Dangerous Jobs

[Rhino]

Dudes got some serious guts.

http://www.youtube.com/watch?v=uEKbMMHAwm0

[Suzie]

As long as what he is in didn't touch the ground he could hit the wire and not be electrocuted. Of course there is a risk hitting it could make him crash I suppose.

[Rhino]

That's what I meant. The rotor was very close to the wires.

[Towerpainter]

How about painting radio station towers for a living???? :thumb:

[Rhino]

Better you than me, dude! :D

[Suzie]

I keep thinking one day the squirrels are going to make just the wrong step from the tree to the wire and ZAP! :faint:

But they don't know they are playing chicken with the wires. This guy does. :lol:

They have some places where they use little trolley cars actually attached to the wires.

[ThomasMore]

Fantastic video, Rhino.

Here is a good companion piece, courtesy of glumbert (http://www.glumbert.com).

http://www.glumbert.com/media/highpower

[CountryGent]

I'll just bet that Helo pilot is a NamVet from the 1st Air Cav......Those guys had testicles the size of bowling balls. Coming into a hot LZ was a cakewalk for them bad boys.......:thumb::thumb:

[DoctorDoom]

No way in the world is that line hot. I spent too long as an industrial electrician to believe otherwise. At the voltage levels of those highlines (usually six figures), even corona discharge would be dangerous.

OTOH, the chopper pilot is well equipped in the nads department.

[ThomasMore]

Doc, did you see the Glumbert video I posted? That line looked hot to me (I don't know, it might be at reduced amperage).

[Rhino]

They work on them when they're hot. I've seen them do it. I've also seen written accounts of how they do it, and what safety precautions they have to observe.

[DoctorDoom]

That's unfathomable. However, I will research it.

[Suzie]

There are some new robots they have been testing when they powered New Orleans back up.

[DesertFox]

I seen this sorta thing on the toob about 15 years ago. Takes more guts than I got just to sit on the skid.

[ThomasMore]

Here is the source (http://www.shaftesbury.org/sk_tvsermov.asp?propertyID=83&propertyCat=4) for the Glumbert video segment, an IMAX movie called "Straight Up," produced by SK Films.

Doc, my knowledge of electricity is rudimentary at best.

I was trying to get information on corona discharge. Is my understanding correct that when the current reaches a certain threshold, the air can switch from an insulator to a conductor, causing arcing? Do high tension lines pair the current in two lines to spread the area and reduce the chance of corona discharge? (Is this also related to Hall Effect?)

One thing I am not clear on is how the three AC phases would act on a Faraday suit. Do they pose a risk of current flowing into the body, instead of consistently passing around it?

[Suzie]

I can find out ... in a couple of weeks. :lol:

[ThomasMore]

I can find out ... in a couple of weeks. :lol:

:p

[Suzie]

Well he's gone right now. :lol:

[DoctorDoom]

Doc, my knowledge of electricity is rudimentary at best.

I was trying to get information on corona discharge. Is my understanding correct that when the current reaches a certain threshold, the air can switch from an insulator to a conductor, causing arcing?

The subject of this investigation is the use of corona discharges (the portion of an electric discharge before the onset of the low-voltage, high current arc discharge) for the initiation of combustion in propulsion systems and internal combustion engines. The corona discharge is basically a plasma that is in a transient, formative phase. Energy-efficient transient plasma ignition and combustion (http://carambola.usc.edu/research/coronaignition/)

Caused by an intense electrical field, corona discharge is the ionization of nitrogen in the air. Corona events cause power loss and degrade insulation for conductors and insulators leading to flash-overs, premature failures, and outages.Powerline Corona Discharge Mapping (http://www.forestone.com/powerlinecoronadischargemapping.cfm)

St. Emo`s fire

Corona discharge is an everyday phenomenon that is also used industrially. One example is that all copiers and laser printers contain a very thin high-tension thread that charges the paper with corona. Negative ion generators that are used as air purifiers are also based on corona. Corona also develops easily around pine needles, masts and lightning rods during thunderstorms. This phenomenon is known as St. Elmo's fire.

Corona-discharge occurs around the conductors in high tension power lines under certain weather condition. You can hear this clearly as a crackling sound. It also occurs when the local electrical field around points, drops of water etc. becomes strong enough to tear electrons away from the surface or from the negative ions that are always present in the air. The free electrons increase their speed in the electronic field and release new electrons from other gas molecules. This is how an avalanche of electrons is created, in the same way as a snow slide gets started by one single snow ball. A snow slide lasts as long the hill is steep, and an electron avalanche lasts as long as the electric field is strong enough.POWER LINES MAY CLEAN AIR POLLUTION (http://www.ntnu.no/gemini/1996-04/9.html)

Here's an example.

http://www.forestone.com/images/PowerlineCorona-Figure-1.jpg

The crackling sound you hear under high-voltage power lines is caused by corona discharge.

