1. 1
Ministry of High Education
Shorouk Academy
The Higher Institute of Engineering
Electrical Power and Machines Department
Power Factor Correction
using
Smart Relay
Under supervision of
Prof. Mohamed Morsy shanab
Dr. Abdel-Rahman Khatib
Prepared by
1. Ibrahim Abdel-Aziz Abdel-Gawad.
2. Ayman Ahmed Mohamed Zayed.
3. Hatem Mohamed Abdel-Rahman Seoudy.
4. Amr Mohamed Mosa.
5. Fayek Ali Fathy.
6. Maged Mahmoud Ibrahim.
2004-2005

2. 2
Abstract
The aim of our project is to improve the power factor for a factory by
measuring the reactive power of the loads of the factory by using the
transducer and convert it to a voltage signal which enters into the controller
(Zelio).
The correction is done by chosen a capacitor steps according to the variation
of the reactive power needed by the loads.
These steps are converted to capacitor steps measured by μf, the capacitor
steps make combinations which satisfy the need of the loads.
Zelio make a decision to connect the steps or to disconnect it according to the
program used, which is programmed before.
The connection and disconnection of the capacitors improves the power
factor.
Improving the power factor reduce the bill paid by the factory, improves
voltage profile, and reduce the losses in cables, which reduced the current
used by the same loads.

3. 3
Acknowledgment
Thanks Allah who gives us the power and hope to succeed.
We would like to record our deepest sense of thanks to Assistant Prof.
Abdel-Rahman Khatib for his excellent supervision, continuous
encouragement, simulating discussion, and scientific support, without which
the present study would not have been carried out.
We wish to express our thanks to Prof. Mohamed Morsy shanab the
chairman of Electrical Power and Machines Department for his valuable
support during the years of our study that led to the preparation of this work.
Our special thanks are also extended to all members of Electrical Power and
Machines Department.

4. 4
Contents
Abstract 2
Acknowledgment 3
Contents 4
CHAPTER 1 INTRODUCTION 7
1.1 General 7
1.2 Electrical power network components 8
1.3 Power in resistive and reactive AC circuits 9
1.4 Project outlines 14
CHAPTER 2 ACTIVE, REACTIVE, AND APPARENT POWER 16
2.1 General 16
2.2 Introduction 16
2.3 Power Equations for different load 17
2.4 Understanding Power Factor 20
2.5 Causes of low power factor 23
2.6 Calculating power factor 24
2.7 Typical Percentage Power Factor Values 28
CHAPTER 3 POWER FACTOR CORRECTION 29
3.1 General 29
3.2 Power factor correction 29
3.3 Benefits of Power Factor Correction 36
3.4 Power factor correction sources 36

5. 5
3.5 Advantages of power factor Improvement 37
3.6 Power factor improvement using shunt capacitors 38
3.7 Power factor improvement using synchronous condensers 42
3.8 Graphical calculations of kVAR Requirement 44
3.9 Practical power factor correction 44
CHAPTER 4 CAPACITOR SIZING 51
4.1 General 51
4.2 General rules for rating capacitors 56
4.3 Correction of power factor with capacitors 60
4.4 Power Factor Improvement 61
4.5 Power Factor Corrective Devices 63
4.6 Harmonics and Their Effects 65
CHAPTER 5 MICROCONTROLLER, PLC & CONVENTIONAL CONTROL 68
5.1. General 68
5.2. Microcontroller 68
5.2. Conventional control panel 72
5.3. Programmable Logic controller PLC 74
CHAPTER 6 LAB IMPLEMENTATION MODEL 89
6.1 General 89
6.2 Introduction 89
6.3 Loads 90
6.4 Transducer 91
6.5 The controller (Zelio) 97

6. 6
CHAPTER 7 POWER FACTOR CORRECTION FOR PUMPING STATION 107
7.1 General 107
7.2 Pumping station 107
7.3 Pumping station Load 109
7.4 Pumping Station Capacitor Sizing 110
CHAPTER 8 CONCLUSIONS AND FUTURE WORK 111
8.1 Conclusion: 111
8.2 Future work 112
References 113
Appendex A A1
Appendex B B1
Appendex C C1

7. 7
Chapter 1
Introduction
1.1. General
In general, electrical systems are made up of three components:
• Resistive.
• Inductive.
• Capacitive.
Resistive loads have a power factor of 1 (100%). This means that all the
power used by resistive equipment is working (real) power. Examples of
purely resistive equipment are heaters, and incandescent lights.
Inductive equipment requires an electromagnetic field to operate. Because of
this, inductive loads require both real and reactive power. The power factor
of inductive equipment is referred to as lagging, and is less than 1 (less than
100%). Examples of inductive equipment are transformers and motors.
Capacitive equipment, or capacitors, also utilizes reactive power; however,
the power factor is referred to as leading. Capacitors are opposite to inductors
in reactive energy consumption; therefore if present in a facility, they
counteract the negative effects of inductive loads.
In modern industrial, shop and office environment the most common of these
is the inductive load. Examples include transformers, fluorescent lights and
AC induction motors.
These types of equipment use windings in order to operate. Through the
proximity or movement of the windings an electromagnetic field is produced

8. 8
which allows the motor or transformer to function. While an inductive load
uses energy in order to do its work, it also needs a certain amount of energy
simply to function properly.
So, there are two distinct types of power needed for an inductive load to
operate active power (measured in kW) which actually performs the work
reactive power (kVA) which sustains the electromagnetic field and does no
actual work.
The apparent power of a system is the total power consumed in operating that
system, or the combination of active power and reactive power.
1.2. Electrical power network components
Electrical power networks consist of three main parts:
A. The source of energy: It is the generators which supply the electrical
energy to the loads as a source or voltage source, its quantity changes with
time as a sinusoidal wave.
B. Loads: it is that components which absorb the electrical energy such as
motors, electrical heating furnaces heaters, lamps ...etc.
C. Distribution equipments: It describes an arrangement of electrical
equipment and components installed in a commercial, industrial, or other
type of facility that provides the necessary electrical power to operate
processes or to provide the desired service in a safe and reliable manner.
The components usually include, but are not limited to, the following
elements:
• Transformers
• Conductors (wire, cable, or bus duct)
• Switches
• Protective devices (fuses, circuit breakers, and relays with voltage and

9. 9
current sensing elements)
• Metering (either electro-mechanical or electronic)
• Line reactors, harmonic filters, and resistors
• Power factor correction capacitors
• Motors, drive systems, power and lighting panels, heaters, lights, and
other system loads.
1.3. Power in resistive and reactive AC circuits
Resistive load:
Consider a circuit for a single-phase AC power system, where a 120 volt, 60
Hz AC voltage source is delivering power to a resistive load:
In this example, the current to the load would be 2 amps, RMS. The power
dissipated at the load would be 240 watts. Because this load is purely
resistive (no reactance), the current is in phase with the voltage, and
calculations look similar to that in an equivalent DC circuit. If we were to
plot the voltage, current, and power waveforms for this circuit, it would look
like this:

10. 10
Figure (1.1) Voltage current, and Power relationship in Resistive circuit
Note that the waveform for power is always positive, never negative for this
resistive circuit. This means that power is always being dissipated by the
resistive load, and never returned to the source as it is with reactive loads. If
the source were a mechanical generator, it would take 240 watts worth of
mechanical energy (about 1/3 horsepower) to turn the shaft.
Also note that the waveform for power is not at the same frequency as the
voltage or current! Rather, its frequency is double that of either the voltage or
current waveforms. This different frequency prohibits our expression of
power in an AC circuit using the same complex (rectangular or polar)
notation as used for voltage, current, and impedance, because this form of
mathematical symbolism implies unchanging phase relationships. When
frequencies are not the same, phase relationships constantly change.

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Inductive reactance:
For comparison, let's consider a simple AC circuit with a purely reactive
load:
Figure (1.2) Voltage current, and Power relationship in inductive circuit
Note that the power alternates equally between cycles of positive and
negative. This means that power is being alternately absorbed from and
returned to the source. If the source were a mechanical generator, it would
take (practically) no net mechanical energy to turn the shaft, because no
power would be used by the load. The generator shaft would be easy to spin,
and the inductor would not become warm as a resistor would.

12. 12
RL circuit:
Now, let's consider an AC circuit with a load consisting of both inductance
and resistance:
We already know that reactive components dissipate zero power, as they
equally absorb power from, and return power to, the rest of the circuit.
Therefore, any inductive reactance in this load will likewise dissipate zero
power. The only thing left to dissipate power here is the resistive portion of
the load impedance. If we look at the waveform plot of voltage, current, and
total power for this circuit, we see how this combination works:

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Figure (1.3) Voltage current, and Power relationship in capacitive circuit
As with any reactive circuit, the power alternates between positive and
negative instantaneous values over time. In a purely reactive circuit that
alternation between positive and negative power is equally divided, resulting
in a net power dissipation of zero. However, in circuits with mixed resistance
and reactance like this one, the power waveform will still alternate between
positive and negative, but the amount of positive power will exceed the
amount of negative power. In other words, the combined inductive/resistive
load will consume more power than it returns back to the source.
Looking at the waveform plot for power, it should be evident that the wave
spends more time on the positive side of the center line than on the negative,
indicating that there is more power absorbed by the load than there is
returned to the circuit. What little returning of power that occurs is due to the
reactance; the imbalance of positive versus negative power is due to the
resistance as it dissipates energy outside of the circuit (usually in the form of
heat). If the source were a mechanical generator, the amount of mechanical
energy needed to turn the shaft would be the amount of power averaged
between the positive and negative power cycles.
The phase angle for power means something quite different from the phase
angle for either voltage or current. Whereas the angle for voltage or current
represents a relative shift in timing between two waves, the phase angle for
power represents a ratio between power dissipated and power returned.
Because of this way in which AC power differs from AC voltage or current,

14. 14
it is actually easier to arrive at figures for power by calculating with scalar
quantities of voltage, current, resistance, and reactance than it is to try to
derive it from vector, or complex quantities of voltage, current, and
impedance that we've worked with so far.
1.4. Project outlines
The projects consists of 8 chapters
Chapter one: is introduction chapter taking about the power system and its
component and the circuits describing it. It also contains the project out lines.
Chapter two: discuss the active, reactive, and apparent power and their
equations for different loads then we would understand the power factor and
its definitions after understanding the power factor we would know the
causes of low power factor and its disadvantages then we would calculate the
power factor and at last there is a typical power factor values for different
load types in the practical life.
Chapter three: discuss the power factor correction and its meaning then show
the benefits of power factor correction. There are different sources of power
factor correction such as static capacitors, synchronous motors, and
synchronous condensers. After discussing the power factor correction sources
we would discuss the advantages of power factor improvement. Then discuss
in brief correcting the power factor by static capacitors and synchronous
motors. Then we must do the power factor correction in practice. So we had
to discuss practical power factor correction.
Chapter four: discuss how capacitors correct the power factor, the capacitors
in single phase and three phase power factor correction applications, general
rules for rating capacitors, size of capacitors for power factor improvement,

15. 15
measurement of capacitor current, power factor choices, correction of power
factor using capacitors, power factor improvement, power factor correction
devices, and harmonics and their effect.
Chapter five: discuss control systems such as microcontroller technique,
conventional methods of control, and plc different techniques.
Chapter six: discuss the lab implementation model its loads, transducer,
Zelio, and some photos of our work.
Chapter seven: discuss correction of power factor for a pumping station. First
there some data of the station and its work and the single line diagram of it.
Then there is some reading taken from it describing its loads. And last is a
capacitor sizing for the station for power factor correction.
Chapter eight: It a conclusion of the project and the future work that can be
done.

