Motor Power Factor Correction

[tofi1878]

The problem i have is a balanced load motor which has a rating of 195A on the name plate, yet it doesn't give a power factor, so we manually measured it with a clamp meter at the supply to 0.56, so does this mean when we measure the current at the supply(using clamp meter),is the maximum we can give the motor still 195A, or can we give it more to compensate for the poor power factor?

 

[jwerthman]

56% power factor is pretty poor unless the motor is lightly loaded. The FLA stamped on the nameplate already takes into account the motor power factor at full load and rated voltage. You can't load the motor up to more than 195 amperes without overloading it (or at least operating into the service factor, which may be 1.15 x FLA). No matter what you do to correct the poor power factor of the motor externally, the motor will still draw the same current for the same load. Correcting the power factor will reduce the current in the supply line, however, which is the goal.

 

[electricpete]

I agree with jwerthman.
#1 - 56% was probably measured at a low load (what was the current? what is nameplate speed?... low-speed motors usually have even lower power factors at low load than high-speed). If I measured 56% at FLA for an integral horsepower 3-phase induction motor, I would start wondering what's wrong with my motor.

#2 - You cannot increase loading above FLA or SF*FLA based on the power factor. The current is most directly associated with the heating that limits the motor capacity. And the power factor is known/accounted for in the motor rating.

 

[peebee]

All the above is true. Not to mention that NEC requires the overload device to be sized based on nameplate data; you would not be in compliance with code if you put in an overload greater than nameplate rating.

 

[infomaniac]

I agree with all the above. It is all true

 

[cuky2000]

Please check if the enclose site could be usefull for you.

http://www.squared.com/us/internet/pfc.nsf?OpenDatabase

 

[jbartos]

Suggestion to tofi1878 (Electrical) Jul 14, 2002 ///\\The problem i have is a balanced load motor which has a rating of 195A on the name plate, ///How many phases?\\\ yet it doesn't give a power factor,
///Which is ?\\ so we manually measured it with a clamp meter at the supply to 0.56, so does this mean when we measure the current at the supply(using clamp meter),is the maximum we can give the motor still 195A, or can we give it more to compensate for the poor power factor? ///Could you describe how you do this or how you intend to do this? The motor nameplate data posted would be very useful.\\