basic electrical 1st &2nd sem common th.4(a). basic

BASIC ELECTRICAL 1ST &2ND SEM COMMON

My channel youtube.com/makeeasyelectricaltechnology | || CHAPTER 01 || 1

Susanta Kumar Sahu(8093349302), Graduated from VSSUT,Burla

Th.4(a). BASIC ELECTRICAL ENGINEERING

(1st sem & 2nd sem Common)

Theory: 2 Periods per Week I.A : 10 Marks

Total Periods: 30 Periods End Sem Exam : 40 Marks

Examination: 1.5 Hours TOTAL MARKS : 50

Marks

Topic wise Distribution of Periods and Marks

Sl.No. Topics Periods

1 Fundamentals 05

2 A C Theory 08

3 Generation of Elect. Power 03

4 Conversion of Electrical

Energy

07

5 Wiring and Power Billing 04

6 Measuring Instrument 03

Total 30

Objective

1. To be familiar with A.C Fundamental and circuits

2. To be familiar with basic principle and application of energy conversion devices

3. To be familiar with generation of Electrical power

4. To be familiar with wiring and protective device

5. To be familiar with calculation and commercial Billing of electrical power & energy

6. To have basic knowledge of various electrical measuring instruments & conservation of

electrical energy

1. FUNDAMENTALS

1.1 Concept of current flow.

1.2 Concept of source and load.

1.3 State Ohm’s law and concept of resistance.

1.4 Relation of V, I & R in series circuit.

1.5 Relation of V, I & R in parallel circuit.

1.6 Division of current in parallel circuit.

1.7 Effect of power in series & parallel circuit.

1.8 Kirchhoff’s Law.

1.9 Simple problems on Kirchhoff’s law.




2. A.C. THEORY

2.1 Generation of alternating emf.

2.2 Difference between D.C. & A.C.

2.3 Define Amplitude, instantaneous value, cycle, Time period, frequency, phase angle,

phase difference.

2.4 State & Explain RMS value, Average value, Amplitude factor & Form factor with

Simple problems.

2.5 Represent AC values in phasor diagrams.

2.6 AC through pure resistance, inductance & capacitance

2.7 AC though RL, RC, RLC series circuits.

2.8 Simple problems on RL, RC & RLC series circuits.

2.9 Concept of Power and Power factor

2.10 Impedance triangle and power triangle.

3. GENERATION OF ELECTRICAL POWER

3.1 Give elementary idea on generation of electricity from thermal , hydro & nuclear

power station with block diagram

4. CONVERSION OF ELECTRICAL ENERGY

(No operation, Derivation, numerical problems)

4.1 Introduction of DC machines.

4.2 Main parts of DC machines.

4.3 Classification of DC generator

4.4 Classification of DC motor.

4.5 Uses of different types of DC generators & motors.

4.6 Types and uses of single phase induction motors.

4.7 Concept of Lumen

4.8 Different types of Lamps (Filament, Fluorescent, LED bulb) its Construction and

Principle.

4.9 Star rating of home appliances (Terminology, Energy efficiency, Star rating Concept)

5. WIRING AND POWER BILLING

5.1 Types of wiring for domestic installations.

5.2 Layout of household electrical wiring (single line diagram showing all the important

component in the system).

5.3 List out the basic protective devices used in house hold wiring.

5.4 Calculate energy consumed in a small electrical installation

6. MEASURING INSTRUMENTS

6.1 Introduction to measuring instruments.

6.2 Torques in instruments.

6.3 Different uses of PMMC type of instruments (Ammeter & Voltmeter).

6.4 Different uses of MI type of instruments (Ammeter & Voltmeter).

6.5 Draw the connection diagram of A.C/ D.C Ammeter, voltmeter, energy meter and

wattmeter. (Single phase only).

Syllabus Coverage upto I.A

Chapter 1,2,3




BOOKS RECOMENDED:

1. ABC of Electrical Enginnering by Jain & Jain (Dhanpat Rai Publication)

2. Fundamentals of Electrical Engg and Electronics by B.L Thereja

3. Concept of Basic Electrical Enginnering ,P.K Das and A.K. Mallick by B.M Publications

4. Fundamentals of Electrical Engg by Asfaq Hussain

5. Fundamentals of Electrical Engg by JB Gupta

6. Basic Electrical Engg. By Chakraborti (Mcgraw Hill)




Contents CHAPTER 01 ............................................................................................................................................ 8

1.0 FUNDAMENTALS ............................................................................................................................... 8

1.1.INTRODUCTION ................................................................................................................................. 8

1.2.Electric charge ................................................................................................................................... 8

1.3.Electric potential and voltage ........................................................................................................... 9

1.4.Electric power ................................................................................................................................. 10

1.5.Electrical Energy .............................................................................................................................. 10

1.5.1Electrical Energy Definition ......................................................................................................... 11

1.5.2Electrical Energy Formula ............................................................................................................ 11

1.5.3Unit of Electrical Energy .............................................................................................................. 11

1.5.4Watt Hours .................................................................................................................................... 11

1.5.5BOT Unit or Board of Trade Unit or Kwh.................................................................................... 11

1.6.Concept of source and load. ........................................................................................................... 11

1.6.1Resistive, Capacitive, Inductive ..................................................................................................... 12

Resistive Load ....................................................................................................................................... 12

Capacitive Load .................................................................................................................................... 12

Inductive Load ...................................................................................................................................... 12

Combination Loads ............................................................................................................................... 12

1.7Ohm's Law: ....................................................................................................................................... 12

1.8Resistance ........................................................................................................................................ 14

1.8.1Resistors in Series ......................................................................................................................... 15

1.9Difference between Series and Parallel circuit ................................................................................ 16

1.9.1Current Divider Rule ..................................................................................................................... 16

General formula .................................................................................................................................... 17

1.10Volage Divider Rule ........................................................................................................................ 20

1.11Kirchhoff’s First & Second Laws ..................................................................................................... 23

1.11.1Kirchhoffs First Law – The Current Law, (KCL) ............................................................................ 23

Kirchhoffs Current Law ........................................................................................................................ 23

1.11.2Kirchhoffs Second Law – The Voltage Law, (KVL) ....................................................................... 24

CHAPTER 02 .......................................................................................................................................... 26

A.C. THEORY .......................................................................................................................................... 26

2.1Generation of Alternating e.m.f....................................................................................................... 26




2.2Difference between D.C. & A.C ........................................................................................................ 28

2.3RMS (Root Mean Square)value ........................................................................................................ 30

2.4Mean value or average value of AC................................................................................................. 32

2.5Ac through Resistor Only ................................................................................................................. 34

2.6Ac through inductor only ................................................................................................................. 35

2.7Ac through Capacitor ....................................................................................................................... 37

2.8Ac through resistor and inductor ..................................................................................................... 38

2.9AC through resistor and capacitor ................................................................................................... 40

2.10AC through inductor, capacitor and resistor ................................................................................. 42

2.11Power and Power factor ................................................................................................................ 43

2.12Power Triangle ............................................................................................................................... 45

2.13Impedance Triangle ....................................................................................................................... 45

CHAPTER 03 .......................................................................................................................................... 46

GENERATION OF ELECTRICAL POWER .................................................................................................. 46

3.1Hydro-electric Power Station ........................................................................................................... 46

3.1.1Factors for Selection of Site ........................................................................................................... 46

3.1.2General Arrangement of Hydro-electric Plant .............................................................................. 47

3.1.3Disadvantaes ................................................................................................................................. 50

3.2Steam Power Station ....................................................................................................................... 51

3.2.1General Arrangement of Steam Power Plant ............................................................................... 52

3.2.2Disadvantages ............................................................................................................................... 55

3.4. Efficiency ...................................................................................................................................... 56

3.5Nuclear Power Station ..................................................................................................................... 56

3.5.1General Arrangement of Nuclear Power Plant ............................................................................. 58

3.5.2Nuclear Reactor............................................................................................................................. 60

3.5.2 Heat exchanger ............................................................................................................................. 61

3.5.3 Steam turbine ............................................................................................................................... 61

3.5.4 Alternator ..................................................................................................................................... 61

3.5.5 Cooling Water Circuit .................................................................................................................. 61

3.5.6 Advantages ................................................................................................................................. 61

3.5.7. Disadvantages ............................................................................................................................ 62

CHAPTER 04 .......................................................................................................................................... 63

CONVERSION OF ELECTRICAL ENERGY.................................................................................................. 63

4.1Introduction ..................................................................................................................................... 63




4.2Fleming's Right Hnad Rule ............................................................................................................... 63

4.3Fleming's left hand rule ................................................................................................................... 64

4.4Construction (parts) of a Practical D.C. Machine: ............................................................................ 64

4.5Classification of DC Machines: ........................................................................................................ 68

4.6Applications of D.C. Motors ............................................................................................................. 71

4.7Applications of Various Types of Generators .................................................................................. 71

4.8Types of Single Phase Induction Motors .......................................................................................... 71

4.8.1Applications of single phase induction motors ............................................................................. 72

4.9Light: ................................................................................................................................................ 72

4.10Concept of Lumen: ......................................................................................................................... 72

4.11Different types of Lamps: .............................................................................................................. 73

4.11.1Filament(incandescent) bulb ...................................................................................................... 73

4.11.2Fluorescent (Tube) lamp: ............................................................................................................ 73

4.11.3LED Bulb: ..................................................................................................................................... 74

4.12Star rating of home appliances: ..................................................................................................... 74

CHAPTER 05 .......................................................................................................................................... 76

5.1WIRING AND POWER BILLING .......................................................................................................... 76

5.2Different Types of Electrical Wiring Systems ................................................................................... 76