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Chapter 2
Active, Reactive, and Apparent power
2.1 General
In this chapter we will discuss the active, reactive, and apparent power and
their equations for different loads then we would understand the power factor
and its definitions after understanding the power factor we would know the
causes of low power factor and its disadvantages then we would calculate the
power factor and at last there is a typical power factor values for different
load types in the practical life.
2.2 Introduction
We know that reactive loads such as inductors and capacitors dissipate zero
power yet the fact that they drop voltage and draw current gives the deceptive
impression that they actually do dissipate power. This is called reactive
power, and it is measured in a unit called Volt-Amps-Reactive (VAR), rather
than watts. The mathematical symbol for reactive power is Q. The actual
amount of power being used, or dissipated, in a circuit is called true power or
active power, and it is measured in watts (symbolized by P). The combination
of reactive power and true power is called apparent power, and it is the
product of a circuit's voltage and current, without reference to phase angle.
Apparent power is measured in the unit of Volt-Amps (VA) and is symbolized
by S.
As a rule, true power is a function of a circuit's dissipative elements, usually
resistances (R). Reactive power is a function of a circuit's reactance (X).
Apparent power is a function of a circuit's total impedance (Z).

17. 17
2.3 Power Equations for different load
There are several power equations relating the three types of power to
resistance, reactance, and impedance:
Please note that there are two equations each for the calculation of true and
reactive power. There are three equations available for the calculation of
apparent power, P=IE being useful only for that purpose. Examine the
following circuits and see how these three types of power interrelate.
Resistive load only:

18. 18
Reactive load only:
Resistive/reactive load:
These three types of power -- true, reactive, and apparent -- relate to one
another in trigonometric form. We call this the power triangle:

19. 19
22
)()( POWERREACTIVEPOWERTRUEPOWERTOTAL +=
The angle "Φ" in the power triangle is called the power factor angle and is
mathematically equal to:
On a single-phase circuit, the current will usually lag behind the voltage. The
amount of the lag can be measured in degrees (360° for one complete cycle).
The cosine of this phase angle also equals the power factor.

20. 20
2.4 Understanding Power Factor
"Power Factor" is an electrical term used to rate the degree of the
synchronization of power supply current with the power supply voltage. This
term is often misunderstood by ourselves and our customers, or simply
ignored.
It is important that we clearly understand the meaning of "Power Factor" and
its effect on the electrical supply system for the following reasons:
1. a low power factor can increase the cost of power to the user
2. a low power factor can increase the cost of power transmission
equipment to the user
3. a customer may request assistance in selecting equipment to correct a
low power factor
4. Over-correction of power factor by the addition of excessive
capacitance is sometimes dangerous to a motor and the driven
equipment. (above 95% power factor)
5. A customer may, to some extent, use motor power factor rating as a
power factor rating as a criterion in choosing among competing
motors, especially when a large motor is involved.
The power factors in industrial plants are usually lagging due to the inductive
nature of induction motors, transformers, lighting, induction heating furnaces,
etc. This lagging power factor has two costly disadvantages for the power
user. First, it increases the cost incurred by the power company because more
current must be transmitted than is actually used to perform useful work. This
increased cost is passed on to the industrial customer by means of power
factor adjustments to the rate schedules. Second, it reduces the load handling
capability of the industrial plants electrical transmission system which means
that the industrial power user must spend more on transmission lines and

21. 21
transformers to get a given amount of useful power through his plant. This is
shown in the figure below.
Figure (2.1) what is power factor
Power factor is defined as the ratio of the actual power (Watts) to the
apparent power (Volt-amperes). Power factor=Actual Power/Apparent Power
Figure (2.2) relation among active, reactive, and apparent power
From figure 2.2 above, it can be seen that the apparent power which is
transmitted by the power plant is actually composed vectorially of the actual
power and the reactive power. The active power is used by the motor and
results in useful work. The reactive power is wasted and merely bounces
energy back and forth between the motor and the generators at the power
company's plant. If the power factor is corrected, figure (2) shows how the
reactive power element decreases in size and the apparent power element
approaches the size of the actual power used. This means that less power
need to be generated to obtain the same amount of useful energy for the
motor. Power factor correction is discussed below. Power factor is also

22. 22
numerically equal to the cosine of the angle of the lag of the primary input
current with respect to its voltage.
Figure (2.3) relation voltage and current in lagging power factor circuit
From Figure (2.3) above, it can be seen that the current is lagging the voltage
by an angle 0. An ideal power supply would have no lag on lead angle and
the power transmitted to the motor would be a useful power. The equation for
useful or actual power is:
P = El cos Ø
Or
Power = Volts x Current x Cosine of the lag angle 0
Where:
Cos Ø = Power Factor
El = KVA
El cos Ø = KW
If the lag Ø is zero then the cos Ø is equal to one, and the useful or actual
power equals E*l and no power is lost due to reactance in the system.

23. 23
2.5 Causes of low power factor
Low power factor is undesirable from economic point of view.
Normally the power factor of the whole load on the supply system is lower
than 0.8. The following are the causes of low power factor:
• Most of the AC motors are of induction type (1-Φ and 3-Φ induction
motors) which have low lagging power factor. These motors work at a
power factor which is extremely small on light loads (0.2 to 0.3) and rises
to 0.8 or 0.9 at full load.
• Arc lamps, electric discharge lamps and industrial heating furnaces
operate at low lagging power factor.
• The load on the power system is varying; being high during morning and
evening and low at other times. During low load period, supply voltage is
increased which increases the magnetization current. This results in the
decreased power factor.
2.4.1 Low power factor disadvantages
The disadvantages of low power factors are three. The first is that
transmission lines and other power circuit elements are usually more reactive
than resistive. Reactive components of current produce larger voltage drops
than resistive components, and add to the total IZ = (I(R + LX)) drop,
therefore, the system-voltage regulation suffers more and additional voltage-
regulating equipment may be required for satisfactory operation of the
equipment using power. The second disadvantage is the inefficient utilization
of the transmission equipment since more current flow per unit of real power
transmitted is necessary due to the reactive power also carried in the power
lines. If the current necessary to satisfy reactive power could be reduced,
more useful power could be transmitted through the present system. The third
disadvantage is the cost of the increased power loss in transmission lines. The

24. 24
increased power loss is due to the unnecessary reactive power which is in the
system. The reactive power losses vary as the square of the reactive current
or as the inverse of the power factor squared.
2.6 Calculating power factor
As was mentioned before, the angle of this "power triangle" graphically
indicates the ratio between the amount of dissipated (or consumed) power and
the amount of absorbed/returned power. It also happens to be the same angle
as that of the circuit's impedance in polar form. When expressed as a fraction,
this ratio between true power and apparent power is called the power factor
for this circuit. Because true power and apparent power form the adjacent and
hypotenuse sides of a right triangle, respectively, the power factor ratio is
also equal to the cosine of that phase angle. Using values from the last
example circuit:
It should be noted that power factor, like all ratio measurements, is a unit less
quantity.
For the purely resistive circuit, the power factor is 1 (perfect), because the
reactive power equals zero. Here, the power triangle would look like a
horizontal line, because the opposite (reactive power) side would have zero
length.
For the purely inductive circuit, the power factor is zero, because true power
equals zero. Here, the power triangle would look like a vertical line, because
the adjacent (true power) side would have zero length.

25. 25
The same could be said for a purely capacitive circuit. If there are no
dissipative (resistive) components in the circuit, then the true power must be
equal to zero, making any power in the circuit purely reactive. The power
triangle for a purely capacitive circuit would again be a vertical line (pointing
down instead of up as it was for the purely inductive circuit).
Power factor can be important; because any power factor less than 1 means
that the circuit's wiring has to carry more current than what would be
necessary with zero reactance in the circuit to deliver the same amount of
(true) power to the resistive load.
Poor power factor can be corrected, paradoxically, by adding another load to
the circuit drawing an equal and opposite amount of reactive power, to cancel
out the effects of the load's inductive reactance. Inductive reactance can only
be canceled by capacitive reactance, so we have to add a capacitor in parallel
to our example circuit as the additional load. The effect of these two
opposing reactances in parallel is to bring the circuit's total impedance equal
to its total resistance (to make the impedance phase angle equal or at least
closer, to zero).
Since we know that the uncorrected reactive power (inductive), so we need to
calculate the correct capacitor size to produce the same quantity of
(capacitive) reactive power. Since this capacitor will be directly in parallel
with the source (of known voltage), we'll use the power formula which starts
from voltage and reactance:

26. 26
Let's use a rounded capacitor and see what happens to our circuit:
The power factor for the circuit, overall, has been substantially improved.
The main current has been decreased, while the power dissipated at the load
resistor remains unchanged. The power factor is much closer to being 1:

27. 27
Since the impedance angle is still a positive number, we know that the circuit,
overall, is still more inductive than it is capacitive. If our power factor
correction efforts had been perfectly on-target, we would have arrived at an
impedance angle of exactly zero, or purely resistive. If we had added too
large of a capacitor in parallel, we would have ended up with an impedance
angle that was negative, indicating that the circuit was more capacitive than
inductive. [2]
It should be noted that too much capacitance in an AC circuit will result in a
low power factor just as well as too much inductance. You must be careful
not to over-correct when adding capacitance to an AC circuit. You must also
be very careful to use the proper capacitors for the job (rated adequately for
power system voltages and the occasional voltage spike from lightning
strikes, for continuous AC service and capable of handling the expected
levels of current).
If a circuit is pure inductive, we say that its power factor is lagging (because
the current wave for the circuit lags behind the applied voltage wave).
Conversely, if a circuit is pure capacitive, we say that its power factor is
leading. Thus, our example circuit started out with a power factor of 0.705
lagging, and was corrected to a power factor of 0.999 lagging.

