Hi,
Have a look at this publication by Yaskawa:
https://www.yaskawa.com/delegate/get...=WP.AFD.10.pdf
In particular look at the formula published to calculate power factor and note how depenant it is on THD (
Total
Harmonic
Distotrion)
and that by definition VFD's have
VERY HIGH harmonic distortion.
The upshot is that a VFD (or RPC or servo drive or any other unmodified rectifier/capacitor input inverter) will appear to asborb much more
current than it outputs. The extra current is not dissapted as heat but reflected back into the supply, traditionally called 'reactive current'.
In the case of VFD's this is beacuse of the distorted current waveform. For small installations you can ignore it but for large installions the power
company will insist you improve the power factor or 'supply pollution' to protect their network and other customers installations.
Even in small installations a low power factor will stress your supply, the current going into the device might be 30A but the output only 20A.
If you use line reactors the input current will reduce to say 22A and the output is still 20A. If you have a 25A breaker then it will pop in the
without the use of line reactors but it will operate normally with line reactors.
Craig