Electric motor efficiency calculation

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SUMMARY

The discussion focuses on calculating the electric efficiency of three-phase electric motors, emphasizing the importance of the power factor in the efficiency formula. The correct formula for work input is established as work in = V * A * PF * √3, while work output is derived from the motor's rated power in watts (hp * 745.7). Participants highlight the necessity of accurately measuring mechanical output, typically requiring a calibrated dynamometer, and stress that efficiency measurements should consider the motor's operating conditions, such as temperature.

PREREQUISITES
  • Understanding of three-phase electric motor principles
  • Knowledge of power factor (PF) in electrical systems
  • Familiarity with the concept of mechanical output measurement
  • Basic grasp of efficiency calculations in electrical engineering
NEXT STEPS
  • Research the use of calibrated dynamometers for measuring mechanical output
  • Explore the impact of temperature on electric motor efficiency
  • Learn about the significance of power factor correction in three-phase systems
  • Investigate methods for calculating energy consumption in kilowatt-hours
USEFUL FOR

Electrical engineers, motor technicians, and anyone involved in optimizing the efficiency of three-phase electric motors.

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Hello everyone,

I am trying to calculate the electric efficiency of some 3 phase electric motors but I am a little confused about the power factor.

efficiency=work out/work in

work out=rated W of my motor (hp*745.7)

work in= V*A*PF*√3

Is the work in correct?

Thanks
 
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Your formula is for POWER. Work is Power * time. Balanced 3 phase P = V*A*PF*√3.

Work = Energy = P*T ( You pay for Kilowatt Hours - not Kilowatts)

However the trick in this type of project is typically accurately measuring the mechanical output - needing a calibrated dyno - or other device.

Also - for efficiency it is important (or more meaningful) to define what the operating point is for the efficiency calculation / measurements. --e.g. A Cold motor is more efficient then a warm motor - etc.
 

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