Power factor(r)

Power Factor basics

By Jafar Khan

Content

What is power factor

What causes low power factor

Why should I improve my power factor

How should I correct (Improve) my power factor

Power factor is the measure of how effectively your electrical equipment converts electric power (supplied by your power utility) into useful power output

What is Power Factor

In technical terms it is the ratio of Active Power (kW)) to the Apparent Power (kVA) of an electrical installation

bull KW is Working Power (also called Actual Power or Active Power or Real Power) It is the power that actually powers the equipment and performs useful work

bull KVA is Apparent Power It is the ldquovectorial summationrdquo of KVAR and KW

bull KVAR is Reactive Power It is the power that magnetic equipment (transformer motor and relay) needs to produce the magnetizing flux

Simple analogy in order to better understand these termshellip

PF = KWKVA

PF = KWKW+KVAR

PF = BeerBeer+Foam

The more foam you have (the higher the percentage of KVAR) the lower your ratio of KW (beer) to KVA (beer plus foam) Thus the lower your power factor The less foam you have (the lower the percentage of KVAR) the higher your ratio of KW (beer) to KVA (beer plus foam) In fact as your foam (or KVAR) approaches zero your power factor approaches 10

Letrsquos look at another analogy helliphellip

Mac here is dragging a heavy load Macrsquos Working Power (orActual Power) in the forward direction where he most wants his load totravel is KW

Unfortunately Mac canrsquot drag his load on a perfect horizontal (he wouldget a tremendous backache) so his shoulder height adds a little ReactivePower or KVAR

The Apparent Power Mac is dragging KVA is this ldquovectorial summationrdquoof KVAR and KW

Power TrainglehellipPower Traingle helliphellip

OslashKW (Real Power)

KVA (Apparent Power)

KV

AR

(R

eact

ive

Po

wer

)

= COS Oslash

Power Factor (COS Oslash) should be close to unity

What causes Low Power Factor

Low power factor results when KW is small in relation to KVA Remembering our beer mug analogy this would occur when KVAR (foam or Macrsquos shoulder height) is large

What causes a large KVAR in a system The answer ishellipinductive loads

1048713 Transformers1048713 Induction motors1048713 Induction generators (wind mill generators)1048713 High intensity discharge (HID) lighting

Reactive power (KVAR) required by inductive loads increases the amount of apparent power (KVA) in distribution system This increase in reactive and apparent power results in a larger angle measured between KW and KVA As θ increases cosine θ (or power factor) decreases

OslashKW

KVA

KV

AR

KW

KVA

KV

AR

KVA

KV

AR

Oslash

bull Lower the Utility bill

Why should I Improve my Power Factor

inductive loads require reactive power caused your low power factor This increase in required reactive power (KVAR) causes an increase in required apparent power (KVA) which is what the utility is supplying

So a facilityrsquos low power factor causes the utility to have to increase its generation and transmission capacity in order to handle this extra demand

By raising your power factor you use less KVAR This results in less KW which equates to savings from the utility

bull Increased system capacity and reduced system losses

By adding capacitors (KVAR generators) to the system the power factor is improved and the KW capacity of the system is increased

Reduces I2R losses in conductors

bull Increased voltage level and cooler more efficient motorsAs uncorrected power factor causes power losses in distribution system As power losses increase you may experience voltage drops Excessive voltagedrops can cause overheating and premature failure of motors and other inductive equipment

So by raising power factor minimizes these voltage drops along feeder cables and avoid related problems Your motors will run cooler and be more efficient with a slight increase in capacity and starting torque

A 10 drop in terminal voltage from the rated Will reduce the Induction motor torque by approx 19 Increase full load current by approx 11 Reduce overload capacity Increase temperature rise by approx 6-7 degrees

No lights on0 Watts total(room is dark) Voltage is normal

One light on14 Watts total(some light in room)Voltage drops some

Two lights on20 Watts total(room gets brighter)Voltage drops more

Three lights on23 Watts total(room gets brighter)Voltage drops more

Four lights on24 Watts total(room gets brighter)Voltage drops more

Five lights on25 Watts total(room gets brighter)Voltage drops more

Six lights on24 Watts total (room gets darker)Voltage drops more

121197 13

bull Reduces loading on transformers

For example a 1000 KVA transformer with an 80 power factor provides 800 KW (600 KVAR) of power to the main bus

1000 KVA = (800 KW)2 + ( KVAR)2

KVAR = 600

By increasing the power factor to 90 more KW can be supplied for the same amount of KVA

1000 KVA = (900 KW)2 + ( KVAR)2

KVAR = 436

The KW capacity of the system increases to 900 KW and the utility supplies only 436 KVAR

How do I correct my Power Factor

We have seen that consumers of Reactive power (Inductive loads) decrease power factor

