OVER AND UNDER VOLTAGE PROTECTION RELAY

7/28/2019 OVER AND UNDER VOLTAGE PROTECTION RELAY

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CHAPTER-1

INTRODUCTION

1.1 Introduction to power electronics:

The study of controlling the flow of electrical energy with the help of electronic

circuits is defined as Power Electronics. Power electronics is the applications of

solid-state electronics for the control and conversion of electric power.

Power Electronics Embraces the study of

(a) Power:-

It deals with both rotating and static equipment for the generation, transmission,

distribution and utilization of vast quantities of electrical power.

(b) Electronics:-

It deals with the study of semiconductor devices and circuits for the processing of

information at lower power levels.

(c) Control:-

It deals with the stability and response characteristics of closed loop system.

Power Electronics deals with the use of electronics for control and conversion of

large amount of electrical power.

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Representation of Power Electronic System:

Fig.1.1.Block diagram of power electronic system

The main power source may be either AC or DC based on the application

.The output of the power electronic circuit may be variable ac or dc, or it may be

variable voltage and frequency based on the requirement.

The feedback component measures a parameter of the load (say forexample speed) and compares it with the command signal.

The difference between these two signals, through the digital circuit

controls the instant of turn on of the semiconductor device. The load circuit can

be controlled over a wide range with the adjustment of the command signal.

In between Power Electronic circuit to load, the Filter is added in most of

the applications. A filter is necessary to prevent any harmonics generated by the

converter from being feedback to the mains or from being radiated into space.

Power electronic converters - to modify the form of electrical energy (voltage,

current or frequency).

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Power range - from some mW (mobile phone) to hundreds of MW (HVDC

transmission system). With "classical" electronics, electrical currents and voltage

are used to carry information, whereas with power electronics, they carry power.

Thus, the main metric of power electronics becomes the efficiency.

The first very high power electronic devices were mercury arc valves. In

modern systems the conversion is performed with semiconductor switching

devices such as diodes, thyristors and transistors. In contrast to electronic systems

concerned with transmission and processing of signals and data, in power

electronics substantial amounts of electrical energy are processed.

An AC/DC converter (rectifier) is the most typical power electronics device

found in many consumer electronic devices, e.g., television sets, personal

computers, battery chargers, etc. The power range is typically from tens of watts

to several hundred watts. In industry the most common application is the variable

speed drive (VSD) that is used to control an induction motor. The power range of

VSDs start from a few hundred watts and end at tens of megawatts power

conversion systems can be classified according to the type of the input and output

power

AC to DC (rectification)

DC to AC (inversion)

DC to DC (chopping)

AC to AC (transformation)

The subject of power electronics is the merger of the field of electrical

power system and solid state electronic devices. It is the discipline that involves

the study, analysis, and design of circuits that convert electrical energy from one

form to another.

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Difference between the linear Electronics and Power Electronics:

The specifications in linear Electronics are Gain and Bandwidth. Whereas

the specifications in Power Electronics are Efficiency and Distortion.

Study of Power Electronics involves

Power Semiconductor Devices like construction, characteristics, operation,

protection

Energy storage elements

Various Power Converter Topologies

Control Strategies, Drive circuits of Topologies

EMI, EMC, Heat Dissipation techniques

Advantages of Power Electronics System:-

High efficiency due to low loss in power semiconductor devices.

High reliability of power electronic converter system.

Long life and less maintenance due to absence of any moving parts.

Flexibility in operation

Fast dynamic response compared to electromechanical converter system.

Small size and less weight, thus low installation cost

Disadvantages of Power Electronics System:-

Circuits in power electronics system have a tendency to generate harmonics

in the supply system as well as the load circuit.

AC to DC and AC to AC converter operate at low input power factor under

certain operating condition.

Regeneration of power is difficult in power electronic converter system.

Power Electronic controllers have low overhead capacity

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Applications:

We can realize the applications of Power Electronics everywhere in our

day-to-day life (home, office, factory, car, hospital, theatre etc.)

