Eero Ahonen nous apporta ses lumieres en ce 2007/11/11 16:44:
> Tim Attwood wrote:
>>> 1. A car runs on 12V electrics, not 250V. Does that make a difference?
>> Yes, lots. Voltage is the size of the elephant, amperage is how fast he's
>> going when he runs you over. I think many cars will pull more than 100 A
>> cold starting though.
> 
> No, not for the sizing of the cable. If the cable has resistance of
> 0,01ohms and the current is 100 A, the cable will heat up with
> 100^2*0,01=100 W (P=I^2*R) and hold up 100*0,01=1 volt (U=I*R) of
> voltage (this 1V is called the voltage loss of the cable). Rest of the
> voltage (11V or 249V) will get to the final device and it'll have matter
> there.
> 
> Practically everyone/-thing (lets say house heating, 10kW) needs power
> (P, measured in watts). While P=U*I, we can produce 10kW of heat eg.
> with either 1A*10kV, 10A*1kV, 100A*100V, 1kA*10V or 10kA*1V. If the
> transmission lines to the house adds up with 1ohm, we'll heat the
> transmission lines up with anything from 1W (1A^2*1ohm) to 100 000 000 W
> = 100MW (10kA^2*1ohm). This is why the main transmission lines do not
> have 230-400V voltage, but ~10-400kV voltages instead - to minimize the
> power loss, which only heats up the outside air.
> 
>> 100 A * 12 V = 1200 W (~1.6 hp)
>> 100 A * 220 V = 22 KW (~29.5 hp)
> 
> True, at the final device.
> 
We have 750KV AC and 1000KV DC transmition lines all over the place. Hydroquebec 
pioneered the 750KV lines with Churchill Falls and the Manic complex. It's 
pioneering 1000000 DC transmition with the Bay James. Why do you think that they 
invested several $1000000's a year for over 20 years on that technology?

-- 
Alain
-------------------------------------------------
You can go anywhere you want if you look serious and carry a clipboard.

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Alain wrote:
> We have 750KV AC and 1000KV DC transmition lines all over the place.

Damn, you people are way front of me and my knowledge.

> Hydroquebec pioneered the 750KV lines with Churchill Falls and the Manic
> complex. It's pioneering 1000000 DC transmition with the Bay James. Why
> do you think that they invested several $1000000's a year for over 20
> years on that technology?

DC transmission? Possibly because DC is more tolerant to ripples, if it
gets hacked back to AC after all.

-- 
Eero "Aero" Ahonen
   http://www.zbxt.net
      aer### [at] removethiszbxtnetinvalid

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Eero Ahonen nous apporta ses lumieres en ce 2007/11/13 12:41:
> Alain wrote:
>> We have 750KV AC and 1000KV DC transmition lines all over the place.
> 
> Damn, you people are way front of me and my knowledge.
> 
>> Hydroquebec pioneered the 750KV lines with Churchill Falls and the Manic
>> complex. It's pioneering 1000000 DC transmition with the Bay James. Why
>> do you think that they invested several $1000000's a year for over 20
>> years on that technology?
> 
> DC transmission? Possibly because DC is more tolerant to ripples, if it
> gets hacked back to AC after all.
> 
No! 750KV AC is an average value, it have a crest value of about 1000KV, whitch 
is about the maximum you can reliably handle without having sheet arcs between 
transmission whires. As DC never goes down to zero, you transmit 100% of the 
time, not about 75% as in the case of AC.
Multi mega-wats lines over 400 to more than 800 miles long. You realy need to 
reduce that current...
Another advantage: you need 1 less whire for the transmission. AC lines normaly 
have 3 whires, while DC lines only use 2.
Yes! it get's transformed back to AC at the converter stations, and reduced down 
to 750KV.

I do know somebody that works at IREQ. (Institut de Recherches Électriques du 
Québec)

-- 
Alain
-------------------------------------------------
WARNING: The consumption of alcohol may make you think you can logically 
converse with members of the opposite sex without spitting.

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> Multi mega-wats lines over 400 to more than 800 miles long. You realy need 
> to reduce that current...
> Another advantage: you need 1 less whire for the transmission. AC lines 
> normaly have 3 whires, while DC lines only use 2.
> Yes! it get's transformed back to AC at the converter stations, and 
> reduced down to 750KV.

It would be interesting to know how they do the DC-->AC conversion with that 
much power.

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Alain wrote:
> No! 750KV AC is an average value, it have a crest value of about 1000KV,
> whitch is about the maximum you can reliably handle without having sheet
> arcs between transmission whires. As DC never goes down to zero, you
> transmit 100% of the time, not about 75% as in the case of AC.

Aaaa. I misread ("750kV AC", I read "750kV DC"), but still I probably
wouldn't have tought the right answer.

> Multi mega-wats lines over 400 to more than 800 miles long. You realy
> need to reduce that current...

True that. 750kV vs. 1Mv has remarkable difference.

> Another advantage: you need 1 less whire for the transmission. AC lines
> normaly have 3 whires, while DC lines only use 2.

OTOH, with 3 wires you can transfer 3 phases of AC - for one phase 2 is
enough (possibly even 1+ground is possible).

> Yes! it get's transformed back to AC at the converter stations, and
> reduced down to 750KV.

Yep. And there goes all the glitches that have been inducted to the DC
voltage, so at the end there's cleaner AC (nearer to sin).

-- 
Eero "Aero" Ahonen
   http://www.zbxt.net
      aer### [at] removethiszbxtnetinvalid

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