交流电源和电感间进行的功率交换就是无功，给电感并上一只电容器，电容器将替代电源和电感进行功率交换，这就是无功补偿。此时电源可有可无（电容器对电感全补偿）。 

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).