Tuesday, April 28, 2009

Introduction to Power Factor Correction

Power factor is the ratio between KW and KVA and is a measure of the usefulness of the current applied to the load. A poor power factor can result due to a significant reactive component to the current, or due to a high level of harmonics in the current flowing. A lagging power factor is common and is due to an inductive load such as induction motors, chokes, lighting ballasts and transformers. A lagging power factor can be corrected by the addition of power factor correction capacitors. Poor power factor due to a high level of harmonic currents as caused by variable speed drives, rectifiers and discharge lighting can not be corrected except by the use of expensive filter circuits.

Power Factor correction is applied to circuits which include induction motors as a means of reducing the inductive component of the current and thereby reduce the losses in the supply. There should be no effect on the operation of the motor itself.
Power factor correction is achieved by the addition of capacitors in parallel with the connected motor circuits and can be applied at the starter, or applied at the switchboard or distribution panel.
Capacitors connected at each starter and controlled by each starter is known as "Static Power Factor Correction" while capacitors connected at a distribution board and controlled independently from the individual starters is known as "Bulk Correction".

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