Corona on 750KV transmission line

Tesladownunder, Thu Nov 11 2010, 05:52PM

Photo courtesy of Michel Tournay from Canada.
More photos here.
1289497952 10 FT0 Hvlinecorona
Re: Corona on 750KV transmission line
Arcstarter, Thu Nov 11 2010, 06:54PM

That looks so cool! I wonder what it sounds like, if you can even hear the crackle of corona. Do you think you could smell O3?

This is also a perfect way to explain how easy it is to overestimate Tesla coil voltage, too, and that high frequency is what causes so much breakout.
Re: Corona on 750KV transmission line
Electra, Thu Nov 11 2010, 07:56PM

Is that caused by ice/snow on the cables? Or does it look like that all of the time do you think? Won’t it be lossy to transmit power, when currents leaking away as visible as that.
I suppose any loss is still going to be small compared to the megawatts flowing through it.
Indecently I thought that was why they made each cable out of a bundle of say four smaller ones spaced apart, rather than one thicker one to reduce corona loss.

Makes a pretty photo all the same very Christmas like.
Re: Corona on 750KV transmission line
klugesmith, Thu Nov 11 2010, 09:22PM

Electra wrote ...

Is that caused by ice/snow on the cables? Or does it look like that all of the time do you think? Won’t it be lossy to transmit power, when currents leaking away as visible as that.
I suppose any loss is still going to be small compared to the megawatts flowing through it.
Indecently I thought that was why they made each cable out of a bundle of say four smaller ones spaced apart, rather than one thicker one to reduce corona loss.

Makes a pretty photo all the same very Christmas like.

The photographer (in link within TDU's original post) writes:
" you need lots of juice (735 000 Volts) cold weather, some humidity (rare over here!) that's why it took 25 years to see it again!"

Each power conductor in the picture -is- made with four ropes in a square bundle. That -does- reduce corona losses, and improves the convective cooling. Imagine the power lost over hundreds of miles when the transmission line current is at 100% of capacity (limited by cable temperature rise).

Maybe they can and do transmit more juice when the weather is cold!

Re: Corona on 750KV transmission line
Tesladownunder, Fri Nov 12 2010, 12:49AM

No doubt this is a 750kV DC line driving huge SCR stacks triggered by lasers via optical fibre to drop down to AC again.
AC at 750kV RMS would peak at over 1MV and lose much more by corona and inductive/capacitative losses.
I am sure the line voltage won't change with demand and that the corona is always there but just takes dark adapted eyes and a long photographic exposure to recognise. Not everyone sits in the cold and dark for 15 minutes to allow this but he was taking "Darth Vader shots with a fluoro lighting up in the field.
Some companies make UV cameras to do corona fault checking in the daytime. Even picks up frayed wires and bird droppings!

Michel says ".. it did make an awful crackling sound...but I couldn't smell the ozone...to high I guess!
They put the wire in a group of 4 in a square configuration to reduce that effect and lose too much power over the 600 miles or so to bring that electricity to Montreal!"


Re: Corona on 750KV transmission line
klugesmith, Fri Nov 12 2010, 01:30AM

Tesladownunder wrote ...

No doubt this is a 750kV DC line driving huge SCR stacks triggered by lasers via optical fibre to drop down to AC again.
AC at 750kV RMS would peak at over 1MV and lose much more by corona and inductive/capacitative losses.
I am sure the line voltage won't change with demand and that the corona is always there but just takes dark adapted eyes and a long photographic exposure to recognise. Not everyone sits in the cold and dark for 15 minutes to allow this but he was taking "Darth Vader shots with a fluoro lighting up in the field.

Thank you for pointing out the spectacular pictures, Peter! Is Michel a buddy of yours?

I agree that corona is always present for long-exposure photographers,
but believe its intensity is highly sensitive to weather variations.
Michel comments that the last time he saw it so brightly was 25 years ago.

I respectfully disagree with your conclusion that the pictures show DC transmission.
Since when have HV DC transmission lines been made with three conductors?
And how do DC fields induce fluorescent lamp tubes to glow?

Here's a great report from a company that owns and operates thousands of miles of conventional 765-kV transmission lines: Link2

Section Q12 has a table of resistive and corona losses in normal weather* .
For example, in a 765 kV line carrying 1000 MW, with their original 4-conductor (“Rail”) bundle,
the losses per 100 miles are 4.4 MW and 6.4 MW respectively, for total of 10.8 MW (1.1%) .
With improved 6-conductor bundles they are getting 3.4 and 2.3 MW, total 5.7 MW (0.6%).
*Yearly average corona loss at sea level based on 20%/2%/78% rain/snow/fair weather conditions, respectively.

The original bundle resistive and corona losses work out to be 27 and 40 watts per meter,
divided among 3 phases of 4 strands each, in normal weather. The fact that the glow is
rarely seen, implies that the parasitic corona-discharge lamps have very poor luminous efficiency.