28. 28
2.7 Typical Percentage Power Factor Values
In industrial and commercial facilities, the majority of electrical equipment
acts like resistors or inductors. Resistive loads include incandescent lights,
baseboard heaters, and cooking ovens. Inductive loads include fluorescent
lights, AC induction motors, arc welders, and transformers.
Typical percentage power factor values for some inductive loads are:
Load Power Factor (% lagging)
Induction motors 70-90
Small adjustable speed drives 90-98
Large adjustable speed drives 40-90
Fluorescent lights:
Magnetic ballast 70-80
Electronic ballast 90-95
Arc furnaces 75-90
Arc welders 35-80

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Chapter 3
Power Factor Correction
3.1 General
In this chapter we will discuss the power factor correction and its meaning
then show the benefits of power factor correction. There are different sources
of power factor correction such as static capacitors, synchronous motors, and
synchronous condensers. After discussing the power factor correction sources
we would discuss the advantages of power factor improvement. Then discuss
in brief correcting the power factor by static capacitors and synchronous
motors. Then we must do the power factor correction in practice. So we had
to discuss practical power factor correction.
3.2 Power factor correction
Capacitive Power Factor correction is applied to circuits which include
induction motors as a means of reducing the inductive component of the
current and thereby reduce the losses in the supply. There should be no effect
on the operation of the motor itself.
An induction motor draws current from the supply, which is made up of
resistive components and inductive components. The resistive components
are:
1) Load current.
2) Loss current and the inductive components are:
3) Leakage reactance.
4) Magnetizing current

30. 30
The current due to the leakage reactance is dependant on the total current
drawn by the motor, but the magnetizing current is independent of the load
on the motor. The magnetizing current will typically be between 20% and
60% of the rated full load current of the motor. The magnetizing current is
the current that establishes the flux in the iron and is very necessary if the
motor is going to operate. The magnetizing current does not actually
contribute to the actual work output of the motor. It is the catalyst that allows
the motor to work properly. The magnetizing current and the leakage
reactance can be considered passenger components of current that will not
affect the power drawn by the motor, but will contribute to the power
dissipated in the supply and distribution system. Take for example a motor
with a current draw of 100 Amps and a power factor of 0.75.The resistive
component of the current is 75 Amps and this is what the KWh meter
measures. The higher current will result in an increase in the distribution
losses of (100 x 100) / (75 x 75) = 1.777 or a 78% increase in the supply
losses.
In the interest of reducing the losses in the distribution system, power factor
correction is added to neutralize a portion of the magnetizing current of the
motor. Typically, the corrected power factor will be 0.92 - 0.95 some power
retailers offer incentives for operating with a power factor of better than 0.9,
while others penalize consumers with a poor power factor. There are many
ways that this is metered, but the net result is that in order to reduce wasted

31. 31
energy in the distribution system, the consumer will be encouraged to apply
power factor correction.
Power factor correction is achieved by the addition of capacitors in parallel
with the connected motor circuits and can be applied at the starter, or applied
at the switchboard or distribution panel. The resulting capacitive current is
leading current and is used to cancel the lagging inductive current flowing
from the supply.
a) Capacitors connected at each starter and controlled by each starter is
known as "Static Power Factor Correction" while capacitors connected at a
distribution board and controlled independently from the individual starters is
known as "Bulk Correction".
b) The Power factor of the total current supplied to the distribution board is
monitored by a controller which then switches capacitor banks in a fashion to
maintain a power factor better than a preset limit. (Typically 0.95) Ideally,
the power factor should be as close to unity as possible. There is no problem
with bulk correction operating at unity.

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3.1.1 Static Correction
As a large proportion of the inductive or lagging current on the supply is due
to the magnetizing current of induction motors, it is easy to correct each
individual motor by connecting the correction capacitors to the motor starters.
With static correction, it is important that the capacitive current is less than
the inductive magnetizing current of the induction motor. In many
installations employing static power factor correction, the correction
capacitors are connected directly in parallel with the motor windings. When
the motor is Off Line, the capacitors are also Off Line. When the motor is
connected to the supply, the capacitors are also connected providing
correction at all times that the motor is connected to the supply. This removes
the requirement for any expensive power factor monitoring and control
equipment. In this situation, the capacitors remain connected to the motor
terminals as the motor slows down. An induction motor, while connected to
the supply, is driven by a rotating magnetic field in the stator which induces
current into the rotor. When the motor is disconnected from the supply, there
is for a period of time, a magnetic field associated with the rotor. As the
motor decelerates, it generates voltage out its terminals at a frequency which
is related to its speed. The capacitors connected across the motor terminals,

33. 33
form a resonant circuit with the motor inductance. If the motor is critically
corrected, (corrected to a power factor of 1.0) the inductive reactance equals
the capacitive reactance at the line frequency and therefore the resonant
frequency is equal to the line frequency. If the motor is over corrected, the
resonant frequency will be below the line frequency. If the frequency of the
voltage generated by the decelerating motor passes through the resonant
frequency of the corrected motor, there will be high currents and voltages
around the motor/capacitor circuit. This can result in severe damage to the
capacitors and motor. It is imperative that motors are never over corrected or
critically corrected when static correction is employed.
Static power factor correction should provide capacitive current equal to 80%
of the magnetizing current, which is essentially the open shaft current of the
motor.
The magnetizing current for induction motors can vary considerably.
Typically, magnetizing currents for large two pole machines can be as low as
20% of the rated current of the motor while smaller low speed motors can
have a magnetizing current as high as 60% of the rated full load current of the
motor. It is not practical to use a "Standard table" for the correction of
induction motors giving optimum correction on all motors. Tables result in
under correction on most motors but can result in over correction in some
cases. Where the open shaft current can not be measured, and the
magnetizing current is not quoted, an approximate level for the maximum
correction that can be applied can be calculated from the half load
characteristics of the motor. It is dangerous to base correction on the full load
characteristics of the motor as in some cases, motors can exhibit a high
leakage reactance and correction to 0.95 at full load will result in over
correction under no load, or disconnected conditions

34. 34
Static correction is commonly applied by using on a contactor to control both
the motor and the capacitors. It is better practice to use two contactors, one
for the motor and one for the capacitors. Where one contactor is employed, it
should be up sized for the capacitive load. The use of a second contactor
eliminates the problems of resonance between the motor and the capacitors.

35. 35
3.1.2 Inverter
Static Power factor correction must not be used when the motor is controlled
by a variable speed drive or inverter. The connection of capacitors to the
output of an inverter can cause serious damage to the inverter and the
capacitors due to the high frequency switched voltage on the output of the
inverters.
The current drawn from the inverter has a poor power factor, particularly at
low load, but the motor current is isolated from the supply by the inverter.
The phase angle of the current drawn by the inverter from the supply is close
to zero resulting in very low inductive current irrespective of what the motor
is doing. The inverter does not however, operate with a good power factor.
Many inverter manufacturers quote a cos Ø of better than 0.95 and this is
generally true, however the current is non sinusoidal and the resultant
harmonics cause a power factor (KW/KVA) of closer to 0.7 depending on the
input design of the inverter. Inverters with input reactors and DC bus reactors
will exhibit a higher true power factor than those without.
The connection of capacitors close to the input of the inverter can also result
in damage to the inverter. The capacitors tend to cause transients to be
amplified, resulting in higher voltage impulses applied to the input circuits of
the inverter, and the energy behind the impulses is much greater due to the
energy storage of the capacitors. It is recommended that capacitors should be
at least 75 Meters away from inverter inputs to elevate the impedance
between the inverter and capacitors and reduce the potential damage caused.
Switching capacitors, Automatic bank correction etc, will cause voltage
transients and these transients can damage the input circuits of inverters. The
energy is proportional to the amount of capacitance being switched. It is

36. 36
better to switch lots of small amounts of capacitance than few large amounts.
[6]
3.3 Benefits of Power Factor Correction
By optimizing your energy use you can:
• Reduce electricity costs by eliminating power factor surcharges
• Enhance equipment operation by improving voltage
• Improve energy efficiency
• Reduce line losses
• Delay costly upgrades
• Free up transformer and distribution system capacity
3.4 Power factor correction sources
We improve the power factor by decreasing the desired reactive power from
the feeding source. The following sources of reactive power are used in
improving the power factor:
1. Synchronous motors.
2. Synchronous condensers.
3. Static capacitors.
When we use the suitable source of reactive power we use it corresponding to
the following factors:
1. The reliability of the equipment.
2. The equipment life time.
3. The cost of the buying and installation.
4. The running cost.
5. The maintenance cost.
6. The requirements of the place and easiest of the installation.
7. System requirements.

37. 37
8. Effect on the environment.
3.5 Advantages of power factor Improvement
Installation of power factor improvement device, to raise the power
factor, results in one or more of the following effects and advantages:
1. Reduction in circuit current.
2. Increase in voltage level at load.
3. Reduction in copper losses in the system due to reduction in current.
4. Reduction in investment in the system facilities per kW of the load
supplied.
5. Improvement in power factor of the generators.
6. Reduction in kVA loading of the generators and circuits. This
reduction in kVA loading may relieve an overloaded condition or
release capacity for additional growth of load.
Reduction in kVA demand charges for large consumers. To encourage large
consumers to install power factor improvement devices at their premises,
supply authorities charge such customers as per two part tariff, the first part
being proportional to the maximum kVA demand. To reduce this charge
large industrial consumers install power factor improvement devices. The
power factor can be improved if the lagging kVAR of the equipment is
balanced by a leading kVAR. This can be done either by use of static
capacitors or synchronous condensers.

38. 38
3.6 Power factor improvement using shunt capacitors
3.5.1 General.
Shunt capacitors are used in rating from 15 kVAR to 10000 kVAR.
Small banks of capacitors, up to a few hundred kVAR rating are used on
individual distribution circuits of customers. Capacitor banks of 500-3000
kVAR are used in small distribution substations and those with still larger
rating at large substations.
Capacitors are installed either in groups at one central location, say at
the primary or the secondary of transformer or individually on each motor or
branch circuit feeding a group of motors. They are arranged in 3-phase banks
connected in star or delta.
It is not economical to raise the power factor to unity for the following
reasons:
1. If the power factor is improved to unity for full load conditions, the
power factor would become leading when the load is less than full
load (unless some capacitors are switched off which is generally
difficult).
2. As the power factor approaches unity, the capacity of power
improvement device increases more rapidly e.g. the power factor of an
installation can be improved from 0.8 to 0.9 by a much smaller
capacitive kVAR than which will be needed to raise the power factor
from 0.9 to unity.
3. Improvement in power factor means a reduction in kVA charge.
However installation of power factor improvement devices needs
capital investment. The power factor should be improved to such an
extent that the savings are the maximum.