Some of the typical applications are

Domestic and theatre lighting

Industrial Process in the chemical, paper and steel industries

Motor drives from food mixers, washing machines through to lifts and

locomotives

Power supplies for laboratories and uninterruptible power for vital loads

Generation and transmission control

Industrial Applications:

Industrial applications mainly consist of two areas, motor control and

power supplies. The motors which are controlled vary from very large to smaller

ones . Power supplies for battery charging, induction heating, electroplating and

welding.

Consumer Applications:

Consumer applications cover many different areas in the home, such as

audio amplifiers, heat controls, light dimmers, security systems, motor control for

food mixers and hand power tools.

Transportation Applications:

Transportation applications like motor drives for electric vehicles,

locomotives. In addition to this non-motor drive applications like traffic signal

control, vehicle electronic ignition and vehicle voltage regulation.

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1.2. INTRODUCTION

Equipment in home or office that can be affected includes computers,digital clocks, answering machines, VCRs, electronic cash registers and security

systems. Other equipment impacted by power quality problems includes energy

management systems, variable speed drives and phone systems.

Most electrical devices can tolerate short-term power disturbances without

any noticeable effects. However, more serious power disturbances can cause data

loss, memory loss, altered data, product loss, and other functional errors-as well

as equipment damage. These problems often cause expensive downtime,

inefficiency, lost orders, scheduling problems and accounting problems. It is often

necessary to troubleshoot to determine the cause of these problems. Having the

right kind of power protection for your electronic systems becomes more

important every day. It is difficult to predict when a minor power-related problem

might become a major problem for your home or business.

Identifying the Problems

Since power disturbances are almost always intermittent problems, they

can be difficult to identity. Once a problem has been isolated as a power problem,

it is important to identify the type of power disturbance so that the cause can be

found and a solution can be implemented. Sometimes identifying the cause of a

power disturbance can point to a low or no-cost solution.

Types of Disturbances

There are three types of irregularities, which could affect your power supply:

1.Voltagefluctuations

2.Switchingtransients

3. Power outages

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Power Outages

Power Outages, often referred to as Power Interruptions, can best be

defined as a complete loss of voltage for a few seconds or longer. Sensitive

electronic equipment generally does not respond well to any type of power

interruption. Momentary (short duration) Outages generally range from less than

one cycle to a few seconds. If the momentary interruption is caused by an event

outside of ones home or business, the interruption is likely caused by a device

known as a recloses. A reclose turns off the power in response to a short circuit or

an electrical fault on the utility system, commonly referred to as the power line.

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CHAPTER 2

COMPONENTS DESCRIPTION

2.1. List of components:

Table. 2.1 List of Components

S.No. Name of the

component

Type Number

1. Diode 1N4007 82. Voltage

regulator

7812 1

3. Capacitor 220f/25

v

1

4. Capacitor 100f/63

v

2

5. Resistor 10k

1/4w

3

6. Resistor 1k 1/4w 47. Variable

resistor

10k pot 2

8. Transistor BC 547 2

9. Op-amp LM 324 1

10. Pin base 14 pin 1

11. LED 5 MM 1

12. Relay 12v 1

13. Transformer 12-0-12v 1

14. General board PCB 1

2.2. Op-amp LM324:

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As the name implies it is an operational amplifier. It performs

mathematical operations like addition, subtraction, log, antilog etc.. The main

reason for OPAMPS used over transistors is that transistor can only amplify AC

while OPAMPS can amplify AC and DC. You can get good amplifier gain in

OPAMPS. The most commonly used OPAMPS are 741 and 324. IC741 is used in

close loop configuration and LM324 in open loop configuration. i.e. LM324

mainly used as comparator while 741 for amplification, addition etc...

2.2.1 Features:

Internally frequency compensated for unity gain.

