Corona Discharge

Why does this rod exist? please give some context to its presence. What is is supposed to do -

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dear thats a lightning arrester, it connects with downward lightning leader and dissipiates it to ground

All ground dissipates to ground...that's why they call it "ground".

You won't be able to build a charge in anything that's connected to "ground", regardless of how blunt the tip is.

The purpose of the rod in the original post is still unknown.

No. It doesn't matter if the tip of the rod is pointy or blunt; you have it connected to ground, therefore, any charge will go to ground.

"... since rod is connected to ground it will acquire positive charge." - what gives you that idea?

Your copper rod is not made capable of storing a charge by rounding the edges. The rod is capable of storing a charge because this conductor it is part of a capacitor created with another conductor and the insulation between them. Now by rounding the edge you have very slightly reduced this tiny capacitance but you've increased the total charge that reside on this conductor without ionizing the insulator with a corona discharge.

Yes, it will hold 157 cc's of electrical charge.

"Yes, it will hold 157 cc's of electrical charge."

Come on. He might believe that.

Actually . . . . since the end is blunt (assumption of a spherical shape) we really only store

CV (charge volume) = (49 + 2/3) * = 156 cc's of charge

Close enough!

Funny, I seem to remember that a static charge gets placed on the surface of a conductor, not in the volume.

True, but don't confuse us with the facts. It's more fun this way.

Yeah, we could get lost in world of dielectric constants, e-field strengths and Guass' Law

Wheeeeeeeeee !!!!

that depends on the type of current. If it is dc current , it will fellow through the core . but if it is a.c of high frequency it will fellow through the surface of the conductor due to skin effect

Funny - I could've sworn #29 stated "static charge".

There's a subtle but to this discussion very critical difference between static charge and current.

How will it 'fellow' it?

The only way to have a charge accumulated on the skin is when you coat it with a decent isolating polymer. Your isolation must be about 10 with 13-14 zeros behind. In this case it will be able to maintain its "acquired" charge for a while, because the cover will discharge too. (sort of condom) And it you turn it upside down, that the isolation connects to the ground, you will be able to put that charge on the rod.

I did plenty of experiments with this in our former laboratorium for electrostatic charges. (SCM - Kivar- Scott)

It accumulates at sharp points,in building's edges,corners etc.That's why in lightning protection,they protect sharp corners/edges.

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Nobody wants to know.

That's not a rod. It's a bar.

Or a pole. Or maybe a perch.

I once caught a perch on a bamboo pole.

GA m8!

If it is a bar and it is in the USA it will be around 14.5psi.

If it is a bar and it is in the USA it will be;

No wonder I get confused on this site.

If for some obscure reason you need to lessen corona discharge, I was taught in school boy physics a curved surface was better. It doesn't propagate the electron wind.

The reason HV terminations have the globe mounted on them.

Look up Van der Graaff generators and the electron wind. It's fun with 500,000V to play with. I could light a match (Lucifer's for the Americans) at about 2½inches, I got one hell of a belt in the process.

Your squared off conductor could only be made worse by making the end pointed. Any sharp angle will form an intense corona field.

Corona discharge emits noise which can be heard near MV/HV/EHV line poles/towers, especially in the night.

Corona can be heard and usually tasted at any time of the day from any power line, normally above 33kV. Corona is a discharging of electrons from a damage conductor surface, i.e a break in the strands, and gouge mark, a scratch, depending on voltage as to the severity of the discharge. Discharge creates ozone gas and it has a distinct taste and smell.

The reason one notices discharge at night is due to dampness in the air making the air, (surrounding the conductor as an insulator), more conductive. Rain, snow, mist, dust will assist discharge as the air passes over any livened bare conductor.

A corona ring controls the discharge at connection points, on outdoor HT equipment, at insulator connections on OHL, and sub stations, mostly . Discharge can also be heard on a radios and cell phones and seen on TV's.

A 500mm x 20mm copper bar buried in the ground with a insulated wire attached 'may' collect stray earth currents from nearby cables, existing earth mats, proximity to a sub station, however, it will never reach a point that it can produce corona unless a very direct lighting bolt hits it and then one will have a hole, glazed sand and rocks and no copper bar.

Where will be the other end of 500x20mm copper bar connected to?.

That would make it a busbar instead. One hopes it is correctly sized...

It can be connected to anything as long as you know the voltages and currents being received. I think you need to look at

http://www.youtube.com/watch?v=OIaz0TzISCw

or look up Tesla Generators on the net. Mr. Tesla designed many free electrical systems and I think this is what you are trying to do.