1. Cleat Wiring ....................................................................................................................................... 76

2. Casing and Capping wiring ................................................................................................................ 77

3. Batten Wiring (CTS or TRS)................................................................................................................ 77

4. Lead Sheathed Wiring ....................................................................................................................... 78

5. Conduit Wiring .................................................................................................................................. 78

5.3Layout of household electrical wiring (single line diagram): ........................................................... 79

5.4Basic protective devices used in house hold wiring.:- ..................................................................... 79

5.4.1Fuses ............................................................................................................................................. 79

5.4.2Miniature Circuit Breaker (MCB) .................................................................................................. 80

5.5Energy consumed in a small electrical installation: ......................................................................... 82

5.6Electrical energy Calculation(Power Billing): ................................................................................... 82

CHAPTER 06 .......................................................................................................................................... 83

MEASURING INSTRUMENTS ................................................................................................................. 83

6.1Introduction: .................................................................................................................................... 83

6.2Torques in instruments: ................................................................................................................... 83

6.2.1Deflecting System ......................................................................................................................... 83




6.2.2Controlling System ........................................................................................................................ 84

6.2.3Damping System ........................................................................................................................... 84

6.3Permanent Magnet Moving Coil Instruments (PMMC) ................................................................... 84

6.4Moving Iron Instruments ................................................................................................................. 87

6.5Connection diagram of Ammeter, voltmeter: ................................................................................. 88

6.6Connection diagram of wattmeter (single phase): .......................................................................... 88

6.7Connection diagram of Energy meter: ............................................................................................. 89




CHAPTER 01

FUNDAMENTALS INTRODUCTION:-

Welcome to this course on Basic Electrical Engineering. Engineering students of almost all

disciplines has to undergo this course (name may be slightly different in different course

curriculum) as a core subject in the first semester. It is needless to mention that how much we

are dependent on electricity in our day to day life.

A reasonable understanding on the basics of applied electricity is therefore important for

every engineer. Apart from learning d.c and a.c circuit analysis both under steady state and

transient conditions, you will learn basic working principles and analysis of transformer, d.c

motors and induction motor. Finally working principles of some popular and useful

indicating measuring instruments are presented.

Electric charge

Electric charge is the physical property of matter that causes it to experience a force when

placed in an electromagnetic field. This force is is directly proportional to the charge

magnitude.

By convention a electron is considered as 1 unit of negative charge and proton as 1 unit of

positive charge.

But in actual flow of electric current or chemical is this electron which participate and not

proton(except in nuclear reaction ). Since electron is -ve, so flow of current is opposite to

flow of electron

Good conductors are generally those which have some free electrons which means. There are

two region called valence band and conduction band. Depending on availability of electron

these energy bands conductivity is determined.

If a conductor gives away some electron, absence of electron is called a hole. Since in general

elements are electrically neutral, after giving up electrons, the overall element is positively

charged.




This means a hole may be considered as a positive charge. What happens is this hole

sometimes takes up an electron from a nearest neighbor, creating a hole there. This way the

hole can move which resembles a positive charge moving.

Suppose a man(electron) left a seat(hole) in the bus at the front, you(electron) were standing

at the back end of the bus. Now the nearest person from the next seat move to that empty

seat. So the empty seat will move to the next row. In this way by readjustment from each next

row, the empty seat will reach you .So though holes moves, it is actually the movement of

electron.

unit of electric charge

1 Coulomb = 1 Ampere (times) 1 second. The SI derived unit of electric charge is the

coulomb (C). In electrical engineering, it is also common to use the ampere-hour (Ah), and,

in chemistry, it is common to use the elementary charge (e as a unit). The symbol Q often

denotes charge

Electric potential and voltage

We define voltage as the amount of potential energy between two points on a

circuit. One point has more charge than another. This difference in charge between

the two points is called voltageConsider a water tank at a certain height above the

ground. At the bottom of this tank there is a hose.

When describing voltage, current, and

resistance, a common analogy is a water tank. In this analogy, charge is represented by

the water amount, voltage is represented by the water pressure, and current is

represented by the water flow. So for this analogy,

remember:

Water = Charge

Pressure = Voltage

Flow = Current

https://www.quora.com/What-is-the-S-I-unit-of-electric-charge

https://www.quora.com/What-is-the-S-I-unit-of-electric-charge

https://physics.stackexchange.com/questions/300934/what-is-the-difference-between-electric-potential-and-voltage

https://physics.stackexchange.com/questions/300934/what-is-the-difference-between-electric-potential-and-voltage




Unit of Voltage or Electric potential

The voltage between two points is equal to the work done per unit of charge against a

static electric field to move a test charge between two points. This is measured in units of

volts (a joule per coulomb); moving 1 coulomb of charge across 1 volt of electric

potential requires 1 joule of work.

Electric power

Electric power, like mechanical power, is the rate of doing work, measured in watts, and

represented by the letter P. The term wattage is used colloquially to mean "electric power in

watts." The electric power in watts produced by an electric current I consisting of a charge

of Q coulombs every t seconds passing through an electric potential (voltage) difference

of V is

P = work done per unit time= 𝑉𝑄𝑡 =VI

Where

Q is electric charge in coulombs , t is time in seconds , I is electric current in amperes, V is

electric potential or voltage in volts

Electrical Energy

Before explaining what electrical energy is, let us try to review the potential difference

between two points in an electric field.

Suppose potential

difference between point A and point B in an electric is v volts.

As per the definition of potential difference we can say, if one positive unit electrical charge

that is a body containing one-coulomb positive charge travels from point A to point B, it will

do v joules

Work.

https://en.wikipedia.org/wiki/Power_(physics)

https://en.wikipedia.org/wiki/Work_(electrical)

https://en.wikipedia.org/wiki/Watt

https://en.wikipedia.org/wiki/Watt

https://en.wikipedia.org/wiki/Electric_potential

https://en.wikipedia.org/wiki/Voltage

https://en.wikipedia.org/wiki/Coulomb

https://en.wikipedia.org/wiki/Second

https://en.wikipedia.org/wiki/Ampere

https://en.wikipedia.org/wiki/Volt

https://www.electrical4u.com/voltage-or-electric-potential-difference/

https://www.electrical4u.com/what-is-electric-field/





Now instead of one-coulomb charge if q coulomb charge moves from point A to B, it will do

vq joules work.

Electrical Energy Definition

Electrical energy is the work done by electric charge. If current i ampere flows through a

conductor or through any other conductive element of potential difference v volts across it,

for time t second, the electric energy is,

Electrical Energy Formula

The expression of electric power is The electrical energy is

Unit of Electrical Energy

Basically, we find the unit of electrical energy is joule. This equals to one watt X one second.

Commercially, we also use other units of electrical energy, such as watt-hours, kilo watt

hours, megawatt hours etc.

Watt Hours

If one watt power is being consumed for 1 hour time, the energy consumed is one watt-hour.

BOT Unit or Board of Trade Unit or Kwh The practical, as well as a commercial unit of electrical energy, is kilowatt hour. The

fundamental commercial unit is watt-hour and one kilowatt hour implies 1000 watt hours.

The electrical supply companies take electric energy charges from their consumer per

kilowatt hour unit basis. This kilowatt hour is board of trade unit that is BOT unit.

Concept of source and load. An electrical source, such as a battery or power supply, provides energy in electrical form,

known as current. The maximum power available from such a source is the product of the

maximum current it can supply into a load and the voltage (potential difference) generated

across the load by the current flowing through it. Loads that approach zero resistance will

draw maximum current at a approaching zero voltage (or potential difference).

An electrical load, such as a motor or light bulb, converts electrical energy into some other

form such as motion, light, heat, sound etc. The load is rarely 100% efficient, so usually the

energy is converted into several forms, the largest quantity being the intended conversion (we

hope) the remainder being energy in a different form that may be wasted. For example, an

incandescent light bulb converts electrical energy into light, but not all of the electrical

https://www.electrical4u.com/electric-charge/

https://www.electrical4u.com/electrical-conductor/


https://www.electrical4u.com/electric-power/




energy is given off as light. Some is radiated as heat, which is considered to be the wasted

proportion.

An electrical load is a device or an electrical component that consumes electrical energy and

convert it into another form of energy. Electric lamps, air conditioners, motors, resistors etc.

are some of the examples of electrical loads. They can be classified according to various

different factors. Some popular classifications of electrical loads are as follows.

Resistive, Capacitive, Inductive

Electrical loads can be classified according to their nature as Resistive, Capacitive, Inductive

and combinations of these.

Resistive Load

Two common examples of resistive loads are incandescent lamps and electric heaters.

Resistive loads consume electrical power in such a manner that the current wave remains

in phase with the voltage wave. That means, power factor for a resistive load is unity.

Capacitive Load

A capacitive load causes the current wave to lead the voltage wave. Thus, power factor

of a capacitive load is leading.

Examples of capacitive loads are: capacitor banks, buried cables, capacitors used in

various circuits such as motor starters etc.

Inductive Load

An inductive load causes the current wave to lag the voltage wave. Thus, power factor of

an inductive load is lagging.

Examples of inductive load include transformers, motors, coils etc.

Combination Loads

Most of the loads are not purely resistive or purely capacitive or purely inductive. Many

practical loads make use of various combinations of resistors, capacitors and inductors.

Power factor of such loads is less than unity and either lagging or leading.

Examples: Single phase motors often use capacitors to aid the motor during starting and

running, tuning circuits or filter circuits etc.