Large DC voltage gain 100 dB

Wide bandwidth (unity gain) 1 MHz (temperature compensated).

Wide power supply range: Single supply 3 V to 32 V or dual supplies 1.5

V to 16 V.

Very low supply current drain (700 A)-essentially independent of supply

voltage.

Low input biasing current 45 nA (temperature compensated).

Low input offset voltage 2 mV and offset current: 5 nA.

Input common-mode voltage range includes ground.

Differential input voltage range equal to the power supply voltage.

Large output voltage swing 0V to V+ - 1.5 V.

2.2.2 Description:

The LM324 series consists of four independent, high gain internally

frequency compensated operational amplifiers which were designed specifically

to operate from a single power supply over a wide range of voltages. Operation

from split power supplies is also possible and the low power supply current drain

is independent of the magnitude of the power supply voltage. Application areas

include transducer amplifiers, DC gain blocks and all the conventional op amp

circuits which now can be more easily implemented in single power supply

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systems. For example, the LM324 series can be directly operated off of the

standard +5V power supply voltage which is used in digital systems and will

easily provide the required interface electronics without requiring the additional

15V power supply.

2.2.3 Pin Diagram and Internal architecture of LM324 :

Fig. 2.1. Internal architecture

Fig. 2.2 Pin diagram

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LM

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2.2.4. Characteristics:

In the linear mode the input common-mode voltage range includes ground

and the output voltage can also swing to ground, even though operated from only

a single power supply voltage

The unity gain cross frequency is temperature compensated

The input bias current is also temperature compensated

2.2.5 Advantages

Eliminates need for dual supplies.

Four internally compensated op amps in a single package.

Allows directly sensing near GND and V out also goes to GND.

Compatible with all forms of logic.

Power drain suitable for battery operation.

2.2.6. LM 324 as Comparator:

Comparator is an analog circuit with two inputs and one output. It watches

and compares two voltages at the inputs and decides if the output should change

or not based on the inputs. For example, if the voltage on one of the inputs goes

above a fixed trigger voltage on the other input, the output could go from LOW to

HIGH. This is only one configuration. There are lots of other possibilities, and the

test circuit will help you understand them. Comparators are good at

"conditioning" analog signals and turning them into digital signals. The output

can be hooked up directly to any logic input on another chip, a BASIC Stamp,

SSR etc. You can hook it up to a transistor (i.e., TIP120/122 or TIP125/127) todrive relays, motors, solenoids etc. We are going to use the LM324 quad

operational amplifier (opamp). There are four general purpose opamps in the

LM324. Each of them can be used as a comparator. We will start with just one, so

connect all unused inputs to ground.

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Fig 2.3 Op-amp as a Comparator

Build this circuit on your breadboard to learn how comparators work. The

pots can be any value, but 10K or more is best. The pots supply adjustable

voltages to the inputs. Measure and set them with a DMM as described. One pot

sets a trip point (reference voltage) called Vref.

Another pot simulates a fluctuating voltage signal, called V in. In your projects

Vin could be from a photocell, flex sensor, microphone etc. A comparator is an

analog circuit with two inputs and one output. It watches and compares twovoltages at the inputs and decides if the output should change or not based on the

inputs. For example, if the voltage on one of the inputs goes above a fixed

trigger voltage on the other input, the output could go from LOW to HIGH. This

is only one configuration. There are lots of other possibilities, and the test circuit

will help you understand them. Comparators are good at "conditioning" analog

signals and turning them into digital signals. The output can be hooked up directly

to any logic input on another chip, a BASIC Stamp, SSR etc. You can hook it up

to a transistor (i.e. TIP120/122 or TIP125/127) to drive relays, motors, solenoids

etc. We are going to use the LM324 quad operational amplifier (opamp). There

are four general purpose opamps in the LM324. Each of them can be used as a

comparator. Well start with just one, so connect all unused inputs to ground.

NonInverting Comparator

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In this example POT1 is used to set the reference voltage and POT2

supplies the input voltage (V in).

