Why transformer rating is in kVA but for all other it is in kW?

There are two type of losses in a transformer;
1. Copper Losses
2. Iron Losses or Core Losses or Insulation Losses

           The transformers, alternators etc. are all electromagnetic devices. Electromagnetic devices do not dissipate energy, but they store the energy in the form of magnetic fields and electric fields when they are energized. Since this is not the same as power dissipation of a resistive load we cannot label it as power dissipation or kW (Watts), this power though being used up is not actually getting dissipated so it is not real but apparent and hence for differentiation with resistive or active power we designate it with kVA (Volt * Amperes = Watts), hence we can say that transformer can drive kW of load but the rating will be kVA.
        When the current is flown through the core wounding made of copper coil due to the joules heating effect lots of heat is generated which is called as copper loss.  And also the flux through the sheet of core also causes some irregular circular looped currents which has no direction which is called as eddy's losses.

          Since the copper loss and eddy current loss depends on the rating of current flowing through the transformer and also depends upon the type of load which determines the power factor, It is necessary to denote the rating of transformer in kVA but not as Kw.

            KVA does not include the term power factor in it while KW does. So since the total losses is dependent only on Voltage and Current values (not on power factor), the ratings of the transformers are also given in terms of VA or KVA.

           In controversy the motor has fixed power factor, and its value also been defined and proved.  which is in kW.  In addition except the transformers all other electrical components converts one form of energy to another form for example motor converts electrical energy to mechanical energy and we are measuring the active power which converted electrical to mechanical energy.  Although the motor power factor does not depend upon the load connected to it the value is fixed to all motors.

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About Sooriyamathy

This blog is created to explain people the concepts, which they are finding difficult to understand in electrical and electronics world. This blog also post stuff related to stargazing.