Ohm's Law: Ohm’s law states that at a constant temperature, current 'I' through a conductor between

two points is directly proportional to the potential difference or voltage 'V', across the

two points. That is,

http://blog.electricalcommunity.com/incandescent-lamp-vs-cfl-vs-led/

http://www.electricaleasy.com/2014/02/working-principle-and-types-of.html

http://blog.electricalcommunity.com/how-does-a-light-bulb-incandescent-lamp-work/

http://www.electricaleasy.com/2015/11/understanding-power-factor.html

http://www.electricaleasy.com/2014/03/electrical-transformer-basic.html

http://www.electricaleasy.com/2014/02/single-phase-motor-schematic.html




Thus, the ratio V : I is a constant. This constant is called as the resistance (R) of the

conductor.

Graph:

After performing experiment for different readings of V & I and recording the

observations, if we plot current on the x-axis of a graph and voltage on the y-axis of the

graph, we will get a straight-line. The gradient of the straight-line graph is related to the

resistance (R) of the conductor.




Resistance

https://www.electronics-tutorials.ws/resistor/res_5.html




Resistors in Series

Resistors in Parallel








Difference between Series and Parallel circuit. Sl no. Parameters Series circuit Parallel circuit

1 Current The current is the same in

all

parts of the circuit

The total current supplied to the

network equals the sum of the

currents in the various branches

2 Voltage The total voltage equals

the

sum of the voltages across

the

different parts of the

circuit

The voltage across a parallel

combination is the same as the

voltage across each branch

3 Resistance The total resistance equals

the sum of the separate

resistances

R= 𝑅1 + 𝑅2 + 𝑅3 …. The reciprocal of the equivalent

resistance equals the sum of the

reciprocals of the branch

resistances

R=1𝑅1 + 1𝑅2 + 1𝑅3 + ⋯

Current Divider Rule

In parallel electrical circuits, the current doesn't remain same. The current divide rule is used

to find the divided current in parallel circuits

Statement: The electrical current entering the node of a parallel circuit is divided into the

branches. Current divider formula is employed to calculate the magnitude of divided

current in the circuits.

Let's understand the basic definitions:

Node: A point where two or more than two components are joined.

Parallel circuit: The circuit in which one end of all components share a common node, and

the other end of all components share the other common node.




General formula

A parallel circuit with 'n' number of resistors and an input voltage source is illustrated below.

We are interested to find the current which is flowing through Rx.

In the above formula:

Ix: The current through Rx.

It: The total current which enters the circuit.

Rx: The resistance of the component whose current value is to be determined

Rt: The equivalent resistance of the parallel circuit

For two resistors

Let's consider a parallel circuit having two resistors R1 and R2. The current It enters the node.

We are interested to calculate the current that is flowing through. The general formula and

circuit now take the form:

http://1.bp.blogspot.com/-N2qCkKhSbLk/WoPosMEnFII/AAAAAAAAEP4/Zd9fKT2IM5Y6mUSrS1VDII1zyRbkHYDPwCK4BGAYYCw/s1600/general-current-divider-formula.jpg




We can modify the previous equation to obtain an alternative formula:

Let's solve an example to better understand the formulas.

http://2.bp.blogspot.com/-KomjnnvhFgM/WoPstVKf86I/AAAAAAAAEQM/ykDt9PuwGsQSrENZgswQT146kIEExgxhwCK4BGAYYCw/s1600/current-divider-for-two-parallel-resistors.jpg

https://1.bp.blogspot.com/-4fe_wa_hRTY/WoPxP6i4pjI/AAAAAAAAEQk/oLioFwavmC84gzPeP_0b8OAOWN6dUU_3ACLcBGAs/s1600/alternative-form-of-current-divider-formula.jpg




Example # 1: A 5 kΩ resistor connects in parallel to a 20 kΩ resistor. 5 A current enters the

node. Find the current across both resistors.

Solution:

Current divider rule for three resistors

Let's consider the third case where we have three parallel resistors. The easy method which

should be followed here is to find the equivalent resistance first, and then to apply the

original formula:

http://3.bp.blogspot.com/-MPjWlhpfa-s/WoPy7to3yOI/AAAAAAAAEQ0/SascUQ8I49Uwo9yH7SCytF1Z5wTR_KKIgCK4BGAYYCw/s1600/current-divider-full-solved-example-1.jpg

http://2.bp.blogspot.com/-jMuFRdtW9ms/WoP2qGic1iI/AAAAAAAAERA/JltqYdmTndU13OqetSE3EVh7MW8ESDdqwCK4BGAYYCw/s1600/current-divider-fully-solved-example-2-with-three-resistors.png




Volage Divider Rule

The electrical current always remains same in the series components. However, the voltage

doesn't remain same in series components. The voltage divider rule is used to find the voltage

divided across different components

The magnitude of divided voltage in a series circuit depends on the magnitude of

resistance.

A series circuit is the one where one end of component connects to other and there is no other

component in between them.

General formula

The general formula for calculating the voltage divider in a series circuit with 'n' resistors is:

Let's simplify the general formula for two resistors.

The circuit below displays a circuit with two resistors R1 and R2. The source Vin powers

circuit.

http://www.basicsofelectricalengineering.com/2018/02/series-vs-parallel-circuit-configuration.html

http://1.bp.blogspot.com/-olhycOw7Zow/WosTPhDpBMI/AAAAAAAAERQ/qF6110XWIHw4txM5UrfeeDxdbLbLBqUfgCK4BGAYYCw/s1600/voltage-divider-formula-general.jpg




We are interested to determine the voltage which is dropped across both resistors. Let's

consider V1 is across dropped across R1 and V2 is across R2.

The formulas are:

Let's solve an example to better understand it.

Example # 1: A circuit has two series resistors having their resistances 5 Ω and 10 Ω. Find the voltage across 10 Ω resistor when an 8 V source is connected to the input.

Solution:

http://2.bp.blogspot.com/-5Xfa-o-Iqhc/WosWEKb4SkI/AAAAAAAAERs/n3M8WL3QnQIfgtpY2euRrzoiAQ5Prz_xgCK4BGAYYCw/s1600/series-circuit-with-two-resistors.jpg

http://2.bp.blogspot.com/-OGcnc-OkynY/WosWz9PBDFI/AAAAAAAAER8/laebTEbIZkUAfde-nvW6P71LSjoqNH85ACK4BGAYYCw/s1600/voltage-divider-formula.jpg

https://3.bp.blogspot.com/-ABmsmsmJ1Pw/WosZGAVz8pI/AAAAAAAAESE/_Gy2dsMyC-kfB3TMQZn-avNkO3pO_wMaQCLcBGAs/s1600/voltage-divider-example-with-5-and-10-ohm-resistor.jpg




In the similar fashion, we can apply the voltage divider rule to three, four, five or any number

of resistors. The formula to calculate voltage V1, V2, and V3 across R1, R2, and

R3 respectively is:

Example # 2: Three resistors of 5, 10, 15 Ω are joined in series to 20 V source. Find the current across R3.

Solution:

http://1.bp.blogspot.com/-QBhBxVmIgWg/WosauJXLoCI/AAAAAAAAESU/WnUjANL9WZAJAZTR-gdLS4jPWiSOxbS6QCK4BGAYYCw/s1600/voltage-divider-rule-for-3-series-resistors.jpg

http://3.bp.blogspot.com/-Ynx_Aw9UbmI/Wosg9fSUoPI/AAAAAAAAESk/Q2JG4FY36LIBvWvQoFoIMocr1J2G2yTQACK4BGAYYCw/s1600/voltage-divider-rule-example-for-3-series-resistors.jpg




Kirchhoff’s First & Second Laws In 1845, a German physicist, Gustav Kirchhoff developed a pair or set of rules or laws

which deal with the conservation of current and energy within electrical circuits. These two

rules are commonly known as: Kirchhoffs Circuit Laws with one of Kirchhoffs laws dealing

with the current flowing around a closed circuit, Kirchhoffs Current Law, (KCL)while the

other law deals with the voltage sources present in a closed circuit, Kirchhoffs Voltage Law,

(KVL).

Kirchhoffs First Law – The Current Law, (KCL)

Kirchhoffs Current Law or KCL, states that the “total current or charge entering a junction

or node is exactly equal to the charge leaving the node as it has no other place to go except

to leave, as no charge is lost within the node“. In other words the algebraic sum of ALL the

currents entering and leaving a node must be equal to zero, I(exiting) + I(entering) = 0. This idea by

Kirchhoff is commonly known as the Conservation of Charge.

Kirchhoffs Current Law

Here, the three currents entering the node, I1, I2, I3 are all positive in value and the two

currents leaving the node, I4 and I5 are negative in value. Then this means we can also rewrite

the equation as;

I1 + I2 + I3 – I4 – I5 = 0

The term Node in an electrical circuit generally refers to a connection or junction of two or

more current carrying paths or elements such as cables and components. Also for current to

flow either in or out of a node a closed circuit path must exist. We can use Kirchhoff’s

current law when analysing parallel circuits.




Example: Find the current through a 20Ω resistance, and current through a 40Ω resistance.

Write KCL at node x

Write in the circuit using Ohm’s Law

Apply last two equation into KCL at node x

The current through a 20Ω resistance

The current through a 40Ω resistance

Kirchhoffs Second Law – The Voltage Law, (KVL)

Kirchhoffs Voltage Law or KVL, states that “in any closed loop network, the total voltage

around the loop is equal to the sum of all the voltage drops within the same loop” which is

also equal to zero. In other words the algebraic sum of all voltages within the loop must be

equal to zero. This idea by Kirchhoff is known as the Conservation of Energy

Kirchhoff’s Voltage Law (KVL):

The algebraic sum of all voltage around the closed loop must be always zero.