In the Youtube,they say below Pyramids there is aquifer,what is the role played by it in conducting electricity..Does it mean lightning will be attracted by a body of water?.

Pyramid: sandstone. Surrounding foundation medium: sand, rock. Both good insulators, very high remittances. So the aquifer is surrounded by insulation, it will not attract lightning and being below ground will enhance the reduction of it attracting lightning. It is only possible if there is a direct connection from the top of the pyramids to the water below.

The oceans, seas, the lightning will strike the water surface. It is the only and best earth out there.
Rivers: the surrounding trees on the river banks will attract the strike before the water surface attracts the strike.

Lakes: the water, depending where the lightning storm is taking place. If near the edges of the lake, trees and surrounding buildings will take the strikes before the water takes it.
Out in the middle of a lake, the water. If there is a small boat on the lake then the chances are the boat will take the strike.

It all depends on streamers, upwards from the ground, and which has the least resistant path to travel to the strike zone. e.g.. Two trees each side of you. You in the middle, the tallest tree has the best chance of taking the strike, but both trees and your head will produce streamers.
When struck ones has entry holes in ones feet, hole in ones head, in at the feet, (heels, ankles normally), out on the head. And lightning cooks your insides faster than a microwave oven, (vital organs suffer most, as they are highest in water content).

The only thing to attract lightning to a pyramid is the Coke machine, the call box or the lightning conductor at the top, or you if you manage or let you climb one

'....When struck ones has entry holes in ones feet, hole in ones head, in at the feet, (heels, ankles normally), out on the head. And lightning cooks your insides faster than a microwave oven, (vital organs suffer most, as they are highest in water content).....'

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Two things bother me with this statement:

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First, why in at the ankles and out at the head? I realize streamers reach up, but they are quite minor compared to the downward flow of electrons once a complete path is formed. Seems like it would be in at the head and out at the feet, since the ground is typically positive and electrons and not ions are likely to be predominant.

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Second, what is this about the vital organs having higher water content? The lungs are filled with air, the heart is fairly dense muscle, I don't think the skin, or the central nervous system or lymphatic system is particularly high in water content. The bladder seems like it would be high in water content, and the the spleen as well. What are the vital organs that have higher water content than these arguably non-vital organs?

Really?

https://www.google.co.uk/search?q=people+struck+by+lightning&client=firefox-a&rls=org.mozilla:en-GB:official&source=lnms&tbm=isch&sa=X&ei=9JpzUsGaE8eVhQfl74DwAg&sqi=2&ved=0CAcQ_AUoAQ&biw=893&bih=524&dpr=0.9

on ground ....

thaaaaa

To where is the insulated wire connected?.

I agree with you.

Doesn't the squared off end actually make a sharp change of direction between the shaft side and the flat end, that could still possibly promote corona discharge? (In a circle?)

Whereas a properly rounded end will not promote discharge anywhere near as much....

What is your opinion?

To minimize corona discharge, the tip of the rod/bar needs to be shaped into a hemisphere.

The self-capacitance of this bar is very small and the amount of charge (and energy) you can theoretically store will also be very small.

Suggested reading...
Self-capacitance

If there is a negatively charged cloud above, it will repel the electrons in the copper bar into the earth causing it to become positively charged. The bar is now one plate of a charged capacitor consisting of the bar, the cloud, and the air as the dielectric.

In my opinion;

Blunting the rod will reduce corona discharge but will not inhibit/prevent it entirely.

The higher the magnitude of charge/voltage induced into/onto the rod, the higher corona activity will be present throughout the length of the conductor/rod at random intervals.

The quantity of electrons discharged/exchanged at any point along the length of the rod will vary depending on the soil condition, soil conductivity, and the amount of rod surface corrosion at that point.

Assuming that the ground will aquire a positive charge is also flawed as in many instances the ground charge is negative as evidenced by lightning originating from the earth's surface and traveling up to the cloud(s).

Can it store a charge? Possible but not probable.

1. The surface area of the rod would have to develop a consistent skin/coating of copper oxide on the outside surface creating a capacitor or battery affect between the surrounding soil and the inner rod.

2. The electrical activity static or induced in the ground would have to become quite elevated for the storage to be significant.

