Microcontroller-Based Automatic Power Factor Correction

A
Project Report
On
“Microcontroller based Automatic Power Factor Correction System”
Presented by:
Arun Gupta

TABLE OF CONTENTS
Chapter No. Topic Name Page No.
ABSTRACT
1 INTRODUCTION
2 WHAT IS POWER FACTOR?
3 WHAT CAN BE DONE TO IMPROVE PF?
4 WHY TO IMPROVE PF?
5 CORRECTION METHODS
6
DETERMINATION OF REQUIRED CAPACITOR
RATING
7 CONFIGURATION OF CAPACITOR
8 WHERE WE SHOULD INSTALL CAPACITOR
9 BLOCK DIAGRAM
10 POWER FACTOR METER
11 ATmega8
12 SEVEN SEGMENT DISPLAY
13 OPTO COUPLER
14 SMPS
15 SPECIFICATIONS
16 PROGRAMMER
17 ALGORITHM
18 MDI PENALTY
19
HOW INSTALLING CAPACITOR TO REDUCE
UTILITY BILLS
20 LIMITATIONS
21 CONCLUSION & FUTURE SCOPE
22 REFERENCES

Abstract
This project report represents one of the most effective automatic power factor improvements
by using static capacitors which will be controlled by a Microcontroller with very low cost
although many existing systems are present which are expensive and difficult to manufacture.
In this study, many small rating capacitors are connected in parallel and a reference power
factor is set as standard value into the microcontroller IC. Suitable number of static capacitors
is automatically connected according to the instruction of the microcontroller to improve the
power factor close to unity. Some tricks such as using resistors instead of potential
transformer and using one of the most low cost microcontroller IC (ATmega8) which also
reduce programming complexity that make it one of the most economical system than any
other controlling system.

CHAPTER 1
INTRODUCTION
1.1 Basic theory
Before venturing into the details in the design of power factor correction systems, we
would first like to present a brief refresher of basic alternating current circuit theory.
1.1.1 Active power
With a purely resistive load with no inductive or capacitive components, such as in an
electric heater, the voltage and current curves intersect the zero coordinate at the same point
(Fig. 1.1).
The voltage and current are said to be ‗in phase‘. The power (P) curve is calculated from
the product of the momentary values of voltage (V) and current (I). It has a frequency which
is double that of the voltage supply, and is entirely in the positive area of the graph, since the
product of two negative numbers is positive, as, of course, is the product of two positive
numbers.
Fig 1.1: Current, voltage and power waveform of purely resistive load.
In this case:
(-V) · (-I) = (+P)
Active or real power is defined as that component of the power that is converted into another
form (e.g. heat, light, mechanical power) and is registered by the meter.

With a purely resistive or ohmic load it is calculated by multiplying the effective value of
voltage [V] by the current [I]: P = V. I
1.1.2 Active and reactive power
In practice, however, it is unusual to find purely resistive loads, since an inductive component
is also present. This applies to all consumers that make use of a magnetic field in order to
function, e.g. induction motors, chokes and transformers. Power converters also require
reactive current for commutation purposes. The current used to create and reverse the
magnetic field is not dissipated but flows back and forth as reactive current between the
generator and the consumer. As Fig.: 1. 2 shows, the voltage and current curves no longer
intersect the zero coordinate at the same points. A phase displacement has occurred. With
inductive loads the current lags behind the voltage, while with capacitive loads the current
leads the voltage. If the momentary values of power are now calculated with the formula
(P) = (V) · (I), a negative product is obtained whenever one of the two factors is negative...
Fig 1.2: Current, voltage, power waveform of partial reactive load.
The active power in this case is given by the
Formula: P = V. I cos

1.1.3 Reactive power
Inductive reactive power occurs in motors and transformers when running under
no-load conditions if the copper, iron and, where appropriate, frictional losses are ignored.
If the voltage and current curves are 90° out of phase, one half of the power curve lies in the
positive area, with the other half in the negative area (Fig.1. 3). The active power
is therefore zero, since the positive and negative areas cancel each other out.
Reactive power is defined as that power which flows back and forth between the generators
And the consumer at the same frequency as the supply voltage in order for the
magnetic/electric field to build up and decay . Q = V. I sin 
Fig 1.3: Current, voltage, power waveform of pure reactive load.

1.1.4 Apparent power
The apparent power is critical for the rating of electric power networks. Generators,
transformers, switchgear, fuses, circuit breakers and conductor cross sections must be
adequately dimensioned for the apparent power that results in the system.
The apparent power is the product obtained by multiplying the voltage by the current
without taking into account the phase displacement. S = V. I
The apparent power is given by the vector addition of active power and reactive power
: S = √P^2+Q^2
Fig 1.4: Reactive power compensation.

CHAPTER 2
2.1 WHAT IS POWER FACTOR?
2.1.1 SPECIAL ELECTRIC REQUIREMENTS OF INDUCTIVE LOADS
Most loads in modern electrical distribution systems are inductive. Examples include motors,
transformers, gaseous tube lighting ballasts, and induction furnaces. Inductive loads need a
magnetic field to operate.
Inductive loads require two kinds of current:
• Working power (kW) to perform the actual work of creating heat, light, motion, machine
output, and so on.
• Reactive power (kVAR) to sustain the magnetic field
Working power consumes watts and can be read on a wattmeter. It is measured in kilowatts
(kW). Reactive power doesn‘t perform useful ―work,‖ but circulates between the generator
and the load. It places a heavier drain on the power source, as well as on the power source‘s
distribution system. Reactive power is measured in kilovolt-amperes-reactive (kVAR).
Working power and reactive power together make up apparent power. Apparent power is
measured in kilovolt-amperes (kVA).
2.1.2 FUNDAMENTALS OF POWER FACTOR
Power factor is the ratio of working power to apparent power. It measures how effectively
electrical power is being used. A high power factor signals efficient utilization of electrical
power, while a low power factor indicates poor utilization of electrical power. To determine
power factor (PF), divide working power (kW) by apparent power (kVA). In a linear or
sinusoidal system, the result is also referred to as the cosine θ.
P.F = kW / kVA = cosine 
For example, if you had a boring mill that was operating at 100 kW and the apparent power
consumed was 125 kVA, you would divide 100 by 125 and come up with a power factor of
0.80.

