To understand power factor in an electrical system, first of all, we should have the knowledge of some basic terms which are used in an electrical system given below.
- kW – 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 – Reactive Power:- It is the power that magnetic equipment (transformer, motor, and relay)needs to produce the magnetizing flux.
- kVA – Apparent Power:- It is the “vectorial summation” of KVAR and KW.
Are you confused about these terms? It is better to understand these term with some simple analogy.
Beer Mug Analogy
- The thirst-quenching portion of your beer is represented by KW. This is the usable power.
- Along with your beer comes a little bit of foam. (And that foam just doesn’t quench your thirst.) This foam is represented by KVAR. This part is the wasted power.
- The total contents of your mug, KVA, is this summation of KW (the beer) and KVAR (the foam).
Also Read: Horse Rail Analogy
Understanding Power Factor
So, we understood some basic terms from the beer mug analogy.
Now we are ready to learn about power factor:
Power Factor (Cos Φ) is the ratio of Working Power (True Power) to Apparent Power.
PF = KW/KVA
Looking at our beer mug analogy above, the power factor would be the ratio of beer (KW) to beer plus foam (KVA).
PF = KW / (KW + KVAR)
Cos Φ = Beer / (Beer +Foam)
Thus, for a given KVA:
- 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.
- 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.
Power Triangle
The “Power Triangle” illustrates this relationship between KW, KVA, KVAR, and Power Factor:
PF = KW/KVAR = Cos Φ
Note that…in an ideal world…looking at the beer mug analogy:
- KVAR would be very small (foam would be approaching zero)
- KW and KVA would be almost equal (more beer; less foam)
So, In order to have an “efficient” system, we want the power factor to be as close to 1.0 as possible.
A power factor of one or “unity power factor” is the goal of any electric utility company.
It is because if the power factor is less than one, they have to supply more current to the user for a given amount of power use. In so doing, they incur more line losses.
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