Since all electric motors depend upon magnetism to work, they must be supplied with VARs in addition to the work-performing Watts. The power lines to the terminals of a motor or other magnetic apparatus must bring both of these types of "electric power" to the device. The wires must be large enough to carry them both.
One analogy that is used to illustrate this is a mug filled with beer and a head of foam. The mug needs to have room for both the liquid and the foam, just as the wires must carry both real (watts) and magnetizing (VAR) power. It is expected that the mug will be oversized relative to the amount of liquid; likewise, the electrical system must be "oversized" enough to carry both Watts and VARs to the motor. The degree of this extra margin depends upon how large the kVAR load is when compared to the motor kilowatts.
If the foam is blown off the mug, there is room for more liquid. This also is true of the electrical system. If the reactive power is taken from part of the system, that part could carry more Watts. This process is called "power factor adjustment" or "power factor correction." This will be discussed in detail in another part of this course. For the present, a simple problem will be sufficient.
Consider a mug with 80% of its volume occupied by the liquid. In terms of the liquid in its total volume, it is 80% full; its "beer factor" is 0.80 (or 80%). This would be similar to an induction motor with an input of 80 kilowatts and 100 kVA. (It has a reactive input of 60 kVARs under these conditions). It must have this reactive power to continue to operate as a motor). This motor is said to have a power factor of 0.80, or 80% for this situation:
Likewise, the Reactive Factor is the ratio of kVARs to kVA:
Power Factor Analogy
What Is Power Factor?