Also thank you, Peter, for the reminder about DayCor boresighted UV cameras for corona inspection.
Here is a terrific clip I had never seen before:
Link2
Re: Corona on 750KV transmission line
Adam Munich, Fri Nov 12 2010, 06:22AM

Wow, that's pretty cool.

A little OT, but once I heard of a guy who got free power by running lines // to the transmision lines on his property. They induced current in his lines, and since they did not cross nor contact the transmission lines it was completley legal. Smart man.
Re: Corona on 750KV transmission line
Tesladownunder, Fri Nov 12 2010, 01:35PM

Klugesmith wrote ...

Thank you for pointing out the spectacular pictures, Peter! Is Michel a buddy of yours?
... I respectfully disagree with your conclusion that the pictures show DC transmission.
Since when have HV DC transmission lines been made with three conductors?
Extremely sheepish look and some complex humbling deltoid shrugging .......
Yes it is an AC line of course. Although technically there are 6 lines present in the photo so it is possible.
"Planning for Hydro-Québec's 735 kV power grid began in 1955, when engineers looked to transmit 5,000 megawatts (MW) hydroelectric power from the Manicouagan-Outardes (Manic-Outardes) dams to Montreal, a distance of 600 kilometres (400 mi).[1] At that time, by using the world standard 300–400 kV voltage level, this feat would have required at least 30 individual power lines.[1] Initially, a voltage level of 500 kV was chosen to transmit electric power, but 500 kV was considered to be a small improvement over the existing voltage level of 315 kV.[5]
To effectively resolve this issue, Jean-Jacques Archambault, now regarded as the pioneer of the 735 kV power line, decided on a voltage level of 735 kV, a level over twice as high as the previous 315 kV.[1] In 1962, Hydro-Québec proceeded with the construction of the first 735 kV power line in the world. The line, stretching from the Manic-Outardes dam to the Levis substation, was brought into service on November 29, 1965 at 1:43 pm.[1][5][6][7][8]"

In fact it does make me wonder whether the advantage of DC which uses 2 conductors outweighs the benefit of 3 conductors with AC particularly with a single pylon.
Michel had seen me a few times on TV in Canada and knew my site and so asked me about the phenomena.
Re: Corona on 750KV transmission line
Killa-X, Sat Nov 13 2010, 04:39AM

Loving the pictures...I'll have to give this a try sometime, We have some >600KV lines around here...Even the 100KV lines make a lot of buzzing and cracking...I have those like 5 mins away...Will indeed try sometime! Just long exposure?

Does look pretty :D
Re: Corona on 750KV transmission line
hsieh, Sat Nov 13 2010, 01:52PM

I live in Taiwan.Here is very humid(RH60% is considered dry here)
And there are a lot of transmission line around my home/school.but the votage is only 345KV.

But I'v never seen this.Is it possible to see this here?


Re: Corona on 750KV transmission line
radiotech, Sat Nov 13 2010, 02:15PM

"And how do DC fields induce fluorescent lamp tubes to glow?

"

Fluorescent lamps work on DC too. There even was a Rectified
Fourescent, With an anode and filament/cathode, but it vanished
about 70 years ago. I've worked on units that use banks of DC
UV tubes:Polarity had to be flipped from time to time to even out
cathanode wear

RF here means rectified fluorescent not radio frequency.


1289657742 2463 FT100386 Fluorescent
Re: Corona on 750KV transmission line
Plasmana, Sat Nov 13 2010, 02:54PM

Wow, that is amazing. I'v always wondered if corona could be seen emitting from transmission lines - Ill have to keep a look out for this phenomenon as winter is right around the corner!
Re: Corona on 750KV transmission line
Thomas W, Sat Nov 13 2010, 03:31PM

one word discribes it:

AWSOME
Re: Corona on 750KV transmission line
Steve Conner, Sat Nov 13 2010, 03:40PM

You'll be lucky if you see it in England. The highest transmission voltage we use in the UK is 400kV, and that's for the "Supergrid". 275 and under is much more common.

In a 3-phase AC system, the voltage is quoted between lines. To get the voltage from line to ground, you have to divide by the square root of three, so 400kV lines are 230kV to ground. The lines are far enough apart that it's the voltage to ground that matters for corona purposes.

I have heard a lot of noise from 132kV lines on the coast. The insulators get encrusted in salt and sizzle away nicely. (Not "nicely" from the point of view of the power company, of course.) But looking at them at night, I couldn't see anything.
Re: Corona on 750KV transmission line
Adam Munich, Sat Nov 13 2010, 04:12PM

I've stood 30 feet under the power lines coming out of tonowanda coal building. I'm not sure what the voltage was, but I could hear the crackling corona quite loudly and it was also pulsating at 60hz. I could also feel the field via the hairs on my arm. It was quite scary actually. I imagine they must glow like neon at night.