Figure 2.1: Power factor triangles
All current will cause losses in the supply and distribution system. A load with a power factor
of 1.0 result in the most efficient loading of the supply and a load with a power factor of 0.5
will result in much higher losses in the supply system.
A poor power factor due to an inductive load can be improved by the addition of power factor
correction, but, a poor power factor due to a distorted current waveform requires a change in
equipment design or expensive harmonic filters to gain an appreciable improvement. Many
inverters are quoted as having a power factor of better than 0.95 when in reality, the true
power factor is between 0.5 and 0.75. The figure of 0.95 is based on the Cosine of the angle
between the voltage and current but does not take into account that the current waveform is
discontinuous and therefore contributes to increased losses on the supply.

2.2 WHAT CAN BE DONE TO IMPROVE POWER FACTOR?
We can improve power factor by adding power factor correction capacitors to your plant
distribution system. 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 that is made up of resistive components
and inductive components
The resistive components are:
I. Load current
II. Loss current
The inductive components are
I. Leakage reactance
II. Magnetizing current
Fig 2.2: Induction motor current components.
The current due to the leakage reactance is dependent 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.
Taking an 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
energy in the distribution system, the consumer will be encouraged to apply power factor
correction.
Fig 2.3: Induction motor current compensation.
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. Capacitors connected at each starter and
controlled by each starter are known as ―Static Power Factor Correction‖.
2.3 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, 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, 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. the resonant frequency will be below the line frequency 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
cannot 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.
Fig 2.4: Capacitors for compensation of reactive power in motor circuit.
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.
Static correction is commonly applied by using on e 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.

2.4 SUPPLY HARMONICS
Harmonics on the supply cause a higher current to flow in the capacitors. This is because the
impedance of the capacitors goes down as the frequency goes up. This increase in current
flow through the capacitor will result in additional heating of the capacitor and reduce its life.
The harmonics are caused by many non linear loads; the most common in the industrial
market today, are the variable speed controllers and switch mode power supplies. Harmonic
voltages can be reduced by the use of a harmonic compensator, which is essentially a large
inverter that cancels out the harmonics. This is an expensive option. Passive harmonic filters
comprising resistors, inductors and capacitors can also be used to reduce harmonic voltages.
This is also an expensive exercise. In order to reduce the damage caused to the capacitors by
the harmonic currents, it is becoming common today to install detuning reactors in series with
the power factor correction capacitors. These reactors are designed to make the correction
circuit inductive to the higher frequency harmonics. Typically, a reactor would be designed to
create a resonant circuit with the capacitors above the third harmonic, but sometimes it is
below. Adding the inductance in series with the capacitors will reduce their effective
capacitance at the supply frequency. Reducing the resonant or tuned frequency will reduce
the effective capacitance further. The object is to make the circuit look as inductive as
possible at the 5th harmonic and higher, but as capacitive as possible at the fundamental
frequency. Detuning reactors will also reduce the chance of the tuned circuit formed by the
capacitors and the inductive supply being resonant on a supply harmonic frequency, thereby
reducing damage due to supply resonance amplifying harmonic voltages caused by non linear
loads.

2.5 SUPPLY RESONANCE
Capacitive Power factor correction connected to a supply causes resonance between the
supply and the capacitors. If the fault current of the supply is very high, the effect of the
resonance will be minimal, however in a rural installation where the supply is very inductive
and can be high impedance, the resonance can be very severe resulting in major damage to
plant and equipment.
To minimize supply resonance problems, there are a few steps that can be taken, but they do
need to be taken by all on the particular supply.
1) Minimize the amount of power factor correction, particularly when the load is light. The
power factor correction minimizes losses in the supply. When the supply is lightly loaded,
this is not such a problem.
2) Minimize switching transients. Eliminate open transition switching - usually associated
with generator plants and alternative supply switching, and with some electromechanical
starters such as the star/delta starter.
3) Switch capacitors on to the supply in lots of small steps rather than a few large steps.
4) Switch capacitors on o the supply after the load has been applied and switch off the supply
before or with the load removal.
Harmonic Power Factor correction is not applied to circuits that draw either discontinuous or
distorted current waveforms. Most electronic equipment includes a means of creating a DC
supply. This involves rectifying the AC voltage, causing harmonic currents. In some cases,
these harmonic currents are insignificant relative to the total load current drawn, but in many
installations, a large proportion of the current drawn is rich in harmonics. If the total
harmonic current is large enough, there will be a resultant distortion of the supply waveform
which can interfere with the correct operation of other equipment. The addition of harmonic
currents results in increased losses in the supply.
Power factor correction for distorted supplies cannot be achieved by the addition of
capacitors. The harmonics can be reduced by designing the equipment using active rectifiers,
by the addition of passive filters (LCR) or by the addition of electronic power factor
correction inverters which restore the waveform back to its undistorted state. This is a
specialist area requiring either major design changes, or specialized equipment to be used.

2.6 WHY TO IMPROVE POWER FACTOR?
You want to improve your power factor for several different reasons. Some of the benefits of
improving your power factor include:
1) Lower utility fees by:
a. Reducing peak KW billing demand
Recall that inductive loads, which require reactive power, caused your low power factor. This
increase in required reactive power (KVAR) causes an increase in required apparent power
(KVA), which is what the utility is supplying. So, a facility‘s low power factor causes the
utility to have to increase its generation and transmission capacity in order to handle this
extra demand.
By raising your power factor, you use less KVAR. This results in less KW, which equates to
a dollar savings from the utility.
b. Eliminating the power factor penalty
Utilities usually charge customers an additional fee when their power factor is less than 0.95.
(In fact, some utilities are not obligated to deliver electricity to their customer at any time the
customer‘s power factor falls below 0.85.) Thus, you can avoid this additional fee by
increasing your power factor.
2) Increased system capacity and reduced system losses in your electrical system
By adding capacitors (KVAR generators) to the system, the power factor is improved and the
KW capacity of the system is increased.
For example, a 1,000 KVA transformer with an 80% power factor provides 800 KW (600
KVAR) of power to the main bus.
(1000) kVA = √ 800 𝐾𝑊 2
+ ? 𝑘𝑉𝐴𝑅 2
}
KVAR = 600
By increasing the power factor to 90%, more KW can be supplied for the same amount of
KVA.
KVAR = 436

