PROCEEDINGS OF WORLD ACADEMY OF SCIENCE, ENGINEERING AND TECHNOLOGY VOLUME 32 AUGUST 2008 ISSN 2070-3740
Improvement of Power Factor for Industrial
Plant with Automatic Capacitor Bank
Marlar Thein Oo, Ei Ei Cho
to sustain the electromagnetic field associated with many
commercial/ industrial loads. It is measured in kilovoltamperes-reactive, or kVAR. The total required capacity,
including working and reactive power, is known as apparent
power. It is expressed in kilovolt-amperes or KVA.
Abstract-This paper is intended to uplift the technological
standard of industrial plants. The overall power factor of
modern industries is very poor because of inductive loads
absorbing reactive power. Especially, industrial plant with
variable load conditions has large inductive loads and its
power factor is very poor. These industries benefit most from
automatic capacitor banks. This bank provides improved
power factor, increased voltage level on the load and reduced
electric utility bills. Besides, automatic capacitor banks may
be able to eliminate kVAR energized at light-load periods and
undesirable over-voltages. In most cases, the main reason why
a customer installs a capacitor bank is to avoid penalization in
the electricity bill. This inappropriate installation without
enough study gives rise to a great variety of technical
problems. Therefore, the fact that capacitor banks are designed
for long-term use should be considered.
Fig.1 kW power
Keywords- industrial plants, poor power factor, automatic
capacitor bank, long term
I.
INTRODUCTION
I
N most industrial and commercial facilities, a majority of
the electrical equipment is inductive loads such as AC
induction motors, induction finances, transformers and
ballast-type lighting. Problems of power quality in industrial
plants are growing due to the increasing number of rectifier
controlled motors and the overall increase of harmonics and
interharmonics. These loads cause poor power factor in
industrial plants. A poor power factor indicates ineffective
utilization of electricity and affects total energy costs. These
problems are aggravated by the proper selection, sizing and
installation of capacitors.
G
M
Motor
Field
Fig. 2 kVAR power
F. A. Miss Marlar Thein Oo is with the Electrical Power Engineering
Department, Mandalay Technological University, Mandalay, Myanmar, ( email: marlartheinoo@gmail.com).
S. B. Miss Ei Ei Cho with the electrical Power Engineering Department,
Mandalay Technological University, Mandalay, Myanmar, (e-mail:
eieicho2006@gmail.com)
Fig. 3 kVA power
FUNDAMENTAL OF POWER FACTOR
Power factor is a measure of how effectively electrical
power is being used by a system. To understand power factor,
we first have to know that power has three components:
working, reactive and apparent power. Working power is the
current and voltage actually consumed. It performs the actual
work, such as creating heat, light and motion. Working power
is expressed in kilowatts (kW), which register as kilowatt-hour
on electric meter. Reactive is not useful work, but it is needed
PWASET VOLUME 32 AUGUST 2008 ISSN 2070-3740
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PROCEEDINGS OF WORLD ACADEMY OF SCIENCE, ENGINEERING AND TECHNOLOGY VOLUME 32 AUGUST 2008 ISSN 2070-3740
generally are the most economical means to improve power
factors.
Power factor correction is the term given to a technology
that has been used since the turn of the 20th century to restore
the power factor to as close to unity as is economically stable.
This is normally achieved by the addition of capacitors to the
electrical network which compensate for the reactive power
demand of the inductive load and thus reduce the burden on
the supply. There should be no effect on the operation of the
equipment.
kVA
kW
cos ș =
kVA
kvar
=PF
ș
kW
Fig. 4 Power triangle
A sample analogy for power factor is to relate it to a garden
hose. Circumstances, if you need 10 liters of water per minute
to come out at the end of the hose, the tap should be turned on
to deliver that amount of water. But if your hose leaks, is
squashed between rocks, or is kinked because it is cheap, you
will experience a drop in pressure. To achieve your target of
10 liters per minute, therefore, you need to turn up the tap and
force more water through the hose. That is Power Factor
Correction.
Power factor is the ratio of working power to apparent
power or kW/kVAR. Power factor values can carry from 0 to
1.00. Typically, values range from 0.80 to 0.98. A power
factor below 0.80 is considered low.
INDUCTIVE LOADS CONTRIBUTING TO POOR POWER
FACTOR
II.
