Electric motors are rated in kW instead of kVA because kW is the amount of ‘actual power’ an electrical system has, which shows how much power is being converted into useful, working output.
kVA, on the other hand, is the measure of ‘apparent’ power, which tells how much is being used in the system overall.
The main difference between kW and kVA is the power factor, which is defined and known, and in the kW to kVA calculations, kVA value will always be more than the kW value¹.
The motor has a 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 account only active power which has to be converted into mechanical load.