apfc analog thesis

7/27/2019 Apfc Analog Thesis

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ABSTRACT

This project discusses the design, implementation and analysis of a single phase

(240V, 50Hz) capacitor bank controller unit. Power factor control using capacitor

banks reduces reactive power consumption which will lead to minimization of losses

and at the same time increases the electrical systems efficiency. Power saving issues

and reactive power management has brought to the creation of single phase capacitor

banks for domestic applications. The development of this project is to enhance and

upgrade the operation of single phase capacitor banks by developing a micro-

processor based control system. The control unit will be able to control capacitor

bank operating steps based on the varying load current. Current transformer is used to

measure the load current for sampling purposes. Fluorescent lamp will be use as

loads in this single phase capacitor bank developments. That fluorescent lamp shall

be divided into different load value to enable capacitor bank model is controlled

systematically.

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Unit -01

INTRODUCTION

&

PROBLEM IDENTIFICATION

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1.1 INTRODUCTION

Electrical energy efficiency is of prime importance to industrial and commercial

companies operating in today's competitive markets. Optimum use of plant and

equipment is one of the main concerns that industry tries to balance with energy

efficiency, for both economical and environmental reasons. As society becomes

increasingly conscious of its impact on the environment, reduced energy consumption

becomes more desirable, which, is an achievable goal for everyone. Through the use

of measures such as power factor control, electricity consumption is optimized, which

ultimately leads to reduced energy consumption and reduced CO2 greenhouse gas

emissions.

Within a cost conscious market, payback considerations are also important. This

report identifies the most appropriate application for power factor control based on

energy consumption, tariff metering, cost payback and emission reduction. Power

factor control is an appropriate means by which to improve the power quality of an

installation. Its application is dependent though on the size of the installation and the

extent that power factor control needs to be applied. The opportunity however exists

to make a significant environmental contribution whilst simultaneously providing

economic benefit.

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Currently, the effective of the capacitor bank as power factor control device was

produced a capacitor bank to domestic use. Also known as energy stability, it will

correct power factor base capacitor concept as compensator reactive current in the

single phase electric circuit. However, this device is less efficiency because the static

operation and did not control load change. The project titled Automatic Power

Factor Control was developed to enable operation single phase capacitor bank to

control follow load change. The operation of present single phase capacitor bank was

not able to operate base of current change according the increase or reduction load.

Because the present system could not detect load rating that changed, the operation

inefficient and power factor control not be optimum. This project is using fluorescent

magnetic ballast as the load.

1.2 Problem Identification

This project developed to improve the weakness of static capacitor bank. Static

capacitor bank is a traditional method was used to improve the power factor by using

capacitor banks. In the configuration of static capacitor bank, the value of capacitor

was fixed and cannot to control. The weakness of the static capacitor bank, which the

operations:

i. Capacitive compensation does not change according to increase or reduction in

loads.

ii. Could not detect load rating that change inefficiency

iii. Operation and power factor control not optimized.

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CUR RENT WAVEFOR MS WITH AND WITH OUT P FC:

Input Voltage

0

DC Bus Output Voltage

Without

PFC

0

Input Curren

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With

PFC


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1.3 Target and Objectives of the Project

There are four objectives of this project, which is stated in the following

texts:

i. To learn the way of power factor control in power systems.

ii. To learn and identify methods to control capacitor banks.

iii. Identify one method of power factor control with the low cost and

practical.

iv. To provide an automatically controlled PFC unit that will bring the

power factor to as near to unity as practical (typically 0.9) and have

sufficient capacity for future PFC requirements or expansion.


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Unit-02

LITERATURE REVIEW


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POWER FACTOR:

Power factor is the ration between the KW and the KVA drawn by an

electrical load where the KW is the actual load power and the KVA is the

apparent load power. It is a measure of how effectively the current is being

converted into useful work output and more particularly is a good indicator

of the effect of the load current on the efficiency of the supply system.

APPARENT POWER REACTIVE POWER

ACTIVE POWER

Fig 2.1

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 can be the result of either a significant phase difference

between the voltage and current at the load terminals, or it can be due to a

high harmonic content or distorted/discontinuous current waveform. Poor


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load current phase angle is generally the result of an inductive load such as

an induction motor, power transformer, lighting ballasts, welder or induction

furnace. A distorted current waveform can be the result of a rectifier,

variable speed drive, switched mode power supply, discharge lighting or

other electronic load.