Use the DMM to measure Vref at TEST POINT A. Turn POT1 to set it.

You can set it to whatever you need, but for now lets set it to 3 volts.

Now measure V in at TEST POINT B. Turning POT2 changes the voltage

up and down.

Whenever V in is HIGHER than 3 V (Vref) the output is HIGH (LED turns

on).

Whenever V in is LOWER than 3 V (Vref) the output is LOW (LED turns

off).

Inverting Comparator

In this example POT2 sets Vref and POT1 supplies V in.

Use the DMM to measure Vref at TEST POINT B. Turn POT2 to set it.

Lets use 3 volts again.

Now measure V in at TEST POINT A. Turning POT1 changes the voltage.

Whenever V in is HIGHER than 3 V (Vref) the output is LOW (LED turns

off).

Whenever V in is LOWER than 3 V (Vref) the output is HIGH (LED turns

on).

2.3. RELAY

2.3.1. Relay Design.

There are only four main parts in a relay. They are

Electromagnet

Movable Armature

Switch point contacts

Spring

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The figures given below show the actual design of a simple relay.

Fig.2.4 Design of relay

2.3.2 Relay Construction:

It is an electro-magnetic relay with a wire coil, surrounded by an iron core.

A path of very low reluctance for the magnetic flux is provided for the movable

armature and also the switch point contacts. The movable armature is connected

to the yoke which is mechanically connected to the switch point contacts. These

parts are safely held with the help of a spring. The spring is used so as to produce

an air gap in the circuit when the relay becomes de-energized.

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2.3.3 Relay working

The working of a relay can be better understood by explaining the following

diagram given below.

Fig. 2.5 Internal diagram of relay

The diagram shows an inner section diagram of a relay. An iron core is

surrounded by a control coil. As shown, the power source is given to the

electromagnet through a control switch and through contacts to the load. When

current starts flowing through the control coil, the electromagnet starts energizing

and thus intensifies the magnetic field.

Thus the upper contact arm starts to be attracted to the lower fixed arm

and thus closes the contacts causing a short circuit for the power to the load. On

the other hand, if the relay was already de-energized when the contacts were

closed, then the contact move oppositely and make an open circuit.

As soon as the coil current is off, the movable armature will be returned by

a force back to its initial position. This force will be almost equal to half the

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strength of the magnetic force. This force is mainly provided by two factors. They

are the spring and also gravity.

Relays are mainly made for two basic operations. One is low voltage

application and the other is high voltage. For low voltage applications, more

preference will be given to reduce the noise of the whole circuit. For high voltage

applications, they are mainly designed to reduce a phenomenon called arcing.

Relay Basics

The basics for all the relays are the same. Take a look at a 4 pin relay

shown below. There are two colors shown. The green color represents the control

circuit and the red color represents the load circuit. A small control coil is

connected onto the control circuit. A switch is connected to the load. This switch

is controlled by the coil in the control circuit. Now let us take the different steps

that occur in a relay.

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Fig. 2.6 4-pin relay

Energized Relay (ON)

As shown in the circuit, the current flowing through the coils

represented by pins 1 and 3 causes a magnetic field to be aroused. This magnetic

field causes the closing of the pins 2 and 4. Thus the switch plays an important

role in the relay working. As it is a part of the load circuit, it is used to control an

electrical circuit that is connected to it. Thus, when the relay in energized thecurrent flow will be through the pins 2 and 4.

Fig. 2.7 Energized Relay (ON)

De Energized Relay (OFF)

As soon as the current flow stops through pins 1 and 3, the switch opens

and thus the open circuit prevents the current flow through pins 2 and 4. Thus the

relay becomes de-energized and thus in off position.

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Fig. 2.8 De-Energized Relay (OFF)

In simple, when a voltage is applied to pin 1, the electromagnet

activates, causing a magnetic field to be developed, which goes on to close the

pins 2 and 4 causing a closed circuit. When there is no voltage on pin 1, there

will be no electromagnetic force and thus no magnetic field. Thus the

switches remain open.

