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

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