induction motor power factor and effect of frequency 3

[Danfossegypt]

i want to know the effect of frequency on power factor of an induction motor?
if i have a pump driven by 1 kw induction motor,50 hz,and the motor is supplied from an inverter,could i reach 100 hz without any proplem?

 

[cbarn24050]

Hi, it's highly unlikely, the faster your pump goes the more torque it requires whereas as soon as the motor goes above its normal speed its torque reduces. If your pump/motor were correctly sized in the first place, you will be able to get allmost no increase before you overload.

 

[jbartos]

Suggestion: The induction motor electrical equivalent circuit may be used to derive the Power Factor, PF, dependency on Frequency, Fs. There are various textbooks including the induction motor equivalent circuit, e.g.
Gordon R. Slemon, "Magnetoelectric Devices Transducers, Transformers, and Machines," John Wiley and Sons, Inc., 1966, Figure 5.21 on page 376 can be used to express PF=arctan[(Xe+XLr')/(Re+Rr'/s)], in per units,
Where
s is slip. It can be assumed approximately constant
Reactance Xe~Fs
(Xe is linked to Thevenin's theorem simplification of the equivalent circuit covering the stator impedance and magnetizing branch)
Re is similarly derived as Xe
Rr' is the rotor resistance transferred to the stator side
XLr'~Fs
(XLr' is rotor inductive reactance transferred to the stator side)
Hence, PF will be increasing with increasing frequency

 

[edison123]

If you double the frequency, the motor speed will double causing severe mechanical stresses (speed squared). Unless the motor designed to withstand such stresses, the motor will fly apart. Same goes to your pump also. Also, in pumps, doubling the speed will require 4 times the input power from your motor causing it to burn out. There are other implications with pump running at double the speed. With such problems, why bother about the motor power factor ?

 

[jbartos]

Suggestion: I agree with the previous posting that the power factor is the lower priority parameter when it comes to a high frequency increase