What is difference between kw and kva?

kW is the unit of real power & kVA is the unit of Apparent power.

Apparent Power= real power + reactive power

Besides this,the ratings which we write on a motor or generator is KVA & not KW. B'coz there are two types of losses in a motor or generator- core losses & ohmic losses. Core loss depends upon the voltage applied & ohmic losses depend upon the current flowing & none of these losses depend upon the power factor i.e. Cos@. As we know that

KW power = V * I *Cos@.

But as the losses are independent of the power factor hence we need to calculate only KVA = V*I.

Comment

Apparent power is the vector sum of real power and reactive power, not the sum.
KVA is the unit of apparent power and KW is unit of active power.

KW is kilowatts, and KVA is kilovoltamps. KW is the apparent power that a normal power meter would measure, while KVA is simply the maximum of the instantaneous product of volts and amps divided by 1000. The difference between these two terms is due to phase angle, which is due to the reactance of the load to an AC power source.

KW (kilowatts) is apparant power, while KVA (kilovoltamps) is true power. They are different when the phase angle between voltage and current is not zero, i.e. when the load is reactive, such as in a motor. The ratio of KW over KVA is Power Factor, and is the cosine of the phase angle between voltage and current. It is zero at a phase angle of 90 degree, which occurs for purely (ideal) inductive or capacitive loads with no resistance in the source or conductors, and it is one for purely resistive loads.