Higher power factors reduce system losses, improve system voltages, increase system capacity, can lower transformer requirements, and (possibly) reduce power costs (depending on the electric utility rate schedule).
Methods for improving power factor are divided into two classifications - one in which equipment operates at unity power factor thereby improving the overall power factor of the system, and the second where auxiliary equipment is used specifically to supply the magnetizing power or kilovars needed by the load.
Equipment that operates at unity power factor includes:
When this type of equipment is added to a system, the overall power factor of the system improves. This additional real power (kilowatts) increases the demand and the energy cost and is never done for the sole purpose of improving the power factor. However, the choice of load (such as a synchronous motor over an induction motor) can improve power factor. For our discussions, we will reduce the kVAR load rather than increase the kilowatt load to improve the power factor.
Improving power factor by reducing the kilovar load requires the use of power factor equipment which operates at a leading power factor such as:
Synchronous motors which are either over-excited or underloaded with full excitation so they will supply kilovars to the electrical system.
Static capacitors which are electrical devices without moving parts that have the ability to provide magnetizing current to the load. Their efficiency is high since losses are less than one-half of 1 percent of their kVAC (or kVAR) rating.
In the past two other types of equipment were used to supply kilovars to a system: synchronous condensers and synchronous converters. The synchronous condenser is a synchronous motor without shaft extensions (so it cannot carry any mechanical load) which idles across the power system. Increasing its field excitation results in its furnishing magnetizing power (kilovars) to the system. Its principal advantage was the ease with which the amount of correction could be adjusted. The synchronous converter was a machine with both slip rings and a commutator connected to the armature windings. This could supply direct current in much the same way as a conventional motor-generator set, but with some economy of size, weight, and material. Adjustment of the field excitation changes the amount of magnetizing power it could supply to the alternating current power lines. Both of these machines have been replaced principally by the use of static capacitors.
Example: Power Factor Improvement