39. 39
3.5.2 Most economic power factor when kW demands constant.
The fig shows the phasor diagram of an installation having an active power
requirement of P kW. Through installation of capacitors the power factor is
improved from cos Φ1 to cos Φ2 thus causing a reduction in kVA from S1 to
S2. The capacitor kVAR is Q. The losses in capacitors can be ignored.
Let annual charges per kVA of maximum demand per year = A
Annual interest and depreciation charges for capacitor installation = B
per kVAR
Annual savings = A (S1 - S2)
= AP ⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
Φ
−
Φ 21 cos
1
cos
1
Annual cost of capacitor installation = B.Q.
= B.P. (tan Φ1- tan Φ2)

40. 40
Net savings = AP ⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
Φ
−
Φ 21 cos
1
cos
1
- BP (tan Φ1- tan Φ2)
For maximum net savings,
2
)(
Φd
savingNetd
should be zero.
AP (0 - sec Φ2 tan Φ2) – BP (0 – sec2
Φ2) = 0
Or sin Φ2 =
A
B
=
demandofkVApereschAnnual
kperoninstallaticapacitoroneschAnnual
.maxarg
vararg
Thus maximum savings are achieved when power factor is improved to
cos Φ2, where Φ2 is given in the last Eq.
3.5.3 Most economic power factor when kVA demand is constant.
The supply authorities try to improve the power factor to reduce the cost of
the plant. The investment in plant is proportional to kVA while the revenue is
a function of active power (kW). The phasor diagram is shown in fig. The

41. 41
kVA output remains constant at S kVA. Addition of leading kVAR in the
system improves the power output from P1 to P2.
Let annual charges on capacitor installation = C per kVAR
Net return per kW of installation per year = D
Annual increase in return = D (P2 – P1)
=D S (cos Φ2 - cos Φ1)
Annual charges on capacitor installation = CQ
= C S (sin Φ1 - sin Φ2)
Net savings = DS (cos Φ2 - cos Φ1) - C S (sin Φ1 - sin Φ2)
For maximum net savings,
2
)(
Φd
savingNetd
should be zero.
- DS sin Φ2 + CS cos Φ2 = 0
OR tan Φ2 =
D
C
=
oninstallatiofkWperreturnAnnual
capacitorsofkVARpereschAnnual arg
Thus the most economic power factor is cos Φ2, where Φ2 is given by
the last Eq.

42. 42
3.7 Power factor improvement using synchronous condensers
When the kVAR requirement is small, it can be met through static
capacitors. However when requirement exceeds 10,000 kVAR it is generally
more economical to use the synchronous condensers.
A synchronous condenser is essentially an over excited synchronous
motor. Generally it does not supply any active mechanical power. The
excitation of the machine is varied to provide the necessary amount of the
leading kVAR. The advantages and disadvantages of using synchronous
condensers as compared to static capacitors are as under:
1. A synchronous condenser can supply kVAR equal to its rating and
absorb kVAR up to 50 % of its capacity. Thus a synchronous
condenser of certain kVAR is equal to a static capacitor of that kVAR
and a shunt reactor of 50 % kVAR.
2. By the use of synchronous condenser a finer control is possible than by
use of static capacitors.
3. A synchronous condenser can be overloaded for short periods but a
static capacitor cannot be overloaded.
4. A momentary drop in voltage causes the synchronous condenser to
supply greater kVAR to the system whereas in the case of static
capacitor, the kVAR supplied is reduced.
5. The inertia of the synchronous condenser improves the system stability
and reduces the effect of sudden changes in load.
6. The power loss in a synchronous condenser is much greater than that in
a capacitor.
7. For small kVAR requirements, static capacitors are preferable and
economical. For requirements above 10,000 kVAR or so synchronous
condensers are more economical.

43. 43
8. Static capacitor installations can be distributed in the system. Thus
capacitors can be located near the loads and are more effective.
However small size synchronous condensers are very uneconomical.
As such the synchronous condensers have to be installed at one point
only.
9. The rating of a static capacitor bank can be changed very easily as per
requirements. Capacitor units can be add to the bank or taken away
from it. This is not possible with synchronous condensers.
10.Installation of a static capacitor bank is easy.
11.A failure of one unit of capacitor bank affects that unit only. The
remaining units continue to do their job. However failure of a
synchronous condenser means loss of total condenser is very small as
compared to the failure rate of a capacitor bank.
12.Synchronous condenser adds to the short circuit currents in the system
and increase the circuit breaker ratings.
Synchronous condensers are mostly used by utilities at large sub-stations
to improve the power factor and voltage regulation. Machines up to 100
MVAR ratings or even higher have been used. The field current is regulated
automatically to give a desired voltage level. A typical instance is of 150
MW to be transmitted over a distance of 240 km. If the receiving end power
factor is 0.85, the sending end power factor is 0.65 and sending end voltage
1.5 times receiving end voltage. Addition of 75 MVAR synchronous
condenser at receiving end improves the sending end power factor to 0.88and
reduces the voltage drop in transmission line by 50%. In addition the
synchronous condenser reduces the switching surges due to the sudden
connection or disconnection of the line to the system. [1]

44. 44
3.8 Graphical calculations of kVAR Requirement
If the kW and initial power factor of an installation are known, the
capacitor kVAR required to improve the power factor to a new value is given
by
)tan(tan 21 Φ−Φ= PQ
Where Q = Capacitor kVAR
P = kW requirement
cos Φ1 = initial power factor
cos Φ2 = new power factor
The capacitor kVAR can also be determined by using the fig which has
been drawn between kVAR and kW for different values of power factors. It
is evident that any intercept (say OK) represents kVA whose horizontal
components OF is the corresponding kW and vertical component kF is the
kVAR.
3.9 Practical power factor correction
When the need arises to correct for poor power factor in an AC power
system, you probably won't have the luxury of knowing the load's exact
inductance in henrys to use for your calculations. You may be fortunate
enough to have an instrument called a power factor meter to tell you what the
power factor is (a number between 0 and 1), and the apparent power (which
can be figured by taking a voltmeter reading in volts and multiplying by an
ammeter reading in amps). In less favorable circumstances you may have to
use an oscilloscope to compare voltage and current waveforms, measuring

45. 45
phase shift in degrees and calculating power factor by the cosine of that
phase shift.
Most likely, you will have access to a wattmeter for measuring true power,
whose reading you can compare against a calculation of apparent power
(from multiplying total voltage and total current measurements). From the
values of true and apparent power, you can determine reactive power and
power factor. Let's do an example problem to see how this works:
First, we need to calculate the apparent power in kVA. We can do this by
multiplying load voltage by load current:
As we can see, 2.308 kVA is a much larger figure than 1.5 kW, which tells us
that the power factor in this circuit is rather poor (substantially less than 1).
Now, we figure the power factor of this load by dividing the true power by
the apparent power:

46. 46
Using this value for power factor, we can draw a power triangle, and from
that determine the reactive power of this load:
To determine the unknown (reactive power) triangle quantity, we use the
Pythagorean Theorem "backwards," given the length of the hypotenuse
(apparent power) and the length of the adjacent side (true power):

47. 47
If this load is an electric motor, or most any other industrial AC load, it will
have a lagging (inductive) power factor, which means that we'll have to
correct for it with a capacitor of appropriate size, wired in parallel. Now that
we know the amount of reactive power (1.754 kVAR), we can calculate the
size of capacitor needed to counteract its effects:
Rounding this answer off to 80 µF, we can place that size of capacitor in the
circuit and calculate the results:

48. 48
An 80 µF capacitor will have a capacitive reactance of 33.157 Ω, giving a
current of 7.238 amps, and a corresponding reactive power of 1.737 kVAR
(for the capacitor only). Since the capacitor's current is 180o
out of phase
from the load's inductive contribution to current draw, the capacitor's reactive
power will directly subtract from the load's reactive power, resulting in:
This correction, of course, will not change the amount of true power
consumed by the load, but it will result in a substantial reduction of apparent
power, and of the total current drawn from the 240 Volt source:

49. 49
The new apparent power can be found from the true and new reactive power
values, using the standard form of the Pythagorean Theorem:
22
)()(Re powerTruepoweractivepowerApparent +=
kVApowerApparent 50009.1=
This gives a corrected power factor of (1.5kW / 1.5009 kVA), or 0.99994,
and a new total current of (1.50009 kVA / 240 Volts), or 6.25 amps, a
substantial improvement over the uncorrected value of 9.615 amps! This

50. 50
lower total current will translate to less heat losses in the circuit wiring,
meaning greater system efficiency (less power wasted).

51. 51
Chapter 4
Capacitor Sizing
4.1 General
In this chapter we will discuss how capacitors correct the power factor, the
capacitors in single phase and three phase power factor correction
applications, general rules for rating capacitors, size of capacitors for power
factor improvement, measurement of capacitor current, power factor choices,
correction of power factor using capacitors, power factor improvement,
power factor correction devices, and harmonics and their effect.
4.1.1 How capacitors correct power factor?
Capacitors are characterized by leading kVAR in the phasor diagram or
power triangle. This is opposite to the inductive kVAR (refer to the following
diagram).
Figure (4.1) Phasor diagram for power factor correction
cosφ = P/S
sinφ = Q/S
Q = P tanφ

52. 52
Q = S sinφ
Φ = phase displacement angle
S1 = uncompensated apparent power
S2 = compensated power with capacitors for compensation
The angle φ:  is the phase angle between the voltage and current waveforms.
The reactive power is defined by
A capacitor of Q kVAR will compensate for the inductive kVAR and
produce cos φ= 1.
It is not common practice to produce cos φ= 1 with capacitors because this
may result in overcompensation due to load changes and the response time of
the controller. Generally public utilities specify a value (cos φ2) to which the
existing power factor (cos φ1) should be corrected.
The reactive power to be compensated is determined as follows.
Connection and rating of capacitors
A general expression for the kVAR rating of a capacitor (single-phase
connection) is:

53. 53
4.1.2 Capacitor in single-phase PFC application
The capacitor is connected across the phase and neutral and is subjected to
the phase voltage. The above equation, without any change, is applicable to
such capacitors.
4.1.3 Capacitor in three-phase PFC application
4.1.3.1 Star connection
The partial capacitor is subjected to a voltage of
Thus total kVAR compensation of all three partial capacitors:
Figure (4.2) Star connection

54. 54
4.1.3.2 Delta connection
The capacitor is subjected to line voltage UN, phase to phase.
Thus total kVAR compensation:
Figure (4.3) Delta connection
From the above equations it follows that for the desired Q kVAR:
Thus for the same amount of kVAR compensation a star connection requires
the triple capacitance of a delta connection. On the other hand, for the same
nominal voltage UN in delta connection a 3 thicker dielectric film is
required to get similar values of electric field strength.
Calculation of capacitor ratings using standard tables
Capacitors can be rated by multiplying the active power P given on the rating
plate of the motor by the value in the table below.
To find the right value, choose your existing power factor (here 0.7), then
move horizontally to the column of the desired power factor (here 0.9). The
value you find there is the one to multiply by the active power of the motor
(0.54).

