In ac circuits the power factor has its own significance. There is a lowest limit beyond which it cannot be permitted. In big industries and organisations, special arrangements are made to indicate and limit the lowest power factor for example the power factor demand indicators etc.
There are the following equipments generally employed for the power factor correction:
Synchronous capacitors: The over excited synchronous motor works as the power factor correction equipment, and in this case it is known as synchronous capacitor. The motor draws leading current and thus leading kVAR which neutralizes or balances the lagging kVAR of the system, thus increasing the power factor. The biggest advantages of this system is to have required power factor improvement just by varying the field excitation. Secondly, the mechanical energy is also available on the shaft which can be utilized.
Capacitor bank or static capacitors: A group or bank of the Capacitors are generally installed in the substation or at the site to improve the power factor of the load. These are frequently used near the group of a.c. motors. The capacitor draws leading current which meets the lagging reactive component of the current hence improving the power factor. These are employed with an automatic switching off arrangement to avoid the over compensation.
Phase advancer: These are also used to improve the power factor.
These are installed with industrial machines.