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Why is a Motor Rated in kW instead of kVA?

Why are Electric Motors Rated in kW or Horsepower (hp), and Not in kVA?

We already know that Transformer rating may be expressed in kVA instead of kW as well as Generator and Alternator rated in kVA. This is because the manufacturer and designer doesn’t know the actual consumer power factor while manufacturing transformers and generators i.e. the P.F (Power factor) of transformer and Generator/Alternator depends on the nature of connected load such as resistive, capacitive, and inductive load etc which affect the overall power factor of transformer and generators as the consume reactive power according to the load as well. The scenario is different in case of rating of eclectic motors.

Why is Motor Rated in kW instead of kVA

On the other hand, Electric Motor has fixed Power factor, i.e. motor has defined power factor (P.F)  and the rating has been mentioned in kW on Motor nameplate data table. That’s why we rated Motor in kW or HP (kilowatts/ Horsepower) instead of kVA. in more clear words, Motor only consumes active power in watts as input and provides mechanical power in HP or kW at motor shaft as output.

In addition, an electric motor is a machine which converts electrical power into mechanical power. In this case, the load is not electrical, but mechanical (Motor’s Output) and we take into the account only active power which has to be converted into mechanical load. Moreover, the motor power factor does not depend on the load and it works on any P.F because of its design. These are the simple reasons why is a motor rated in horsepower (hp) or watts (W) instead of volt-amperes (VA).

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  1. Dex Banner says:

    Glad to have found your site. Keep up the good work!

    1. There is a AC synchronous generator with cosθ = 0.85 supply for a AC asynchronous motor with cosθ = 0.92
      Could you explain for me the different between two power factors.
      Thanks so much !

  2. GanpatiEngineering says:

    Thanks for such an informative post. The difference between kW and kVA is not known to most of the people.

  3. Anonymous says:

    How do you calculate the size compasitor needed on any motor

  4. Anonymous says:

    It was great thank you very much

  5. There is a AC synchronous generator with cosθ = 0.85 supply for a AC asynchronous motor with cosθ = 0.92
    Could you explain for me the different between two power factors.
    Thanks so much !

  6. Amreek. Sing Rajiana says:

    No . Motor power factor depends upon the load. Increasing the load increasing the power factor. So a induction motor should always be pit on maximum load. If we have only induction motor loads in a factory then we we use capacitor bank

  7. if exitation are falling how to make new it

  8. biswajit halder says:

    it is very good said for all eng student

  9. Its interesting while reading the informations. but answers are not clear in many topics. many of the answers are specified with some reasons. There wont be any explanation for those reasons. At the time, we get struck to believe the answers which are specified is really a correct. so please explain the reason along with the answer. then only the reader get to understand it clearly. just i expressed my suggestion. :-)

  10. raju patel says:

    Is there really 1 ton ac consume 3.516 kw power ?

  11. raju patel says:

    If we have three phase and neutral supply and we get deferent voltage between each phase and neutral. I want to know that how can we get equal voltage in between each phase and neutral.

    1. muhammad ilyas says:

      equalize the phase angle between each phase i.e 120.

  12. The in formation provided clears the doubts and makes the concept very clear of an interested reader.

  13. Its really good and had gain knowlage from it
    thank a lot

  14. AK Behera says:

    it is really interview based questtion

  15. AK Behera says:

    excellent rly satisfied

  16. Devendra Kumar says:

    it is very good site for all engineering student

  17. Asad Khan says:

    Cos 0.85 will not affect the motor which has a pf of 0.92

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