You will need
  • - power factor;
  • tester.
To calculate the reactive power of the appliance, carefully read its documentation it should be given the power factor Cos(φ). With a multimeter measure the power consumption of the device, then from number subtract 1 power factor, and the resulting number multiply by the measured power (PP=P•(1 - Cos(φ)). The result will be the reactive power of the device. In some devices develops significant reactive power, for example, arc furnaces or welding machine AC its value can reach 40% of the nominal power.
If the device does not indicate the power factor, calculate the reactive power independently. For this, use a tester that is configured in the mode voltmeter, measure the voltage drop across the device, the effective value. Find out the frequency of the AC network where the connection device, for standard home network, this value is 50 Hz.
Switch the tester to the measurement of inductance and find out its value for this device in Henry. Then switch the tester to measure the capacity to learn it, expressed in Farads. In both cases, the tester connect a parallel device to its clips.
Calculate the reactance for this:

1. Multiply the number of 6.28 for the frequency of the current and the inductance, the result will be the inductive reactance XL=6,28•f•L.
2. The number 1 divide by 6.28, the frequency of the current in the network and the capacitance of the device, the result is a capacitive resistance XC=1/(6,28•f•C).
3. Find the reactance of the folding of the results obtained in PP.1 and 2.
4. Find the reactive power by dividing the square of the voltage on the reactance RR=U2/Rp.
Thus, the reactive power depends on the frequency of the current in the network, inductance and capacitance in the load.