The output of a generator is measured in KVA.
The V is the voltage being used (if you change the voltage from 240V to 208V the KVA drops accordingly.), the A is the maximum allowable current without over heating.
The KW is determined by the available power of the prime mover.
A generator rated at 100 KVA and 0.8 PF will deliver 80 KW.
Another way of looking at it is that the builders said
"The power factor of the load will never be 100% so lets save some money and just install an 80 KW prime mover."
This is quite common in diesel generators above about 15 KVA.
respectfully
You have Active and reactive Power. If you have nominal power of generator S than real power is E=k*S+jkr*S where k^2+kr^2=1
E - (also known as S underlined)
k*S=P active power
kr*S=Q reactive power
Now you can make your generator to produce different pow factors but 0.8 is used because the nowadays network has the same P factor. I had dealings with network where you have that factor on 0.95 (that is almost pure resistance) run on stand alone generator networks and of course you had pow. factor 0.95
The OP asked that question. And then she/he asked a little more about vars.
The first question has a simple answer: You cannot specify at PF = 1, simply because there are very few practical loads with PF = 1 (pls, don't tell me about heaters and lamps). So, what PF should you use then? Since .8 is a very common PF in a mixed load grid, it is a good and practical choice.
I worked for a genset packager once - it just comes down to tradition and safe margins.
If you have a site taking say 80kW load from the utility, and require a standby genset, then a typical site pf is 0.85. This equates to 95kVA or so. To avoid overloading the alternator, a rating of 100kVA (0.8pf) is selected when buying the alternator. The alternator then runs slightly underloaded.
What is occasionally forgotten is that this does not work in reverse - running a 100kVA genset at 0.85pf (85kW) would overload the engine.
Someone, somewhere must have created this rule of thumb. Anyone know?
