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Power Factor Introduction

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Power Factor.

Power Factor Definition : Power factor is the ratio between the KW and the KVA drawn by an electrical load where the KW is the actual load power and the KVA is the apparent load power. It is a measure of how effectively the current is being converted into useful work output and more particularly is a good indicator of the effect of the load current on the efficiency of the supply system.

All current will cause losses in the supply and distribution system. A load with a power factor of 1.0 results in the most efficient loading of the supply and a load with a PF of 0.5 will result in much higher losses in the supply system.
A poor power factor can be the result of either a significant phase difference between the voltage and current at the load terminals, or it can be due to a high harmonic content or distorted/discontinuous current waveform.
Poor load current phase angle is generally the result of an inductive load such as an induction motor, power transformer, lighting ballasts, welder or induction furnace.
A distorted current waveform can be the result of a rectifier, variable speed drive, switched mode power supply, discharge lighting or other electronic load.

Last Updated ( Wednesday, 06 April 2011 22:31 ) Read more...

Capacitive Power Factor Correction

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Power Factor Correction.

Capacitive Power Factor correction (Power Factor Compensation) 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.

In the interest of reducing the losses in the distribution system, power factor correction is added to neutralize a portion of the magnetizing current of the motor. Typically, the corrected power factor will be 0.92 - 0.95 Some power retailers offer incentives for operating with a power factor of better than 0.9, while others penalize consumers with a poor power factor. There are many ways that this is metered, but the net result is that in order to reduce wasted energy in the distribution system, the consumer will be encouraged to apply power factor correction.

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. The resulting capacitive current is leading current and is used to cancel the lagging inductive current flowing from the supply.

Last Updated ( Wednesday, 06 April 2011 22:48 ) Read more...

Displacement Power Factor

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Displacement Power Factor.

Displacement Power Factor Definition : Displacement Power factor is the Cosine of the angle between the supply voltage and the current flowing in the load.

A poor power factor due to an inductive load can be improved by the addition of power factor correction capacitors to the load or to the supply.

Reactive current flowing in the supply is refered to as reactive power and is usually expressed in VARs or KVARs. A VAR is the product of the reactive current and the applied voltage. A KVAR is equal to 1000 VARs.

Common loads causing a poor displacement power factor are induction motors, transformers, reactive ballasts used for lighting and voltage control, welding systems (non inverter based).

An induction motor draws current from the supply, that is made up of resistive components and inductive components. The resistive components are:

1) Load current.
2) Loss current.
and the inductive components are:
3) Leakage reactance.
4) Magnetizing current.

Last Updated ( Monday, 09 June 2008 22:11 ) Read more...

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