calculating motor power output/micrologix to ac inverter with modbus

[sthompson]

Eccan:

This doesn't help you with your VFD supplying KW via Communications, but it a possible solution if you can't get it working satisfactorily. I saw this in another thread compliments of OkiePC.

http://www.plctalk.net/qanda/showthread.php?t=57980

Stu...

 

[DickDV]

Yes, thanks for that, KAMenges. That would seem to indicate that that is PF on the motor side of the drive.

 

[Lancie1]

Am I correct in now using the following formula to calculate the output power of my motor?

Power = V x I x 1.732 (for 3 phase) x PF ?

Eccan, I think that your drive is reporting "Power Factor Angle", not the Power Factor (Power Factor Ratio)

Power Factor = Cosine(Power Factor Angle)
If Power Factor Angle is 79.1 degrees, then Power Factor = Cos(79.1) = 0.189
If Power Factor Angle is 90 degrees, then Power Factor = Cos(90) = 0.0
If Power Factor Angle is 0 degrees, then Power Factor = Cos(0) = 1.0

On the other hand, your Power Factor Angle could be given in Radians, so the formula then is different....

EDIT: Oh, I see you figured it out.

 

[sthompson]

Stu, I think that your drive is reporting "Power Factor Angle", not the Power Factor (Power Factor Ratio)

Power Factor = Cosine(Power Factor Angle)
If Power Factor Angle is 79.1 degrees, then Power Factor = Cos(79) = 0.19
If Power Factor Angle is 90 degrees, then Power Factor = Cos(90) = 0.0
If Power Factor Angle is 0 degrees, then Power Factor = Cos(0) = 1.0

On the other hand, your Power Factor Angle could be given in Radians, so the formula then is different....

Actually Eccan was the OP for this topic Lancie. However, I appreciate you chiming in. He posted the information he received from AD Tech Support in post 12, which I presume you are referring to.

http://www.plctalk.net/qanda/showpost.php?p=390699&postcount=12

It seems like an odd way of doing it to me, but there may be technical reasons. It sure would be nice if it reported HP or KW directly.

Stu.....

 

[briancr]

motor output power

the op stated he wanted to measure to motor output power, thing can get tricky here. motor input power from a drive is not the same as the shaft output power.

you have to take into account the slip of the motor, as well as copper losses in the stator, iron losses in the rotor, frictional and windage losses.

on bigger motors the difference between the two can be fairly large. this alone is a science on its own