If the plant inductive loads, which require the use of a
magnetizing current to create a magnetic field, Power factor
corrections are required. Inductive characteristics are more
pronounced in motors and transformers and are found more
often in commercial and industrial facilities. One of the worst
offenders is a lightly loaded induction motor, often found in
“cycle processes” –for example, in the operation of saws,
conveyors, and grinders- where the motor must be sized for
the heaviest load. Other sources include: induction furnaces,
standard stamping machines, weaving machines, single stroke
presses, automated machine tools, welders and certain
fluorescent lamp ballasts. Table 1 shows incorrect power
factor of some industrial plants.
Fig. 5 Standard power factor correction
TABLE 1
IV. BENEFITS OF POWER FACTOR CORRECTION
TYPICAL LOW POWER FACTOR INDUSTRIES
Industry
1.
Environmental benefit-reduction of power consumption
due to improved energy efficiency. Reduced power
consumption means less greenhouse gas emissions and
fossil fuel depletion by power stations.
65% - 75%
2.
Reduction of electricity bills.
70% - 80%
3.
Extra kVA available from the existing supply.
4.
Reduction of I2R losses in transformers and distribution
equipment
5.
Reduction of voltage drop in long cables
6.
Extended equipment life- reduced electrical burden on
cables and electrical components.
Saw Milk
45% - 60%
Plastic
55% - 70%
Machine Tools, Stamping
60% - 70%
Planting, Textile, Chemicals
Hospitals, Foundries
The advantages that can be achieved by applying the correct
power factor correction are:
Uncorrected power
factor
III. POWER FACTOR CORRECTION
If the power factor of the plant is low, it uses more power
than it needs to do the work. Poor power factor should be
corrected as it substantially increases costs. Capacitors
V. METHODS OF CAPACITOR INSTALLATIONS
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TABLE II
We need to choose the optimum type, size and number of
capacitors for the plant. There are four methods of capacitor
installations:
Method 1:
SUMMERY OF ADVANTAGES AND DISADVANTAGES
Method
Capacitor at load
Installed a single capacitor at each sizeable
motor and energize it whenever the motor is in operation. This
method usually offer the greatest advantage of all, and the
capacitors could be connected either in location (A) as (B) in
Figure below.
Advantages
Disadvantages
Most
technically
efficient, most
flexible
Higher
installation and
maintenance
cost
Fixed Bank
Most
economical,
fewer
installations
Less flexible,
requires
switches and/
or circuit
breakers
Automatic
Bank
Best for
variable loads,
prevents over
voltages, low
installation cost
Higher
equipment cost
Combination
Most practical
for larger
numbers of
motors
Least flexible
Individual
Capacitors
Fig. 6 Location of the capacitor connections
Location A- Normally used for most motor applications.
Location B- Used when motors are jogged, plugged,
revered: for multi-speed motors, as reduced voltage start
motors.
Method 2:
Fixed capacitor bank
Installed a fixed quality of kVar electrically
connected at one or more locations in the plant’s electrical
distribution systems, and energized at all times. This method is
often used when the facility has few motors of any sizeable
horsepower to which capacitors can economically be added.
When the system is lightly loaded, and the amount of kVar
energized is too large, the voltage can be so great that motors,
lamps, and controls can burn out.
VI. PARTICULAR NEDS OF THE PLANT
When deciding which type of capacitor installation best
meets weight the advantages and disadvantages of each and
consider several plant variables, including load type, load
constancy, load capacity, motor starting method.
A. Load type
It is a important fact to remember that kVar equal to 20%
of the transformer kVA is the maximum size of a fixed kVar
bank. Valued greater than this can result in a large resonant
current, which is potentially harmful to the system.
Method 3:
If the plant consist of many large motors, 50 Hp and above,
it is usually economical to install one capacitor per motor and
switch the capacitor and motor together. If the plant has many
small motors, ½ to 25 hp, group motors and install one
capacitor at a control point in the distribution system. The best
solution per plants with large and small motor is to used both
types of capacitor installation.
Automatic capacitor bank
It is installed at the motor control centre at
the service entrance. This bank will closely maintain a preselected value of power factor. This is accomplished by
taming a controller switch steps of kVar on, as off, as needed.
Automatic switching ensures exact amount of power factor
correction, eliminates over capacitance and resulting over
voltages.