1. if the positive (+) side of the voltage is encountered first, assign a positive “+”sign to the

voltage across the element.

2. If the negative (-) side of the voltage is encountered first, assign a negative “-”sign to the

voltage across the element.




For the following figure

To use KVL to analyze a circuit,

1. Write KVL equations for voltages

2. Use Ohm’s law to write voltages in terms of resistances and currents.

Solve to find values of the currents and then voltages.

Example : Find the current i and voltage v over the each resistor.

KVL equations for voltages




Using Ohm’s Law

Substituting into KVL equation

CHAPTER 02

A.C. THEORY

Generation of Alternating e.m.f.

We know that an alternating e.m.f. can be generated either by rotating a coil within stationary

magnetic field or by rotating a magnetic field within a stationary coil. The magnitude of

e.m.f. generated in the coil depends upon the number of turns on coil, strength of magnetic

field and the speed at which the coil or magnetic field rotates.

Consider a coil of N turns rotating with angular velocity ω radians per second in a uniform magnetic field, as shown it.

Let the time be measured from the instant of coincidence of the plane of the instant of

coincidence of the plane of the coil with the X-axis. At this instant maximum flux, φmax links

with the coil. Let the coil assume the position as shown in after moving in counter clock wise




direction for t seconds.

The angle θ through which the coil has rotated in t seconds = ωt

In this position, the component of flux along perpendicular to the plane of coil = φmax cos ωt

Hence flux linkage of the coil at this instant = Number of turns on coil x linking flux =

φmax cos ωt

i.e. instantaneous flux linkage = N φmax cos ωt

Since e.m.f. induced in a coil equal to the rate of change of flux linkage with minus sing.

so e.m.f. induced at any instant, e = - d/ dt [ N φmax cos ]

= φmax N d ( - cos ωt ) = φmax Nω sin ωt dt

when ωt = 0, sin ωt = 0

therefore, induced e.m.f. is zero, when ωt = π/2 , sin π /2 = 1,

therefore induced e.m.f is maximum, which s denoted by Emax and is equal to Nω.

Substituting, φ max Nω = Emax

Instantaneous e.m.f. e = Emax sin ωt

So the e.m.f. induced varies as the since function f the time angle ωt and if e.m.f. induced is plotted against time, a curve of sine wave shape is obtained, as shown in . Such an e.m.f. is

called the sinusoidal e.m.f. The since curve is completed when the coil moves through an




angel of 2π radians.

Difference between D.C. & A.C.

Basis Alternating current(A.C) Direct current(D.C)

Definition The direction of the current

reverse periodically.

The direction of the

current remain same.

Causes of flow of

electrons

Rotating a coil in a uniform

magnetic field or rotating a

uniform magnetic field within

a stationary coil

Constant magnetic field

across the wire

Frequency 50 or 60 Hertz Zero

Direction of flow

of electrons.

Bidirectional Unidirectional

Power Factor Lies between 0 and 1 Always 1

Polarity It has polarity (+, -) Do not have polarity

Obtained From Alternators Generators, battery,

solar cell, etc.

Type of load Their load is resistive,

inductive or capacitive.

Their load is usually

resistive in nature.

Graphical

Representation

It is represented by irregular

waves like triangular wave,

square wave, square tooth

wave, sine wave.

It is represented by the

straight line.

Transmission Can be transmitted over long

distance with some losses.

It can be transmitted

over very long distance

with negligible losses.

Convertible Easily convert into direct

current

Easily convert into

alternating current

Substation Few substation is required for More substations are




Basis Alternating current(A.C) Direct current(D.C)

generation and transmission required for generation

and transmission

Passive

Parameter

Impedance Resistance

Harazdous Dangerous Very dangerous

Application Factories, Industries and for

the domestic purposes.

Electroplating,

Electrolysis, Electronic

Equipment etc.

Some Important terms and Defination:

Waveform

The shape of the curve of the voltage or current when plotted against time as abscissa (base)

is called the waveform. The waveform of an alternating voltage varying sinusoidal is shown

in Fig. 1. The waveform of the induced emf in an alternator differs slightly from that of sine

wave but for calculation purposes it is treated as such.




Alternation and Cycle.

When a periodic wave, such as sinusoidal wave, goes through one complete set of positive or

negative values, it completes one alternation and when it goes through one complete set of

positive and negative values it is said to have completed one cycle.

Alternation and cycle can also be defined in terms of angular measure. One alternation

corresponds to 180° (or radians) while one cycle corresponds to 360° (or radians).

Time Period and Frequency.

The time taken in seconds by an alternating quantity to complete one cycle is known as time

period or periodic time and is denoted by T.

The number of cycles completed per second by an alternating quantity is known as

frequency,and is denoted by f. In SI system, the frequency is expressed in hertz (pronounced

as hurts). One hertz (or Hz)

Time period, T = Time taken in completing one cycle = 1/f, sec

The commercial ac power is generated at frequency of 50 Hz or 60 Hz.

Amplitude.

The maximum value, positive or negative, which an alternating quantity attains during one

cycle is called the amplitude of the alternating quantity. The amplitude of an alternating emf

(or Voltage) and current is designated by Emax (or Vmax) and Imax respectively.

Instantaneous value.

The value of alternating quantity (emf, voltage or current) at any particular instant is called

the instantaneous value and is designated by a small italic letter (e for emf, v for voltage

and i for current). The instantaneous values of an alternating quantity can be determined

either from the curve or from an equation of the alternating quantity. For example, the

instantaneous values of emf represented by the curve shown in Fig. 1 at

0, π/2, and 3π/2 are zero, +Emax, zero and -Emax respectively.

RMS (Root Mean Square)value:

The r.m.s. value of an alternating current is given by that steady (d.c.) current which when

flowing through a given circuit for a given time produces the same heat as produced by the

alternating current when flowing through the same circuit for the same time.

To calculate the mean value of ac, Let us consider an ac given by

the small amount of work done by an ac in small time dt is

So total work done is obtained by integrating equation ii from t = 0 to t = T we get

https://notes.tyrocity.com/wp-content/uploads/rms.png

https://notes.tyrocity.com/wp-content/uploads/rms1.png




If Irms be the RMS value of ac then it would do the same work as in equation iii while passing

through R in time T

Now from equation iii and iv we get

This relation shows that the root mean square value of ac is about 70.7% of its pick value.

Similarly the root mean square value of alternating emf is






My channel youtube.com/makeeasyelectricaltechnology | || Mean value or average

value of AC ||

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Mean value or average value of AC

The mean value or average value of AC over a complete cycle is zero. So we do not consider

the average value of AC over one cycle. We therefore take the average value of AC over a

half cycle only I.e. from t=0 to t=T/2

The average value of AC over a half cycle is that value of steady current that would send

same amount of charge in same interval of time that would be sent by the DC in same time.

To calculate the mean value of ac, Let us consider an ac given by

the small amount of charge sent by an ac in small time dt is

total charge carried by ac in half cycle is obtained by integrating equation ii from t = 0 to t =

T/2


https://notes.tyrocity.com/wp-content/uploads/RMS-01.png




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If Im be the average ac then charge carried by it in half cycle is

Now from equation iii and iv we get






value of AC ||

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Similarly the average value of ac over negative half cycle (t = T/2 to t = T) is

Therefore the average ac over a complete cycle is zero.

Similarly the average value of alternating emf over a half cycle is

Form Factor

It is defined as the ratio, Kf =𝑟𝑚𝑠 𝑣𝑎𝑙𝑢𝑒𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑣𝑎𝑙𝑢𝑒

=0.707𝐼𝑚0.637𝐼𝑚=1.11 (for sinusoidal alternating currents only)

As is clear, the knowledge of form factor will enable the r.m.s. value to be found from the

arithmetic

mean value and vice-versa.

Crest or Peak or Amplitude Factor

It is defined as the ratio Ka = 𝑚𝑎𝑥𝑖𝑚𝑢𝑚 𝑣𝑎𝑙𝑢𝑒𝑟𝑚𝑠 𝑣𝑎𝑙𝑢𝑒 =

𝐼𝑚𝐼𝑚/√2

= √2 = 1.414

(for sinusoidal a.c. only)

Ac through Resistor Only




https://notes.tyrocity.com/wp-content/uploads/ac-through-resistor-only.png



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Let an alternating emf be applied to a circuit containing resistor R only such type of circuit is

called resistive circuit.

Let the emf applied to the circuit is

Let I be the current in the circuit then potential difference across the resistor is

Comparing

with ohm’s law, we see that current is equal to voltage/resistance

This means the resistance R is resistance for ac which is in fact the resistance for dc.

Therefore the behavior of R is same for ac and dc.

Ac through inductor only

Let an alternating emf be applied to a circuit containing inductor only such type of circuit is

called inductive circuit.


https://notes.tyrocity.com/wp-content/uploads/ac-through-resistor-only1.png



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then the induced emf across the inductor is

This emf opposes the growth of current in the circuit.

Applying kirchhoff’s voltage law in the loop of fig a

integrating above expression we get

This is the form of alternating current developed in the purely inductive circuit. equation i

and ii shows that in a purely inductive circuit alternating emf leads the alternating current by

π/2

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Ac through Capacitor

Let an alternating emf be applied to a circuit containing capacitor only such type of circuit is

called capacitive circuit.


Let q be the charge in the capacitor of capacitance C then the potential developed in the

capacitor is

Equation ii is the type of current developed in the purely capacitive circuit.

Comparing equation i and ii we see that the alternating current leads to the alternating emf by

π/2 as shown in fig.

https://notes.tyrocity.com/wp-content/uploads/ac-through-capacitor-only.png

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Ac through resistor and inductor

Let a pure inductance and a pure resistance be connected in series to an alternating emf. Let

Ebe the rms value of applied emf and I be the rms value of the current flowing in the circuit.

