Easy-To-Understand 'Power Factor'
Q: I’m confused by the term 'power factor.' Do you have a simple explanation for a guy who’s really not very technical?
A: Well, for those of you who are a little technical, the power factor is the ratio of real power to apparent power—or, in other words, pF = Real Power/Apparent Power.
Real power is that which performs work for you, and apparent power is the product of the voltage and the total current—or V x I.
Power factor correction can benefit any facility that uses electric motors through reduced power consumption and wear on both motors and power grids.
Volumes have been written for those of you who need to know precisely what ‘power factor’ is in a very technical way. For the rest of you—including you, P.T.—I provide the following explanation.
Years ago, when we were little, some of us had HO scale race cars that we did our best to demolish by sending them around the track faster than the little pin could hold them. Maybe your kids have them now. When they crashed—especially when there was a spectacular "crash and burn"—we were left with the job of reassembling all the parts that could be found.
Inside their tiny little motors were two magnets, which we discovered were necessary for the operation of the motor. Failure to locate and reinstall both magnets meant the car would not run. Without the magnets, we could put the car on the track and squeeze the hand control to provide electricity to the motor—but nothing happened.
Fast forward 20 or 30 years, and we now have much larger motors powering conveyors, pumps, and fans in our facilities. These are different motors operating on AC instead of DC power, but all motors have in common are that they all require a magnetic field to operate. The magnetic field in our facility's motors is generated with the electric current—not tiny permanent magnets. That "electro-magnet" current does not do any work for us; it merely allows other current provided to the motor to spin the motor within the magnetic field.
So, if it does not do any work for us or provides any power, what should we call it? Some call it "imaginary power," others call it "phantom power. " But the proper term is "reactive power." Whatever you call it, it is very real, very necessary, and very measurable.
It is current that is responsible for the concept of ‘power factor’—the ratio of real power to apparent power. Real power is calculated as the product of the voltage and the current that performs work for us. Apparent power is computed as the product of the voltage and the total current utilized—both that which does work for us (the real current) and that which merely creates a magnetic field (the reactive current).
I hope that helps, P.T.
Written by Christopher T. Burke, P.E., Lead Electrical Engineer