Home › Electrical Engineering Forum › General Discussion › how to find apparent power and reactive power? › Re: how to find apparent power and reactive power?

Hi

Static or rotating device : this is a mechanical difference (even for AC inductive motors which have electrical rotating magnetic flux)

But the general rule is : as long as there is inductance (or capacitor) inside the load, their is an apparent power and reactive power,

Please note that reactive power is the power responsible of creating the magnetic flux (which is 90% of cases apply on rotating machines :)

To know the apparent and reactive power on any machine, I'll use an inductive motor as an example,

On every motor there is a name plate, which must indicates the apperant power ( Pn in W or KW or HP ) , Voltage ( in V ), and the phase shift ( cos phy ), and nominal current ( In in A)

Those values are for the full load,

for lower loads you should measure the current I and compare it to the nominal current In and devide with the calculated ration I/In=A

P =Pn x A, Q=Qn x A

Now for Q reactive power in VAR

Q=P x tg (Phy)

Phy can be known by any scientefic calculator,

Please note that the Harmonics effects are not considered here.

Take care