Power Factor Fundamentals

Power Factor Fundamentals

What we will learn:

• Most Industrial loads require both Real power and Reactive power to produce useful work


• You pay for BOTH types of power

• Capacitors can supply the REACTIVE power thus the utility doesn’t need to

• Capacitors save you money!

Why Apply PFC’s?

Power Factor Correction Saves Money!

• Reduces Power Bills


• Reduces I2R losses in conductors

• Reduces loading on transformers

• Improves voltage drop

What is PF ?

Introduction:

• Most plant loads are Inductive and require a magnetic field to operate:

• Motors


• Transformers

• Florescent lighting


• The magnetic field is necessary, but produces no useful work


• The utility must supply the power to produce the magnetic field and the power to produce the useful work: You pay for all of it!


• These two types of current are the ACTIVE and REACTIVE components

The Basics:

The Power Triangle:



Similarly, motors require REACTIVE power to set up the magnetic field while the ACTIVE power produces the useful work (shaft horsepower). Total Power is the vector sum of the two & represents what you pay for:


Power Factor is the ratio of Active Power to Total Power:



Power Factor is a measure of efficiency (Output/Input)

Why do we Install Capacitors?

Capacitors supply, for free, the reactive energy required by inductive loads.

• You only have to pay for the capacitor !


• Since the utility doesn’t supply it (kVAR), you don’t pay for it!

• 

Other Benefits:

1. Released system capacity:

The effect of PF on current drawn is shown below:


Decreasing size of conductors required to carry the same 100kW load at P.F. ranging from 70% to 100%

1. Reduced Power Losses:

• As current flows through conductors, the conductors heat. This heating is power loss.


• Power loss is proportional to current squared (P Loss=I2R)


• Current is proportional to P.F.

• Conductor loss can account for as much as 2-5% of total load.

Capacitors can reduce losses by 1-2% of the total load

3. Voltage Improvement:

• When capacitors are added, voltage will increase


• Typically only a few percent


• Not a significant economic or system benefit

Severe over-correction (P.F.>1) will cause a voltage rise that can damage insulation & equipment; or result in utility surcharges!

• Usually a result of large fixed capacitors at mains

Summary of Benefits:

Reduced Power Costs:

• Since Capacitors supply reactive power, you don’t pay the utility for it


• You can calculate the savings

Off-load transformers

• Defer buying a larger transformer when adding loads

Reduce voltage drop at loads

• Only if capacitors are applied at loads


• (minimal benefit at best)