Power factor correction

Power factor correction capacitors will change your life.

Ok, maybe I’m over selling it a bit but it is pretty cool.

Here is the scenario:

Inductive loads use true power (watts) to get the job done.  However they also have a reactive component.  This reactive component dissipates power too but it does it by transferring energy back and forth to and from magnetic lines of flux.  It is sometimes called wattless power because there is no actual work being done.

Because we have true power and we are adding it to reactive power we have to add them vectorally (they are 90 degrees out of phase remember) .  This gives us our apparent power (VA)  and it is this number that we use to determine current.  This can sometimes suck because the reactive component can be quite high, which in turn gives us a high apparent power.  This means we are using more current than we need to.

Awww man!!!

I know, I know, but don’t worry.  There is a solution!

We send in a capacitor for power factor correction.

Capacitors and inductors are opposites.  By putting a capacitor in the circuit we have something that is pushing back on the inductor.  It shrinks the inductive vars to what ever value we want.

Phew. So I don’t have to give up the trade and become a barista?

Maybe as a side job but no, you can still be an electrician.  The question is how do we size a capacitor for power factor correction?  Well lucky for you we have a complete walkthrough of how to calculate this.

To sum up the video though.

Calculate each branch into a power triangle.

Create one triangle to rule them all.  Add all your true power for the bottom of the triangle.  Add all your reactive power for the side of the triangle.  Using the power of pythagoras calculate the apparent power.  This now is the triangle you have.

Create the triangle you want by using the desired power factor and the true power of the circuit from the previous triangle (resistance never changes).

Subtract the Vars from the triangle you want from the Vars of the triangle you have and boom; you have the size of capacitor needed for power factor correction.

It isn’t that easy, is it?

Yup it is.  Power factor correction can be made to be as complicated as you want it to sound.  However when you strip away all the big words it is a very simple concept.

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