The KW capacity of the system increases to 900 KW and the utility supplies only 436
KVAR.
Uncorrected power factor causes power system losses in your distribution system. By
improving your power factor, these losses can be reduced. With the current rise in the cost of
energy, increased facility efficiency is very desirable. And with lower system losses, you are
also able to add additional load to your system.
3) Increased voltage level in your electrical system and cooler, more efficient
Motors
As mentioned above, uncorrected power factor causes power system losses in your
distribution system. As power losses increase, you may experience voltage drops. Excessive
voltage drops can cause overheating and premature failure of motors and other inductive
equipment.
So, by raising your power factor, you will minimize these voltage drops along feeder cables
and avoid related problems. Your motors will run cooler and be more efficient, with a slight
increase in capacity and starting torque.

CHAPTER 3
3.1 Correction methods
3.1.1 Individual power factor correction
In the simplest case, an appropriately sized capacitor is installed in parallel with each
individual inductive consumer. This completely eliminates the additional load on the cabling,
including the cable feeding the compensated consumer. The disadvantage of this method,
however, is that the capacitor is only utilized during the time that its associated consumer is
in operation. Additionally, it is not always easy to install the capacitors directly adjacent to
the machines that they compensate (space constraints, installation costs).
Applications:
 To compensate the no-load reactive power of transformers
 For drives in continuous operation
 For drives with long power supply cables or cables whose cross section allows no
margin for error
Advantages:
 Reactive power is completely eliminated from the internal power distribution system
 Low costs per kvar
Disadvantages:
 The PFC system is distributed throughout the entire facility
 High installation costs
 A larger overall capacitor power rating is required as the coincidence factor cannot be
taken into account.

Fig.3.1: Typical individual power factor correction.
3.1.2 Group power factor correction
Electrical machines that are always switched on at the same time can be combined as a group
and have a joint correction capacitor. An appropriately sized unit is therefore installed instead
of several smaller individual capacitors.
Applications:
 For several inductive consumers provided that these are always operated together.
Advantages:
 Similar to those for individual power factor correction, but more cost-effective.
Disadvantages:
 Only for groups of consumers that are always operated at the same time.

Fig.3.2: Typical group power factor correction.
3.1.3 Central power factor correction
The PFC capacitance is installed at a central point, for example, at the main low voltage
distribution board. This system covers the total reactive power demand. The capacitance is
divided into several sections which are automatically switched in and out of service by
automatic reactive power control relays and contactors to suit load conditions.
This method is used today in most instances. A centrally located PFC system is easy to
monitor. Modern reactive power control relays enable the contactor status, cos φ, active and
reactive currents and the harmonics present in the power distribution system to be monitored
continuously. Usually the overall capacitance installed is less, since the coincidence factor for
the entire industrial operation can be taken into account when designing the system. This
installed capacitance is also better utilized. It does not, however, eliminate the reactive
current circulating within the user‘s internal power distribution system, but if adequate
conductor cross sections are installed, this is no disadvantage.
Applications:
 Can always be used where the user‘s internal power distribution system is not under
dimensioned.
Advantages:
 Clear-cut, easy-to-monitor concept
 Good utilization of installed capacitance
 Installation usually relatively simple
 Less total installed capacitance, since the coincidence factor can be taken into account
 Less expensive for power distribution systems troubled by harmonics, as controlled
devices are simpler to choke

Disadvantages:
 Reactive currents within the user‘s internal power distribution system are not reduced.
 Additional costs for the automatic control system.
Fig.3.3: Typical centralized power factor correction.

CHAPTER 4
4.1 Determination of required capacitor rating
4.1.1 Tariffs
Utility companies as a rule have fixed tariffs for their smaller power consumers, while
individual supply contracts are negotiated with the larger consumers.
With most power supply contracts the costs for electrical power comprise:
 Power [kW] – measured with a maximum demand meter, e.g. monthly maximum
demand over a 15 minute period.
 Active energy [kWh] – measured with an active current meter usually split into
regular and off-peak tariffs.
 Reactive energy [kvarh] – measured with a reactive current meter, sometimes split
into regular and off-peak tariffs.
It is normal practice to invoice the costs of reactive energy only when this exceeds 50% of
the active power load. This corresponds to a power factor cos φ = 0.9. It is not stipulated that
the power factor must never dip below this value of 0.9. Invoicing is based on the power
factor monthly average. Utility companies in some areas stipulate other power factors, e.g.
0.85 or 0.95.
With other tariffs the power is not invoiced as kW but as kVA. In this case the costs for
reactive energy are therefore included in the power price. To minimize operating costs in this
case, a power factor cos φ =1 must be aimed for. In general, it can be assumed that if a PFC
system is correctly dimensioned, the entire costs for reactive energy can be saved.
4.1.2 Approximate estimates
Accurate methods for determining the required reactive capacity are given in a subsequent
section of this manual. Sometimes, however, it is desirable to estimate the approximate order
of magnitude quickly. Cases may also occur where an engineer has performed an accurate
calculation but is then uncertain of the result, in case somewhere a mistake has occurred in
his or her reasoning. This can then be used to verify that the results calculated have the right
magnitude.

