>> But what are you going to do with all the money if nobody uses you 
>> anymore because of your reputation of shoddy back-up plans?  How long 
>> will that money last paying everyones salaries? ;-)
>
> Well, it's not really my field, but presumably the people responsible for 
> this stuff have looked into it quite thoroughly. ;-)

Yeh you'd hope so.  Presumably if the penalty amount is high enough, CAT 
would hire a helicopter or something to get you the generator on time (if it 
came to that) :-)

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scott wrote:
>>>> Like I said, when they hook up the external generator, it comes with a
>>>> cable well over 10 cm thick (!)
>>>
>>> A lot of that thickness will be insulation, shielding and armor.
>>
>> Probably.
> 
> It will probably be 3-phase as well if you are running large bits of lab 
> equipment...
> 

Never ceases to amaze me how thick 3-phase power cables appear, yet cut 
one open, and the wires encased in the cable aren't *that* thick, but 
there's a ton of "wadding" around the actual wires inside the cable. 
Extra fun when attempting to unplug a 3-phase device for the first time. 
I had no idea it had to twist-on.

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> Never ceases to amaze me how thick 3-phase power cables appear, yet cut 
> one open, and the wires encased in the cable aren't *that* thick, but 
> there's a ton of "wadding" around the actual wires inside the cable. Extra 
> fun when attempting to unplug a 3-phase device for the first time. I had 
> no idea it had to twist-on.

Yeh, we had this oven that was 3-phase, but only something like 23A. 
However, like you say, the cable was about 10x wider than a normal 13A mains 
cable, so cross-section 100x bigger.  I didn't see inside the cable, but I 
guess it was mostly shielding, armour and insulation...

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Darren New wrote:
> Tor Olav Kristensen wrote:
>>> 2. Is maximum load proportional to diameter or cross section area? (The
>>> latter is quadratically propertional to diameter.)
>>
>> Cross section area.
> 
> Also depends on AC vs DC.

At 50 Hz, does it matter?

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scott nous apporta ses lumieres en ce 2007/11/12 09:18:
>> Never ceases to amaze me how thick 3-phase power cables appear, yet 
>> cut one open, and the wires encased in the cable aren't *that* thick, 
>> but there's a ton of "wadding" around the actual wires inside the 
>> cable. Extra fun when attempting to unplug a 3-phase device for the 
>> first time. I had no idea it had to twist-on.
> 
> Yeh, we had this oven that was 3-phase, but only something like 23A. 
> However, like you say, the cable was about 10x wider than a normal 13A 
> mains cable, so cross-section 100x bigger.  I didn't see inside the 
> cable, but I guess it was mostly shielding, armour and insulation...
> 
> 
Each individual live whire is isulated, then there is a metal mesh protection, 
then an outer protective layer. Then, there is a ground (not isolated) and 
possibly a neutral whire. The neutral is also isolated and protected by a metal 
mesh. The whole thing is paded with ropes, encassed in an additional isolating 
layer, then 1 to 5 metal mesh armouring, plus, possibly a metal sheet shelding, 
all wrapt in an outer PVC or polypropylen outer shell.
It all adds up.

-- 
Alain
-------------------------------------------------
When the bosses talk about improving productivity, they are never talking about 
themselves.

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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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