motor pfc

[puckman]

If a motor is operating at 50% or less is causing poor power factor should getting motors sized to operate at near to full load as possible be a way to go to correct low power factor ?
Should a load survey of motors be conducted to check pf ?
The reason I am asking this is because the pf meter at the service is reading .7 never much higher.
Thanks in advance for the help.

 

[Besoeker]

If a motor is operating at 50% or less is causing poor power factor should getting motors sized to operate at near to full load as possible be a way to go to correct low power factor ?
Should a load survey of motors be conducted to check pf ?
The reason I am asking this is because the pf meter at the service is reading .7 never much higher.
Thanks in advance for the help.

It is one way. Power factor correction capacitors might be cheaper.

 

[ptonsparky]

10 motors or 1500? Some loads may require that 10HP to get moving but only 5 to maintain. Caps are probably easier now but a load survey would pay off for those items where a motor is oversized. PF is only part of the billing and KW usage is the bigger part.

Then the question: I have a paid for $3000 motor that is oversized. A new High Efficiancy one of proper size is $3000 plus installation and down time. Hmm.

 

[PowerQualityDoctor]

A rule of thumb for motor loading and PF: PF = P% + 0.1 (i.e., 0.7 PF means 60% load).

The problem with partial loading is not the PF, but the efficiency. If the motor is lightly loaded, you pay more than required. The loading inefficiency point depends on the motor size and type. If it is less than 50% - consider replacing. Of course, it depends on the size of motor, how long it is used etc.

If you choose to correct PF - fixed capacitor may be sufficient since the reactive power does NOT change (or almost doesn't) with load. Calculate the capacitor for full load and put the required capacitor.

Important note - if you have VFDs, it is strongly recommended to use reactors with the capacitors.

 

[Jraef]

The fist step is to determine why the motor is over sized. If it is just because someone got a deal on a larger motor, then you need to look at getting the correct size because of the efficiency issues raised in earlier posts. In many areas of the country, PoCos are still providing energy efficiency improvement rebates that can defray the costs of changing the motor, as long as the replacement is properly sized and is an energy efficient design.

but if the motor is over sized because you needed the starting torque, or there is an occasional overload situation in the normal process it is involved in, then you need to leave it alone. IF YOUR UTILITY PENALIZES YOU for poor PF, then add PFC capacitors to the motor circuit. If they don't penalize you, they are a waste of money unless you need to add capacity to an existing transformer or something.