Three Phase Motor Calculation

One 3-phase induction motor is running, voltage=415, current=0.8, hp=7.5, speed=1440rpm, pf=0.8.  How to calculate motor efficiency and torque, give the formula.
asked 5/11/2013
senthil kumar4
senthil kumar

1 Answer

7.5 hp =  5.6 kW - output power

phase voltage = 415/√3 = 239.6 V

239.6 (V) x 0.8 (A) x 0.8 (pf) x 3 (phases)  = 0.46 kw - input power

The input power cannot be less than the output, so I think there is something wrong with your values.  Once you sort this out you can get the efficiency be dividing the output power by the input power.

For the torque, there is a calculator on the site, which can help you (around 35 Nm for your example):

answered 5/25/2013 Steven McFadyen 208
Steven McFadyen
  • One 3-phase induction motor is running, voltage (RY=392V, YB=394V, BR=380V), current (R=2.1A, Y=2.9A, B=2.1A), speed=2900rpm, pf=0.8. How to calculate motor efficiency and torque, give the formula. - senthil kumar 5/27/2013

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