What’s common for Beer Mug and Power Factor?

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What's common for Beer Mug and Power Factor?
What’s common for Beer Mug and Power Factor?

Understanding power factor is not that hard. We have some very common example from the real life you will understand for sure, but first let’s start with some introduction of power factor.

To understand power factor, we’ll first start with the definition of some basic terms:

kW is Working Power (also called Actual Power or Active Power or Real Power). It is the power that actually powers the equipment and performs useful work.

kVAR is Reactive Power. It is the power that magnetic equipment (transformer, motor, relay etc.) needs to produce the magnetizing flux.

kVA is Apparent Power. It is the “vectorial summation” of KVAR and KW.

Example From the Real Life ;)

Power factor - Example from real life
Ok, these folks must’ve been running some heavy reactive power compensation – ’cause there’s no foam P.F.=1 ;)

Let’s look at a simple analogy in order to better understand these terms….

Let’s say it’s friday evening, and you are with your friends at your favorite pub after really hot day. You order up a big mug of your favorite beer for you and for your friends. The thirst-quenching portion of your beer is represented by KW (the big pic on top).

Unfortunately, life isn’t perfect. Along with your ale comes a little bit of foam. (And let’s face it…that foam just doesn’t quench your thirst.) This foam is represented by KVAR.

The total contents of your mug, KVA, is this summation of KW (the beer) and KVAR (the foam).

So, now that we understand some basic terms, we are ready to learn about power factor:

Power Factor (P.F.) is the ratio of Working Power to Apparent Power.

Power factor formula

Looking at our beer mug analogy above, power factor would be the ratio of beer (KW) to beer plus foam (KVA).

Power factor formula - Analogy with beer mug

Thus, for a given KVA:

  1. The more foam you have (the higher the percentage of KVAR), the lower your ratio of KW (beer) to KVA (beer plus foam). Thus, the lower your power factor.
  2. The less foam you have (the lower the percentage of KVAR), the higher your ratio of KW (beer) to KVA (beer plus foam). In fact, as your foam (or KVAR) approaches zero, your power factor approaches 1.0.

Our beer mug analogy is a bit simplistic. In reality, when we calculate KVA, we must determine the “vectorial summation” of KVAR and KW. Therefore, we must go one step further and look at the angle between these vectors.

Power Triangle

The “Power Triangle” illustrates this relationship between KW, KVA, KVAR,  and Power Factor:

Power Triangle

Note that in an ideal world looking at the beer mug analogy:

  1. KVAR would be very small (foam would be approaching zero)
  2. KW and KVA would be almost equal (more beer; less foam)

There are dosen of tools and technical articles/guides published at EEP that can help you to understand power factor and its controlling. Hope these can help:


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About Author


Edvard Csanyi

Edvard - Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry fascilities. Professional in AutoCAD programming. Present on