Similarly Sources of Reactive Power increase power factor

1048713 Capacitors1048713 Synchronous generators (utility and emergency)1048713 Synchronous motors

One way to increase power factor is to add capacitors to the system

bull Installing capacitors (KVAR Generators)

Installing capacitors decreases the magnitude of reactive power (KVAR) thus increasing your power factor

Reactive power (KVARS) caused by inductive loads always acts at a 90-degree angle to working power (KW)

Capacitance (KVAR)

Reactance (KVAR)

Working power (KW)

Capacitors store KVARS and release energy opposing the reactive energy caused by the inductor

True power delivered to load

Feeder line

Generator Outputmdashapparent power (Combination of true and reactive power)

Reactive power In both directions between the generator and the motor

If the motor is unloaded and is located a short distance from the generator the energy from the generator causes magnetic fields to form around the motor coils

Since the coils of the motor are reactive the current causes a magnetic field to expand around the coils during one portion of the alternation During another portion of the alternation the magnetic field collapses induces a voltage at the coil and causes current from the motor to flow back to generator

Reactive power from the generator to the motor

For Ascending Positive Alternation

The current causes a magnetic field to expand around the coils during one portion of the alternation

Reactive power from the motor to the generator

For Descending Positive Alternation

During another portion of the alternation the magnetic field collapses induces a voltage at the coil and causes current from the motor to flow back to generator


For Ascending Negative Alternation



For Descending Negative Alternation


Individual Correction

Group Correction

Capacitor sizing

KVAr required = kW (tan Oslash 1 ndash tan Oslash 2)

PF1 and PF2 are initial and finalPower factors respectively

Where Oslash 1 = Cos-1 (PF 1) and Oslash 1 = Cos-1 (PF 2) and

Q = S2 - P2

Conclusion

PF is the ratio of Active Power (kW)) to the Apparent Power (kVA)

More the reactive power less is the power factor Power factor can be improved by locally providing required

Reactive power

Thank You

Power Factor basics

Content

Slide 3

Slide 4



Power Trainglehellip

Slide 8

Slide 9

Slide 10

Slide 11

Slide 12

Slide 13

Slide 14

Slide 15

Slide 16

Slide 17


Group Correction

Capacitor sizing

Conclusion

Slide 30

Content

What is power factor

What causes low power factor

Why should I improve my power factor

How should I correct (Improve) my power factor








PF = KWKVA

PF = KWKW+KVAR

PF = BeerBeer+Foam









KV

AR

(R

eact

ive

Po

wer

)

= COS Oslash







OslashKW

KVA

KV

AR

KW

KVA

KV

AR

KVA

KV

AR

Oslash



















121197 13



1000 KVA = (800 KW)2 + ( KVAR)2

KVAR = 600


1000 KVA = (900 KW)2 + ( KVAR)2

KVAR = 436










Capacitance (KVAR)

Reactance (KVAR)

Working power (KW)



Feeder line


















Group Correction

Capacitor sizing




Q = S2 - P2

Conclusion



Reactive power

Thank You

Power Factor basics

Content

Slide 3

Slide 4




Slide 8

Slide 9

Slide 10

Slide 11

Slide 12

Slide 13

Slide 14

Slide 15

Slide 16

Slide 17


Group Correction

Capacitor sizing

Conclusion

Slide 30








PF = KWKVA

PF = KWKW+KVAR

PF = BeerBeer+Foam









KV

AR

(R

eact

ive

Po

wer

)

= COS Oslash







OslashKW

KVA

KV

AR

KW

KVA

KV

AR

KVA

KV

AR

Oslash



















121197 13



1000 KVA = (800 KW)2 + ( KVAR)2

KVAR = 600


1000 KVA = (900 KW)2 + ( KVAR)2

KVAR = 436










Capacitance (KVAR)

Reactance (KVAR)

Working power (KW)



Feeder line


















Group Correction

Capacitor sizing




Q = S2 - P2

Conclusion



Reactive power

Thank You

Power Factor basics

Content

Slide 3

Slide 4




Slide 8

Slide 9

Slide 10

Slide 11

Slide 12

Slide 13

Slide 14

Slide 15

Slide 16

Slide 17


Group Correction

Capacitor sizing

Conclusion

Slide 30








KV

AR

(R

eact

ive

Po

wer

)

= COS Oslash







OslashKW

KVA

KV

AR

KW

KVA

KV

AR

KVA

KV

AR

Oslash



















121197 13



1000 KVA = (800 KW)2 + ( KVAR)2

KVAR = 600


1000 KVA = (900 KW)2 + ( KVAR)2

KVAR = 436










Capacitance (KVAR)

Reactance (KVAR)

Working power (KW)



