Is a 1kW generator always a 1kW generator? I can give you a generator and a load with a matching (or slightly lower) kilowattage and the generator, under certain conditions, won't be able to run it. For example, if I had a 1.2kW generator and a 1kW HMI fixture then the generator should be able to run it, right? But what if the HMI fixture had a magnetic ballast and no power factor correction? Would the generator still be able to run the load? …It might depend on how the power factor is. If it was much lower than 1, say, 0.8, then the generator would be slightly over capacity and the HMI lamp might flicker badly or not stay on at all. In this case, our 1kW load is undersupplied by a "1.2kW" generator…Perhaps a better way of describing the supply capacity of a generator is to use a value that is unaffected by the power factor of the connected load. There is a unit of measure that is similar to kW except it takes into account the increased current caused by a lower power factor. That unit of measure is kVA. kVA is simply the product of the kV and the A, or the kilovolts times the amps. In the case of a 120V system, the kV is 0.12, so a 1.2kVA generator could supply 10A, regardless of the power factor of the load…If you don't understand the difference between kW and kVA then you might be confused about what full capacity is for a portable generator. But if you simply keep an eye on the kVA and compare it to the kVA of the portable generator you'll be better off.
From "Focus on Fundamentals" by Richard Cadena, PLSN, May 2010
