[Explained] Why Alternator rated in KVA but Motor rated in KW or HP?


alternator rating and motor rating


Hey, today we are going to know why alternator rated in KVA or MVA but electric motors are rated in KW or MW or HP. Electric motor and alternator both are electrical machine and have windings or coil inside them but why the rating is not the same? KVA, MVA, KW, MW are used for AC supply purposes so remember that we are talking about AC motors and AC generators or alternators.


Before going to our main topic you should know the difference between KVA and KW

KVA, MVA are the large units of apparent power and KW, MW are the large units of active power.

(KVA = Kilo Volt X Kilo Ampere) that means it is the simple product of current and voltage.

(KW = Kilo Volt X Kilo Ampere X power factor) that means it is the product of current, voltage, and power factor.


Why Alternator rated in KVA or MVA?


(1) Power Factor is depended on the type of load or power consumers, not on the power generators.

        Resistive load = unity power factor
        Inductive load = lagging power factor
        Capacitive load = leading power factor

As the alternator is not a load so there is no power factor concept comes. So the alternator is rated only based on current and voltage that is VA, KVA or MVA.



(2) When engineers design an alternator they do not know what type of load will be connected with the alternator so they cannot decide the power factor as the power factor depends on types of load. They only know the voltage and current can be delivered by the alternator. So this can be called as a reason why alternator rated in KVA.

(3) The losses occur in an alternator such as copper loss and iron loss do not depend upon the power factor. The copper loss depends upon the flow of current through the windings, and the iron loss depends upon the voltage produced by the alternator.


Why Electric Motor rated in KW or MW?


As the electric motor is load or power consumer so the power factor comes in the rating. The electric motor is an inductive load so it has always lagging power factor. The current drawn by the motor depending upon the power factor so the power factor must be taken in the power rating. So as the power consumed by the motor depends on the voltage, current, and power factor that is why electric motor rated in Watt, or KW or MW.

HP or Horse Power is also a unit of power. In the case of electrical power,

1 HP = 746 watt (approx.)




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[Explained] Why Alternator rated in KVA but Motor rated in KW or HP? [Explained] Why Alternator rated in KVA but Motor rated in KW or HP? Reviewed by ETechnoG on 16:58 Rating: 5
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