4.1.3 Consumer list
When designing a new installation for a new plant or a section of a plant, it is appropriate to
first make an approximate estimate of requirements. A more accurate picture is achieved by
listing the consumers to be installed, together with their electrical data, by taking into account
the coincidence factor. In cases where a later extension may be considered, the PFC system
should be designed and installed so that the extension will not involve great expenditure. The
cabling and protected circuits to the PFC system should be dimensioned to cater for
expansion, and space should be reserved for additional capacitor units.
4.2 Determination of required capacitor rating by measurement
4.2.1 Measurement of current and power factor
Ammeters and power factor meters are often installed in the main low voltage distribution
board, but clamp meters are equally effective for measuring current. Measurements are made
in the main supply line (e.g. transformer) or in the line feeding the equipment whose power
factor is to be corrected. Measuring the voltage in the power distribution system at the same
time improves the accuracy of the calculation, or the rated voltage (e.g. 380 or 400 V) may
simply be used instead.
The active power P is calculated from the measured voltage V, apparent current IS and power
factor:
P =√3. V. IS. Cos. 10-3
If the target power factor cos φ has been specified, the capacitor power rating can be
calculated from the following formula. It is, however, simpler to read off the factor f from
Table 1 and multiply it by the calculated active power.
QC = P. (tan actual - tantarget) or from table we have, QC = P. f

Table1: Table for finding factor f.

4.2.2 Measurements with recording of active and reactive power
More reliable results are obtained with recording instruments. The parameters can be
recorded over a longer period of time, peak values also being included. Required capacitor
power rating is then calculated as follows:
QC = QL - ( P . tantarget )
QC = required capacitor rating
QL = measured reactive power
P = measured active power
Tan φtarget = the corresponding value of tan φ at the target cos φ
4.2.3 Measurement by reading meters
The active and reactive current meters are read at the start of a shift. Eight hours later both
meters are read again. If there has been a break in operation during this time, the eight hours
must be extended by the duration of this break.
RM2 – RM1 = tan
AM2 AM1
RM1 = reactive current meter reading at start
RM2 = reactive current meter reading at finish
AM1 = active current meter reading at start
AM2 = active current meter reading at finish
Using this calculated value of tan φ and the target cos φ we can then obtain the factor f from
Table. The required capacitor power rating can then be calculated from the following
equation,
QC = (AM2 – AM1) k . F
8
Where k is the CT ratio of the current transformers for the meters:

CHAPTER 5
5.1 TYPES OF CAPACITORS USED IN APFC AS PER CONSTRUCTION
Different types of capacitors used for APFC include:-
1) STANDARD DUTY CAPACITORS
Construction: rectangular and cylindrical (resin filled / resin coated – dry)
Application: a) steady inductive load.
b) Non linear up to 10 %
c) For agriculture duty.
2) HEAVY DUTY CAPACITORS
Construction: rectangular and cylindrical (resin filled / resin coated – dry/ oil/ gas)
Application: a) suitable for fluctuating load.
b) Non linear up to 20%
c) Harmonic filtering.
3) LT CAPACITORS
Application: a) suitable for fluctuating loads.
b) Non linear up to 20%
c) Suitable for APFC and harmonic filtering.

CHAPTER 6
6.1 CONFIGURATION OF CAPACITORS
Power factor correction capacitor banks can be configured in following ways:-
1) STAR SOLIDLY GROUNDED
 Initial cost may be low since neutral does not have to be insulated from
ground.
 Capacitor switch recovery voltages are reduced.
 High inrush currents may occur in the station ground system.
 The ground star configuration provides a low impedance fault path which
may require revision to the existing system ground protection scheme.
 APPLICATION: typical for smaller installations (since auxillary
equipment is not required )
2) STAR UNGROUNDED
 Industrial and commercial capacitors banks are normally connected like
this, with parallel units to make up the total kvar.
 In industrial and commercial power systems the capacitors are not
grounded for a variety of reasons. Industrial systems are often resistance
grounded. A grounded star connection on the capacitor bank would
provide a path for zero sequence currents and the possibility of false
operation of ground fault relays.
 APPLICATION: industrial and commercial.
3) DELTA CONNECTED BANKS
 Generally used only at distribution voltages and are configured with a
single series group of capacitors rated at line to line voltage with only one
series group of units no overvoltage occurs across the remaining capacitors
from the isolation of a faulted capacitor unit.
 Therefore, unbalance detection is not required for protection.
APPLICATION: in distribution systems.

CHAPTER 7
7.1 Where should we install capacitors in our plant distribution system?
7.1.1 at the load
Because capacitors act as kVAR generators, the most efficient place to install them is directly
at the motor, where kVAR is consumed.
Three options exist for installing capacitors at the motor. Use figure and the information
below to determine which option is best for each motor.
Location A—motor side of overload relay
• New motor installations in which overloads can be sized in accordance with reduced current
draw.
• Existing motors when no overload change is required
Location B—line side of starter
• Existing motors when overload rating surpasses code
Location C—line side of starter
• Motors that are jogged, plugged, reversed
• Multi-speed motors
• Starters with open transition and starters that disconnect/reconnect capacitor during cycle
• Motors that start frequently
• Motor loads with high inertia, where disconnecting the motor with the capacitor can turn the
motor into a self-excited generator

Figure 7: Locating capacitors on motor circuit
Fig 7.2: Methods of connecting capacitors for p.f improvement to motors
7.1.2 At the service feeder
When correcting entire plant loads, capacitor banks can be installed at the service entrance, if
load conditions and transformer size permit. If the amount of correction is too large, some
capacitors can be installed at individual motors or branch circuits.
When capacitors are connected to the bus, feeder, motor control centre, or switchboard, a
disconnect and over current protection must be provided.

Fig 7.3: Methods of connecting capacitors for p.f improvement to supply line.

CHAPTER 8
BLOCK DIAGRAM
Fig 8.1: Block diagram of APFC.
The power factor meter is used to calculate the present power factor of the system. The power
factor is corrected using the true power technique. The power factor value so obtained is
communicated to the microcontroller Atmega8 via the pins TX and Rx. The program fed to

the microcontroller then analysis the power factor. The power factor gets displayed on the 7-
segment display connected to the Atmega8 project. If the power factor is above the pre-set
value, then the microcontroller won‘t take any action and the relays will remain in their
normal positions of NO and NC. Once the power factor lowers to a value below the pre-set
mark, the signal is sent to the relay card.
The relay card consists of relays along with LED‘s for detecting the operation of relays. The
input to relays is sent via an opto-coupler and then through a current amplifier before it
reaches the relay. The particular relay operates and connects the respective capacitor bank to
it. The operation of relay is detected by the LED, thereby leading to emission of light from
the LED.
The microcontroller has been programmed in such a way that out of the three relays, it will
make the relay or combination of relays in such a way that the capacitor banks are included
which correct the power factor in the best possible way to the best possible value. The
capacitor banks are present as C, C/2 and C/4, which have been created using series
combinations of capacitors of value C.
Along with these, a current transformer and a voltage transformer have been provided so as
to analyse the particular waveforms at different instants of time with the help of an
oscilloscope.