Power lines produce an audible sound or buzz because they are producing something called a corona discharge that is interacting with the surrounding air. The corona discharge is a side-effect of the electric field the power line generates by carrying electricity. The discharge can be greater, and the buzzing louder if there is increased moisture or pollutants in the air.Why Do Power Lines Buzz? (http://atomic-molecular-optical-physics.suite101.com/article.cfm/why_do_power_lines_buzz)

In Lenox, MA, GE constructed Project EHV (http://scienceservice.si.edu/pages/040041.htm) (Extra- High Voltage) in the 1960s to experiment with transmission line voltages of a half a million volts or higher. I was in there when I worked for GE. It's not for the timid. The circuit breakers sounded like shotgun blasts when closing. Being near or under it caused tingling and hair standing on end. One way to know that it was running was to carry a fluorescent tube. If it was lit in your hand, the power was on. And corona discharges were common.

One thing to note: they're not easy to see, since much of their light radiation is in the ultraviolet. This is the reason for the cameras sold by the company in the second link. However, the buzzing/crackling and the smell of ozone (if downwind) are diagnostic.

Fair warning as summer approaches: if one is out in a thunderstorm and that crackling is heard, or a dim discharge is seen, from high points such as tree tops, it's not a good place to be. Ma Nature has found a handy spot for fireworks, and the fuse is lit.

Imagine being on the 84th-floor observation deck of the Empire State building when ...

http://img.photobucket.com/albums/v349/DocDoom777/Science/ESBLightning.jpg

Do high tension lines pair the current in two lines to spread the area and reduce the chance of corona discharge? That's the primary consideration.

Bundle conductors are used for voltages over 200 kV to avoid corona losses and audible noise. Bundle conductors consist of several conductor cables connected by non-conducting spacers. For 220 kV lines, two-conductor bundles are usually used, for 380 kV lines usually three or even four. American Electric Power[1] is building 765 kV lines using six conductors per phase in a bundle. Spacers must resist the forces due to wind, and magnetic forces during a short-circuit.Overhead powerline (http://en.wikipedia.org/wiki/Overhead_powerline)

A side-benefit is that multiple conductors allow using smaller, more easily deployed conductors for a given current level.

(Is this also related to Hall Effect?)Here's a good explanation of the Hall Effect.

The Hall effect refers to the potential difference (Hall voltage) on the opposite sides of an electrical conductor through which an electric current is flowing, created by a magnetic field applied perpendicular to the current. Edwin Hall discovered this effect in 1879.

The ratio of the voltage created to the product of the amount of current and the magnetic field divided by the element thickness is known as the Hall coefficient. It is a characteristic of the material from which the conductor is made, as its value depends on the type, number and properties of the charge carriers that constitute the current.Hall Effect (http://en.wikipedia.org/wiki/Hall_effect).

It would be a factor with bundled conductors, since the magnetic fields of parallel conductors interact in ways that a single conductor affected only by Earth's magnetic field wouldn't experience.

One thing I am not clear on is how the three AC phases would act on a Faraday suit. Do they pose a risk of current flowing into the body, instead of consistently passing around it?FARADAY SUIT

A Faraday suit is a metal jump suit with fitted gloves worn by electrical engineers to enable them to safely work on high tension power lines. The suit works on the Faraday Cage principle, that it the suit conducts the electricity, but within the conductor there is no charge, and the engineer is protected from the lethal electricity.Faraday Suit (http://www.probertencyclopaedia.com/cgi-bin/res.pl?keyword=Faraday+Suit&offset=0)

If they're close enough to more than one phase of a high-tension line that a current will flow between them, their asses are dead by definition.

High Voltage Cable Inspection (http://www.youtube.com/watch?v=9tzga6qAaBA)

After viewing that, I bow to Rhino's post #11.

BTW, that's one crazy mofo.

[Rhino]

This is called "live line" maintenance. They attach a bonding wire to the line before actually touching it. That brings the line and the maintenance man/helicopter to the same voltage potential, thus making them neutrally charged with respect to each other. That pretty much eliminates the possibility of an arc caused by differing voltage potentials. They also wear special suits to protect them from the charged air around them. It's actually kinda neat.

http://www.fortwaynereader.com/story.php?uid=260

[DoctorDoom]

Watching that arc zapping off the line while the chopper and tech are being "charged" to several hundred thousand volts is something that yours truly is more than happy to leave to someone else, TYVM.

[Rhino]

Ditto. You'd never get me to do it.

[Tazeeyore]

How about painting radio station towers for a living???? :thumb:
I don't like climbing on to a huge dozer much less a tower over 4' high. :thumb:

[ThomasMore]

In Lenox, MA, GE constructed Project EHV (http://scienceservice.si.edu/pages/040041.htm) (Extra- High Voltage) in the 1960s to experiment with transmission line voltages of a half a million volts or higher. I was in there when I worked for GE. It's not for the timid. The circuit breakers sounded like shotgun blasts when closing. Being near or under it caused tingling and hair standing on end. One way to know that it was running was to carry a fluorescent tube. If it was lit in your hand, the power was on. And corona discharges were common.

One thing to note: they're not easy to see, since much of their light radiation is in the ultraviolet. This is the reason for the cameras sold by the company in the second link. However, the buzzing/crackling and the smell of ozone (if downwind) are diagnostic.

