voltages. Primarily done to reduce corona discharge but also mitigates aga inst skin effect and inductance losses plus runs cooler.
s of resistance per metre at room temp. I reckon skin effect and self heati ng must increase this number by many times.
power emerging at the far end at all.
Al 100mm * 1km @ 50Hz ~= 0.00821 Ohm Al 100mm * 1km @ DC = 0.00338 Ohm
-Lasse
Phil Allison:
** That DC resistance number is based on solid Aluminium with no allowance for the steel core or air spaces that exist in a real high tension cable.I estimated the effective cross section at 6000 sq mm ( instead of 7853 ) - but then mucked up the conversion from Copper to Aluminium.
So my figure should have been 4.8 micro ohms and adding the effect of skin depth should double this.
... Phil
Especially for HV lines, one has to consider also the phase to ground capacitance, which is charged and discharged every cycle, causing useless charge and discharge (reactive) currents in the conductor, reducing the net current carrying capacity. This, in combination of increased skin effect losses, limits the maximum distance, unless some compensation methods are used.
The much higher capacitance limits the length of undersea cables, since ultimately all current flowing in the conductor would carry reactive power only. Thus HVDC has to be used with longer cables.
** For a single wire at very HV that could be considerable - but with 3 lines, 120 degrees apart in phase the electric field at a distance cancels to zero.
I figure line to line capacitance has a far greater effect.
... Phil
See plot on P.10 of
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
That link takes me to a google search. Is this the article?
There's a pic on page 21 of "track resistance". But not talked about later. (From which one might assume it's less than the other terms.)
George H.
Searching for "track resistance" brings up PCB's.... But one book quoted a track resistacne of a small fraction of a lb. to 1.5 lb/ton.
George H.
Ah, right, 99, the old tinyurl-for-this-link trick. ;)
Try
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
It may be possible to design AC transmission lines in such a way that the inductance and capacitance form the equivalent of a coaxial cable or a matched impedance that virtually eliminates reflected waves and other losses. I don't know enough about transmission line theory to work out the details, however. And DC is now probably the easiest and most efficient to implement.
Paul
On Mon, 18 May 2015 23:28:18 -0400, Martin Riddle Gave us:
snipped Larkin retardation.
It tells what they use now, and in the past. Sheesh..
The L and C are not a problem. It's mostly the series ohms that cause losses, and some corona (shunt losses) at higher voltages.
DC eliminates the skin losses and uses the conductors better. And reduces corona by lowering the peak voltage. But that costs expensive conversion gear on both ends.
A half-megavolt DC/AC converter must be an interesting circuit design.
-- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
I wonder if they'd use GTO's for that. Semikron makes hockey puck GTOs that can be stacked end to end. Hmmmmmm
Cheers
I think they use LASCRs (light-activated, with fiber optic connections). For turn-off, they might use the old trick of injecting a brief reverse-current pulse through the stack with a CT. Some old fork lifts and golf carts used that method with SCRs for PWM to the (usually series wound brushed DC) motors.
Paul
P E Schoen wrote: "Phil Allison"
** Really ?You do realise that the wavelength of 60Hz is 5000 kms.
... Phil
wavelength at 60Hz is quite long, and the load impedance is variable
inductors are added to the lines to compensate.
-- umop apisdn
it's kind of hard to send a turn off pulse up the optical trigger cable.
this one is for 350kV
looks like 116kV per layer.
-- umop apisdn
Those big ones uses thyristors and are line-commutated and require an active AC network on the load side.
The slightly smaller voltage sourced converters (VSC) use IGBTs can be used to start a dead AC network. These are essentially huge variable frequency drives (VFD) and are much more flexible than the thyristor based systems.
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