Hi all..
does a VSD or VFD drive affect the power factor for a pump?. It's not like it has coils in it that require magnetising. The reason I am asking is because I saw a brochure for a VSD/VFD saying that it comes with power factor correction.
Thank for the reply
The power factor problem with a pump (assuming it has an induction motor) comes from the magnetizing current needed to excite the rotor. This current is out of phase with the line voltage, so represents energy that is borrowed and returned twice per cycle, raising the RMS line current. The power factor problem with a VFD is completely different. It is the result of the current drawn in large pulses at the peak of each half cycle as the rectifier forward biases and connects the capacitive bus filter to the line. This produces a flattened line voltage waveform and lots of harmonic current that raises the RMS line current above that which represents energy delivered to the motor.
A capacitor across the line can correct the power factor of a motor, but a harmonic filter is needed to correct the power factor of the drive.
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