Feeder line


















Group Correction

Capacitor sizing




Q = S2 - P2

Conclusion



Reactive power

Thank You

Power Factor basics

Content

Slide 3

Slide 4




Slide 8

Slide 9

Slide 10

Slide 11

Slide 12

Slide 13

Slide 14

Slide 15

Slide 16

Slide 17


Group Correction

Capacitor sizing

Conclusion

Slide 30






OslashKW

KVA

KV

AR

KW

KVA

KV

AR

KVA

KV

AR

Oslash



















121197 13



1000 KVA = (800 KW)2 + ( KVAR)2

KVAR = 600


1000 KVA = (900 KW)2 + ( KVAR)2

KVAR = 436










Capacitance (KVAR)

Reactance (KVAR)

Working power (KW)



Feeder line


















Group Correction

Capacitor sizing




Q = S2 - P2

Conclusion



Reactive power

Thank You

Power Factor basics

Content

Slide 3

Slide 4




Slide 8

Slide 9

Slide 10

Slide 11

Slide 12

Slide 13

Slide 14

Slide 15

Slide 16

Slide 17


Group Correction

Capacitor sizing

Conclusion

Slide 30



















121197 13



1000 KVA = (800 KW)2 + ( KVAR)2

KVAR = 600


1000 KVA = (900 KW)2 + ( KVAR)2

KVAR = 436










Capacitance (KVAR)

Reactance (KVAR)

Working power (KW)



Feeder line


















Group Correction

Capacitor sizing




Q = S2 - P2

Conclusion



Reactive power

Thank You

Power Factor basics

Content

Slide 3

Slide 4




Slide 8

Slide 9

Slide 10

Slide 11

Slide 12

Slide 13

Slide 14

Slide 15

Slide 16

Slide 17


Group Correction

Capacitor sizing

Conclusion

Slide 30



1000 KVA = (800 KW)2 + ( KVAR)2

KVAR = 600


1000 KVA = (900 KW)2 + ( KVAR)2

KVAR = 436










Capacitance (KVAR)

Reactance (KVAR)

Working power (KW)



Feeder line


















Group Correction

Capacitor sizing




Q = S2 - P2

Conclusion



Reactive power

Thank You

Power Factor basics

Content

Slide 3

Slide 4




Slide 8

Slide 9

Slide 10

Slide 11

Slide 12

Slide 13

Slide 14

Slide 15

Slide 16

Slide 17


Group Correction

Capacitor sizing

Conclusion

Slide 30









Capacitance (KVAR)

Reactance (KVAR)

Working power (KW)



Feeder line


















Group Correction

Capacitor sizing




Q = S2 - P2

Conclusion



Reactive power

Thank You

Power Factor basics

Content

Slide 3

Slide 4




Slide 8

Slide 9

Slide 10

Slide 11

Slide 12

Slide 13

Slide 14

Slide 15

Slide 16

Slide 17


Group Correction

Capacitor sizing

Conclusion

Slide 30


Feeder line


















Group Correction

Capacitor sizing




Q = S2 - P2

Conclusion



Reactive power

Thank You

Power Factor basics

Content

Slide 3

Slide 4




Slide 8

Slide 9

Slide 10

Slide 11

Slide 12

Slide 13

Slide 14

Slide 15

Slide 16

Slide 17


Group Correction

Capacitor sizing

Conclusion

Slide 30















Group Correction

Capacitor sizing




Q = S2 - P2

Conclusion



Reactive power

Thank You

Power Factor basics

Content

Slide 3

Slide 4




Slide 8

Slide 9

Slide 10

Slide 11

Slide 12

Slide 13

Slide 14

Slide 15

Slide 16

Slide 17


Group Correction

Capacitor sizing

Conclusion

Slide 30

Capacitor sizing




Q = S2 - P2

Conclusion



Reactive power

Thank You

Power Factor basics

Content

Slide 3

Slide 4




Slide 8

Slide 9

Slide 10

Slide 11

Slide 12

Slide 13

Slide 14

Slide 15

Slide 16

Slide 17


Group Correction

Capacitor sizing

Conclusion

Slide 30

Conclusion



Reactive power

Thank You

Power Factor basics

Content

Slide 3

Slide 4




Slide 8

Slide 9

Slide 10

Slide 11

Slide 12

Slide 13

Slide 14

Slide 15

Slide 16

Slide 17


Group Correction

Capacitor sizing

Conclusion

Slide 30

Thank You

Power Factor basics

Content

Slide 3

Slide 4




Slide 8

Slide 9

Slide 10

Slide 11

Slide 12

Slide 13

Slide 14

Slide 15

Slide 16

Slide 17


Group Correction

Capacitor sizing

Conclusion

Slide 30

Power factor(r)

Education

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