Data analysis of asynchronous motor with VFD 1

[Sebastijonas]

Hello,
I've been doing data analysis of asynchronous motor under load with frequency inverter. I've got active power and current values exported from the frequency inverter (as .xls file) in one second intervals. My question is as follows: do i need to take into account efficiency of the motor, when evaluating output (mechanical) power of the motor? Frequency inverter input data does not seem to include motor efficiency.
Additionally: Frequency inverter used - Danfoss FC102. Also, this is the data that I've got from the technicians on site.

https://1drv.ms/x/s!AmAvxaM1dzRcjzF-_sj2_A4EJvZa?e=07bbOI

P.s As a mechanical engineer I'm somewhat familiar with the concepts of power factor , efficiency of motor, etc, yet I have very little knowledge of VFD's operation and data they provide for analysis.
Thank You in advance !

 

[waross]

Are you aware of distortion power factor?
The power factor that we have been familiar with forever is displacement power factor.
This is the result of a phase shift between the applied voltage and the current drawn by the load.
With the growing proliferation of non-linear loads another effect has become apparent;
Distortion power factor.
Distortion power factor is an expression of a ratio between apparent power and real power that is not caused by a phase shift but is caused by harmonic currents.
While displacement power factor may be corrected with capacitors, distortion power factor may be mitigated by filters.
Unfiltered VFD output waveforms are rich in harmonics.
The effect is that the apparent efficiency of an induction motor driven by an unfiltered VFD may be less than the apparent efficiency of the same motor driven by a clean waveform from direct connection to the grid.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[jraef]

What is your goal here? Are you trying to ascertain mechanical load power requirements via the data from the VFD output?

Most of the time, if a VFD provides you with a value of "Output KW", they have developed an internal algorithm that can calculate that with their known parameters of voltage, frequency, torque and power factor. I don't know if the Danfoss FC02 line is providing that, but they are not a "bottom feeder" type of drive supplier, so I would imagine they do. If you are trying to get there by looking at those individual data points, you may be in for a challenge.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[Sebastijonas]

Thanks for the a quick reply. "Are you trying to ascertain mechanical load power requirements via the data from the VFD output" Yes. I'm trying to do that. I'm trying to compare calculations vs measured mechanical power. in other words, how well calculated value correlate with measured results. My idea was to multiply motor efficiency x power value exported from VFD. I understand, that this value won't be 100% accurate (due to reasons mentioned by warossand due to load dependent change in efficiency itself), but it might be somewhat representative. Maybe You have done something similar?