VFD power factor at reduced loads

I do not like the I thd or PF measurements done by most power meters.

The I thd will likely increase as the current is reduce and become useless at low current. While the amount of real harmonics current is reduced, the RMS current may be reduced faster and their ratio (I thd) increases. This gives a false interpretation and often forces manufacturers to install harmonics filters that are not necessarily needed.

The Power factor also becomes meaningless at low current as the KVARs generated and the real power are both low. Their ratio can look very bad but it has no effect on the plant because very little KVARs are actually generated.

What is important is not how bad a load looks but what is its effect on the plant feeder. That depends on its size with respect to the feeder.

I hope that this will clear some of the confusion.

Regards

Marco