3-phase AC motor efficiency
3-phase AC motor efficiency
(OP)
Ok this may seam like a basic question, but my background is mechanical engineering and I seam to be failing to remember what I learned in EE class.
I have a 250 hp motor that is driving an air compressor and it is rated at 440v and 262.5 amps and has a PF 1. I want to find the efficiency of this motor and I was using this equation
I=(0.746*hp)/(1.73*E*eff*PF)
I = amps
hp = horsepower
E = line to line voltage
eff = efficiency
PF = power factor
I run this equation and I keep getting an efficiency of like 0.09%
Any ideas what I'm doing wrong?
Thanks
I have a 250 hp motor that is driving an air compressor and it is rated at 440v and 262.5 amps and has a PF 1. I want to find the efficiency of this motor and I was using this equation
I=(0.746*hp)/(1.73*E*eff*PF)
I = amps
hp = horsepower
E = line to line voltage
eff = efficiency
PF = power factor
I run this equation and I keep getting an efficiency of like 0.09%
Any ideas what I'm doing wrong?
Thanks





RE: 3-phase AC motor efficiency
and I suspect your PF would be slightly less than 1, depending on the motor used.
RE: 3-phase AC motor efficiency
.746*hp = I*E*PF*1.73*Eff
I/m a bit rusty on that but I think that's correct. Of course, the motor isn't at a PF of 1.00 either. Depending on load, it could be anywhere from .92 to .30.
RE: 3-phase AC motor efficiency
Gunnar Englund
www.gke.org
RE: 3-phase AC motor efficiency
RE: 3-phase AC motor efficiency
Gunnar Englund
www.gke.org
RE: 3-phase AC motor efficiency
RE: 3-phase AC motor efficiency
Gunnar Englund
www.gke.org
RE: 3-phase AC motor efficiency
If you do not have an instrument to measure the power factor (PF), you can adjust the motor excitation to fit PF = 1.0.
The procedure is simple, under the desired operating load, move the field excitation up slowly and watch the line currents, increase excitation until you notice that the line currents increase too, now reduce gradually the excitation; the line current must decrease up to a point when reducing the field increases the line current again. The point of minimum line current is when the motor has unit power factor (PF=1.0). Then you can calculate the efficiency corresponding to PF=1.0 with your formula and the recommendations above .
RE: 3-phase AC motor efficiency