3. There would have to be a high difference of potential created between the conductor and the ground surface or surrounding atmosphere which in most cases would be due to static charge created by a moving medium (person, machine, air/wind).

http://electricalnotes.wordpress.com/2011/03/23/what-is-corona-effect/

Very good explanation of corona. As stated previously, a high voltage is required and corona could not possibly occur with a copper rod/bar in the ground as it would only be a receiver of stray currents and not producing voltages or currents.

...which makes it a lightning conductor [#1↑]. Ta-daaaaaa!

In fact, not. An earth mat in a sub station is not a lightning conductor, the structures are the conductors and the mat an equal spread for the dispersion for the voltage and current in the strike.

A tree, building, person, giraffe, is the conductor.

Wrong! Well maybe.

It depends on how one defines the term conducting lightning. If one chooses to consider conducting lightning as only the visible strikes that cause permanent damage then your comment has some validity. However as Ben Franklin demonstrated with his Lightning Detector Bells, current flow from lightning happens without catastrophic damage occurring. Additionally when lightning strikes happen, even cloud to cloud, an electromagnetic pulse (EMP) radiates from the bolt in all directions and induces coupled current in many loops. These lightning induced currents are certainly orders of magnitude smaller than the current of the bolt itself but this is still conduction from lightning.

If something conducts a lightning strike, it conducts. Lightning strikes do not always leave visible damage. Perhaps you should define conducting for me. If lightning is transfered through a cloud, the water vapour of the cloud, (as we know it, actually conducted and electrical charge). And no damage.

If it does not conduct, it is an insulator. If it partially conducts it is a semi conductor.

I should have clarified something important, Air has a dielectric constant. However, moving air, temperatures, humidity, weather conditions all change the electrical resistance of air and it is not uniform in resistance. Rain, snow, dust, wind changes the electrical characteristic of air and this affects lightning and corona from power lines and equipment at elevated voltages operating in air insulated conditions.

Wow. You know the buzz words but you do not understand their meaning.

Everything has a dielectric constant. This is a physical property of our universe. The dielectric constant of air is very close to a vacuum. Water has a high dielectric constant due to the dipole moment of the molecule.

Another critical physical property of our universe is the dielectric strength of things. Air has less of a dielectric strength than a vacuum. Pure distilled water has a higher dielectric strength than a vacuum. Now droplets of water (cloud) will frequently contain ionic impurities (salt) that will make random localized paths with a significantly lower dielectric strength.

I should do, it is my job, So what did you not understand? Air has a constant! Moving air has a change in resistance due to weather. You did not know that air changes with altitude? The constant is measured at sea level and it is not the same at 6000ft, but is is taken as a constant for design. water booils at 100 degrees C at sea evel and bolis at 93.7 degrees C at 6000ft, but yes we shall take the constant to be 100 degrees C.

There you go mixing parameters again. Did you even look at the links I provided.

The dielectric constant (more accurately the relative permittivity) of a material effects the capacitance of a topology not the resistance of that topology. The dielectric strength of a material effects the breakdown voltage of a topology, not the resistance. A third parameter expressed as either resistivity or conductivity determines the resistance of a topology. Now moving air (aka wind) will carry ions suspended in air but it does not change the resistivity of air.

As for your comment that air will be different at 6000 feet you are correct. The pressure will now be a nominal 11.777 psi instead of 14.696 psi. However the relative permittivity will not significantly change. If it did change then devices with air gap trim capacitors would have to be readjusted when delivered to Denver Colorado.

I assure you that the poor OP has been totally and completly lost since after his brilliant statement #4.

All this is wasted on them and is mostly wasted on the rest of us as well.

It doesn't really matter.

I think this may be of value and you may find the equipment is in fact adjusted for the elevation.

http://www.neiengineering.com/technical-publications/high-altitude-considerations-of-electrical-power-systems-and-components/

Abstract: The design and application of electrical systems at elevations in excess of 1000m (3000ft) requires knowledge of the effects of atmospheric conditions on each particular component. Failure to understand adequately and include the effects of high altitude in the design and application of the equipment may result in its poor performance, premature aging, and/or failure. The relationship of relative air density and altitude is discussed, followed by the effects of altitude on electric power system components. Along with the discussion of the effects of high altitude on each component are suggestions or solutions to the high-altitude problem. Although the subject deals with high-altitude applications of equipment, the performance of equipment from sea level to 1000m may be affected by the relative air density. Since the relative air density decreases at a rate of approximately one percent per 100m above sea level, the operation of any piece of equipment which is dependent on the air density will be different at 3300 ft compared to sea level. This subject is discussed so that independent conclusions may be drawn.

