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What's the Power Factor?


Power Factor is a measure of how efficiently electrical power is consumed. In the ideal world Power Factor would be unity (or 1). Unfortunately in the real world Power Factor is reduced by highly inductive loads to 0.7 or less. This induction is caused by equipment such as lightly loaded electric motors, luminaire transformers and fluorescent lighting ballasts and welding sets, etc.


What does it do to my electricity bill?


In a 3 phase supply, kW consumed is (VOLTS x AMPS x 1.73 x Power Factor) / 1000. The Electricity Company supply you VOLTS x AMPS and they have to supply extra to make up for the loss caused by poor Power Factor. When the power factor falls below a set figure, the electricity supply companies charge a premium on the kW being consumed, or, charge for the whole supply as kVA.


What causes Power Factor to change?


Inductive loads cause the AMPS to lag behind the VOLTS. The wave forms of VOLTS and AMPS are then "out of phase" with each other. The more out of phase they become then the lower the Power Factor. Power Factor is usually expressed as Cos Phi. (Ø)In 3 phase power supplies the "power" can be measured as a triangle. ACTIVE Power is the base line and is the real usable power measured in kW.


REACTIVE power is the vertical or that part of the supply which causes the inductive load. The reactive power in is measured in kVAr (kilo volt-amperes reactive)APPARENT Power is the hypotenuse. This is the resultant of the other two components and is measured in kVA


The effects of power factor


Consider a canal boat being pulled by a horse. If the horse could walk on water then the angle (Phi) Ø would be zero and COSINE Ø=1. Meaning all the horse power is being used to pull the load.


However the relative position of the horse influences the power. As the horse gets closer to the barge, angle Ø1 increases and power is wasted, but, as the horse is positioned further away, then angle Ø2 gets closer to zero and less power is wasted.


Why do I need Power factor correction?


Capacitive Power Factor correction (PFC) is applied to electric circuits as a means of minimising the inductive component of the current and thereby reducing the losses in the supply.


The introduction of Power Factor Correction capacitors is a widely recognised method of reducing an electrical load, thus minimising wasted energy and hence improving the efficiency of a plant and reducing the electricity bill.It is not usually necessary to reach unity, ie Power Factor 1, since most supply companies are happy with a PF of 0.95 to 0.98.


How does it work?


By installing suitably sized switched capacitors into the circuit, the Power Factor is improved and the value becomes nearer to 1 thus minimising wasted energyand improving the efficiency of a plan.


When the investment return?


Once in place, the cost of PFC can usually be recovered in less than 6 to 24 months.


How to Saving reduce the CO2 emission by power factor correction?


Generating and using energy of 100KWh produces 87,5kg of Carbon!

Following the expectations of the 2009 G8 summit in Copenhagen, develop thePower Factor Correction !


Next page:

Definitions and common formulas

Calculation reactive power compensation

Planning reactive power compensation

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