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.

POWER FACTOR CORRECTION:

Capacitive Power Factor correction is applied to circuits which include

induction motors as a means of reducing the inductive component of the

current and thereby reduce the losses in the supply. There should be no

effect on the operation of the motor itself.


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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

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 between20% 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


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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.


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Fig 2.3

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".


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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


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motor is critically corrected, (corrected to a power factor of 1.0) the

inductive reactance equals the capacitive reactance at the line frequency and

therefore the resonant frequency is equal to the line frequency. If the motor

is over corrected, the resonant frequency will be below the line frequency. If

the frequency of the voltage generated by the decelerating motor passes

through the resonant frequency of the corrected motor, there will be high

currents and voltages around the motor/capacitor circuit. This can result in

severe damage to the capacitors and motor. It is imperative that motors are

never over corrected or critically corrected when static correction is

employed.

Static power factor correction should provide capacitive current equal to

80% of the magnetizing current, which is essentially the open shaft current

of the motor.

The magnetizing current for induction motors can vary considerably.

Typically, magnetizing currents for large two pole machines can be as low

as 20% of the rated current of the motor while smaller low speed motors can

have a magnetizing current as high as 60% of the rated full load current of

the motor. It is not practical to use a "Standard table" for the correction of

induction motors giving optimum correction on all motors. Tables result in

under correction on most motors but can result in over correction in some

cases. Where the open shaft current cannot be measured, and the


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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

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 one contactor to control both

the motor and the capacitors. It is better practice to use two contactors, one


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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.

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


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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.

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


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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


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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.


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UNIT-3

WORKING METHODOLOGY

3.1 BLOCK DIAGRAM


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FIG 3.1

3.2 CIRCUIT DIAGRAM


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FIG 3.2


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3.3 COMPONENT DESCRIPTION

CURRENT TRANSFORMERS

Principle of operation of CT:

A current transformer is defined as as an instrument transformer

in which the secondary current is substantially proportional to the

primary current (under normal conditions of operation) and differs

in phase from it by an angle which is approximately zero for an

appropriate direction of the connections.

Current transformers are usually either measuring or

protective types.


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FIG 3.3


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Related Terms:

1) Rated primary current:

The value of primary current which appears in the designation of the

transformer and on which the performance of the current transformer

is based.

2) Rated secondary current:

The value of secondary current which appears in the designation of

the transformer and on which the performance of the current

transformer is based.

Typical values of secondary current are 1 A or 5 A. In the case of

transformer differential protection, secondary currents of 1/ root 3 A

and 5/ root 3 A are also specified.

3) Rated output:

The value of the apparent power (in volt-amperes at a specified power

(factor) which the current transformer is intended to supply to the

secondary circuit at the rated secondary current and with rated burden

connected to it.


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12-0-12 Transformer

Transformers are composed of a laminated iron core with one or more

windings of wire. They are called transformers because they transform

voltage and current from one level to another. An alternating current

flowing through one coil of wire, the primary, induces a voltage in one or

more other coils of wire, the secondary coils. It is the changing voltage

of AC current that induces voltage in the other coils through the changing

magnetic field. DC voltage such as from a battery or DC power supply

will not work in a transformer. Only AC makes a transformer work. The

magnetic field flows through the iron core. The faster the voltage

changes, the higher the frequency.

The lower the frequency, the more iron is required in the core for the

efficient transfer of power. In the USA, the line frequency is 60 Hertz

with a nominal voltage of 110 volts. Other countries use 50 Hertz, 220

volts. Transformers made for 50 Hertz must be a little heavier than ones

made for 60 Hertz because they must have more iron in the core. Line

voltage can vary a little and usually runs between 110 volts and 120 volts

or between 220 and 240 volts depending on country or power

connections. A house in the USA has 220 volts coming in but is split to

two legs of 110V by grounding the centre tap.


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The ratio of input voltage to output voltage is equal to the ratio of turns

of wire around the core on the input side to the output side. A coil of

wire on the input side is called the primary and on the output side is

called the secondary. There can be multiple primary and secondary coils.

