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Corona on 750KV transmission line

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Tesladownunder

Thu Nov 11 2010, 05:52PM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

Photo courtesy of Michel Tournay from Canada.
More photos here.

Arcstarter

Thu Nov 11 2010, 06:54PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

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.

Electra

Thu Nov 11 2010, 07:56PM

Registered Member #816 Joined: Sun Jun 03 2007, 07:29PM
Location:
Posts: 156

Is that caused by ice/snow on the cables? Or does it look like that all of the time do you think? Wonâ€™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.

klugesmith

Thu Nov 11 2010, 09:22PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Electra wrote ...

Is that caused by ice/snow on the cables? Or does it look like that all of the time do you think? Wonâ€™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!

Tesladownunder

Fri Nov 12 2010, 12:49AM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

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!"

klugesmith

Fri Nov 12 2010, 01:30AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

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:

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 (â€œRailâ€) 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:

Adam Munich

Fri Nov 12 2010, 06:22AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

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.

Tesladownunder

Fri Nov 12 2010, 01:35PM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

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-QuÃ©bec'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 300â€“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-QuÃ©bec 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.

Killa-X

Sat Nov 13 2010, 04:39AM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039

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

hsieh

Sat Nov 13 2010, 01:52PM

Registered Member #1412 Joined: Thu Mar 27 2008, 04:07PM
Location: Taipei Taiwan
Posts: 278

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?

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