55. 55
Thus, for the last example:
Capacitor output in case of operating voltage and/or frequency different to
nominal ratings
Note:
1) U (new) < UN
2) f (new): 50 or 60 Hz; in case of higher frequencies, losses have to be taken
into consideration, thermal data sheet can be used.
Desired power factor (cos φ2)Existing power
factor (cos φ1)
1.0 0.98 0.96 0.94 0.92 0.90 0.85 0.80 0.75 0.70
0.40 2.29 2.09 2.00 1.93 1.86 1.81 1.67 1.54 1.41 1.27
0.45 1.99 1.79 1.70 1.63 1.56 1.51 1.37 1.24 1.11 0.97
0.50 1.73 1.53 1.44 1.37 1.30 1.25 1.11 0.98 0.85 0.71
0.55 1.52 1.32 1.23 1.16 1.09 1.04 0.90 0.77 0.64 0.50
0.60 1.33 1.13 1.04 0.97 0.90 0.85 0.71 0.58 0.45 0.31
0.65 1.17 0.97 0.88 0.81 0.74 0.69 0.55 0.42 0.29 0.15
0.70 1.02 0.82 0.73 0.66 0.59 0.54 0.40 0.27 0.14 -
0.75 0.88 0.68 0.59 0.52 0.45 0.40 0.26 0.13 - -
0.80 0.75 0.55 0.46 0.39 0.32 0.27 0.13 - - -
0.85 0.62 0.42 0.33 0.26 0.19 0.14 - - - -
0.90 0.48 0.28 0.19 0.12 0.05 - - - - -

56. 56
4.2 General rules for rating capacitors
In a plant that is still in the design phase an average power factor of cos φ1 =
0.7 can be assumed for the reactive power loads. To compensate to cos φ=
0.9, the value 0.54 for (tan φ1–tan φ2) can be taken from the table above. In
this case a capacitor rating of about 50 % of the active power rating would be
selected.
With existing operating plant the necessary values can be taken by
measurements.
To determine the correct capacitor rating, accurate values of the connected
power and operating times should be known.
This calculation is only valid where the load conditions are more or less
constant. Under extreme load variations, e.g. heavy motor loads (inductive)
during production hours and only heating and lighting during the night, the
average values used to determine capacitor ratings would not be sufficient for
peak inductive loads. In such cases it is recommended to take meter readings
during a one-day period, for example, to obtain exact instantaneous values of
current, voltage and cos φ
4.2.1 Size of capacitors for power factor improvement
The size of capacitors to improve the power factor of the system at certain
point can be computed with the help of the computer studies of the system.
Manual calculations can also be made of comparatively small distribution
system for the capacitor kVAR required to improve the power factor say
from cos φe (existing) to cos φd (desired) with the following equation:
KVAR = KW (tan φe – tan φd)
Or
KVAR = Kw * MF
Where MF = multiplying factor

57. 57
The monogram shown in fig. 15.12 solves this equation. With the help of this
monogram the MF for any improvement in the power factor can be read
directly. Capacitor kvars required for this improvement shall be the simple
multiplication of MF and KW as shown in the following example.
Fig (4.4) Nomogram for calculating multiplying factor required to determine
capacitor kVAR; Multiplying factor (MF) = tan φe – tan φd
Example: We are required to find out the capacitor rating to improve the
power factor of 100 kw load from 65 % to 85 %(desired power factor) on the
respective scales and extend to the multiplying factor scale to get MF as 0.55.
Then the required kVAR rating of capacitor is 100*0.55 = 55.0.
4.2.2 Measurement of capacitor current
The current drawn in each phase of an LT capacitor may be measured by
means of a low rang tong tester and these values are compared with the
standard values for the capacities mentioned below in Table 15.5 at different
operating voltages within a tolerance of 5 to 10%.
These values are based on the relation:
(KVAR) 2 = (kVAR) 1*(V2/V1) ^2; (kVAR) 1 =3V1 I1

58. 58
Where, (kVAR) 2 and V2 are the rated values and (kVAR) 1 is the kVAR at
measured voltage V1 and I1.
The difference in the amperage drawn from supply mains with and without
capacitors at the normal operating load can be noted and the values for the
following capacities of motors can be compared with the current values given
against each.
3HP 1 kVAR 0.65-0.92 A
5 HP 2 kVAR 1.0-1.5 A
7.5 HP 3 kVAR 1.45-1.75 A
10 HP 4 kVAR 2.5-3.4 A
Table (4.1)
KVAR 390 V
(A)
400 V
(A)
415 V
(A)
430 V
(A)
440 V
(A)
1 1.30 1.34 1.39 1.42 1.47
2 2.6 2.65 2.78 2.84 2.94
3 3.9 4.0 4.16 4.23 4.40
4 5.25 5.35 5.56 5.72 5.87
5 6.5 6.7 6.96 7.2 7.34
6 7.85 8.5 8.32 8.62 9.81
7.5 8.80 10.00 10.40 10.60 11.20
10 13.00 13.40 13.9 14.40 14.7
12.5 16.3 16.8 17.4 18.00 18.4
15.0 19.4 20.0 20.8 21.5 21.87
20.0 26.0 26.6 27.8 28.5 29.40
25 32.6 33.5 34.8 36.0 38.00

59. 59
If the difference in amperage agrees with the above value for that particular
rating of the motor, the capacitor may be taken as genuine.
4.2.3Power Factor choices
Power Factor correction can be done when you are moving, building or
releasing new premises. In this case you should ensure that your assessments
of power costs include an analysis of Power Factor. In the near future you
will probably be charged according to your Power Factor, particularly if you
are a large user.
Power Factor correction can also be improved in existing facilities. Initially,
you should measure the Power Factor at your workplace and discuss your
options with your power supplier or consultant.
The use of Power Factor correction equipment has a number of advantages:
• In the form of a capacitor bank, it can be installed as close as possible
to the meter point or the equipment that is the main culprit. This
reduces the total current supplied by the electricity utility to your
premises, but has no detrimental impact on plant.
• It has often been used to increase the power-carrying capacity of long
cables. For example, new equipment may need to be installed which
will overtax the amp rating in existing underground cabling. Instead of
replacing cables or installing new switchboard equipment—an
expensive task–it is possible to increase capacity through Power Factor
correction equipment.
• It can be an economical solution to the problem of filtering out the
spikes that cause equipment failure. An increase in the use of
electronic equipment in offices and manufacturing situations means
that this is an expensive problem that needs to be dealt with.

60. 60
• Installing filter reactor equipment in series with the capacitor bank
increases the continuity and integrity in your supply. This results in
fewer fluctuations and circuit breaks, and reduced equipment damage.
Installing capacitors will have a typical pay back period of one year.
4.3 Correction of power factor with capacitors
4.3.1 Description
Power factor is the relationship (phase) of current and voltage in AC
electrical distribution systems. Under ideal conditions current and voltage are
"in phase" and the power factor is "100%." If inductive loads (motors) are
present, power factors less than 100 % (typically 80 to 90 % can occur)
Low power factor, electrically speaking, causes heavier current to flow in
power distribution lines in order to deliver a given number of kilowatts to an
electrical load.
4.3.2 The Effects
The power distribution system in the building, or between buildings, can be
overloaded by excess (useless) current.
Electrical costs are increased, generating and power distribution systems have
their capacity measured in KVA (kilovolt amps).
KVA = VOLTS X AMPS X 1.73 (three phase System) ÷ 1,000
With unity power factor (100%), it would take 2,000 KVA of generating and
distribution network capacity to deliver 2,000 KW. If the power factor
dropped to 85%, however, 2,353 KVA of capacity would be needed. Thus we
see that low power factor has an adverse effect on generating and distribution
capacity.

61. 61
Low power factor overloads generating, distribution, and networks with
excess KVA.
If there is a large building, there should be considering correcting poor power
factor for either or both of these reasons:
• To reduce additional power factor charges and
• To restore the (KVA) capacity of overloaded feeders within the
building or building complex. [5]
4.4 Power Factor Improvement
When using power factor correction capacitors, the total KVAR on the load
side of the motor controller should not exceed the value required to raise the
no-load power factor to unity. Over corrective ness of this value may cause
high transient voltages, currents, and torques that can increase safety hazards
to personnel and possibly damage motor driven equipment.
Never connect power factor correction capacitors at motor terminals on
elevator motors, plugging or jogging applications, multi-speed motors or
open transition, wye-delta, auto-transformer starting and some part-winding
start motors.
If possible, capacitors should be located at position 2 (see diagram). This
does not change the current flowing through motor overload protectors.
Connection of capacitors at position 3 requires a change of overload
protectors. Capacitors should be located at position 1 for applications listed in
paragraph 2 above. Be sure bus power factor is not increased above 95%
under all loading conditions to avoid over excitation.

62. 62
Diagram
Desired Power Factor Percent
Original
Power
Factor
Percent
80%85%90%95%100%
0.5830.7130.8491.0041.33360%
0.5160.6460.7820.9371.26662%
0.4510.5810.7170.8721.20164%
0.3880.5180.6540.8091.13866%
0.3280.4580.5940.7491.07868%
0.2700.4000.5360.6911.02070%
0.2140.3440.4800.6350.96472%
0.1590.2890.4250.5800.90974%
0.1050.2350.3710.5260.85576%
0.0520.1820.3180.4730.80278%
0.0260.1560.2920.4470.77679%
0.1300.2660.4210.75080%
0.1040.2400.3950.72481%
0.0780.2140.3690.69882%
0.0520.1880.3430.67283%
0.2060.1620.3170.64684%
0.1360.2910.62085%
0.1090.2640.59386%
0.0830.2380.56787%
0.0280.1830.51289%
0.1550.48490%
0.1270.45691%
0.0970.42692%
0.0660.39593%

63. 63
0.0340.36394%
0.32995%
0.29296%
0.25197%
0.14399%
Assume Total plant load is 100 KW at 60% power factor. Capacitor KVAR
rating necessary to improve power factor to 80% is found by multiplying KW
(100) by the multiplier in table (0.583) which gives KVAR (58.3), nearest
standard rating (60 KVAR) should be used.
4.5 Power Factor Corrective Devices
4.5.1Capacitors
Power factor correction capacitors are the most common method of
correcting power factor. They can be:
• Installed at various locations on your electrical system
• Switched on by large loads such as electric motors
4.5.2Controlling capacitors
A controller provides automatic switching of capacitor units and
maintains the power factor level under any changes in operation or
load.
4.5.3 Adjusting existing capacitors
Existing capacitors may be correctly sized but incorrectly controlled,
leading to poor overall power factor. Blown protection fuses on
capacitors take the capacitor off-line.
Looking at the condition and control of existing capacitors and fuses,
especially after a shutdown, may solve some power factor problems.

