# Generator Power factor Calculation with varying Output Power

We are operating a generator (Stirling engine in particular) that outputs a certain active power in the range of 6.5-8.9 kW. The power output is adjusted with pressure variation. The electrical machine is rated at 400V and 15.5A nominal voltage and current. For calculating the power factor is it correct to assume that the power factor varies between 0.62 to 0.83????

I'm not sure whether changing the power output changes the current draw so as to lower the apparent power and maintain the same power factor at different loads, or the apparent power is defined as S=sqrt(3)VI with the nominal values?

One thing to mention, there is no information concerning the set power factor of the engine. The results I provided are the actual output of the engine.

• Power factor depends on the load. Commented May 22, 2021 at 23:09

The power and the power factor are both determined by the load characteristics and the response of the load to changing frequency and voltage. The engine speed controls the generator's output voltage and frequency. The engine determines the maximum power. If the generator delivers too much electrical power to the load, it will require more torque than the engine can deliver and overload the engine.

The generator has a maximum safe output voltage and output current. The minimum power factor will mostly be determined by the maximum current. Wound-field synchronous generators have additional limitations determined by the maximum field current limitation and control considerations.