Reactive power Q is an apparent power component and arises during power transmission by means of alternating current, since the strength and direction of the current change regularly. However, it does not contribute to power generation in the load, since it is periodically exchanged between the source and the load. Reactive power is described in units of volt-ampere-reactive (var) and occurs due to a phase shift between current and voltage. The reactive power Q is composed of an inductive (QL) and a capacitive reactive power (Qc): |Q| = |QL| - |QC|
The formula shows that the total reactive power is the difference between the inductive and capacitive reactive power. This is because loads usually represent ohmic-inductive loads. In addition to the active power, they use the inductive reactive power. Therefore, it is necessary to compensate the reactive power and thus reduce the apparent power and the associated load on a power system. To achieve this, capacitive loads can be connected to the actual load (capacitor banks) so that the reactive power is not exchanged between the load and the source, but between the load and the capacitor.