交流電源和電感間進行的功率交換就是無功，給電感并上一只電容器，電容器將替代電源和電感進行功率交換，這就是無功補償。此時電源可有可無（電容器對電感全補償）。 

What is reactive power compensation？

Reactive power refers to the power exchanged between an AC power source and an inductor.If you connect a capacitor in parallel with the inductor, the capacitor will take the place of the power source to exchange power with the inductor. That’s what reactive power compensation is all about.And when that happens, the power source is no longer needed (this is what we call full compensation of the inductor by the capacitor).