Technical Information

Ratings of Generators

Generators are rated in either kVA (kilovolt amperes) of kW (kilowatts), Kilo meaning 1000. The kVA is always higher than the kW. This is because kVA is divided by the power factor to give the kW. Most generators are rated with a power factor of 0.8.

Power and Power Factor

It is common to use mechanical kW to indicate the engine power but for alternators there are two ways to indicate the power:

kW (active power) and kVA (apparent power) the ratio of these two is the Power Factor.

kW = kVA x P.F

What does Power Factor mean?

In a DC circuit the power in Watts is a product of Voltage x Current.

In an AC circuit the Active Power is not always the product Voltage x Current. It is related to the Power factor, which depends on the type of load:

RESISTIVE LOAD (Incandescent lights, heaters)

The voltage and current peaks coincide to enable that the in-phase and the power factor are in unity.

INDUCTIVE LOAD (Motors, transformers)

On an inductive load the current waveform is LAGGING behind the voltage waveform, the voltage peaks and current peaks are not in phase, the amount of phase delay is given by the cosine of the angle (Cos) between the vectors representing voltage and current.

Technical Info