Power factor of Large Motor

[Designer69]

Gents,

good afternoon, pereviously I posted about an 8000HP motor we are using. I have a question about the power factor of this motor. It is at 88% at full load.

this seems pretty low to me, would you concur?

Also, this should tell me that this is not a synchronous motor right? Don't synchronous motors have power factor close to unity?

Sorry my motor knowledge is kind of limited and I am trying to get the big picture, Thanks

 

[dkarst]

I just glanced at a couple of spec sheets for motors in the 400 - 750 HP range and they appear to have a PF of 86 - 88% at full load. Although they are quite a ways smaller than your machine and someone with more experience may chime in, the 88% seems reasonable.

On your second question, the power factor of a synchronous motor can be controlled by changing the field current and if you don't have this, you don't have a synchronous motor.

 

[Besoeker]

Gents,

good afternoon, pereviously I posted about an 8000HP motor we are using. I have a question about the power factor of this motor. It is at 88% at full load.

this seems pretty low to me, would you concur?

Doesn't seem inordinately low.
We put in a 6.6 MW (8,800 HP) with a pf of 0.91.
Another 6.3 MW (8,500 hp) machine we did had a full load pf of 0.878.
So your 0.88 is in the ball park.

 

[GeorgeB]

I'm not an expert, but had an associate some 30 years ago who told me that induction motors can have any of many characteristics optimized, but that old "choose any 2" idea holds true. Starting torque, efficiency, run slip, power factor, voltage sensitivity, etc, etc, are all under the designer's control.

Higher efficiency motors, for example, tend to have lower LOW LOAD power factors ... that is, a premium 100HP motor will draw more current (but probably not power) than a low$ version. Some of the methods to lower the pf hurt efficiency ... in the extreme, a resistor has unity power factor.

 

[RoberteFuhr]

It should state on the nameplate if it is an induction or Synchronous motor. With a synchronous motor, you can vary the PF by changing the field voltage. Most operators will set up the synchronous motors to have a leading PF. Synchronous motors produce VARs and increasing the field voltage will produce more VARs.