2.3.4 Pole and Throw

Relays have the exact working of a switch. So, the same concept is also applied.

A relay is said to switch one or more poles. Each pole has contacts that can be

thrown in mainly three ways. They are

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Normally Open Contact (NO) NO contact is also called a make contact.

It closes the circuit when the relay is activated. It disconnects the circuit when the

relay is inactive.

Normally Closed Contact (NC) NC contact is also known as break

contact. This is opposite to the NO contact. When the relay is activated, the circuit

disconnects. When the relay is deactivated, the circuit connects.

Change-over (CO) / Double-throw (DT) Contacts This type of contacts

are used to control two types of circuits. They are used to control a NO contact

and also a NC contact with a common terminal. According to their type they are

called by the names break before make and make before breakcontacts.

Relays are also named with designations like

Single Pole Single Throw (SPST) This type of relay has a total of four

terminals. Out of these two terminals can be connected or disconnected. The other

two terminals are needed for the coil.

Single Pole Double Throw (SPDT) This type of a relay has a total of

five terminals. Out of these two are the coil terminals. A common terminal is also

included which connects to either of two others.

Double Pole Single Throw (DPST) This relay has a total of sixterminals. These terminals are further divided into two pairs. Thus they can act as

two SPSTs which are actuated by a single coil. Out of the six terminals two of

them are coil terminals.

Double Pole Double Throw (DPDT) This is the biggest of all. It has

mainly eight relay terminals. Out of these two rows are designed to be change

over terminals. They are designed to act as two SPDT relays which are actuated

by a single coil.

2.3.5. Types of Relays

Before going on to a deeper classification of the relays there are some basic relay

circuits that must be kept in our mind. They are

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Voltage Suppression Relays

As relays are used in industrial purposes very often, they are mostly controlled

with the help of computers. But when relays are controlled with such devices,

there will surely be the presence of semi-conductors like transistors. This will in

turn cause the presence of voltage spikes. As a result, it is really necessary to

introduce voltage suppression devices , otherwise they will clearly destroy the

transistors.

This voltage suppression can be introduced in two ways. Either the

computer provides the suppression or the relay provides the suppression. If the

relay provides the suppression they are called voltage-suppression relays. In

relays voltage suppression is provided with the help of resistors of high value and

even diodes and capacitors. Out of these diodes and resistors are more commonly

used. Whatever device is used, it will be clearly stated in the relay. Take a look at

the diagram of a voltage suppressed relay with the help of a diode.

Fig. 2.9 Voltage suppression relay using diode

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De-spiking Diode Relays

A diode in the reverse-biased position is connected in parallel with the relay coil.

As there is no flow of current due to such a connection, an open circuit of the

relay will cause the current to stop flowing through the coil. This will have effect

on the magnetic field. The magnetic field will be decreased instantly. This will

cause the rise of an opposite voltage with very high reverse polarity to be induced.

This is mainly caused because of the magnetic lines of force that cut the armature

coil due to the open circuit.

Thus the opposite voltage rises until the diode reaches 0.7 volts. As soon

as this cut-off voltage is achieved, the diode becomes forward-biased. This causes

a closed circuit in the relay, causing the entire voltage to pass through the load.

The current thus produced will be flowing through the circuit for a very long time.

As soon as the voltage is completely drained, this current flow will also stop.

Take a look at the figure given below.

Fig. 2.10 De-spiking diode relays

De-spiking Resistor Relays

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A resistor is almost efficient as that of a diode. It can not only suppress the

voltage spikes efficiently, but also allows the entire current to flow through it

when the relay is in the on position. Thus the current flow through it will also be

very high. To reduce this, the value of the resistance should be as high as 1 Kilo

Ohm. But, as the value of the resistors increases the voltage spiking capability of

the relay decreases. Take a look at the circuit diagram below to understand more.