8.1 POWER FACTOR METER
Fig 8.2: Power factor meter used in the project.
Measurement of power factor accurately is very essential everywhere. In power transmission
system and distribution system we measure power factor at every station and electrical
substation using these power factor meters. Power factor measurement provides us the
knowledge of type of loads that we are using, helps in calculation of losses happening during
the power transmission system and distribution. Hence we need a separate device for
calculating the power factor accurately and more precisely.
General construction of any power factor meter circuit includes two coils pressure coil and
current coil. Pressure coil is connected across the circuit while current coil is connected such
it can carry circuit electric current or a definite fraction of current, by measuring the phase
difference between the voltage and electric current the electrical power factor can be
calculated on suitable calibrated scale. Usually the pressure coil is splits into two parts
namely inductive and non-inductive part or pure resistive part. There is no requirement of
controlling system because at equilibrium, there exist two opposite forces which balance the
movement of pointer without any requirement of controlling force.

We are using Digital True Power Factor Meter (DTPF-1) and its make is UMA Electronics.
The power factor meter has a Tx which is connected to Rx of the microcontroller. This allows
communication between the DTPF and Atmega8, so as to provide the current power factor
value to the controller.
Following are the important specifications of the power factor meter:
 Display : 4-Digit bright red seven segment display
 Lag and Lead indication.
 Measurement ; Power/(Voltage X Current) calculation
 Microcontroller Based Accurate and Reliable.
 Accuracy : Class 0.5
 Voltage Range : 300 V / 600 V AC
 Current Range : 5A/10A/20A AC
 Aux. Supply : 230V + 20% / 110V + 20% AC
 Dimension (mm): 96 by 96 (Front). 65 (Depth) & 48 by 96 (Front). 110 ( Depth)
Current:-
This meter is not shunt based, so external CT can be applied without loss of signal

8.2 Atmega8
Fig 8.3: Microcontroller ATmega8 used in the project.
We are using ATMEL Atmega8 microcontroller for the programming in our project. It is a
high performance, low power, AVR microcontroller. It has 28 pins in all and uses 5 volts for
its operation.
Features:
• 8-bit Microcontroller
• Advanced RISC Architecture
– 130 Powerful Instructions – Most Single-clock Cycle Execution
– 32 × 8 General Purpose Working Registers
• High Endurance Non-volatile Memory segments
– 8Kbytes of In-System Self-programmable Flash program memory
– 512Bytes EEPROM
– 1Kbyte Internal SRAM
– Write/Erase Cycles: 10,000 Flash/100,000 EEPROM
– Data retention: 20 years at 85°C/100 years at 25°C.

• Peripheral Features
– Two 8-bit Timer/Counters with Separate Prescaler
– One 16-bit Timer/Counter with Separate Prescaler
Mode
– Real Time Counter with Separate Oscillator
– Three PWM Channels
– 8-channel ADC
Six Channels 10-bit Accuracy
– Programmable Serial USART
– Programmable Watchdog Timer with Separate On-chip Oscillator
– On-chip Analog Comparator
• Special Microcontroller Features
– Power-on Reset and Programmable Brown-out Detection
– Internal Calibrated RC Oscillator
– External and Internal Interrupt Sources
– Five Sleep Modes: Idle, ADC Noise Reduction, Power-save, Power-down, and
Standby
• I/O and Packages
– 23 Programmable I/O Lines
– 28-lead PDIP
• Operating Voltages
– 4.5V - 5.5V (ATmega8)
• Power Consumption at 4 MHz, 3V, 25C
– Active: 3.6mA
– Idle Mode: 1.0mA
– Power-down Mode: 0.5µA

Chapter 8.3
PIN DIAGRAM OF ATmega8
Fig 8.4: Pin diagram of ATmega8

Pin Descriptions
VCC
Digital supply voltage.
GND
Ground.
Port B (PB7-PB0)
Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit).
Port C (PC5-PC0)
Port C is a 7-bit bi-directional I/O port with internal pull-up resistors (selected for each bit).
PC6/RESET
If the RSTDISBL Fuse is programmed, PC6 is used as an I/O pin. Note that the electrical
characteristics of PC6 differ from those of the other pins of Port C. If the RSTDISBL Fuse is
unprogrammed, PC6 is used as a Reset input. A low level on this pin for longer than the minimum
pulse length will generate a Reset, even if the clock is not running. Shorter pulses are not guaranteed
to generate a Reset.
Port D (PD7-PD0)
Port D is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit).
RESET
Reset input. A low level on this pin for longer than the minimum pulse length will generate a reset,
even if the clock is not running. Shorter pulses are not guaranteed to generate a reset.
AVCC
AVCC is the supply voltage pin for the A/D Converter, Port C (3-0), and ADC (7-6). It should be
externally connected to VCC, even if the ADC is not used. If the ADC is used, it should be connected
to VCC through a low-pass filter. Note that Port C (5-4) use digital supply voltage, VCC.
AREF
AREF is the analog reference pin for the A/D Converter.
ADC7-6
In the TQFP and QFN/MLF package, ADC7-6 serves as analog inputs to the A/D converter.
These pins are powered from the analog supply and serve as 10-bit ADC channels.

Chapter 8.5
MICROCONTROLLER CONNECTIONS
Fig 8.5: Microcontroller connections.
INPUT PINS
Selection lines S1, S2, S3, and S4 are connected to the pins 2, 3, 4 and 5 of Port D.
This input is given to the microcontroller through program.

OUTPUT PINS
Output pins can be divided into two sections:
 RELAYS
The three relays are connected to the pins 5, 4 and 3 of Port C.
The respective relays are switched on according to the input provided by the Power
Factor Meter.
 SEVEN SEGMENT DISPLAY
The data lines of the seven segment display are connected to pins 0-5 of Port B, pin 7
of Port D, and pin 6 of Port C.
Seven segment displays are driven by the Selection lines S1, S2, S3 and S4.

