First Semester Project
Power Factor Correction for Power Systems
V2
P=
R
2
P
=
I
R
P =True Power
Where P is measured in Watts
Types of Power
Pamela Ackerman, Electrical Engineering Undergraduate
True Power - Symbolized by P, measured in Watts and a function of dissipative elements (R)
Reactive Power - Symbolized by Q, measured in VAR and a function of reactive elements (X)
Apparent Power - Symbolized by S, measured in VA and a function of total impedance (Z)
Advisement By:
Jerry E. Hager P.E., Vice President, Electrical Systems Consultants, Inc.
Dr. George Collins, Electrical and Computer Engineering
Q = I2X
V2
Q=
X
Q = Reactive Power
Where Q is measured in VoltVolt-AmpsAmps-Reactive (VAR)
V2
S=
Z
2
S = VI
S
=
I
Z
S = Apparent Power
Where S is measured in VoltVolt-Amps (VA)
Definition of Power Factor
Power System Loads
Power system have resistive,
resistive inductive and capacitive loads
P = True power = I2R = 240 Watts
P = True power = I2R = 0 Watts
Q = Reactive power = I2X = 0 KVAR
Q = Reactive power = I2X = 238.73 KVAR
S = Apparent power = I2Z = 240 VA
S = Apparent power = I2Z = 238.73 VA
Purely Resistive Load:
• All power dissipated by resistor
• Voltage and Current in phase
• Apparent Power = True Power
Purely Reactive Load:
• All power alternately absorbed and returned by reactive load
• Voltage and Current out of phase (θ=90)
• Apparent Power = Reactive Power
Resistive/Reactive Load:
• More power dissipated
than returned to load
• Voltage and Current out
of phase (0< θ <90)
• Apparent power is a
linear combination of
True and Reactive power
P = True power = I2R = 119.365 Watts
Q = Reactive power = I2X = 119.998 KVAR
Fixed capacitor bank — connected to transformer or switchgear
•
Sized to regulate maximum operational inductive loading
Drawbacks include utility regulations and addition of inductive loads change max
Fixed capacitor bank and individual capacitors — same as above
with addition of caps in parallel with some of the large motors
•
•
Provides power factor correction while motors are energized
Sometimes not physically or economically feasible (maintenance is costly)
Variable capacitor bank — connected to transformer or switchgear
•
•

TruePower
KW 

 PF =
=
ApparentPo wer KVA 

Power factor is a unitunit-less
measurement
Power factor measures how
efficiently the current is being
converted into real power
S = Apparent power = I2Z = 169.256 VA
Methods of Power Factor Correction
•
Power factor is defined as the ratio of
true power and apparent power:
Centrally located capacitor bank regulates power factor as loads connected to system change
Draw backs include initial and maintenance costs
A power factor of 1 is the most
efficient loading of supply
The three types of power are related by the “Power Triangle”
• Purely resistive circuits have PF=1, power triangle is a horizontal line
• Purely inductive circuits have PF=0, power triangle is a vertical line pointing up
• Purely capacitive circuits have PF=0, power triangle is a vertical line pointing down
Benefits of PFC
•
•
•
Protection
Efficiency
Savings
References
Lessons In Electric Circuits Volume II, Sixth Edition, Tony R. Kuphaldt, 2007
Power Factor Correction, Ralph A. Frye III, P.E., http://www.wagesterlease.com/aboutus/articles/powerfactor.html
Power Factor, L M Photonics Ltd, http://www.lmphotonics.com/pwrfact.htm?gclid=CJbHjdTMjosCFSUeGAodtRe8VQ
Power Factor Correction, Wikipedia, http://en.wikipedia.org/wiki/Power_factor_correction