OT: They shouldn't be shops like these!

...and Paul S. Brown spake unto the tribes of Usenet, saying...

Built by merchant bankers, for merchant bankers.

More or less, got to admit I'm hazy about the difference between the kVA and kW rating of generators. I think the kVA rating is the better measure as, I think again, it takes into account the phase angle, thus is more indicative of the true power available. In broad terms the kVA rating is normally about 80% of the kW one.

Maybe some one will come along an enlighten the two of us?

I don't thjink this is easy to explain, but here goes.

kW are what is delivered as real power to your load. WHAT is delivered depends on your actual electrical load. A resisitive load like a heater of 24Ohms resistance will consume say 10Amps at 240V and will obviously "burn" 240 x 10 amps , or 2400 Watts. The voltage changes and the current changes IN PHASE, so if you draw a graph of current through the load (a nice sine wave) and a graph of voltage acrosss the load (another nice sine wave), then the two graphs will lie exactly on top of each other.

Now, if you have what we call a "reactive load", like an induction motor, or a bloody BIG pile of fluorescent lights it WILL NOT draw current in phase with the voltage, and yor pretty graph will show a nice sine wave of current, and a nice sine wave of voltage NOT in phase - in the worst case, the current graph will be at a maximum when the volts are at zero and vice versa, essentially now, since power = current X volts ZERO real power is consumed - NO heat is generated !

Unfortunately though, your genny still has to supply the maximum voltas and the maximum current as if it still fed the purely resistive load, so if your reactive load showed 240 V and 10 A on its meters, even if its out of phase, your genny is still supplying 240 X 10 *VA* This is why they are rated in (k)VA not in (k)W

Technically now, the cosine of the phase angle between the current and voltage waves is called the Power factor, and Power = Power factor X Volts X current. In a pure heating load power factor = 1, in a purely reactive load it equals 0. A typical motor load will have a power factor of roughly 0.6..0.8

You will find an electricity supplier is VERY unhappy if you feed a highly reactive load with their service, because though you are taking nothing they can bill you for, their wires are still feeding volts and current.

HTH

Steve

Dorothy Parker had a budgie called Onan - because it spilled its seed.....

Steve

Ah yes - the good old "Power Factor Correction" gimmick.

/me goes to buy some *big* capacitors....

P.

Modern electronic meters aren't "phased" by that at all - you get billed for VA.

Steve

Got a big spinning thing with "Ferranti" written on it here - I suspect that may just get its knickers in a twist :)

P.

...and Steve Taylor spake unto the tribes of Usenet, saying...

Remind me to tell you the joke about a dog called "Tosser" when we next meet up...

Reminds me I have a computer game ( nothing to do with barbarians) featuring a movie clip(s) on the subject as a reward for completeing the game. Derek

On or around Sat, 18 Mar 2006 22:38:56 +0000, Steve Taylor enlightened us thusly:

of course, if said item is not consuming any power, it's not gonna do any work... do there's something wrong with the theory.