don't wave metal ladders or C/L wires at them,'cause they will BITE you! 2) See how close you can come to those wires, and while you are at it, pee on an electric fence. Get that last (in more ways than one) flight in, while you watch the thundrstorm approach. You are guaranteed stimulating results! 3)A life, maybe yours, is a wonderful thing--don't waste it in foolhardy pursuits. Voltage and amperage don't care if you are a Really Good Person, sunday school teacher, a marvelous husband and father, or Man of the Year. That just means your funeral will be well-attended.

The AMA says 16 feet?? No doubt they have good information, but for me, 100 feet may not be good enough--much more, if I can get it, and don't fly if things don't suit you, regardless of what the "experts" may say.