64. 64
4.5.4 Installing the right size motor
Over sizing motors without proper power factor correction is a leading
cause of low power factor. One of the most effective means of
improving power factor is by installing correctly sized motors for the
job. This will also reduce energy consumption and your total energy
bill.
4.5.5 Power Quality Effects
Harmonics, a power quality phenomenon, may be generated by some
electrical equipment, such as:
• Adjustable speed drives
• Switched power supplies
• Electric smelters
These installations require carefully designed power factor capacitors
or in some cases harmonic filters to avoid amplifying harmonics which
may damage components of your electrical system. The presence of
harmonics in your electrical system points to a power quality problem.

65. 65
4.6 Harmonics and Their Effects
4.6.1 Introduction
Disturbances are caused in the electrical supply system by non-linear
loads, and particularly by present day equipment. These modern equipments
are designed to offer optimum performance at lower running costs, but in turn
they play havoc with the supply and hence affect the performance of other
equipment connected in the system. These disturbances include harmonic
distortions, voltage unbalance, voltage surges, voltage impulses etc. The
effect of voltage and current harmonics can be noted at far of places in
equipment connected to the same circuit. This paper discusses briefly the
cause of harmonics, effect of electrical equipment with stress on the effect of
harmonics distortion on capacitors.
4.6.2 Sources & Effect of Harmonics
Harmonics distortion is produce due to the presence of non-linear
loads. These non-linear loads draw non-sinusoidal currents, which when
flow through the system result in non-sinusoidal voltage distortion. The
amount of distortion in a system depends on the characteristics of the
transmission and distribution system.
Following are some of the sources of harmonics:
1. Transformers under no loads and light loads.
2. Saturated reactors.
3. Rotating machines.
4. Arc furnaces.
5. Induction furnaces.
6. Gas discharge lighting.
7. Rectifiers.

66. 66
8. Industrial drives.
9. Electrolysis plants.
10. Energy conservation devices like soft starters, electronics chokes for
tubular fluorescent lamps, electronic fan regulators, etc.
11. Equipment with switched mode power supplies such as T.V. receivers
& personal computers.
4.6.3 Effect on Capacitors
The impedance of a capacitor is inversely proportional to the
frequency. Hence capacitor offers a low impedance path for the harmonic
currents.
The fact effects of harmonics on capacitors are:
1. Increased capacitor current.
2. Increased kVAR losses.
3. Higher temperature rise.
4. Blowing of fuses.
5. Bursting of capacitors.
6. Resonance between the capacitors and the system inductance.
The capacitors can be mathematically modeled to find the effect of harmonics
on them. The Dielectric losses depend on the loss angle (tand) of the
capacitor. The loss angle increases with the increase in the harmonic order.
This results in increase in the dielectric losses.

67. 67
4.6.4 Reduction of Harmonic Distortion
Harmonic currents can be significantly reduced in an electrical system by
using a harmonic filter.
In its basic form, a filter consists of a capacitor connected in series with a
reactor tuned to a specific harmonic frequency. In theory, the impedance of
the filter is zero at the tuning frequency; therefore, the harmonic current is
absorbed by the filter. This, together with the natural resistance of the circuit,
means that only a small level of harmonic current will flow in the network.
4.6.5 Harmonic Analysis
The first step in solving harmonic related problems is to perform an analysis
to determine the specific needs of your electrical distribution system. To
determine capacitor and filter requirements, it is necessary to establish the
impedance of the supply network and the value of each harmonic current.
Capacitor, reactor and filter bank equipment are then specified under very
detailed and stringent computer analysis to meet your needs. [8]

68. 68
Chapter 5
Microcontroller, PLC & conventional control
5.1. General
In this chapter we will discuss control systems such as microcontroller
technique, conventional methods of control, and plc different techniques.
5.2. Microcontroller
5.1.1 Introduction
The easiest way to meet the requirements Specified by the project’s objective
with a limited amount of hardware was by the use of a microcontroller. But
the decreased complexity in hardware offered by the microcontroller results
in increased complexity in the software within it. It was natural to expect that
this project would require a considerable amount of software, but also
hardware skills. Before going into details about these three units, a
description of all the components Used to build them will be given.
5.1.2 What is a Microcontroller?
“A microcontroller is a computer-on-a-chip, or, if you Prefer, a single-chip
computer. Micro suggests that the Device is small, and controller tells you
that the device Might be used to control objects, processes, or events.”
1. “Primarily, the microcontroller is capable of storing and Running a
program (its most important feature). The Microcontroller contains a
CPU, RAM, ROM, I/O lines, Serial and parallel ports, timers, and
sometimes other Built in peripherals such as A/D and D/A
converters.”
2. The “heart” of each of the three devices Described in this project is
in fact a microcontroller. Two different models were used; the

69. 69
AT90S2313 [Figure 2] and the more powerful AT90S8515 [Figure
1]. Both are 8 bit Microcontrollers with RISC architecture
manufactured by Atmel. They belong to a family of microcontrollers.
Figure 5.1. Pin description of
AT90S8515
Figure 5.2. Pin description
of AT90S2313
Table (5.1) is a comparison between the AT90S2313 and AT90S8515
microcontrollers.
AT90S2313 AT90S8515
Units
Program Memory 2 8 KB
RAM 128 512 Bytes
EEPROM 128 512 Bytes
Max Clock Speed 10 8 MHz
UART Yes Yes
SPI No Yes
8bit timer Yes Yes
16bit timer Yes Yes
I/O Lines 15 32
Power Consumption 2.8 3 mA(at 4MHz, 3V)

70. 70
The I/O Ports are of course essential to a microcontroller, for its ability to
Control. The AT90S8515 delivers four ports with 8 pins each, a total of 32
I/O pins. Any pin can be configured as an input or an output, and this pin
Assignment does not have to remain static but can change dynamically in
runtime. All signal levels are Digital, so the microcontroller can connect only
to digital devices. The pressure sensor used in the altimeter unit is an
analogue device. Therefore for it to interact with the microcontroller, an ADC
was used, to convert from analogue to digital signal levels. Two
timers/counters an 8bit and a 16bit, are available in both microcontrollers for
counting and timing Purposes. The number of bits determines the accuracy of
the measurement. A timer is for example used for measuring the width of a
pulse in the Camera Trigger Unit.
5.1.3 Using of microcontrollers:
A lot of microcontrollers are used in modern equipment and electronic
devices. Some of them are used by small companies in control, measurement
or other equipment; others are used for serious applications by the military,
security services, banks, medical services etc. Each microcontroller executes
the algorithm or program uploaded into its memory. Usually this algorithm is
written in Assembler (even if you write the program in C it will be translated
into Assembler during compilation); rarely the algorithm is written in Basic
or Java. If you write a program for a microcontroller you are interested in
your work being protected against unauthorized access or copying, so you
want to control distribution of your devices. Each microcontroller should be
programmed before using. There are different techniques to do it depend on
manufacturer and type of microcontroller.

71. 71
5.1.4 How we can use microcontroller in power factor correction?
As modern appliance designs begin implementing variable speed Induction
(IM), Brushless DC (BLDC) and Switched Reluctance (SR) motors, the use
of an Active Power Factor Correction (APFC) circuit will become
Unavoidable Unlike universal motors, in which the speeds are controlled by
varying the firing angle of TRIACs, these motors require multi-phase
inverters that operate from a DC bulk power supply. While a simple diode
bridge and capacitors are commonly used in generating a DC voltage for
small equipment, applying this technique for appliances with large motors
will cause excessively high current harmonic content on the power line.
Many of the new appliances will need an APFC circuit to satisfy the IEC
61000-3-2 current harmonic requirements. An APFC circuit will also give a
close-to-unity power factor, thus significantly reducing the RMS current
drawn from the AC supply. Therefore, depending on the power level, using
an APFC circuit can eliminate the need for special AC power wiring, giving
the end-user more flexibility in powering the appliance. An APFC circuit has
a bank of capacitors at its output to function as a reservoir and to supply the
instantaneous current demands from the load. The circuit draws power from
the AC mains to keep the storage capacitors charged at a constant average
voltage. The APFC controller shapes its input current waveform on the AC
mains to maximize its power factor and minimize harmonic contents. With a

72. 72
properly designed circuit, the AC mains recognize the APFC circuit as an
ideal resistor.
5.1.5 Microcontroller benefits
Implementing an APFC circuit using a microcontroller is more involved than
using a stand-alone chip solution. The most obvious impact is a longer
development time, therefore cost. The microcontroller-based solution,
however, does offer several benefits as discussed below.
Manufacturing flexibility: The first obvious benefit is manufacturing
flexibility. Using a microcontroller-based APFC design gives manufacturing
the flexibility to build one design for multiple products.
Monitoring complex conditions: Having a microcontroller on board also adds
the ability to monitor complex conditions and implement advanced safety
features that can not easily be implemented in a purely analog solution. For
example, if the design incorporates a temperature sensor, a programmable
current or power limit as a function of temperature can be implemented.
Digital communication: While communication may not be applicable for
most appliances today, the ability for the APFC circuit in future appliances to
communicate to other systems may be required. Having a microcontroller on
board will enable this capability.
5.2. Conventional control panel
At the outset of industrial revolution, especially during sixties and seventies,
relays were used to operate automated machines, and these were
interconnected using wires inside the control panel. In some cases a control
panel covered an entire wall. To discover an error in the system much time
was needed especially with more complex process control systems. On top of

73. 73
everything, a lifetime of relay contacts was limited, so some relays had to be
replaced. If replacement was required, machine had to be stopped and
production too. Also, it could happen that there was not enough room for
necessary changes. Control panel was used only for one particular process,
and it wasn’t easy to adapt to the requirements of a new system. As far as
maintenance, electricians had to be very skillful in finding errors. In short,
conventional control panels proved to be very inflexible. Typical example of
conventional control panel is given in the following picture.
In this photo you can notice a large number of electrical wires, time relays,
timers and other elements of automation typical for that period. Pictured
control panel is not one of the more “complicated” ones, so you can imagine
what complex ones looked like. [11]

74. 74
Disadvantages of a classic control panel
- Too much work required in connecting wires
- Difficulty with changes or replacements
- Difficulty in finding errors; requiring skillful work force
- When a problem occurs, hold-up time is indefinite, usually long.
5.3. Programmable Logic controller PLC
5.3.1 Introduction
Of all the devices that are used to control manufacturing operations. The
programmable logic controller (PLC) is one of the most important. The first
PLCS were introduced in the early 1960S. Mainly by the automobile industry
up until then the automatic control of manufacturing equipment was achieved
using hundreds, and even thousands, of relays enclosed in metal cabinets.
The annual automobile-model changes required frequent modifications to the
production lines and their associated relay-control system. Because the
control systems were complex, the modifications took a lot of time, and
errors often occurred when making connections. For these reasons, control
engineers developed a computerized programmable system to replace the
relay racks.
This presented a big challenge for many companies. In effect, computers that
had previously been used to do accounting jobs were modified to respond to
the needs of industry. Little by little, the techniques were improved and more
users of the new technology were found. However, a full decade went by
before the new concept was systematically adopted by manufacturers.
Today, the programmable logic controller is the main control devise used in
industry. More than 50 manufacturers offer hundreds of different models.

