Almost exclusively AC (Alternate Current) is used for production, transmission and distribution of electric energy. Two kinds of efficiencies are distiguished at this form of energy.

• effective power (e.g. engine drive power, furnace heat power, etc.)

The specification of the power: customer takes it from the network, use it.

• reactive power: there is another power available at every machines and equipments working on the bases of electromagnetic principles (e.g. transformers, reactors, motors) due to operating activities. A magnetic field is coming up and ceases in these equipments in the beat of the frequency of the connected alternate current.
  The necessary power is coming from the network. This power is not used, only stored in the magnetic field, and will flow back to the network when the magnetic field goes off.
  This power is called as commuter or reactive power.

The commute transportation of the reactive power of the magnetic field between the energysupplier and energyconsumer happens by the help of an inductive reactive power, which causes loss heat in the energy generator and the wires. In order to avoid this, the energy generator and the wires has to be immunized from the reactive power. The result is that both equipments can be better loaded with effective power, that is better utilisation.

The decontamination of the inductive reactive power can be best achieved with a similar type reactive power, which is flowing in the opposite direction, terminating (compensating) the inductive reactive power.
This requirement can be ideally achieved by the reactive power necessary to create the electric field in the condensators, because it is fluctuating in the same tempo as the inductive current, with such a timely faseshift, that the necessary compensation will be created.
The appropriate scaling of the tuned filtercircuit is necessary to it's realization.
After this the reactive power is commuting between the consumer and the compenzating equipment.

The Power Factor Correction can be made in several modes:

• individual compensation (used at constans consumption loads, every consumptive get a suitable size condensator)
• group compensation (more consumptives are compensated with a  tuned filtercircuit, which is usually operated by a magnetic switch)
• center compensation (installing a compensating equipment on a unique point)
• mixed compensation (individual compensation of the important consumptives, group or centralised compensation of the rest)