For those that want to determin the voltage/current: 3x 3" thick Al lines, 6 feet apart, hung from 3' insulators.
Re: Corona on 750KV transmission line
Adam Munich, Wed Nov 17 2010, 10:11PM

Hey TDU, what about putting that image on these two articles?

Link2

Link2
Re: Corona on 750KV transmission line
Martin King, Wed Nov 17 2010, 10:54PM

Steve McConner wrote ...

You'll be lucky if you see it in England. The highest transmission voltage we use in the UK is 400kV, and that's for the "Supergrid". 275 and under is much more common.

Pop quiz, I once stood about 2 feet away from an energised supergrid line without any special protective precautions. It was quite warm. Where was I ?

Martin.
Re: Corona on 750KV transmission line
Martin King, Wed Nov 17 2010, 10:58PM

Grenadier wrote ...

Wow, that's pretty cool.

A little OT, but once I heard of a guy who got free power by running lines // to the transmision lines on his property. They induced current in his lines, and since they did not cross nor contact the transmission lines it was completley legal. Smart man.

Some years ago a farmer in the UK buried a coil in a field under a transmission line and got prosecuted for stealing power. Smart lawmakers wink

Martin.
Re: Corona on 750KV transmission line
Steve Conner, Thu Nov 18 2010, 11:52AM

Martin King wrote ...

Pop quiz, I once stood about 2 feet away from an energised supergrid line without any special protective precautions. It was quite warm. Where was I ?

Somewhere you really shouldn't have been. Maybe on the roof of a house under some power lines, on a really hot day, at half-time of the Cup Final? tongue

It shouldn't have been inside one of the supergrid substations, because there are safety clearance rules in there that you're supposed to observe.

Re: Corona on 750KV transmission line
Luca, Thu Nov 18 2010, 12:12PM

Once my hand was few cm from a conductor that was carrying 220kV... tongue

Regards

Luca
Re: Corona on 750KV transmission line
Martin King, Thu Nov 18 2010, 12:45PM

Steve McConner wrote ...

Somewhere you really shouldn't have been. Maybe on the roof of a house under some power lines, on a really hot day, at half-time of the Cup Final? tongue

It shouldn't have been inside one of the supergrid substations, because there are safety clearance rules in there that you're supposed to observe.


I was supposed to be there and it was an underground oil insulated/cooled cable in London. I was doing some tests on a leaky feeder comms system in the tunnel. I was with a National grid guy (obviously) and we had some emergency re-breathers with us but he did say that if we needed to use them we probably wouldn't get the chance ! He also reassured me that they weren't due another cable explosion just yet smile The tunnel was VERY warm and that was with the ventilation fans switched on. I am beginning to doubt whether it was a 400kV cable though, he defiantly told me it was a "supergrid" cable and this was the tunnel Link2 but I can only find references to 275kV cables. There were two levels of tunnel the upper one was apparently "grid" and the lower one "supergrid" ?

Martin.

Martin.

Martin.
Re: Corona on 750KV transmission line
Steve Conner, Thu Nov 18 2010, 12:55PM

Oh, "line" means overhead line.

Scottish Power recently laid some 132kV cables down my street, why I have no idea. I certainly didn't order 132kV service. smile I'm sure a city the size of London will have 400kV ones.
Re: Corona on 750KV transmission line
Martin King, Thu Nov 18 2010, 09:18PM

Incidentally there is a series of programs about the National grid still available for a few more days on iPlayer (UK only, sorry) Link2 I haven't seen them yet so don't know if they're any good.

Martin.
Re: Corona on 750KV transmission line
tobias, Thu Nov 18 2010, 11:44PM

Anyone can watch this movie. Just configurate a UK free proxy.
Re: Corona on 750KV transmission line
Frosty90, Mon Nov 22 2010, 02:51PM


The photographer (in link within TDU's original post) writes:
" you need lots of juice (735 000 Volts) cold weather, some humidity (rare over here!) that's why it took 25 years to see it again!"

I have some 66kv lines near my house, they have old porcelain suspension insulators on them, when there is a light rain/fog etc, they all hiss and crackle with corona, you can easily see the corona on the surface of the insulators too, when it is dark...
Re: Corona on 750KV transmission line
Steve Conner, Mon Nov 22 2010, 03:36PM

Martin King wrote ...

Incidentally there is a series of programs about the National grid still available for a few more days on iPlayer (UK only, sorry) Link2 I haven't seen them yet so don't know if they're any good.

I've watched the first two now. They were pretty good, thanks for the heads up. No hardcore tech stuff, but interesting nonetheless. My favourite bit was the film of what happens inside the National Grid control room when Eastenders finishes. smile