Fig. 2.11 De-spiking resistor relays

2.3.6 Relay Applications

Relays are used to realize logic functions. They play a very important role

in providing safety critical logic.

Relays are used to provide time delay functions. They are used to time the

delay open and delay close of contacts.

Relays are used to control high voltage circuits with the help of low voltage

signals. Similarly they are used to control high current circuits with the help of

low current signals.

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They are also used as protective relays. By this function all the faults

during transmission and reception can be detected and isolated .

Relay Selection

Some factors are included during selection of relay. They are

Protection Different protections like contact protection and coil

protection must be noted. Contact protection helps in reducing arcing in circuits

using inductors. Coil protection helps in reducing surge voltage produced during

switching.

Look for a standard relay with all regulatory approvals.

Switching time Ask for high speed switching relays if you want one.

Ratings There are current as well as voltage ratings. The current ratings

vary from a few amperes to about 3000 amperes. In case of voltage ratings, they

vary from 300 Volt AC to 600 Volt AC. There are also high voltage relays of

about 15,000 Volts.

Type of contact used Whether it is a NC or NO or closed contact.

Select Make before Break or Break before Make contacts wisely.

Isolation between coil circuit and contacts

2.4. TRANSISTOR BC-547:

Features:

Low current (max. 100 mA)

Low voltage (max. 65 V).

Applications:

General purpose switching and amplification.

Description:

NPN transistor in a TO-92; SOT54 plastic package. NPN complements: BC546 and BC547.

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Fig 2.12 Transistor BC547

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Table-2.2 Transistor BC547 characteristics

2.5. Diode 1N4007:

Features:

Diffused Junction

High Current Capability and Low Forward Voltage Drop

Surge Overload Rating to 30A Peak

Low Reverse Leakage Current.

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Diode symbol:

Fig 2.13 Diode 1N4007

Typical forward bias characteristics:

Fig 2.14 Typical forward bias characteristics

2.6. Transformer:

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Transformer is a constant frequency, constant flux device. Transformers convert

AC electricity from one voltage to another with little loss of power. Transformers

work only with AC and this is one of the reasons why mains electricity is AC.

Step-up transformers increase voltage, step-down transformers reduce voltage.

A step down power transformer is used to step down the AC voltage from

the line voltage of 110 VAC or 220 VAC i.e., it converts higher voltage at the

input side to a lower voltage at the output.

Fig 2.9 Transformer Characteristics

Fig 2.10 center tapped step down transformer 230V to 12V-0-12V

Working Principle of transformer:

The working principle of transformer is very simple. It depends upon Faradays

laws of Electromagnetic Induction. Actually mutual induction between two or

more winding is responsible for transformation action in an electrical transformer.

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Faradays laws of Electromagnetic Induction

According to these Faradays laws,

"Rate of change of flux linkage with respect to time is directly proportional to the

induced EMF in a conductor or coil".

Basic Theory of Transformer:

The alternating current through the winding produces a continually

changing flux or alternating flux surrounds the winding. If any other winding is

brought nearer to the previous one, obviously some portion of this flux will link

with the second. As this flux is continually changing in its amplitude and

direction, there must be a change in flux linkage in the second winding or coil.

According to Faradays laws of Electromagnetic Induction, there must be an EMF

induced in the second. If the circuit of the latter winding is closed, there must be

electric current flows through it. This is the simplest form of electrical power

transformer and this is most basic of working principle of transformer.

For better understanding we are trying to repeat the above explanation in

more brief here. Whenever we apply alternating current to an electric coil, there

will be an alternating flux surrounding that coil. Now if we bring another coil

nearby this first one, there will be an alternating flux linkage with that second

coil. As the flux is alternating, there will be obviously a rate of change of flux

linkage with respect to time in the second coil. Naturally emf will be induced in it

as per Faradays laws electromagnetic induction.