Thanks, Doc. I read all the articles and the contained PowerPoint, too. I was confusing corona with arcing. Good explanations of corona and descriptions of its use. My old plane (Beechcraft 1900 (http://en.wikipedia.org/wiki/Beechcraft_1900)) occasionally had St. Elmo's fire on the propellers -- I only saw it once.

My first day in the simulator on my new airplane (McDonnell Douglas MD-80 (http://en.wikipedia.org/wiki/MD-80)) surprised me when I heard loud bangs as we turned systems on or off. The electrical panel is right behind the captain's seat, and large-current relays open and close less than a foot behind him.

Fair warning as summer approaches: if one is out in a thunderstorm and that crackling is heard, or a dim discharge is seen, from high points such as tree tops, it's not a good place to be. Ma Nature has found a handy spot for fireworks, and the fuse is lit.A good time to get away from any trees or poles, and curl down into a ball (on your feet, not on the ground).

I have heard of lightning "leaders" before, but I didn't know that they were the same as corona.

Imagine being on the 84th-floor observation deck of the Empire State building when ...http://img.photobucket.com/albums/v349/DocDoom777/Science/ESBLightning.jpg

I watched lightning hit the top of the John Hancock building (http://en.wikipedia.org/wiki/John_Hancock_Center) during a thunderstorm in Chicago on Halloween, 1994. It was a really eerie sight. That same storm generated freezing rain just southeast of Chicago, causing American Eagle flight 4184 (http://en.wikipedia.org/wiki/American_Eagle_Flight_4184) to crash about the same time, killing all 68 aboard.

Here's a good explanation of the Hall Effect.Thanks. My old plane, the 1900, used Hall Effect Devices to determine current. (It was unusual inasmuch as it had DC generators: airplane had cables, not wires.) I tried to make a connection between Hall Effect and corona discharge where there wasn't a direct one.

If they're close enough to more than one phase of a high-tension line that a current will flow between them, their asses are dead by definition.That makes sense.

After viewing that, I bow to Rhino's post #11.

BTW, that's one crazy mofo.Same as the Glumbert video in my post #4.

Thanks again, Doc. It was "enlightening." ;)

[DoctorDoom]

I have heard of lightning "leaders" before, but I didn't know that they were the same as corona.Here's a kid's page on it, but it's informative.

It's the negative charges in the bottom of the cloud that cause lightning to strike the ground. When the negatively charged particles group together, they begin to seek out positive charges from the ground below. The excess electrons create a channel of charged air called a leader that reaches down to the ground below. The leaders attract other charged ground-based channels called streamers.

When the stepped leader from the cloud meets a returning streamer from the ground, the path is ready. An electrical current called the return stroke, travels back up the path. This return stroke releases tremendous energy, bright light and thunder.Lightning - The Big Spark (http://weathereye.kgan.com/cadet/lightning/bigspark.html)

Here's a better description from Wiki.

Leader formation

As a thundercloud moves over the Earth's surface, an equal but opposite charge is induced in the Earth below, and the induced ground charge follows the movement of the cloud.

An initial bipolar discharge, or path of ionized air, starts from a negatively charged mixed water and ice region in the thundercloud. The discharge ionized channels are called leaders. The negative charged leaders, called a "stepped leader", proceed generally downward in a number of quick jumps, each up to 50 meters long. Along the way, the stepped leader may branch into a number of paths as it continues to descend. The progression of stepped leaders takes a comparatively long time (hundreds of milliseconds) to approach the ground. This initial phase involves a relatively small electric current (tens or hundreds of amperes), and the leader is almost invisible compared to the subsequent lightning channel.

When a step leader approaches the ground, the presence of opposite charges on the ground enhances the electric field. The electric field is highest on trees and tall buildings. If the electric field is strong enough, a conductive discharge (called a positive streamer) can develop from these points. This was first theorized by Heinz Kasemir. As the field increases, the positive streamer may evolve into a hotter, higher current leader which eventually connects to the descending stepped leader from the cloud. It is also possible for many streamers to develop from many different objects simultaneously, with only one connecting with the leader and forming the main discharge path. Photographs have been taken on which non-connected streamers are clearly visible. When the two leaders meet, the electric current greatly increases. The region of high current propagates back up the positive stepped leader into the cloud with a "return stroke" that is the most luminous part of the lightning discharge.Lightning (http://en.wikipedia.org/wiki/Lightning)

Ergo, the corona discharges might be called the predecessors to the leaders, sort of the trumpet signalling the arrival of the procession that precedes the coming of the king.

[ThomasMore]

Ergo, the corona discharges might be called the predecessors to the leaders, sort of the trumpet signalling the arrival of the procession that precedes the coming of the king.

I guess if you get hit by lightning, that description might quite literally be true.

[DoctorDoom]

You might hear the Snap and the Crackle, but it would be too late for the Pop.

[DoctorDoom]

How about painting radio station towers for a living????Wanna paint this beast (http://www.kvlytv11.com/info/info_tower.html)?

http://upload.wikimedia.org/wikipedia/commons/thumb/b/ba/KVLYFromBase.jpeg/452px-KVLYFromBase.jpeg

It's 2063 feet tall.