Why is a Capacitor Added in Parallel for Power Factor Correction in an RL Load?

[naismith15]

Hey,

Theres something I'm curious about. If you consider a voltage source connected to an RL load , in order to compensate for the lagging power factor produced by the inductor in the load all the textbooks say we should add a capacitor IN PARALLEL to the load. Wouldn't a capacitor added in series (or any other combination for that matter) to the load accomplish the same thing? if so, For what reasons is the parallel combination chosen?

 

[lilrex]

The capacitor in parallel acts as a resonant circuit with the inductive load. When the field collapses off of the inductor it will send its stored power back through the lines, this causes the PF to reduce. By adding a capacitor in parallel that back EMF is accumulated in the capacitor and when the voltage reverses the capacitor feeds the inductor and only what is needed to top off the capacitor is used by the system. Ideally you would use a perfect match but practically you would mismatch it a little about 95% or so to prevent harmonics that can throw the voltage pretty high destroying the cap or inducer.
Technically the relationship would be explained by the reactance of the inducer is matched by the exactly opposite characteristics of the reactance of the capacitor, thus canceling out each others reactance. You can look up power factor correction on Wiki to get a more detailed explanation. It is interesting to note that to increase the power factor of a capacitive load you add inductors in parallel, funny how that works (math! can’t get away from it) . And of course if I am leading you a stray I am sure I will be corrected.

I know it only answers half of your question but I hope this helps.