Let VR and VL be the potential drop across R and L respectively.

The potential drop across inductor is

The potential drop across resistance is

Since the potential leads the current by π/2 phase in inductive circuit so the potential has been represented by OB at π/2 of OA

Since the potential and the current are in the same phase in case of resistive circuit so they

have been represented by the same line OA.

From the fig the resultant OH is given by

https://notes.tyrocity.com/wp-content/uploads/ac-through-resistor-and-inductor.png

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This is the effective opposition offered by LR circuit for the flow of current.

Also

This shows that the potential leads the current by π/2 in LR circuit.

Since the potential lags the current by π/2 phase in case of capacitor circuit so the potential has been represented by OA at π/2 of OB

Since the potential and the current are in the same phase in case of resistive circuit so they

have been represented by the same line OB.





value of AC ||

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AC through resistor and capacitor

Let a pure resistor and a pure capacitor be connected in series to an alternating emf. Let E be

the rms value of applied emf and I be the rms value of the current flowing in the circuit. Let

VR and VC be the potential drop across R and C respectively.

The potential drop across capacitor is



https://notes.tyrocity.com/wp-content/uploads/ac-through-resistor-and-capacitor.png

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value of AC ||

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This is the effective opposition offered by RC circuit for the flow of current.

Also

This shows that the potential lags the current by π/2 in RC circuit.





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AC through inductor, capacitor and resistor:

A pure inductor, an ideal capacitor and a pure resistor are connected in series to an alternating

current source. Since the components are connected in series,same current flows across each

of them while each of them suffer different potential drop.

Let E be the rms value of applied emf and I be the rms value of the current flowing in the

circuit. Let VL , VC and VR be the potential drop across L, C and R respectively.

The potential drop across inductor is

The potential drop across capacitor is



https://notes.tyrocity.com/wp-content/uploads/AC-through-inductor-capacitor-and-resistor.png

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This is the3 impedance of LCR circuit. It is the effective opposition offered by LCR circuit

for the flow of current.

Also

Power and Power factor

Real Power: (P)

Alternative words used for Real Power (Actual Power, True Power, Watt-full Power, Useful

Power, Real Power, and Active Power)





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In a DC Circuit, power supply to the DC load is simply the product of Voltage across the load

and Current flowing through it i.e., P = V I. because in DC Circuits, there is no concept of

phase angle between current and voltage. In other words, there is no Power factor in DC

Circuits.

But the situation is Sinusoidal or AC Circuits is more complex because of phase difference

between Current and Voltage.

Therefore average value of power (Real Power) is P = VI Cosθ is in fact supplied to the

load.

Reactive Power: (Q)

Also known as (Use-less Power, Watt less Power)

The powers that continuously bounce back and forth between source and load is known as

reactive Power (Q) Power merely absorbed and returned in load due to its reactive properties

is referred to as reactive power. The unit of Active or Real power is Watt where 1W = 1V x 1

A. Reactive power represent that the energy is first stored and then released in the form of

magnetic field or electrostatic field in case of inductor and capacitor respectively.

Reactive power is given by Q = V I Sinθ which can be positive (+ve) for inductive, negative

(-Ve) for capacitive load.

The unit of reactive power is Volt-Ampere reactive. I.e. VAR where 1 VAR = 1V x 1A. In

more simple words, in Inductor or Capacitor, how much magnetic or electric field made by

1A x 1V is called the unit of reactive power.

Apparent Power: (S)

The product of voltage and current if and only if the phase angle differences between current

and voltage are ignored. Total power in an AC circuit, both dissipated and absorbed/returned

is referred to as apparent power The combination of reactive power and true power is called

apparent power

In an AC circuit, the product of the r.m.s voltage and the r.m.s current is called apparent

power. It is the product of Voltage and Current without phase angle The unit of Apparent

power (S) VA i.e. 1VA = 1V x 1A. When the circuit is pure resistive, then apparent power is

equal to real or true power, but in inductive or capacitive circuit, (when Reactances exist)

then apparent power is greater than real or true power. S = V I

http://electricaltechnology.org/?p=117



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Power Triangle

Power factor, cos(θ) , cosine angle between voltage and current

cos(θ)= 𝑃(𝐴𝑐𝑡𝑖𝑣𝑒 𝑃𝑜𝑤𝑒𝑟)𝑆(𝐴𝑝𝑝𝑎𝑟𝑎𝑛𝑡 𝑃𝑜𝑤𝑒𝑟), unit less

Impedance Triangle

Where R=Resistance in Ohm, XL=Inductive Reactance in Ohm

Xc=Capacitive Reactance in ohm

Power factor, cos(θ) , cosine angle between voltage and current

cos(θ)= 𝑅𝑍, unit less




CHAPTER 03

GENERATION OF ELECTRICAL POWER

Hydro-electric Power Station

A power generation station which uses the potential or kinetic energy of water for the

generation of an electrical energy is called hydro-electric power station.

Water has a kinetic energy when it is in motion. While the water stored at high level has

a potential energy. The difference in level of water between the two points is called head.

Such a water head is practically created by constructing reservoirs across river or lake.

Generally a dam is constructed at high altitudes, which can be used as a continuous source of

the water for the hydro-electric power stations. The water from the dam is taken through

pipes and canals to the water turbine, which is at lower level. The turbine obtains the energy

from the falling water and changes it into a mechanical energy. This mechanical energy of the

turbine is then used to drive the alternator, which converts the mechanical energy into an

electrical energy. The energy conversion involved in hydro-electric power generation is

shown in the Fig. 1.

Fig.3. 1 Energy conversion

3.1.Factors for Selection of Site

The water reservoir like dam can not be constructed anywhere. There are number of

factors of affecting the choice of site for the hydroelectric power station.

1. Availability of water : As the basic requirement of hydro-electric plant is the water, the

availability of huge quantity of water is the main consideration. The plant must be

constructed where sufficient quantity of water is available at a good head. The previous

rainfall records are studied and the maximum and minimum quantity of water available

during the year estimated. Considering the losses such as evaporation, the water necessary for

the plant is calculated. Then by comparing both the estimations, the choice of the site is done.

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2. Storage of water : The rainfall is not consistent every year. Hence the available water

should be stored. This makes necessary to construct dams. The storage helps in equalizing the

flow of water throughout the year. So site should be provide sufficient facilities for erecting

dam and the storage of water.

3. Head of water : For getting sufficient head, the dam or reservoir should be constructed at

a height in a hilly area. The availability of the head directly affects the cost and economy of

the power generation. So site should be selected in proper geographical area, which can give

sufficient water head.

4. Cost and type of land : The initial cost of the project includes the cost of the land. Hence

land must be available at a reasonable price. Similarly the type of the land must be such that

it should able to withstand the weight of the heavy equipments to be installed.

5. Transportation facilities : For transporting the equipments and the machinery, the site

selected must be easily accessible by rail and road.

6. Distance from load centers : The load center is connected to the site by the transmission

lines. Hence to keep the cost of the transmission lines minimum and the losses occurring in

the line minimum, the distance of the site from the load centers must be less. Otherwise the

overall cost increases considerably.

All these factors affect the selection of site for the hydro-electric power station.

General Arrangement of Hydro-electric Plant

Though hydro-electric power station simply involves the conversion of hydraulic energy

to the mechanical energy, it requires many types of supporting arrangements. The Fig. 2

shows the schematic arrangement of hydro-electric power station which uses water supply

from an artificially constructed dam.

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Fig. 3.2 Schematic arrangement of hydro-electric power plant

The dam is constructed across the river and water from catchment area is collected

behind the wall of the dam, in high mountains. A pressure channel is taken from such a water

reservoir which takes water to a surge tank. The surge tank is a controlling room which

controls the flow of water i.e. adjusts the discharge of water according to the need of the

turbine and load on it. Trash rack does not allow floating and other impurities to pass to the

turbine. The pressure channels plays a very important role. It relieves the pressure on the

penstocks when the turbine valves are open or closed suddenly. The water is then taken to a

valve house from where the penstocks start. The valve house contains main sluice valve and

the automatic isolating valves. These valves also regulate the flow of water to the power

house and isolates the supply of water if there is any emergency such as bursting of a

penstock. Through the penstocks, the water is taken to the power house which consists of

turbine and the alternator. The penstock are nothing but the steel pipes which are arranged in

the form of open or closed conduits, supported by the anchor blocks.

When the water from the penstock is hammered through a nozzle, on the turbine blades,

the turbine starts rotating. At this stage the hydraulic energy is converted to a mechanical

energy. The turbine drives the alternator which is coupled to the shaft of the turbine. The

alternator converts the mechanical energy into an electrical energy. This electrical energy is

then transmitted to the load centers. The water collected from the turbine is called tail race.

This tail race is then taken off to the river.

3.2. Constituents of Hydro-electric Power Station

Let us discuss the constituent and their functions in the operation of the hydroelectric

power station.

Dam

The water reservoir in the form of a dam is the main part of the power station. It stores

the water, provides the continuous supply of water and maintains the necessary water head.

The dams are built up of stones and concrete. The design and type of the dam us selected

according to the topography of the site and economical aspects.

Spillways

There are certain times when the river flow exceeds the storage capacity of the dam, due

to the heavy rainfall. The spillways are provided to discharge this surplus water and maintain

safe water level in the dam.

Surge Tank

This is an important projecting device in a hydro-electric power plant. It is built just

before the valve house. It protects the penstocks from bursting due to sudden pressure

changes.