Method 4:
B. Load Size
Facilities with large loads benefit from a combination of
individual load, group load and banks of fixed and
automatically-switched capacitor units. A small facility may
need only one capacitor as the control board.
Combination of methods
Sometimes, only an isolated trouble spot requires power
factor correction. This may be the case if the plant has welding
machines, induction heaters or dc drives. If a particular feeder
serving s low power factor load is connected, it may raise
Since no two electrical distribution systems
are identical, each must be carefully analyzed to arrive at the
most cost- effective solution, using are or more of the method.
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overall plant power factor enough that additional capacitors
are unnecessary.
= 360, 000 kyats
Net gain (Annual saving)
C. Load Constancy
= 1, 080, 000 + 360, 00
If the plant operates around the clock and has a constant
load demand, fixed capacitors offer the greatest economy. If
lead is determined by eight-hour shift five day a week,
switched units are wanted more to decrease capacitance during
times of reduced load.
= 1, 440, 000 kyats
Therefore, annual saving is 1.2 percent of annual charge.
This is to illustrate a hypothetical annual estimate. Single line
diagram and control circuit diagram of 200 kVAR automatic
capacitor bank are designed in appendix.
D. Load capacity
If the feeder or transformers are overloaded, or if additional
load is added to already load lines, correction needs at the load
if the facility has surplus amperage, the capacitor banks are
installed at main feeders. If load varied a great deal, automatic
switching is probably the solution.
The linear payback period of this installation is described
below.
Total cost of installation (survey cost, advice, capacitance
and labour) is 3, 2000, 000 kyats.
VII. METHODOLOGY FOR POWER FACTOR BILLING
ADJUSTMENT
Annual saving is 1, 440, 000 kyats.
Therefore, the payback period is 2 years and 3 months.
Assume a 400 kW load with a power factor of 70 percent.
To improve power factor to 90 percent, the total kVar added to
your plant (rating of capacity bank) is 200kVar.
VIII.
The most frequent case at industrial plants is to compensate
the reactive power at low voltage. To do this, there are on the
market a large no. of manufacturers that offer standardized
products with power ratings up to and even exceeding 1000
kVar. This is a very well known and widespread product and,
as a result, on many occasions it is installed without enough
study.
572 kVA
408 kVar
445 kVA
194 kVar
P.f 70%
P.f 90%
400 kW
400 kW
Therefore, the effects of disturbances are suffered mostly by
the owner of the capacitor bank. Please ensure that installation
meet your requirements, manufacturers, installations and all
applicable codes, standards and regulations.
Total annual kWh
= 2, 400, 000
Average kWh charge
= 50 kyats
Annual charge
= 120, 000, 000 kyats
DISCUSSIONS AND CONCLUSION
IX. RECOMMENDATIONS
¾
Power factor adjustment is 0.06 percent or each percentage
point below or above 85 percent.
¾
Power factor adjustment for 70 percent (penalty value)
¾
= 85 – 70
Size electric motors to match mechanical loads to increase
the overall p.f.
Use capacitor banks at motor control centre or service
entrances to facilitate switching for varying load.
Install conditions as harmonic filters to avoid harmonic
resonance problems and excessive voltage distortion
levels.
= 15 x 0.06 %
ACKNOWLEDGEMENT
= 0.9 % x 120, 000, 000
= 1, 080, 000 kyats
I would like to appreciate and thank His Excellency U
Thaung, Minister, Ministry of Science and Technology.
I’m also dedicated to acknowledge to Dr. Myo Myint
Aung, Head of Electrical Power Engineering Department,
M.T.U, U Myint Oo, Management Engineer, S n Q
Electrical Engineering Service and all my teachers.
Power factor adjustment for 90 percent (credit value)
= 90 – 85
= 5 x 0.06%
= 0.3 % x 120, 000, 000
PWASET VOLUME 32 AUGUST 2008 ISSN 2070-3740
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REFERENCES
[1] Electrical Transmission and Distribution Reference
Book, 4th edition, 1950, Westinghouse Electric
Corporation.
[2] IEEE Standard 141-1993, Recommended practice for
Electrical Power Distribution for Industrial Plants.
