POWER FACTOR FUNDAMENTALS

What we will learn

qMost Industrial loads require both Real power and
      Reactive power to produce useful work
q   You pay for BOTH types of power
q   Capacitors can supply the REACTIVE power thus
      the utility doesn’t need to
q   Capacitors save you money!

WHY POWER FACTOR CORRECTION IS REQUIRED?

»  Reduces Power Bills

»  Reduces I2R losses in conductors

»  Reduces loading on transformers

»  Improves voltage drop

What is PF ?

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 currents are the ACTIVE and REACTIVE

    components

The Power Triangle:

q  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!

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%

Reduced Power Losses:

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

» Power loss is proportional to current squared (PLoss=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

Voltage Improvement:

» When capacitors are added, voltage will increase.

» Typically only a few percent – Not a significant economic or system benefit.

q  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)

What we learned..

 Most Industrial loads (i.e. motors) are Inductive and draw REACTIVE power

The Utility supplies this energy therefore you pay for it

 Power Factor Capacitors supply REACTIVE energy thus the utility doesn’t need to

 Power Factor Capacitors save money

There are other benefits to correcting power factor,

  Reduced heating in cables

  Reduced heating in transformer (s)

  Frees up system capacity