If the load on the turbine is thrown off suddenly then by the governing action, the turbine

input gates get suddenly closed. Thus there is sudden stopping of water at the lower end of

the penstock. This time the excess water at the lower end of the penstock, rushes back to the

surge tank. The surge tank water level increases. Thus the penstock is protected from bursting

due to high pressure. The surge tank absorbs this high pressure swing by increasing its water

level.



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On the other hand, when the load on the turbine suddenly increases, the additional water

required is drawn from the surge tank. This satisfies the increased water demand instantly.

Thus the surge tank controls the pressure changes created due to rapid changes in the

water flow in penstock and hence protects the penstock from water hammer effects which

might burst the penstock.

Penstocks

The penstocks are made up of steel or concrete and arranged in the form of conduits,

supported by the anchor blocks. The penstocks are used to carry water to the turbine. For the

low head (less than 30 m) power stations, the concrete penstocks are used. The steel

penstocks are suitable for any head.

Fig.3. 3 Protecting devices of penstock

There are certain protective devices attached to the penstocks. These devices are shown

in the Fig.3.3.

The automatic butterfly valve completely shuts off the water flow if the penstock bursts.

The air valve maintains the air pressure inside the penstock equal to the outside

atmospheric pressure.

The anchor block supports the penstock and holds it in the proper position.

The surge tank also protects the penstock from sudden pressure changes.

3.3.5 Water Turbines

The main two types of water turbines are,

i) Impulse and ii) Reaction

In an impulse turbine, the entire pressure of water is converted into a kinetic energy in a

nozzle. Then the water jet is forced on the turbine which a large velocity which drives the

wheel. The pelton wheel is an example of impulse turbine which is shown in the Fig. 3.4.

Fig. 3.4 Impulse turbine

It contains elliptical buckets mounted on the periphery of a wheel. The force of water jet

on the buckets, drives the wheel and the turbine. There is a needle or spare at the tip of the

nozzle. The governor controls the needle which controls the force of the jet, according to the

load demand. The impulse turbines are used for the high head power stations.

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In the reaction turbines, the water enters the runner, partly with pressure and partly with

velocity head. There are two type of reaction turbines.

i) Francis and ii) Kalpan

The Fig.3. 5 shows the basic principle of reaction turbine. The reaction turbine consists

of an outer ring of stationary guided blades and an inner ring of rotating blades. The guided

blades control the flow of water to the turbine. Water flows radially inwards and changes to a

downward direction when it passes through the rotating blades. While passing over the

rotating blades, the pressure and velocity of water are decreased. This causes reaction force to

exist which drives the turbine. For large variation of head, Kalpan is used as its efficiency

does not vary with change in load. For fairly constant head, a Francis or propeller turbine is

used.

The reaction turbines are used for the low head power stations.

Fig.3. 5 Reaction turbine

Advantages

1. If the proper site is selected, the continuous water supply is available.

2. Requires no fuel as water is used.

3. No burning of fuel hence neat and clean site as no smoke or ash is produced.

4. It does not pollute the atmosphere.

5. The operating cost is very low as free water supply is available.

6. The turbines in this plants can be switched on and off in a very short period of time.

7. It is relatively simple in construction, self contained in operation and requires less

maintenance.

8. It is robust and has very long life.

9. It gives high efficiency over a considerable range of load. This improves the overall system

efficiency.

10. It provides the additional benefits like irrigation, food control, afforestation etc.

11. Being simple in design and operation, highly skilled workers are not necessary for the

daily operation. Thus man power requirements is low.

3.5 Disadvantaes

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1. Due to the construction of dam, very high capital cost.

2. The low rate of return.

3. Uncertainity of availability of water due to unpredictable rainfall.

4. As its location is in hilly areas and mountains, the long transmission lines are necessary for

the transmission of generated electrical energy. This requires high cost.

5. The large power stations disturb the ecology of the area by the way of disforestation,

destroying vegetation and uprooting people.

6. Highly skilled and experienced persons are necessary at the time of construction.

Steam Power Station

A generating station which converts the heat energy of local combustion into an electrical

energy is called steam or thermal power station.

In this power station, the steam is produced in the boiler by using the heat of the cool

combustion. The steam is then expanded in steam turbine which drives the alternator which

converts the mechanical energy of the turbine into an electrical energy. The exhaust steam

gets condensed in the condenser and fed back into the boiler again, completing the cycle of

the power station. This principle is called Rankine cycle.

The energy conversion involved in steam power station is shown in the Fig. 1.

Fig. 1 Energy conversion

Factors of Selection of Site

The following factors are to be considered for the selection of site for the steam power

station, in order to achieve the economical and successful operation of the plant.

1. Supply of fuel : The main fuel for the steam power plant is coal. Thus the power station

should be located near the coal mine so that the fuel supply is continuous and adequate. If the

plant is located away from the coal mine then sufficient transportation facility must be

available.

2. Availability of Water : For the condenser, huge amount of water is required. Hence site

must near be the river so that abundant quantity of cooling water is available.

3. Transportation facilities : For transporting the equipments and the machinery required by

a modern steam power plant, he site selected must be easily accessible by rail and road.

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4. Cost and type of land : The land must be available at a reasonable price to keep the initial

cost low. There must be provision for the extension of the plant. The type of the land must be

such that it should be able to withstand the weight of the heavy equipments to be installed.

5. Distance from load centers : To keep the cost of the transmission and transmission losses

to minimum, the site must be nearer to the load centers. For d.c. system, transmission loss

plays an important role but a.c. power can be transmitted at high voltage with reduced

transmission cost. Thus this factor is more important for d.c. supply system.

6. Distance from populated area : The continuous burning of coal at the power station

produces smoke, Fumes and ash, which pollutes the surrounding area. Such a pollution due to

smoke is dangerous for the people living around. Hence the site of the plant must be at a

considerable distance from the populated area.

All these factories affect the selection of site for the steam power station.

General Arrangement of Steam Power Plant

Though steam power plant simply involves the conversion of heat energy to the

mechanical energy, it requires many types of supporting arrangements. The Fig. 2 shows the

schematic arrangement of steam power station.

The coal is burnt in a place called grate in a boiler. The flue gases are evolved which

heats the water in a boiler. The water is converted to a steam by absorbing heat from the flue

gases. This steam is called wet steam as it contains suspended water particles. This steam is

passed to the superheater where it is converted to superheated steam from the wet steam. This

superheated steam is then expanded in the turbine which rotates the turbine. Thus the heat

energy is converted to a mechanical energy. The turbine shaft is coupled to an alternator

which converts the mechanical energy into an electrical energy. This is then given to the

busbar through a transformer and proper switchgear arrangement.

After expanding in the turbine, the exhaust steam is passed through the condenser. In the

condenser, the steam is converted into liquid condensate. Using the condensate extraction

pump, the condensate is taken to economizer. The economiser again transfer the heat from

flue gases to the condensate and then transfer the heated water to the boiler. Thus the cycle is

completed. The exhaust flue gases are released to the atmosphere through the chimney.

Constituents of Steam Power Station

The various constituents of steam power station can be divided into the following stages

for the ease of understanding the working of the power plant.

1. Fuel and ash circuit 2. Steam generating circuit

3. Steam turbine 4. Alternator

5. Feed water circuit 6. Cooing water circuit



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Fig 2 Schematic arrangement of steam power station

1.3.1 Fuel and Ash Circuit

In steam power plant, the coal is used as a fuel. The coal is stored in a coal storage plant

where coal is transferred from all the parts of the country by the rail or the road. The storage

helps to supply the coal continuously, in case of situations like strikes, failure of

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transportation system etc. Then the coal is transferred to the coal handling plant where the

coal is pulverized i.e. crushed into small pieces. The pulverization increases the surface

exposure of the coal and this helps for rapid combustion of coal without using large quantity

of air. Such a crushed coal is transferred to the boiler from the local handling plant.

As a result of combustion of the coal. large quantity of ash is produced in the boiler. For

the proper combustion of the coal, ash is removed to the ash handling plant. Then it is

delivered to the ash storage plant, from where it is disposed off.

1.3.2 Steam Generating Circuit

The main component of steam generating circuit is the boiler. But many other auxiliary

equipments are used so as to completely utilize the heat of flue gases.

1. Boiler : The boiler is a closed vessel where water is converted to the steam using the heat

of the local combustion. Hence the boiler is called steam generator. In the boilers, the grate is

provided for the combustion of coal. The steam produced in the boiler contains suspended

water particles and hence called wet steam.

2. Superheater : It is an accessory attached to the boiler and located in the path of flue gases

leaving the boiler and flowing towards chimney. By using the heat of the flue gases, the

superheater converts the wet steam into superheated dry steam. There are two advantages of

superheating that it increases the overall efficiency and it avoids the corrosion of the turbine

blades due to wet steam. The superheated steam is then passed to the turbine through a main

valve between the two. The two types of superheaters used are radiant type and convection

type.

3. Economizer : It is another accessory attached to the boiler and located in the path of flue

gases. Thus it utilizes the heat of flue gases which would otherwise wasted to the atmosphere.

The water from the feed pump is passed through the economizer to the boiler drum so that

before entering the boiler, it is heated and hence less efforts are required to convert it into

steam. This increases the overall boiler efficiency, saves the fuel and reduces the stress on the

boiler.

4. Air preheater : This is also an accessory attached to the boiler and located in the path of

flue gases. The air is required for the local combustion. Air is drawn from the atmosphere by

a forced draught fan and is supplied to the air preheater. The air preheater extracts the heat

from the flue gases and makes the air hot before supplying to the boiler. This increases the

temperature of the furnace and helps in the production of the steam. This increases the

thermal efficiency and the steam capacity per square meter of the boiler surface.