75. 75
5.3.2 What exactly a Plc?
The programmable controller is basically a computer controlled
System containing a micro processor that is programmed with a
programming panel or keyboard.
The PLC receives input signal and sends output signal in response to the
programmer logic. The program generally consists of contacts timers
counters and math function. Chart of programmable controller developments:
Nature of developmentsYear
Programmable controller concept developed1968
Hardware CPU controller, with logic instructions, 1k
of memory and 128 I/O points
1969
Use of several (multi) processors within a PLC –
timers and counters; arithmetic operations; 12k of
memory and 1024 I/O points.
1974
Remote input / output systems introduced1976
Microprocessor-based PLC introduced1977
Intelligent I/O modules developed
Enhanced communications facilities
Enhanced software features (e.g. documentation)
Use of personal microcomputers as programming
aids
1980
Low cost small PLCs introduced1983
Networking of all levels of PLC, computer and
machine under standard, hierarchical control of
industrial plants
1985 on

76. 76
5.3.3 Programmable logic controller consists of 5 basic parts
1. A central processing unit (CPU), which is a computer that can
simulate the required relay contacts and relay coils, as well as the
connections between them.
2. An input module, which serves as an interface between the actual
control devices and the CPU.
3. An output module, which serves as an interface between the CPU and
the actual devices that are being controlled.
4. A programming unit consisting of a keyboard and monitor to program
the CPU. It enables us to select different types of relays and contacts
that the computer can simulate, as well as the way they are to be
connected.
5. A power supply that furnishes the power needed by the CPU by the
input / output modules. And by the programming unit.
The five parts of a PLC
Output
Module
CPU
Central
Processing
Unit
Input
Module
Control
Devices
Controlled
Devices
Programming
Unit
Power
Supply

77. 77
5.3.4 Logic circuit
1- AND circuit
LS2S1
000
010
001
111
2- OR- circuit
HS2S1
000
110
101
111
3- NOT circuit
LS
10
01
S1 S2
L
+
‫ـــ‬
H
S1
S2
+
‫ــــ‬
L
S
&S1 L
S2
≥S1 L
S2
S L

78. 78
5.3.5 Coils and contacts
All programmable controllers receive input signals and send output signals.
The programmable controller must have a program in its memory to react to
when it receives these input signals and sends output signals.
The program symbols for a PLC input will look like a normally open or
normally closed contact used in typical electrical diagrams.
These symbols are shown in fig (5.3).
The program symbol for a PLC output will also look similar to symbols
used in typical electrical diagrams. In fig (5.4) we can see close together.
The easiest way to be introduced to these program symbols is to see a
typical electrical diagram of a start-stop switch controlling a motor starter
converted to a PLC program. Figure (5.5) shows this
In fig 5.5 we can see that normally open and normally closed push-
button switch symbols are used to represent the start and stop switches, and a
contacts symbol is used to represent the motor starter auxiliary contacts,
Typical PC normally
open contact symbol
Typical PC normally
closed contact symbol
Figure 5.3
Tropical P.C. output symbols
MS1
MS1
Stop
Typical electrical diagram
converted to a P.C. program.
Figure
5.5
Figure 5.4
Start

79. 79
which are used to seal the normally open start push button. A circle is
normally used to represent coils.
5.3.6 Counters:-
The function of the counters is like to the timers, but the counters are
recording the number of times that the two ends of the counter can touch each
others, where the timer is counting periods.
Fig is showing the main idea for the function of simple counters that when
we conduct the tow points of counting (100/03) , the stored number will be
increased by the value of (1) and will be stored in the record number (046) ,
and we be stored in the record number (046) , and we can see here in this
example that the final value of counting is (100)and the accumulated value is
(80)so the rest will be (20) , and when the counting reaches to (100)the point
(046/15)will be changed from (0) to ( 1 ) so the output (010/02)will be
changed too.
5.3.7 Function block counter
The block is containing a
number called (preset value)
and a middle symbol of counter
(CTR) ,and there is a recorder
at the bottom , which stores the
times of switching off the keys
, at the right there are tow
inputs , the first for counting
and the other for preset . and also at the right, there are tow outputs, the first
at the top, and the output signal will be sent through it, that this signal will be
(0), when the counting is less than the preset value, and when the counting
Preset
Value
CTR
Storage
Register
Enable
(Count)
Reset
Output
Not
Outpu

80. 80
reaches to this value (0) the output will be changed from (0) to (1) and the top
output and the bottom output will be opposite to each other.
5.3.8 The up counting and the down counting:-
There are many kinds of counters with different applications. There is a kind
which is counting by up counting that when the input signal will be positive
(+), the accumulated value will be (0) and the counting will start to increase,
when the two ends will be conducted. Also, there is counter that the counting
is starting from the preset value and the counting will be decreased by the
value of (1) when we conduct the two ends, and every time we repeat this
process, the accumulated counting will be decreased until it reaches to (0),
here the position will be sent.
010
02
046
15
CTU
Pr 100
AC 80
046
20
CTR
4003
0007
4
CTR
4003
1003
0007
1003
0005
0005

81. 81
The reset end:-
Here, the accumulated value will be (0) and the counting will start again, and
there are two outputs for the counter, one is at the top which called (output),
and the other will be at bottom. Shape 37 will show the different applications
for the different kinds of counter which have been pre explained.
5.3.9 Timers:-
Clock in fig (1) is set for
10 seconds. When switch 1
closes and the clock motor
has operated for 10
seconds, which is the
preset time, the timer's
20
CTR
4003
0006
20
CTR
4003
1003
0006
0006
1004
01
12
TMR
1
10 Second
Lamp 1
Lamp 2
TMR 1
TMR 1
Up
(Storage Register)
S12
DOWN
CLEAR
=900(Preset value)
01
12
CTR

82. 82
contacts change. This means that normally closed contacts would open and
de-energize lamp 2, and the normally open contacts would close and energize
lamp 1.
The TON timer in fig 2 is reset by opening the enable contacts that are marked
11101. This means that any time these contacts open, timer 030
accumulative value returns to zero. When the accumulative value of a timer is
0, it is said to be in the reset condition. When the contacts close again, the
timer will begin timing and the accumulative value will increase until the
accumulative value equals the preset time or until the enabled contacts are
open again.
Fig 3 shows the program for retentive timer with the RTR reset instruction.
We can see that the retentive
timer can keep track of the
accumulative times when the
motor is running. Any time the
motor is not running, the enabled
contacts are opened, and the
timer stops. When the motor
begins running again, the timer
starts accumulating time again. When the motor accumulates enough running
time for maintenance, the timer can be reset to record running time until the
next maintenance interval.
The timer in fig 4 consists of several basic parts, there are two sets of
contacts used with this timer that control it but are not actually a part of the
timer .the contacts on the top left side of the timer function block are the
timer enable contacts.
The contacts on the bottom left side of the timer function block are called
reset that mean the timers accumulative value resets to 0.
03
111
RTO
02
111
031
031
RTR

83. 83
5.3.10 Math Function:-
1-Addition
2-subtraction
3-multiplication
4-Division
4 xxx
Preset
Value
Time
Base
4XXX
Register where
Accumulative value
Stored
10
T 1 .0
4003
1005
1006
0002
111
11
030
G
520
031
G
514 1034
+
111
03
033
G
742
034
G
100 642
-
035
111
04
036
G
20
038
G
24 000
X
039
X
480
040
111
05
041
G
150
042
G
025 006
X
0٤٣
X
000
044

84. 84
5- Data comparison
5.3.11 PLC programming method
1. Ladder diagram (LAD)
2. Control System Flowchart (CFS)
3. Statement List (STL)
5.3.12 Programming the PLC
In order to program a PLC, we must ''write'' the operations it has to perform.
These instructions are typed on the programming unit keyboard, observed on
the monitor, and stored in the CPU memory. From the very beginning,
particular attention was devoted to the method of programming. The
technical criteria stipulated that the system should be quickly and easily
programmable and reprogrammable by the user. The plc was therefore
carefully designed to make it simple to use. However, it is useful to have
some computer knowledge to program a PLC.
110
00
070
G
100
075
=
100 00
010
110
00
070
G
050
075
100 00
010
>
110
00
075
G
100
070
050 00
010
<

85. 85
5.3.13 How PLC controller works
Basis of a PLC function is continual scanning of a program. Under scanning
we mean running through all conditions within a guaranteed period. Scanning
process has three basic steps:
Step 1
Testing input status. First, a PLC checks each of the inputs with intention to
see which one of them has status ON or OFF. In other words, it checks
whether a sensor or a switch etc. connected with an input is activated or not.
Information that processor thus obtains through this step is stored in memory
in order to be used in the following step.
Step 2
Program execution. Here a PLC executes a program, instruction by
instruction. Based on a program and based on the status of that input as
obtained in the preceding step, an appropriate action is taken. This reaction
can be defined as activation of a certain output, or results can be put off and
stored in memory to be retrieved later in the following step.
Step 3
Checkup and correction of output status. Finally, a PLC checks up output
status and adjusts it as needed. Change is performed based on the input status
that had been read during the first step, and based on the results of program
execution in step two. Following the execution of step 3 PLC returns to the
beginning of this cycle and continually repeats these steps. Scanning time is
defined by the time needed to perform these three steps, and sometimes it is
an important program feature.

