Why Motor rated in kW/Horsepower instead of kVA?
We already know that Transformer rating may be expressed in kVA instead of kW as well as Generator and Alternator rated in kVA. 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.
At the other hand, 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 are rated Motor in kW or HP (kilowatts/ Horsepower) instead of kVA. in more clear words, Motor only consume active power and provide mechanical power in HP or kW at motor shaft.
In addition, Motor is a device 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.
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