Let say
A 440-V 60Hz three-phase star-connected four-pole induction motor
developed 10 hp at 1745. The input power is 10kw at 0.85 lagging power
factor. the no load input power is 0.6kw
My question is that what does the power factor mean in this sentence?
What is this power factor value derived from and the meaning of it ?
Best Answer
First things first there is something called Displacement Power Factor This is basically related to the phase difference between the voltage applied and the current drawn $$ DPF = \cos( \Theta ) $$ What this means for your case is if 10kW of real power is being consumed then there is 11.76kVA of apparent power (industry are charged based upon their VA consumption as oppose to W consumption hence why PF/DPF is important)
For linear loads and an induction machine will appear as a linear load: PowerFactor == DisplacementPowerFactor
For non-linear loads (rectifier-based systems etc) the disctinction between DPF and PF becomes important. PowerFactor takes into account harmonic distortion
$$ PowerFactor = DisplacementPowerFactor * DistortionPowerFactor $$ $$ Power Factor = \cos( \Theta ) * \tfrac{1}{\sqrt{1 + THD_{i}^{2}}} $$
So you can see for a linear load the THD = 0 and thus the DistortionPowerFactor = 1 and thus PowerFactor = DisplacementPowerFactor and is the cosine of the phase difference between the voltage and current