If you bother to read your own proffered article you will see that the paragraph on page one just prior to figure one states: "Therefore a seemingly good analogy is that if air is a good insulator and vacuum is even better then the thinner the air the better the insulator. The fallacy to this is easily shown in Fig. 1 by the relative dielectric strength of air as a function of pressure." Yes, that's right. This article discusses the dielectric strength and not the dielectric constant. These are different attributes. The change in the dielectric strength of air will also effect the interruption of large circuit breakers. Small voltage (<600V) circuit breakers are rated up to 2000m (about 6500 ft) so Denver households should not worry. I do find the discussion of hydrogen production from batteries as an unexpected risk at high elevations an interesting insight but this has nothing to do with any electrical property.

The dielectric constant that effects the value of capacitance does not change significantly with pressure. There is a section in here about shunt power capacitors but the dielectric strength of the bushings is the concern.

Redfred. I rest my case.

Yep, you know the buzz words but you do not understand what they mean.

It is clear we are talking cross purposes. However, in returning to the original question, copper bar, buried, sharp point or rounded, corona. If it was possible to store energy on a copper bar/rod, buried in the ground, they would not dig out copper mines. They would simply install a wire/cable and tap the energy resource into a sub station.

'....tree, building, person, giraffe...'

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Oh no! First it was man-bear-pig. Now tree-building-person-giraffe?!? Has anyone mentioned this to Al Gore?

I think you should understand lightning strikes and how it works, and where streamer emerge from. This may help you understand why golfers get struck by lightning, why trees blow up and wood OH line poles, why taller animals are killed by lightning in open spaces and why they actually put lightning spikes on church steeples, and oddest of all, why thatched roof houses have lightning spikes surrounding the house.

May be you venture near a sub station and look at the perimeter gantries and understand why there is a 45 degree coverage from the taller structures, over the entire sub station. I am almost certain if you don't know this, Al Gore does not know it either. But perhaps you should take it up with him.

Perhaps if you read the standard it may help you :

New International Standard for Lightning Protection,

IEC 62305, and related documents.

Easy to talk on the net and offer critique when its not quite your field, but learning is a hardship for some. I know my discipline, I don't know yours!

While you learn about lighting on earth, look up the below and be amazed, You might just teach Al Gore something interesting. Common knowledge to some of us, these phenomenons.

Mysterious Lightning 'Sprites' Caught in High-Speed, 3D Video

Enjoy learning, I shall welcome your comment!

http://science1.nasa.gov/science-news/science-at-nasa/1999/essd18jun99_1/

A NASA site which will help you gain some basics of what can happen to a human body with a lightning strike. What I have provide is generalities, and not every lightning strikes kills a person, most do but not all.

And as for those still sceptical: http://www.bbc.co.uk/news/magazine-11734228

I assisted in an investigation while in SA about 2 giraffe struck by lightning, while standing near an 11kV overhead wood pole line. One male directly struck, the female standing next to the male dies to due proximity to the male, Two walking lightning conductors.

Ripley's quote: believe it or not!!!! Keep those eyes wide shut.

Come on. Learn to recognize when someone is just having a little fun (in this case with a South Park reference).

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Just because I joke around doesn't mean I am unfamiliar with even the more esoteric aspects of the subject at hand. I'm familiar with red sprites, and also blue jets, elves and fairies... as whimsical as they sound.

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I also can tell you from being enlisted to help bury numbers of lightning struck cattle, that often it isn't just the taller animals that are killed.

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I also have a solid basic understanding of lightning protection and the theory behind it.

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What I don't understand is the condescension with which you rattle of a list of rather rudimentary phenomena/observation related to the subject.

Condescension shouldn't come from somebody that has difficulty telling the difference between the words "constant" and "strength". Then again condescension does go hand in hand with difficulty admitting a mistake. Bazinga.

I apologise, I typed in English and used punctuation.

No hassle having the 'urine' taken at all, Just read the paragraph again this time, utilise the punctuation, full stops (.), and comas (,). They are used for specific reasons. I assumed you knew how to work with them. My mistake. Apology above.

As the distance between legs of animals are big they get more step voltage than humans at the same location.

Somebody tell me again why we allow anonymous posters?

Your system looks like a ground lifter. It brings the ground potential 50 cm up when the connection to the ground is firm (how is that?) You will have no corona discharge in normal operation. How do you charge your ground positive? Or is it natural? Where do you live and experience this?