Understanding Active and Reactive Power

Electrical Engineering students find it difficult to understand the difference between active and reactive power. The tool given in here enables changing relevant parameters and observe the behavior of apparent power, active power, and reactive power.

Apparent Power

Let's drive an equation for instantaneous apparent power.

The equation for the instantaneous voltage:

The equation for the instantaneous current:

where;

 is instantaneous voltage

 is instantaneous current

 is RMS voltage

 is RMS current

 is system frequency

 is phase angle between the voltage and the current

if you  substitute  and  and apply little bit of trigonometry,

This shows that apparent power can be decomposed into two components. The green color component is active power and the red color component including the negative sign is reactive power.

Active Power

You may observe that the direction of the active power is always positive. This means active power always flows from the source to the load.

Reactive Power 

The direction of the reactive power change in a frequency of two times the system frequency. This means loads absorb and release reactive power. The released reactive power should be absorbed by the source.

Tool

You can change RMS voltage, RMS current, frequency, and the load power factor and observe the changes in apparent power, active power, and reactive power. 

When the power factor is 1, there is no reactive power and when the power factor is 0, there is no active power.