Chapter 8.5
SEVEN SEGMENT DISPLAY
FIG 8.6: SEVEN SEGMENT DISPLAY.
WHAT IS 7-SEGMENT LED DISPLAY?
A seven-segment display (SSD), or seven-segment indicator, is a form of electronic display
device for displaying decimal numerals that is an alternative to the more complex dot
matrix displays.
Seven-segment displays are widely used in digital clocks, electronic meters, and other
electronic devices for displaying numerical information.
7-segment LED Display is display device which can display one digit at a time.
Actually one digit is represented by arrangement of 7 LEDs in a small cubical box.
For representing 3 digit numbers, we need three 7-segment LED Displays.

CHAPTER 8.5.1
INTERNAL STRUCTURE
• There are two types of 7-segment LED Display
1. Common Cathode
2. Common Anode
In a simple LED package, typically all of the cathodes (negative terminals) or all of
the anodes (positive terminals) of the segment LEDs are connected and brought out to a
common pin; this is referred to as a "common cathode" or "common anode" device. Hence a
7-segment plus decimal point package will only require nine pins (though commercial
products typically contain more pins, and/or spaces where pins would go, in order to match
standard IC sockets. Integrated displays also exist, with single or multiple digits. Some of
these integrated displays incorporate their own internal decoder, though most do not: each
individual LED is brought out to a connecting pin as described.
COMMON CATHODE
Fig 8.7: Common cathode type 7 segment display.

COMMON ANODE
Fig 8.8: Common anode type 7 segment display.
In our project, we are using common anode 7-segment display, so in order to display various
digits on it, respective LED‘s have to be switched ON or OFF.
The following table shows the values that have to be sent on the data lines of the 7- segment
display, in order to display the characters being used in the project.

TABLE
Value Code
0x00 0x18
0x01 0xde
0x02 0x34
0x03 0x94
0x04 0xd2
0x05 0x91
0x06 0x11
0x07 0xdc
0x08 0x10
0x09 0x90
Table 2 the values that have to be sent on the data lines of the 7- segment display, in order to display the
characters being used in the project.
Chapter 8.5.2
Operation of 7-segment display
Fig 10.5 Operation of 7 segment display. The four selection lines S1, S2, S3, S4, respectively
drive the four displays. At any instant, that display will be ON whose respective selection line
has a high signal. All the four displays are turned on and off one by one, but the time delay
involved is so small that they appear to turn on simultaneously.
For e.g. When S1=1; output from the microcontroller is fed to the lines a1, b1… g1 of display
one and so on for other displays.

CHAPTER 8.6
8.6.1 OPTOCOUPLER
Fig 8.9: Schematic diagram of an opto-isolator showing source of light (LED) on the left, dielectric barrier in
the centre, and sensor (phototransistor) on the right
In electronics, an opt coupler, also called an opto-isolator, photo coupler, or optical isolator,
is a component that transfers electrical signals between two isolated circuits by using
light. Opto-isolators prevent high voltages from affecting the system receiving the signal.
Commercially available opto-isolators withstand input-to-output voltages up to 10 kV and
voltage transients with speeds up to 10 kV/us.
An opto-isolator contains a source (emitter) of light, almost always a near infrared light-
emitting diode (LED), that converts electrical input signal into light, a closed optical channel
(also called dialectical channel, and a photo sensor, which detects incoming light and either
generates electric energy directly, or modulates electric current flowing from an external
power supply. Opto-isolator can transfer the light signal not transfer the electrical signal. The
sensor can be a photo resistor, a photodiode, a phototransistor, a silicon-controlled
rectifier (SCR) or a triac. Because LEDs can sense light in addition to emitting it,
construction of symmetrical, bidirectional opto-isolators is possible. An opto-coupled solid
state relay contains a photodiode opto-isolator which drives a power switch, usually a
complementary pair of MOSFETs. A slotted optical switch contains a source of light and a
sensor, but its optical channel is open, allowing modulation of light by external objects
obstructing the path of light or reflecting light into the sensor.

Electronic equipment and signal and power transmission lines can be subjected to voltage
surges induced by lightning, electrostatic discharge, radio frequency transmissions, switching
pulses (spikes) and perturbations in power supply. Remote lightning strikes can induce surges
up to 10 kV, one thousand times more than the voltage limits of many electronic components.
A circuit can also incorporate high voltages by design, in which case it needs safe, reliable
means of interfacing its high-voltage components with low-voltage ones. The main function
of an opto-isolator is to block such high voltages and voltage transients, so that a surge in one
part of the system will not disrupt or destroy the other parts.
We are employing PC817 as the photo coupler in our project. It is connected to the two pins
of microcontroller (Vcc and PV3, PC4 or PC5) at its pin number 1 and 2. The output of
PC817 is sent to the relay PCB. The voltage input at pin 4 is coming from the SMPS.
When the Vcc has +5 V and Rel 1 (for first relay) has +5 V as well, no current flows in the
LED connected between these two points of the opto coupler. Thus, there will be no
connection between pin 3 and 4 of the opto coupler. Thus the 5 V voltages would be received
at pin 4 i.e. R1. On the other hand, if the Rel 1 receives 0 V, there will be a potential
difference created between pin 1 and 2. Thus current will flow and the LED will glow,
thereby leading to the making of connection at the secondary. This will give pin 4, ground
potential and thus R1 won‘t receive the 5 V voltages from the SMPS.
In other words, the relay card will get current when the voltage at the Rel1 is 5V only, and
there will be no current in the relay PCB if the Rel1 pin is at ground voltage.

Fig 8.10: Operation details of opto coupler used in project.

