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 - tantarget) 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 . tantarget )

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, 25C

– 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

C2C/2

C3C/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.

10.4 POGRAMMING

Source code

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