[3] R.C. Dugan, M.F. McGranaghan, S. Santoso, and
H.W. Beaty, Electrical Power Systems Quality,
Second
Edition,
McGraw-Hill,
Professional
Engineering Series, New York, 2003.
Marlar Thein Oo studied in Electrical Power Engineering Major and held
B.E degree in 2004 from Mandalay Technological University, Mandalay,
Myanmar. Then I was awarded M.E degree of Electrical Power Engineering
in 2006 from Yangon Technological University, Yangon, Myanmar. Now I
am a Ph.D candidate.
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700
C1
20Kvar
FR 1
14-22A
KM C1
40A
2
C2
20Kvar
FR 2
14-22A
KM C2
40A, 3P
MCB2
6mm2 3
40A, 3P
MCB1
1
6mm2 3
40A
6mm2 3
C3
20Kvar
FR 3
14-22A
KM C3
40A, 3P
MCB3
3
40A
6mm2 3
40A
C5
20Kvar
FR 5
14-22A
KM C5
40A, 3P
MCB5
5
40A
6
600A, 3P
DS
C6
20Kvar
FR 6
14-22A
KM C6
40A, 3P
MCB6
40A
7
A
C7
20Kvar
FR 7
14-22A
KM C7
40A, 3P
MCB7
6mm2 3
40A
8
C8
20Kvar
FR 8
14-22A
C9
20Kvar
FR 9
14-22A
KM C9
40A, 3P
MCB9
9
Controller
FU 1,2,3
40A
cosĭ
FU 7,8
KM C8
40A, 3P
MCB8
FU 4,5,6
V
Fig. 7 Single Line Diagram of 200 kVAR Automatic Capacitor Bank
C4
20Kvar
FR 4
14-22A
KM C4
40A, 3P
MCB4
4
G 10
6mm2 3
Feeder Bus
6mm2 3
From Sensor CT 4
6mm2 3
Distribution Bus
6mm2 3
PWASET VOLUME 32 AUGUST 2008 ISSN 2070-3740
40A
10
C10
20Kvar
FR 10
14-22A
KM C10
40A, 3P
MCB10
40A
Control Source
10A, 3P
MCB
11
T.C.L = 200 Kvar
Control Source
Selector SW
Auto-Man
6mm2 3
APPENDIX
PROCEEDINGS OF WORLD ACADEMY OF SCIENCE, ENGINEERING AND TECHNOLOGY VOLUME 32 AUGUST 2008 ISSN 2070-3740
© 2008 WASET.ORG
Bus 1
S1
Distribution Bus
CT1
S2
N Bus
L11,L12,L13
630A,3P,DS
L1,L2,L3
CT4
CT2
CT3
L11
L12
L13
0
A3
A2
A1
To AS
Power capacitor
Selector SW
10A,3P
M C B
13
16
15
18
17
20
22
19
21
24
23
26
25
28
27
11
AU1
1X11
N11
AU2
3X6
3X5
3X4
K
Fig. 8 Control Circuit Diagram of 200 kVAR Automatic Capacitor Bank
21
14
31
11
41
9
12
51
10
M1
M2
M3
M4
M5
M6
M7
M8
M9
M10
7
61
2.5Sq mm
2L111
2L211
2L311
5
8
71
K
2L11
2.5Sq mm
2L12
2L21
2L31
C
B
3
6
81
3X3
3X2
3X1
4X2
4X1
4
91
2L1
2L2
2L3
3L3
3L2
1
101
FU 3, 10A
FU 2, 2A
FU 1, 2A
FU 8, 2A
FU 7, 2A
CT 41
CT 40
2
To VS
FU 4,2A
1L1
Bus 2
N 11
Distribution Bus
FU 5,2A
1L2
701
FU 6,2A
PWASET VOLUME 32 AUGUST 2008 ISSN 2070-3740
1L3
Bus 3
US
US
US1
US2
IS1
IS2
IS2
4X5
C
B
4X4
1
2
3
4
5
6
i A
7
8
9
10
K10
Internal connection
of the Controller
CT412
Cos ĭ
CT411 I A
K1 K2 K3 K4 K5 K6 K7 K8 K9
US1 US2
IS1
4X3
PROCEEDINGS OF WORLD ACADEMY OF SCIENCE, ENGINEERING AND TECHNOLOGY VOLUME 32 AUGUST 2008 ISSN 2070-3740
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