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Fig. 2.17 Basic transformer

The winding which takes electrical power from the source, is generally

known as Primary Winding of transformer. Here in our above example it is first

winding. The winding which gives the desired output voltage due to mutual

induction in the transformer, is commonly known as Secondary Winding of

Transformer. Here in our example it is second winding.

The above mentioned form of transformer is theoretically possible but not

practically, because in open air very tiny portion of the flux of the first winding

will link with second so the electric current flows through the closed circuit of

latter, will be so small that it may be difficult to measure.

The rate of change of flux linkage depends upon the amount of linked flux,

with the second winding. So it desired to be linked almost all flux of primary

winding, to the secondary winding. This is effectively and efficiently done byplacing one low reluctance path common to both the winding. This low reluctance

path is core of transformer, through which maximum number of flux produced by

the primary is passed through and linked with the secondary winding. This is most

basic theory of transformer.

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Fig. 2.18. Practical Transformer

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CHAPTER-3

BLOCK DIAGRAM

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Block diagram:

Fig. 3.1 Block diagram of voltage protection relay

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3.1. Main blocks

1. Power supply

2. Sensing circuit

3 .Reference and comparator circuit

4. Relay driver circuit

3.1.1 Power Supply

Power supply consists of step down transformer, bridge rectifier consisting

of four diodes, filter capacitors and voltage regulator IC7812.

Diode Bridge is an arrangement of four diodes in a bridge circuit

configuration that provides in the same polarity of output for either polarity of

input. When used in its most common application, for conversion of an alternating

current (AC) input into a direct current (DC) output, it is known as a bridge

rectifier.

Filter capacitors are capacitors used for filtering of undesirable frequencies.

They are common in electrical and electronic equipment and cover a number of

applications such as glitch removal on DC power rails, radio frequency

interference, capacitors used after a voltage regulator to further smooth DC power

supplies.

LM7812 is a three terminal fixed voltage regulator. It has many built in

features like thermal shut down, short circuit protection etc. It gives 12v DC

output voltage for operation of circuit.

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3.1.2 Sensing circuit

Sensing circuit consists of step down transformer, one rectifier diode, a

resistor divider network, and a filter capacitor. The output is given to non-

inverting terminal of op-amp.

The sensing circuit senses output voltage of the AC generator. As the

generator is loaded or unloaded, the output voltage changes and the sensing

circuit provides a signal of these voltage changes. This signal is proportional to

output voltage and is sent to the comparison circuit.

3.1.3 Reference and comparator circuit

It consists of sensing circuit and LM324. Two sections of IC are used as

comparator. References are generated by using resistor, potentiometer divider

network and are given to non-inverting terminal.

The reference circuit maintains a constant output for reference. This

reference is the desired voltage output of the AC generator. The comparator

circuit electrically compares the reference voltage to the sensed voltage and

provides an error signal. This error signal represents an increase or decrease in

output voltage.

3.1.4 Relay driver circuit

It consists of diodes connected to output pins of comparators, transistors

and a relay. A diode is connected across relay coil to protect the transistor when

relay is switched off. An LED is connected across the relay coil to know on/off

status of relay.

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The relay is connected between the positive rail and the collector of the

transistor. When the input signal passes through 1K resistor to the base of

transistor, it conducts and pulls the relay. By adding an electrolytic capacitor at

the base of relay driver transistor a short lag can be induced so that the transistor

switches on only if the input signal is persisting. Again even if the input signal

ceases, the transistor remains conducting till the capacitor discharges completely.