The two types of air preheaters used are recuperative type and the other is regenerative

type.

1.3.3 Steam Turbines

The dry and superheated steam from the supeheater is supplied to the turbine. The hat

energy of the steam is converted to the mechanically energy as steam passes over the turbine

blades. There are two types of steam prime movers available, steam engine and steam

turbine. The steam turbine is practically used because of the following advantages,

i) High efficiency ii) Simple construction iii) Low maintenance

iv) High speed v) Less floor area vi) No flywheel required

vii) Less problems of vibrations

The steam turbines are classified into two types as impulse turbine and reaction turbine.

In the impulse turbine, the steams expands completely in the nozzle and pressure over the

moving blades remaining constant. While doing so, the steam attains very high velocity and



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impacts on moving blades giving rise to an impulsive force on them. Thus the turbines starts

rotating.

In the reaction turbine, steam is partially expanded in the stationary nozzle and

remaining expansion takes place on the moving blades. This causes reaction force on the

moving blades and the turbine stats rotating.

The commercial turbines nowadays use series combination of impulse and reaction

turbines, due to which steam can be used more efficiently.

1.3.4 Alternator

The alternator shaft is coupled to the turbine. When the turbine shaft rotates, the

alternator shaft rotates and converts the mechanical energy into an electrical energy. The

electrical energy from the alternator is given to the busbar through transformer, circuit

breakers and isolators.

1.3.5 Feed Water Circuit

The condensate leaving the condenser is used as the feed water. Because it goes to the

boiler, It is first heated in a closed feed water heater. Then it is passed to economizer where it

is further heated and then passed to the boiler. This increases the overall efficiency of the

plant.

The feed water source is generally river or a canal. It contains suspended and dissolved

impurities. The boilers needs clean and soft water for loner life and better efficiency. Hence

the feed water is purified. It is stored in the tanks and by the different actions like

sedimentation, filtration etc., it is made soft and pure. Such a pure feed water is used for the

steam generation in the boiler.

1.3.6 Cooling Water Circuit

For improving the plant efficiency, the expanded steam coming out of the turbine,

passes through the condenser where it is condensed into water. The condenser is very

important as it creases a very low pressure at the exhaust of the turbine thus helps in the

expansion of steam in the turbine at low pressure.

For condensation of steam, a flow of natural cold water is circulated through the

condenser. This takes the heat from the exhaust steam and gets heated. This hot water is

discharged at a suitable location or is passed through a cooling tower so that it is again

converted to cold water. Then it is recirculated through the condenser by a pump. The

condensed steam can be used as a feed water to the boiler.

The two types of condensers used are jet condenser and surface condenser.

Advantages

1. The fuel used is a coal, which is cheap.

2. The initial cost is less compared to other power station.

3. It requires less floor space area compared to hydro-electric power station.

4. The fuel is easily available.

5. The fuel can be easily transported top the site hence site can be anywhere ad not always

near the coal mines.

6. The cost of the generation is less than the diesel.

Disadvantages



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1. Due to the smoke and fume, pollutes the surrounding atmosphere.

2. Running cost is higher than hydro-electric power palnt

3.11. Efficiency

For a steam power station, two efficiencies are defined which are thermal efficiency and

the overall efficiency.

The thermal efficiency is the ratio of heat equivalent of the mechanical energy

transmitted to the turbine shaft to the heat of the combustion of coal.

The overall efficiency is the ratio of heat equivalent of electrical output from alternator to

the heat of coal combustion. The overall efficiency pf steam power station is very low about

20 to 25%.

The overall efficiency depends on number of factors and hence can be expressed as,

Where,

ηelectrical = Electrical efficiency of an alternator which is practically high, above 90%.

ηboiler = Boiler efficiency considering the effect of economizer and air preheater, which is

about 85%.

Nuclear Power Station A generating station which converts the nuclear energy into an electrical energy is called

nuclear power station.

In such a power station, heavy radioactive elements like uranium (U235

), Thorium

(Th232

), are subjected to the nuclear fission. The fission is breaking of nucleus of heavy atom

into the parts by bombarding neutrons. This is carried out in a special nuclear reactor. During

the nuclear fission, huge amount of energy is released.

The heat energy that released is used in rising the steam at high pressure and

temperature. The steam turbines are operated using the high temperature steam. The turbines

converts the heat energy into a mechanical energy. The turbine drives the alternator which

converts mechanical energy into an electrical energy.

The energy conversion involved in the nuclear power station is shown in the Fig.1.

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Conversion of Nuclear Energy

According to Einstein's hypothesis, the relation between the energy released by the

nuclear reaction of the mass given by,

E = mc2

where E = Energy released in jouls

m = Actual mass converted into energy in kg

c = Velocity of light = 3 x 108

m/s

There are three types of nuclear reaction, radioactive decay, fission and fusion. Out of

this, only fission is used to produce the energy.

The fission reaction is achieved by bombarding an electrically neutral neutron, on the

positively charged nucleus of radioactive element. This results in the sustained reaction to

release two or three neurons for eacj one absorbed in fission.

The immediate products of fission reaction such as xenon (Xe140

) and strontim (Sr94

) are

fission fragments and are the decay products. The complete fission of 1 gm of U235

nucleus

produces 0.948 MW energy per day.

Factors selection of site

The following factors are to be considered for the selection of site for the nuclear power

station.

1. Availability of water : Water is a secondary working fluid and used as a coolant for the

cooling purpose, in the nuclear power station. A huge amount of water is necessary for this

purpose. Hence site must be near the river or canal so that abundant quantity of cooling water

is availabe.

2. Disposal of waste : The immediate products of fission reaction are the waste products

which are radioactive in nature. These can cause problems to the health of the people and

hence must be disposal quickly. Such a waste is either burried in deep pits or disposal off in

the sea. Hence the site should be selected so that their is sufficient arrangement for disposal

of such radioactive waste products.

3. Distance from populated area : The radioactive elements are hazardous to the health of

the people around. There is always danger of presence of radioactivity in the atmosphere near

the plant. Hence as a safety measure the site itself must selected to far away from the

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populated area. Practically a dome is used in the plant, which restricts radioactivity to spread

in the atmosphere.

4. Transportation facilities : For transporting the equipments and the machinery required,

there must be adequate transportation facilities. The site must accessible by a rail or road so

that it is easy for the movement of the workers, working in the plant.

5. Nearness to the load centres : Though the site should be away from the populated area

near the river or sea, it should not be too large distance, due to which transmission cost may

increase tremendously.

6. Cost and type of land : The land price must be reasonable and the bearing capacity of the

land should be good enough to withstand the forces due to heavy equipments of the plant.

All these factors affects the selection of site for the nuclear power station.

General Arrangement of Nuclear Power Plant

The Fig. 2 shows the schematic arrangement of a nuclear power plant.

The entire arrangement can be divided into following stages.

1.Nuclear reactor 2. Heat exchange (Steam generator)

3. Steam turbine 4. Alternator 5. Cooling water circuit.



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Fig.2 Schematic arrangement of nuclear power station

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3.15 Nuclear Reactor This represents that part of a nuclear power plant where U fuel is subjected to a

controlled fission chain reaction, during which tremendously energy is generated.

The Fig. 3 shows the various components of a nuclear reactor and a heat exchanger.

The following are the components of the nuclear reactor.

Fig. 3 Nuclear reactor and heat exchanger

1. Fuel : The commonly used fuel is uranium containing 0.7 % U235

or enriched uranium

containing 1.5 - 2.5 U235

. The fuel is used in the form of rods or plates which are surrounded

by the moderators. The fuel rods are arranged in cluster and the entire assembly is called

core. The minimum amount of the fuel required to maintain the chain reaction is called the

critical mass.

2. Moderators : The main function of the moderators is to reduce the energy of neutrons

evolved during fission. By slowing down the high energy neutron, the possibility of escape of

neutrons is reduced while possibility of absorption of neutrons by fuel to cause further fission

is increased. This also educes the amount of fuel required for the chain reaction. The

commonly used moderators are graphite, beryllium and heavy water. Some other functions of

moderators include prevention of corrosion of fuel element, retain the radioactivity and to

provide structural support.

3. Reflector : The reflector is placed around the core to reflect back some of the neutrons

which may leak out from the surface of the core, without taking part in the fission. A blancket

of reflector can reduce the critical mass required.

4. Control rods : The cadmium rods are used as control rods which are strong neutron

absorber. Thus control rods can regulate the supply of neutrons for chain reaction. If the

number of neutrons are not controlled, there is a possibility of explosion due to large amount

of energy released. By pushing or pulling out of these rods, the rate of chain reaction and

hence the heat produced can be controlled. The control rods are operated automatically as per

the next requirement. The other material used for the control rods is boron or hafinium.

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5. Coolant : The main purpose of the coolant is to transfer heat generated in the reactor core

and use it for the system generation. he coolant in the reactor keeps the temperature of fuel

below safe level by continuous removable of the energy from the core. The liquid metals like

sodium or potassium are used as coolants.

6. Radiation shield : The radiation of a radioactive substances are harmful to the human life.

Hence radiation shield is used to prevent the escape of these radiations to the atmosphere.

Generally 50 to 60 cm thick steel plate and few meters of the concrete outside are used as the

radiation shield.

1.5 Heat exchanger

It is a device which is used to exchange the heat from the primary circuit to the

secondary circuit. The coolant carries the heat in the reactor to the exchanger where it is

exchanged to the water, to convert water to steam. Thus the heat exchanger is nothing but a

steam generator. Once the heat exchanged, the coolant is fed back to the reactor, using the

coolant recirculating pump.

