Alternating Current Power Factor
Monitoring and Correction
Bryan Underwood
Advisor: Prof. Gutschlag
Power Factor is the
ratio of the active
power to the
apparent power
P.F. =
Complex Power Diagram
P
S
=
VI * cos(  )
VI


Poor power factor is due to inductive loads
such as induction motors in air conditioners
and refrigerators
A very low power factor usually results in the
power company charging more on a utility bill

Ameren Illinois requires Residential
customers (rate DS-1) and Light Industrial
Non-Residential customers (rate DS-2, DS-3)
to maintain a power factor of 0.90 while
Heavy Industrial Non-Residential customers
(rate DS-4) must maintain a power factor of
0.951


If the power factor falls below the minimum
specified by Ameren and ComEd, they require
corrective devices to be installed
Pacific Gas and Electric (PG&E) charges 0.6% more
on a utility bill for each percentage point below a
power factor of 0.852


About 60% of the electrical load in the United
States is due to AC electric motors3
According to the U.S. Energy Information
Administration (EIA), only about 25,000 out
of 200,000 manufacturing companies
participate in power factor correction (PFC)4


Increased I2R losses in transmission lines due
to the additional current requirements
needed to provide excess reactive power
reduces efficiency, capacity, and profit
margins
Increased current requirements result in
higher transmission line, transformer, and
switch gear current ratings

Usually done by capacitor banks
◦ Generate “negative” reactive power
http://accessscience.com/content/Reactive-power/802370
Hampden Type WRM-100 3-Phase Motor
 220 V
 1.4 A
 1725 RPM
 1/3 HP
Power Factor & Efficiency vs. Output Power (W)
0.9
Power Factor & Efficiency
0.8
0.7
0.6
0.5
Power Factor
Efficiency
0.4
0.3
0.2
0.1
0
0
50
100
Output Power (W)
150
200
250
SATEC PM172E-N 3-Phase Programmable Power Meter


SATEC Power Analysis Software V1.4 Build 5
Configure basic setup of meter, set trigger points, and view event
logs and waveforms
 Larger meters have more relay inputs and outputs to
permit more incremental values of capacitors to be switched
as needed for more precise control of the power factor
 More programming options provide more robust control
for better power factor correction
news.thomasnet.com
directindustry.com
Potter & Brunfield KRPA-11AG-120 Power Relays
 Capacitance is added to each line and can be varied from 1.6uF to 50uF

Resistors are placed in series with the
capacitor banks to reduce inrush currents
I
120[V ]

 4.8[ A]
25[]

120 0
Current through resistor I 
 0.450395 84.6159 [ A]
266 .433  84.6159 
with 10uF Capacitor

Power losses

Current w/ 20uF

Power losses
P  I 2 R  (0.450395)2 * 25  5.07139[W ]
I
120 0
 0.889119 79.3252 [ A]
134 .965   79.3252 
P  19.7633[W ]

Current w/ 30uF

Power losses
I
120 0
 1.30597 74.2121 [ A]
91.8857   74.2121 
P  42.639[W ]

Relay coils are energized from SATEC meter when the power factor
drops below a certain point
◦ Line current is also monitored to ensure no switching occurs when no load is present

Capacitors are added to the circuit in parallel with the motor
◦ Placed in parallel to maintain the same line voltages into the motor


Power factor can be varied over any desired range to avoid electric
utility company charges
Project system maintains a power factor of above 0.98
Experimental Results
Source Power Factor vs. Motor Power Factor
1.3
-0.7
1.2
-0.8
10 uF
Source Power Factor
1.1
-0.9
Meter
1
20 uF
Meter
0.9
30 uF
0.8
Meter
0.7
40 uF
Meter
0.6
0.5
0.3
0.45
0.6
Motor Power Factor
0.78

Complete the theoretical circuit model and
compare with experimental results
◦ Research how the meter calculates its values

Write tutorial on how to use power meter
◦ Will use as an appendix for final paper

Write final paper
1
http://www.ameren.com/sites/aiu/Rates/Documents/AIel14rtds4.pdf
http://www.ameren.com/sites/aiu/Rates/Documents/AIel48rdimf.pdf
2
http://www.pge.com/includes/docs/pdfs/mybusiness/customerservice/energystatus/powerquality/power%20factor--revised-8-907.pdf
3
http://www.pge.com/includes/docs/pdfs/mybusiness/customerservice/energystatus/powerquality/power%20fa
ctor--revised-8-9-07.pdf
4
http://www.eia.gov/emeu/mecs/mecs2002/data02/excel/table8.1_02.xls
Motor
Load
Apparent
Power
(VA)
Power
Factor
Active
Power
(W)
Motor
Speed
(RPM)
No Load
345
0.312
107
1777
¼ Load
354
0.435
156
1705
½ Load
394
0.554
216
1683
¾ Load
419
0.658
276
1677
Full Load
520
0.776
405
1585