This avoids relay clicking and offers clean switching of the relay

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Fig.3.2. Block diagram of relay driver circuit

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CHAPTER-4

WIRING DIAGRAM AND WORKING

Fig. 4.1 Schematic diagram of voltage protection relay

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List of components:

Table 4.1. Parts list in wiring diagram

38

S.NO. Component Type

1

IC 1 LM

324

2

IC2 LM

7812

3

Q1 2N39

04

4

D1-

D4

1N40

07

5

ZD1 6 V

6

ZD2 6.8 V

7

C1 470

F

8

C2,

C3

0.1 F

9

LED -


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4.1 Working

From the circuit when the voltage is 220 V AC through a transformer T1. It

serves to reduce the pressure remaining 12 volts, through a D1-D4 connected to

direct rectifier bridge circuit. To convert the voltage, alternating current to direct

current. Then, through the C1 and C2 to the power filter smoothing .And entering

a pin. Or input pin of IC1, a loan IC Rex bit computing to 12-volt power supply is

fixed to the IC2. That it is IC Op Amp. Pressure acts edge IC2/1 High Voltage

Detector, High Voltage ICs, if this current work to the Q1 and relay function; it

works with, thus cutting off power from the load instantly. The IC2/2 serves to

detect the lower voltage. The two components can be specified by VR1, VR2.

LED 1 display when power or low power over a specified.

4.2. Explanation

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Generally, LM 324 consists of four op-amps, of which only two op-amps

are required.LED is an indication of relay position. In this IC, we have an

inverting terminal and non-inverting terminal. The voltage at inverting terminal is

6.0 Vand at non-inverting terminal is 6.8 V.

When input AC voltage is 200-250V, then comparator1 output goes high and

comparator2 output goes low.so the LED glows.

When input voltage exceeds 250 V the voltage at non-inverting terminal

increases more than 6.8v then output of op-amp1 is pulled high and output of op-

amp2 is also high.So electrical appliance is turned off by means of a relay

connected to the output pin of op-amp. So device is protected.

When input voltage is below 200 V , the voltage at inverting terminal is less

than the voltage at non-inverting terminal, then output1 and output2 of op-amp is

low.So electrical appliance is turned off by means of a relay connected to the

output pin of op-amp. So device is protected.

When comparator1 output goes high and comparator2 output goes low

then only LED glows, otherwise LED is in off position.

4.3 Advantages:

1. Fit and Forget system

2. Low cost and reliable circuit

3. Complete elimination of manpower

4. Can handle heavy loads up to 7A

5. Auto switch OFF in abnormal conditions

6. Auto switch ON in safe conditions

4.4. Applications:

1. Industrial machinery

2. House hold items like TV, refrigerator, AC

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3. Agriculture Motors

4. Water pump

CHAPTER-5

CONCLUSION

Thus over and under voltage protection relay is used to get output

voltage efficiently ,it is mainly preferable when sudden fluctuations is there

in input and to protect the electronic devices like refrigerators, AC.

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CHAPTER-6

FUTURE SCOPE

The present invention generally relates to devices and systems for

providing protective control to power networks. To further enhance the utility

of a digital protective relay, and to provide more comprehensive protective

control of power distribution systems, it would be desirable to improve the

communications capabilities of digital protective relays. More particularly, it

would be desirable for a protective relay to include a Human Machine

Interface which incorporates a common off-the-shelf software package

which is not product-specific. Known protective relays do not sufficiently

address these needs.

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The Universal Relay family of protection and control products are built

on a common modular platform. All UR products feature high performance

protection, expandable I/O, integrated monitoring and metering, high speed

communications, and extensive programming and configuration capabilities.

The UR is the basis of simplified power management for the protection of

critical assets.

Appendix

Reference books1.Power electronic circuits by John Wiley, 2003

2. R. W. Erckson, D. Maksimovic, Fundamentals of power electronics, 2 nd ed.,

Springer, 2001

References

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1 Fadooengineers.com

2 www.wikipedia.org

3 www.engineersgarage.com

4 www.electrofriends.com
http://www.wikipedia.org/http://www.engineersgarage.com/http://www.electrofriends.com/http://www.wikipedia.org/http://www.engineersgarage.com/http://www.electrofriends.com/

Documents

OVER AND UNDER VOLTAGE PROTECTION RELAY