86. 86
5.3.14 Advantages of PLCs over relay cabinets:-
There are many reasons for the universal popularity of PLCS we list them as
follows:
1. The PLC is flexible. Because it is programmable, it is easy to modify
as the need arises. In the case of control system using physical relays,
any change means replacing relays and reconnecting them. This is
risky because connection errors can easily be made.
2. The flexibility of PLCs is extraordinary. Thus, when ever a given
control system is no longer required, it can readily be reprogrammed
for a completely different system. With relay racks, such a change
over is not feasible and the racks would simply be scrapped, replaced,
and rewired.
3. The PLC is much less bulky than a conventional relay control system
for example, a CPU having a volume of 0.1m3
replaces hundreds of
control relays, as well as the hard wiring needed to connect the
contacts and holding coils furthermore, the PLC consumes for less
energy.
4. A PLC is more reliable than a relay cabinet. One important reason is
the absence of moving parts relays have moving parts that deteriorate
as the equipment gets older. Relay contacts wear out and have to be
replaced. All of which requires a sustained maintenance program.
"Relay coil" and "contacts" in CPUs never wear out.
5. In addition, the opening and closing of relay contacts, while rapid,
takes a certain time. The time interval is not the same for all relays and
moreover, it may change with time. In some applications where the
opening and closing sequence is important, the time variations may
introduce control errors. Such errors are very difficult to diagnose
because of their random nature. In the case of PLCs, the "contact"
opening and closing times are fixed. Consequence operations are

87. 87
never a problem the relay cabinet has to be assembled by hand-
hundreds and even thousands of wires must be connected between the
contacts and relay coils, which imply a big chance of making errors.
These errors are difficult to locate. By contrast, with a PLC, all that is
needed in to draw a ladder diagram according to a plan. Here again, if
an error is made, the hand-held programming unit (or the more
sophisticated computer) contains utility functions that make it easy to
correct a mistake.
5.3.15 Control panel with a PLC controller
With invention of programmable
controllers, much has changed in
how a process control system is
designed. Many advantages
appeared. Typical example of
control panel with a PLC controller
is given in the following picture.
5.3.16 Advantages of control panel that is based on a PLC controller:
1. Compared to a conventional process control system, number of wires
needed for connections is reduced by 80%.
2. Consumption is greatly reduced because a PLC consumes less than a
bunch of relays.

88. 88
3. Diagnostic functions of a PLC controller allow for fast and easy error
detection.
4. Change in operating sequence or application of a PLC controller to a
different operating process can easily be accomplished by replacing a
program through a console or using a PC software (not requiring changes
in wiring, unless addition of some input or output device is required).
5. Needs fewer spare parts.
6. It is much cheaper compared to a conventional system, especially in cases
where a large number of I/O instruments are needed and when operational
functions are complex.
7. Reliability of a PLC is greater than that of an electro-mechanical relay or a
timer.

89. 89
Chapter 6
Lab Implementation Model
6.1 General
In this chapter we would discuss the lab implementation model its loads,
transducer, Zelio, and some photos of our work.
6.2 Introduction
To build the practical model we have to:
• Choose suitable loads.
• Measure the reactive power needed by the load, and convert it to
analog signal.
• Use the analogue signal as an input to the controller (Zelio).
• Program Zelio (the controller) to decide to connect or disconnect the
capacitors.
• Connect the output to contactors and connect the contactors to the
capacitors to connect or disconnect it after the controller decides
according to the program.
• Connect the capacitors in parallel with the loads to give it the reactive
power needed, if it is connected.
The practical model consists of:
1. Loads.
2. Transducer.
3. Controller (Zelio).
4. Contactors.
5. Capacitors.

90. 90
6.3 Loads
The first step that we have done in the practical model was chosen the loads.
We have chosen 4 different loads to cover almost all types of loads that may
be in a factory, these loads are:
1. Shock coil
This load is a representation for a pure inductive load. The power
factor of the pure inductive load is 0 theoretically, but practical the chock coil
has a small resistance of coil itself. So the real power factor of the chock coil
is 0.1. And to have different values of power factor we put a resistive load in
series with it. This resistive load is a tungsten lamp. The lamp is 60W. By
adding the lamp in series with the coil the net power factor becomes 0.89.
2. Fluorescent lamps:
This load is a representation for a lighting load in a factory. There are 3
lamps each lamp is connected to single phase of the 3 phase. The power
factor of the fluorescent lamps is about 0.4.
3. No load motor:
The last 2 loads are static loads. This load can be classified as a
dynamic load. This motor is taken at no load to improve that the motor at no
load have a worst power factor. The power factor of this motor is 0.15.
4. Loaded motor:
This load is a dynamic one too. As we know all the mechanical
processes are driven by an electric motors. So we take a loaded motor to be a
representation for that motors which drive the mechanical load. The motor
loading of the motor is variable, so it can represent different values of power
factor. This load also improves that the power factor is improved by loading
the motor. In other words the motor has the best power factor at full load. The
power factor of full load of this motor is 0.8. Most of the AC motors are of
induction type (1-Φ and 3-Φ induction motors) which have low lagging

91. 91
power factor. These motors work at a power factor which is extremely small
on light loads (0.2 to 0.3) and rises to 0.8 or 0.9 at full load.
From load 3, 4 we can notice the different power factor from no load to
full load in motors.
A1: chock coil + lamp
A2: florescent lamp
A3: no load motor
A4: loaded motor
A4*: loaded motor at no load
The following readings were taken from the loads we have chosen:
Load pf(cos Φ) Q P
A1 0.89 22 46
A2 0.41 66 30
A3 0.16 95 17.5
A4 0.81 68 92
A1A2 0.64 88 76
A1A3 0.48 116 65
A1A4 0.84 89 140
A2A3 0.29 160 50
A2A4 0.69 133 132
A3A4 0.57 160 113
A1A2A3 0.45 181 95
A1A2A4 0.75 154 170
A1A3A4 0.65 180 163
A2A3A4 0.53 225 145
A1A2A3A4 0.6 250 190
6.4 Transducer
To improve the power factor for the loads we must measure the reactive
power that the load need. And connect a source of reactive power to feed
the load, instead of the power source so we reduce our consumption of the
reactive power from the public electricity network. We need a device that

92. 92
measure the load reactive power and the output of that device is a signal
of voltage or current that connected after that to the controller.
This device is a transducer, which is defined as:" A transducer is a sensor
that changes energy from one form to another. More technically a
transducer converts a physical parameter into another form". With
electronic-measuring systems, the input transducer converts a quantity to
be measured (temperature, humidity, flow rate, weight) in our project
reactive power into an electrical parameter (voltage, current) that can be
processed by an electronic instrument or system. The output signal is dc
signal.
The transducer that we use called "smart power transducer" and it can
measure the following parameters:
• Active power (W).
• Apparent power (VA).
• Reactive power (VAR).
• Average active power (Wavg).
• Power factor (cosφ).
• Maximum current (I max).
• Average phase to phase voltage.
• Phase to neutral voltage for each phase.
• Frequency.
The transducer that we use can be programmed so we can choose the
quantity to be measure.
In our project we have the reactive power to be measured by the
transducer, so the transducer is measuring the reactive power (Q) and
convert it to DC analogue signal (0-20mA).
The full description and programming procedure is (as follows) mentioned
in the attached catalogue.

93. 93
After we know the programming and the connection of the transducer we
now able to make a calibration for it to cover all of the range of the
reactive power of the loads.
This calibration done in the laboratory using the loads mentioned before.
Q I mA
22 5
70 7.9
70 7.8
95 9
95 9
105 9.8
125 10.8
142 11.5
160 12.9
174 13
175 13.1
195 14.5
195 14
240 16.8
260 17.5
The following curve is between Q on horizontal and I mA on vertical.

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ImA
0
5
10
15
20
0 100 200 300
ImA
And by using curve fitting we have:
Chart Title
y = 0.0522x + 4.1145
0
5
10
15
20
0 100 200 300
ImA
Linear (ImA)
The equation 1145.40522.0 += xy represents the relation between the
measured Q and the output signal I mA and it can be 1145.40522.0 += QmA
The controller we use only accepts dc voltage (0-10V) so we had to add at
the output of the transducer a resistance of 500Ω and take a voltage of 0-
10V from its terminals to connect it to the controller (Zelio).
So we have to make a calibration for the transducer with V, and it will be
as follows:

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Q V
22 2.83
66 3.72
95 4.35
68 3.73
88 4.19
116 4.79
89 4.18
160 5.77
133 5.08
160 5.68
181 6.15
154 5.51
180 6.13
225 7.02
250 7.46
82 4.04
104 4.5
150 5.41
170 5.88
180 6.07
200 6.51
246 7.42
270 7.9
Chart Title
y = 0.0206 x + 2.3713
0
2
4
6
8
10
0 100 200 300
V
Linear (V)
The following curve is between Q on horizontal and V on vertical.
V
0
2
4
6
8
10
0 100 200 300
V
And by using curve fitting we have:

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Chart Title
y = 0.0261x + 2.0572
0
2
4
6
8
10
0 100 200 300
V
Linear (V)
The equation 0572.20261.0 += xy represents the relation between the
measured Q and the output signal V and it can be 0572.20261.0 += QV
After we have calibrated the transducer with voltage, we have to make
steps in voltage ranges which help us in programming Zelio. These ranges
are as follows:
load fixed(1uF) 2uF 3uF 4uf 6uf V
A1 √ ‫ـــ‬ ‫ـــ‬ ‫ـــ‬ ‫ـــ‬ 2.6
A2 √ ‫ـــ‬ √ ‫ـــ‬ ‫ـــ‬ 3.71
A4 √ ‫ـــ‬ √ ‫ـــ‬ ‫ـــ‬ 3.73
A1A4 √ √ √ ‫ـــ‬ ‫ـــ‬ 4.27
A1A2 √ √ √ ‫ـــ‬ ‫ـــ‬ 4.28
A3 √ √ √ ‫ـــ‬ ‫ـــ‬ 4.43
A1A3 √ ‫ـــ‬ √ √ ‫ـــ‬ 5.01
A2A4 √ √ ‫ـــ‬ ‫ـــ‬ √ 5.41
A1A2A4 √ ‫ـــ‬ √ ‫ـــ‬ √ 5.95
A2A3 √ ‫ـــ‬ √ √ ‫ـــ‬ 6.14
A3A4 √ ‫ـ‬‫ــ‬ ‫ـــ‬ √ √ 6.17
A1A3A4 √ √ √ ‫ـــ‬ √ 6.66
A1A2A3 √ √ √ ‫ـــ‬ √ 6.7
A2A3A4 √ √ √ √ √ 8
A1A2A3A4 √ √ √ √ √ 8.42