The current ratio is opposite the voltage ratio. When the output voltage is

lower than the input voltage, the output current will be higher than the

input current. If there is 10 times the number of turns of wire on the

primary than the secondary and you put 120 volts on the primary, you

will get 12 volts out on the secondary. If you pull 2 amps out from the

secondary, you will only be using 0.2 amps or 200 milliamps going into

the primary.

Transformers can be built so they have the same number of windings on

primary and secondary or different numbers of windings on each. If they

are the same, the input and output voltage are the same and the

transformer is just used for isolation so there is no direct electrical

connection (they are only linked through the common magnetic field). If

there are more windings on the primary side than the secondary side, then

it is a step down transformer. If there are more windings on the primary

side, then it is a step up transformer.

A transformer can actually be used in reverse and will work fine. For

example, if you have a step up transformer built for transforming 120


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volts to 240 volts, you can also use it for a step down transformer by

putting 240 volts into the secondary side and you will get 120 volts on

the primary side. Effectively, the secondary becomes the primary and

vice versa.

Transformer Power Ratings

Voltage is measured in volts, current is measured in amps, and the unit of

measure for power is watts. Watts is equal to the volts times the amps.

There is a little loss of power in a transformer due to the combination of

resistance and reactance. Reactance is similar to resistance except it is the

resistance to an AC current or more technically, the resistance to change

in a change in current due to the change in the field created. This heat is

what limits the amount of current or power a transformer can handle. The

higher the current, the more heat is produced. When the wires get too

hot, the insulation breaks down and shorts with adjacent wires which

cause more heat which eventually melts wires and ruins the transformer.

A basic transformer has no additional components and so nothing to

protect it from overloading. If you were to connect the two output wires

directly together, that will constitute a short circuit and cause far too

much current to flow in both the primary and secondary and you will

burn out the transformer. In the same way, if you use the transformer to

power a hot wire foam cutter and you are using a wire with too little


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resistance for your foam cutter, you will burn out your transformer if you

don't have it protected by a proper value fuse or breaker. It has to be

made sure that the wire resistance, in other words, the gage or diameter,

and the length is correct to limit the amount of current to under the rating

of the transformer.

The higher the current, the larger the wires need to be that carry that

current. When the wires are larger, there is less resistance and so less

heat. The power that is changed to heat and lost can be calculated as

P=I2R. That means that if you double the current, the power lost to heat

increases by four times. If the transformer is a step down transformer,

then there will be more current on the output and so the wire in the

secondary windings will be heavier than the primary. The reverse is true

for a step up transformer.

A transformer may be rated in Amps, Volt-Amps (VA), or Watts (W).

For small transformers, VA and Watts is the same thing for all practical

purposes. In large industrial transformers, power factors get involved

and the two can be different. If the transformer is rated in amps, it

usually says X amps at X volts and is rated on the output or secondary

side. A 120V transformer with 24V out rated at 2 amps means that you

can only safely pull 2 amps from the secondary side. You can find the


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power rating of the transformer by multiplying the rated amps times the

output voltage so 2 X 24 = 48 watts.

If the transformer is rated in VA or watts, you can calculate the

maximum allowable output current by dividing the VA or watts by the

output voltage. So if the transformer is rated at 48 VA with 24 volts

output, the allowable output current is 48 / 24 = 2 amps.

Transformer Configurations

A 120 volt transformer with two wires in and two wires out is very

simple. You hook up the two wires on the primary side, the 120V side,

to a wall outlet and your output voltage is on the two wires coming from

the secondary side.

When a transformer is shown in an electronic circuit, it is shown as a

diagram like shown here. The parallel lines represent the laminated iron

core, the curved lines represent the primary and secondary windings, the

circles represent the terminations whether terminals or short wires.

Centre Tap

A common configuration is a centre tap or CT. The secondary side has

three wires out. The middle wire on the output side is attached to the


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secondary coil, usually at the middle. If the winding ratio is 5 to 1, then

with 120V input, you get 24 volts output on the two outside wires but if

you connect an outside wire and the centre wire, you get 12 volts because

you are using only half the secondary winding making the connection a

10 to 1 ratio. If the transformer is rated at 2 amps, you still can only use

2 amps output whether you use 12 volts or 24 volts. Often the centre tap

is grounded so you then have two 12 volt sources that can be used to

make + and - 12V DC after running through a converter (rectifier and

filter).

