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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.

Power factor Current Vectors

The current due to the leakage reactance is dependant on the total current drawn by the motor, but the magnetizing current is independent of the load on the motor. The magnetizing current will typically be between 20% and 60% of the rated full load current of the motor. The magnetizing current is the current that establishes the flux in the iron and is very necessary if the motor is going to operate. The magnetizing current does not actually contribute to the actual work output of the motor. It is the catalyst that allows the motor to work properly. The magnetizing current and the leakage reactance can be considered passenger components of current that will not affect the power drawn by the motor, but will contribute to the power dissipated in the supply and distribution system. Take for example a motor with a current draw of 100 Amps and a power factor of 0.75 The resistive component of the current is 75 Amps and this is what the KWh meter measures. The higher current will result in an increase in the distribution losses of (100 x 100) /(75 x 75) = 1.777 or a 78% increase in the supply losses.

Power Factor Introduction
Displacement Power Factor
Power Factor Correction
Bulk Correction
Static Correction
Power Factor Calculations
Distortion Power Factor

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