Chapter 8.7
8.7.1 SMPS (Switching-Mode Power Supply)
Fig 8.11: SMPS
A switched-mode power supply (switching-mode power supply, SMPS, or switcher) is an
electronic power supply that incorporates a switching regulator to convert electrical
power efficiently. Like other power supplies, an SMPS transfers power from a source,
like mains power, to a load, such as a personal computer, while
converting voltage and current characteristics. Unlike a linear power supply, the pass
transistor of a switching-mode supply continually switches between low-dissipation, full-on
and full-off states, and spends very little time in the high dissipation transitions, which
minimizes wasted energy. Ideally, a switched-mode power supply dissipates no
power. Voltage regulation is achieved by varying the ratio of on-to-off time. In contrast, a
linear power supply regulates the output voltage by continually dissipating power in the
pass transistor. This higher power conversion efficiency is an important advantage of a
switched-mode power supply. Switched-mode power supplies may also be substantially
smaller and lighter than a linear supply due to the smaller transformer size and weight.
The SMPS is supplying the output of the optocoupler with 5V.

Chapter 8.8
8.8.1 Current Amplifier
Fig 8.12 Circuit showing Darlington amplifier used in project.
A current of sufficiently high value is required to energise the coils of a relay, but the output
current received via the optocoupler cannot serve the purpose. Thus, we require a current
amplifier for in series with the optocoupler for each relay. The amplifier we are using is
ULN2803APG.

Chapter 8.9
8.9.1 Relays
Fig 8.13: Relay circuit of project.
A relay is an electrically operated switch. Many relays use an electromagnet to mechanically
operate a switch, but other operating principles are also used, such as solid-state relays.
Relays are used where it is necessary to control a circuit by a low-power signal (with
complete electrical isolation between control and controlled circuits), or where several
circuits must be controlled by one signal.
A simple electromagnetic relay consists of a coil of wire wrapped around a soft iron core, an
iron yoke which provides a low reluctance path for magnetic flux, a movable iron armature,
and one or more sets of contacts (there are two in the relay pictured). The armature is hinged
to the yoke and mechanically linked to one or more sets of moving contacts. It is held in
place by a spring so that when the relay is de-energized there is an air gap in the magnetic
circuit. In this condition, one of the two sets of contacts in the relay pictured is closed, and
the other set is open. Other relays may have more or fewer sets of contacts depending on their
function. The relay in the picture also has a wire connecting the armature to the yoke. This
ensures continuity of the circuit between the moving contacts on the armature, and the circuit
track on the printed circuit board (PCB) via the yoke, which is soldered to the PCB.

When an electric current is passed through the coil it generates a magnetic field that activates
the armature and the consequent movement of the movable contact either makes or breaks
(depending upon construction) a connection with a fixed contact. If the set of contacts was
closed when the relay was de-energized, then the movement opens the contacts and breaks
the connection, and vice versa if the contacts were open. When the current to the coil is
switched off, the armature is returned by a force, approximately half as strong as the
magnetic force, to its relaxed position. Usually this force is provided by a spring, but gravity
is also used commonly in industrial motor starters.
Fig 8.14: Relay connections with the capacitor bank and the line.

Fig 8.15: Internal circuit of the relay.
We are using Leone SC5-S type relay. It operates on 6V dc, and can handle an ac voltage of
300V and current of 7A. When the current is amplified by an amplifier, it is sent to the coils
of the relay, which get energised, thereby leading to the closing of NO contacts. Thus the
relay operates and brings the respective capacitor bank in parallel with it. When a particular
relay operates, an LED connected to it also glows for the user to know which relay is
functional at that load to improve the current power factor.

CHAPTER 9
9.1 SPECIFICATIONS
Name of equipment Specifications No. of units used
Power factor meter Voltage Range : 300 V / 600
V AC
Current Range : 5A/10A/20A
AC
Current Transformer is used
as a Current Transducer for
durability.
Aux. Supply : 230V + 20%
/ 110V + 20% AC
Dimension (mm): 96 by 96
(Front). 65 (Depth) & 48 by
96 (Front). 110 ( Depth)
1
Microcontroller pcb General purpose pcb 1
Microcontroller Atmel Atmega8 1
Optocoupler PC817 3
SMPS Input - 230 v ac
Output - 5V DC ,1 A
1
Relay pcb Special purpose pcb 1
Current amplifier ULN2803AP 1
Relays Leone SC5-S-DC 6V
7 A, 300 VAC
50 Hz
Coil- 6 V DC
3
Capacitor banks C1 C= 2.5µF
C2C/2
C3C/4
3
Led‘s 5mm LEDs 4

Load - variable
Connecting wires - -
Capacitances and resistances - -

CHAPTER 10
10.1 PROGRAMMER
Programmer used in our project is USBasp. It is a USB in circuit programmer for Atmel
AVR controllers. It simply consists of an ATMega8 and a couple of passive components. The
programmer uses a firmware – only USB driver, no special USB controller is needed.
FEATURES
 Works under multiple platforms. Linux, Mac OS and windows are tested.
 No special controllers are needed.
 Programming speed is up to 5 Kb/second.
 Planned: serial interface to target (e.g. for debugging).
10.2 COMPILER
Compiler used in the project is WinAVR. It is a suite of executable, open source software
development tool for Atmel AVR series of RISC microprocessors hosted on WINDOWS
platform. It includes the GNU GCC compiler for AVR target for C and C++.
10.3 BURNER
Extreme Burner – AVR is used in the project. It is a full graphical user interface (GUI) AVR
series of MCU that supports several types of clock sources for various applications. It enables
us to read and write a RC oscillator or a perfect high speed crystal oscillator.