Power Supply Diagram

ELECTRO MAGNETIC RELAY:


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These are varying much reliable devices and widely used on field. The

operating frequency of these devices are minimum 10-20ms.That is 50Hz

100Hz.The relay which is used here can care 25mA currents continuously.

The electromagnetic relay operates on the principle magnetism. When the

base voltage appears at the relay driver section, the driver transistor will be

driver transistor will be


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driven into saturation and allow to flow current in the coil of the relay,

Which in turn create a magnetic field and the magnetic force produced

due to that will act against the spring tension and close the contact coil.

Whenever the base voltage is withdrawn the transistor goes to cutoff .So

no current flow in the coil of the relay. Hence the magnetic field

disappears so the contact point breaks automatically due to spring

tension. Those contact points are isolated from the low voltage supply, so

a high voltage switching is possible by the help of electromagnetic relays.

The electromagnetic relays normally having 2 contact points. Named as

normally closes (NC) , normally open (NO). Normally closed points will

so a short CKT path when the relay is off. Normally open points will so a

short CKT path when the relay is energized.


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2.5UF 400V 450VAC CBB60A CAPACITOR:

2.5UF 400V 450VAC CBB60A Motor Run Capacitors takes heavy-edge

metalized Al/Zn PP film or web-like fuse film as dielectric. Its

components are sealed with flame-retardant epoxy resin. It has cylindrical

outline with high reliability and stability.CBB60 capacitor has features of

small size, light weight, small tangent in waste angle, and good self-

concrescence. Applicable to start and operation with 50/60Hz. A. C

single motor, specially suit for micro pump, baric pump, micro motor and

so on.


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Transistor SL100:

SL100 is a general purpose, medium power NPN transistor. It is mostly

used as switch in common emitter configuration. The transistor terminals

require a fixed DC voltage to operate in the desired region of its

characteristic curves. This is known as the biasing. For switching

applications, SL100 is biased in such a way that it remains fully on if

there is a signal at its base. In the absence of base signal, it gets turned off

completely.

The emitter leg of SL100 is indicated by a protruding edge in the

transistor case. The base is nearest to the emitter while collector lies at

other extreme of the casing.

Rated Capacitance Motor Run Capacitor

Tolerance 2.5uF

Rated Voltage 5%

Brand 400/450VAC

Housing Material Cinco or Custom-made

Housing Shape Plastic

Terminal Round

Dielectric Material 2+2 6.35mmx0.8 pins

Operating Temperature Metallised Polypropylene Film

Frequency 25/70/21

explosion-proof Class 50/60Hz

P0


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UNIT-4

CONCLUSION

&

RESULT

CONCLUSION:

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


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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.

ADVANTAGES OF IMPROVED POWER FACTOR:

Reactive power decreases

Avoid poor voltage regulation

Overloading is avoided

Copper loss decreases

Transmission loss decreases

Improved voltage control

Efficiency of supply system and apparatus increases

ADVERSE EFFECT OF OVER CORRECTION:

Power system becomes unstable

Resonant frequency is below the line frequency

Current and voltage increases


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REFERENCES:

P. N. Enjeti and R martinez, A high performance si ngle phase

rectifier with input power factor correction ,IEEE Trans. Power

Electron..vol.11,No.2,Mar.2003.pp 311-317

J.G. Cho,J.W. Won,H.S. Lee , Reduced conduction lo ss zero-


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voltage-transition power factor correction converter with low cost,IEEE

Trans.Industrial Electron..vol. 45,no 3,Jun. 2000,pp395-400

The 8051 Microcontroller and Embedded Systems by

Muhammad Ali Mazidi and Janice Gillispie Mazidi

8052 simulator for windows version 3.604

25Jun1999,[email protected]

www.fsinc.com

www.keil.com

Eleectric power industry reconstructing in India,Present scenario

and future prospects,S.N. Singh ,senior member,IEEE and S.C.

Srivastava,Senior Member,IEEE

Power factror correction, Reference design from Freescale

http://www.freescale.com

apfc analog thesis

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