Generators and transformers are rated in kilo-volt amperes (kVA). But the motors are rated in Horse Power (HP) or in kilo-watts (kW). Do you feel confused? If so, this article would definitely help you in alleviating your confusion regarding the rating of motors and alternators.
The rating or specification of these electrical devices has a significant relation with its voltage-current characteristics. The transformer is an electromagnetic device whose power factor depends on the type of load connected to it. It has primary and secondary winding. Based on the electromagnetic induction, the emf is generated at the secondary. This inductive property makes the consumption of active as well as reactive power in a transformer. Thus the total power consumed by a transformer is the apparent power. That is why it is rated in kVA. This is applicable to generators as well. The nature of the load connected to the generators/transformers determines the power factor. But in the case of motors, the load connection does not depend upon the power factor.
The motor converts electrical energy to mechanical energy. This energy conversion is independent of the load connected to a motor. That is it has a fixed or defined power factor. The reactive power dissipation in a motor is equal to zero. That is only active power is taken into account. Hence the motors are rated in kW.