CHAPTER 11
11.1 ALGORITHM FOR THE PRINCIPLE OF APFC
Fig 11.1: Algorithm for APFC
The following diagram shows the algorithm of the working method of the project. Reference
power factor has been chosen as 0. 95. If the power factor as read by power factor meter is
greater than or equal to the reference value i.e. 0.95 then the system does not require any
compensation and hence the microcontroller won‘t actuate the relay. Now when the power
factor is less than the reference value two cases arise:
The load is either 1) inductive or 2) capacitive
When the load is inductive, power factor would be less than reference value as read by PF
meter and hence the microprocessor would actuate the relay and firstly minimum available

capacitor would be switched on. If this does not bring power factor to reference value the
microcontroller would send signal to second relay and hence more capacitance is introduced
in circuit and so on till the desired power factor of 0.95 is displayed.
In case of capacitive load, the microcontroller would first switch off the minimum connected
capacitance and go on taking out capacitances till we get the desired power factor of 0.95.
11.2 TIME LINE REPRESENTATION OF POWER FACTOR CORRECTION
Time line representation of power factor correction using microcontroller describes the way
how capacitances are added and disconnected from circuit with time as the load is connected
or disconnected from the circuit.
Fig 11.2

The above figure is an example of time line representation of APFC. Here at t = 0, say motor
is ON and connected to the circuit. The power factor with motor in circuit without
compensation is 0.482. Now the microcontroller would send the signal to relay and actuate it
to bring into the circuit the minimum possible capacitance. As shown in the figure when C1
is added to the circuit the power factor improves to 0.872. Here reference power factor has
been chosen to be 0.95 hence more compensation is required. This is done by adding more
capacitance C2 in the circuit. As C2 is added it is seen that power factor improves way
beyond 0.95 to 0 .98 and hence we need not to add any more capacitance into the circuit.
Now at t = 45 seconds the user turns OFF the motor with the capacitance C1 and
C2 still connected in the circuit . The power factor worsens as a result the microcontroller
comes into action and sends signal to the relay R1 to take out capacitance C1 of the circuit,
which improves power factor but further action of microcontroller on relay R2 to take out
capacitance C2 brings our power factor to 0.990 which is desired.

CHAPTER 12
PICTORIAL REPRESENTATION OF THR PROJECT
Figure 12.1: Circuitry for automatic power factor compensation using microcontroller

Figure12.2: Automatic power factor compensation showing circuitry with various capacitors.

CAPACITOR BANKS AND LOAD
Capacitor banks are automatically inserted into the circuit or out of it using respective relays.
We are using 3 capacitor banks, each of rating, C/2 and C/4. The relays with the best
combination of capacitor banks provide an improved power factor.
The loads we are using are incandescent bulbs (for resistive load), and cooler pump (for
inductive load).
Fig 12.3: Capacitor bank
Figure12.4: Different types of loads that have been used in APFC project.

CHAPTER 13
MDI PENALTY
If you are an office owner or a shop owner and you get electricity on commercial connection
with more than 20 KW, you would have heard of power factor penalty and / or demand
charges. Have you ever wondered what does power factor penalty mean or what are demand
charges? Have you ever paid something called as MDI (Maximum Demand Indicator)
penalty? These are the terms that are used in commercial connections in various parts of India
but very few people understand what they are.
THE COFFEE CUP ANALOGY
In electricity there are mainly two kinds of loads. Resistive loads (heater, coil heater, etc) and
inductive loads (e.g. motors, fans, A.C, refrigerators etc). Resistive loads are like glass of
water whereas inductive loads are like cup of coffee where current is used up to create a
magnetic field which is like ―Froth‖ and is not really useful as it is not used for doing actual
work. The ratio between the actual work that you get and the total energy supplied by the
utility is called power factor.
So, total coffee is one full cup of coffee and what you actually get without froth is actual
coffee.
When we sign up for commercial electricity connection from a utility, we have to specify the
―maximum demand‖ in KVA that we need. During the month if we exceed our maximum
demand we have to pay penalty i.e. extra charges for the same. That is the MDI penalty that
appears on electricity bills.

CHAPTER 14
HOW INSTALLING CAPACITORS REDUCE UTILITY BILLS 
• KVA billing
Assume an uncorrected 460 KVA demand, 400V, 3 at 0.87 power factor
 Billing say Rs 50/ KVA demand per month (say)
Correct power factor to 0.97
Sol. KVA x p.f = KW
Uncorrected 460 x 0.87 = 400 KW
Corrected KVA demand with improved p.f = KW / p.f = 400 / 0.97 = 412 KVA
Using table for KW multiplier, to raise the p.f from 0.87 to 0.97 requires 126 kvar
So, using capacitors of rating higher than 126 kvar to ensure proper correction
Uncorrected billing = KVA x Rs 50
460 x 50= Rs 23,000
Corrected billing = 412 x 50 = Rs 20,600
Annual savings = (Rs 23,000 – Rs 20,600) x 12
= Rs 2400 x 12 = Rs 28,800

CHAPTER 15
LIMITATIONS
Power factor is very important part of utility company as well as for consumers. Utility
company gets rid of power losses and consumers are freed from low power factor penalty
charges.
However this comes with a disadvantage that as the compensation value i.e. kvar
compensation rating lowers, the cost of the project is increases i.e. are relatively large as
compared to other methods. The high values of compensation (kvar) pay back relatively
quicker as compared to smaller compensations. The commercial set ups‘ however require
quite a sizable amount of compensation so the payback period is relatively smaller than
household set ups‘.

CHAPTER 16
CONCLUSION AND FUTURE SCOPE
It can be concluded that power factor correction techniques can be applied to the industries,
power systems and also households to make them stable and due to that the system becomes
stable and efficiency of the system as well as the apparatus increases. The use of
microcontroller reduces the costs. Due to use of microcontroller multiple parameters can be
controlled and the use of extra hard wares such as timer, RAM, ROM and input output ports
reduces. Care should be taken for overcorrection otherwise the voltage and current becomes
more due to which the power system or machine becomes unstable and the life of capacitor
banks reduces.

REFERENCES
 ―Power factor correction‖, Reference design from Free scale
http://www.freescale.com
 Electric power industry reconstructing in India, Present
Scenario and future prospects, S.N. Singh, senior
Member, IEEE and S.C. Srivastava, Senior Member, IEEE
 The 8051 Microcontroller and Embedded Systems‖ by
Muhammad Ali Mazidi and Janice Gillespie Mazidi
 Power System Analysis and design by J. Duncan Glover, Mulukutla S. Sarma,
and Thomas J. Over bye……..fourth edition chapter 1 ,2
 www.theorytopractical.com
 Power systems by J. B Gupta 10th
edition part 2 transmission and distribution of
electrical power pg 367
 Power factor correction www.wikipedia.com
 Power factor basics by PowerStudies.com

Microcontroller-Based Automatic Power Factor Correction

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