1.6 Steam turbine

The steam generated from the water in the secondary circuit is taken to the steam turbine

through a main valve, where it is expanded. Due to this, turbine starts rotating and thus the

heat energy is converted to a mechanical energy.

1.7 Alternator

The shaft of an alternator is coupled to the turbine shaft. Thus when the turbine rotates,

the alternator starts rotating. The alternator converts mechanical energy into an electrical

energy. The energy output of an alternator is given to the bus bars through transformer,

circuit breakers and isolators.

1.8 Cooling Water Circuit

The expanded steam from the turbine is the exhausted steam which is taken to the

condenser. In the condenser, the steam is condensed into water. For the condensation of

steam , a flow of natural cold water is circulated through the condenser. This water takes heat

from the exhaust steam. This hot water is passed through cooling tower, where it is again

converted to cold water. The it is recirculated through the condenser by pump. The condensed

steam is then recirculated through the secondary circuit of exchanger, using the feed water

pump.

3.16 Advantages

1. The amount of fuel required is very small

2. Three is saving in the transportation cost of fuel as fuel required is less.

3. It requires less space compared to any other type of the power plant.

4. The running cost per unit energy generated is lower than the thermal power plant.

5. It is very much economical.

6. There is a lake of environmental problems which are associated with the thermal power

plant.

7. Large deposits of nuclear fuels are available so such plants can ensure continued supply of

the fuel.

8. It ensures reliability of the operation.


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3.17. Disadvantages 1. The fuel is very expensive.

2. The fuel is difficult to recover.

3. The capital cost is very high compared to other types.

4. The waste products are radioactive and can cause pollution.

5. The waste disposal problem is severe.

6. The maintenance charges are very high.

7. It is not suitable for the varying load conditions, as the reactor can not respond instantly to

the load fluctuations.

8. The fuel may be misused in weapons.




CHAPTER 04

CONVERSION OF ELECTRICAL ENERGY

Introduction A motor is a device which converts an electrical energy into the mechanical energy . The

energy conversion process is exactly opposite to that involved in a d.c. generator. In a

generator the input mechanical energy is supplied by a prime mover while in a d.c. motor,

input electrical energy is supplied by a d.c. supply. The construction of a d.c. machine is

same whether it is a motor or a generator.

Fleming's Right Hnad Rule

If three fingers of a right hand, namely thumb, index finger and middle finger are

outstretched so that every one of them is at right angles with the remaining two, and if this

position index finger is made to point in the direction of lines of flux, thumb in the direction

of the relative motion of the conductor with respect to flux then the outstretched middle

finger gives the direction of the e.m.f. induced in the conductor. Visually the rule can be

represented as shown in the Fig.1.

Fig. 1

This rule mainly gives direction of current which induced e.m.f. in conductor will set up

when closed path is provided to it and used for DC Generator

The principle of operation of a d.c. motor can be stated in a single statement as 'when a

current carrying conductor is placed in a magnetic field' it experiences a mechanical force'. In

a practical d.c. motor, field winding produces a required magnetic field while armature

conductors play a role of a current carrying conductors and hence armature conductors

experience a force. As a conductors are placed in the slots which are in the periphery, the

individual force experienced by the conductors acts as a twisting or turning force on the

armature which is called a torque. The torque is the product of force and the radius at which

this force acts. So overall armature experiences a torque and starts rotating

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Fleming's left hand rule

The rule states that, 'Outstretch the three fingers of the left hand namely the first finger,

middle finger and thumb such that they are mutually perpendicular to each other. Now point

the first finger in the direction of magnetic field and the middle finger in the direction of the

current then the thumb gives the direction of the force experienced by the conductor'.

The Fleming's left hand rule can be shown as in the Fig

Construction (parts) of a Practical D.C. Machine:

whether a machine is d.c. generator or a motor the construction basically remains the same as

shown in the Fig. 1.

It consists of the following parts :

1.1 Yoke

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a) Functions :

1. It serves the purpose of outermost cover of the d.c. machine. So that the insulating materials

get protected from harmful atmospheric elements like moisture, dust and various gases like

SO2, acidic fumes etc.

2. It provides mechanical support to the poles.

3. It forms a part of the magnetic circuit. It provides a path of low reluctance for magnetic flux.

The low reluctance path is important to avoid wastage of power to provide same flux. Large

current and hence the power is necessary if the path has high reluctance, to produce the same

flux.

b) Choice of Material : To provide low reluctance path, it must be made up of some magnetic

material. It is prepared by using cast iron because it is cheapest. For large machines rolled steel,

cast steel, silicon steel is used which provides high permeability i.e. low reluctance and gives

good mechanical strength.

1.2 Poles

Each pole is divided into two parts namely, I) Pole core and II) Pole shoe.

This is shown in the Fig. 2.

Fig. 2 Pole Structure

a) Functions of pole core and pole shoe :

1. Pole core basically carries a field winding which is necessary to produce the flux.

2. It directs the flux produced through air gap to armature core, to the next pole.

3. Pole shoe enlarges the area of armature core to come across the flux, which is necessary to

produce larger induced e.m.f. To achieve this, pole shoe has been given a particular shape.

b) Choice of Material : It is made up of magnetic material like cast iron or cast steel. As it

requires a definite shape and size, laminated construction is used. The laminations of required

size and shape are stamped together to get a pole which is then bolted to the yoke.

1.3 Field Winding (F1-F2)

The field winding is wound on the pole core with a definite direction.

a) Functions : To carry current due to which pole core, on which the field winding is placed

behaves as an electromagnet, producing necessary flux.

As it helps in producing the magnetic field i.e. exciting the pole as an electromagnet it is

called Field winding or Exciting winding.

b) Choice of material : It has to carry current hence obviously made up of some conducting

material. So aluminium or copper is the choice. But field coils are required to take any type of

shape and bend about pole core and copper has good pliability i.e. it can bend easily. So copper

is the proper choice.

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Note : Field winding is divided into various coils called field coils. These are connected in series

with each other and in such a direction around pole cores, such that alternate 'N' and 'S' poles are

formed.

By using right hand thumb rule for current carrying circular conductor, it can be easily

determined that how a particular core is going to behave as 'N' or 'S' for a particular winding

direction around it. The direction of winding and flux can be observed in the Fig 3.

Fig. 3

1.4 Armature

It is further divided into two parts namely,

I) Armature core and II) Armature winding

I) Armature core : Armature core is cylindrical in shape mounted on the shaft. It consists of

slots on its periphery and the air ducts to permit the air flow through armature which serves

cooling purpose.

a) Functions :

1. Armature core provides house for armature winding i.e. armature conductors.

2. To provide a path of low reluctance to the magnetic flux produced by the field winding.

b) Choice of Material : As it has to provide a low reluctance path to the flux, it is made up of

magnetic material like cast iron or cast steel.

It is made up of laminated construction to keep eddy current loss as low as possible. A single

circular lamination used for the construction of the armature core is shown in the Fig. 4.

Fig. 4 Single Circular lamination of Armature core

II) Armature winding : Armature winding is nothing but the interconnection of the armature

conductors, placed in the slots provided on the armature core periphery. When the armature is

rotated, in case of generator, magnetic flux gets cut by armature conductors and e.m.f. gets

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induced in them.

a) Functions :

1. Generation of e.m.f takes place in the armature winding in case of generators.

2. To carry the current supplied in case of d.c. motors.

3. To do the useful work in the external circuit.

b) Choice of material : As armature winding carries entire current which depends on external

load, it has to be made up of conducting material, which is copper.

Armature winding is generally former wound. The conductors are placed in the armature

slots which are lined with tough insulating material.

1.5 Commutator

We have seen earlier that the basic nature of e.m.f. induced in the armature conductors is

alternating. This needs rectification in case of d.c. generator, which is possible by a device called

commutator.

a) Functions :

1. To facilitate the collection of current from the armature conductors.

2. To convert internally developed alternating e.m.f. to unidirectional (d.c.) e.m.f.

3. To produce unidirectional torque in case of motors.

b) Choice of material : As it collects current from armature, it is also made up of copper

segments.

It is cylindrical in shape and is made up of wedge shaped segments of the hard drawn, high

conductivity copper. These segments are insulated from each other by thin layer of mica. Each

commutator segment is connected to the armature conductor by means of copper lug or strip.

This connection is shown in the Fig. 5.

Fig. 5 Commutator

1.6 Brushes and Brush Gear

Brushes are stationary and resting on the surface of the commutator.

a) Function : To collect current from commutator and make it available to the stationary external

circuit.

b) Choice of material : Brushes are normally made up of soft material like carbon.

Brushes are rectangular in shape. They are housed in brush holders, which are usually of box

type. The brushes are made to press on the commutator surface by means of a spring, whose

tension can be adjusted with the help of lever. A flexible copper conductor called pig tail is used

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to connect the brush to the external circuit. To avoid wear and tear of commutator, the brushes

are made up of soft material like carbon.

1.7 Bearings

Ball-bearings are usually used as they are more reliable. For heavy duty machines, roller

bearings are prederred.

Classification of DC Machines:

DC Machines

Separately Excited Self Excited

Series machine Shunt machine Compound machine

Short shunt Long shunt

compound compound

The d.c. Generator are classified depending upon the way of connecting the field winding

with the armature winding. The difference types of d.c. motors are ;

1. Shunt Generator

2. Series Generator

3. Compound Generator

The compound Generator are further classified as ;

1. Short shunt compound

2. Long shunt compound

Separately Excited Generator When the field winding is supplied from external, separate d.c. supply i.e. excitation of field

winding is separate then the generator is called separately excited generator. Schematic

representation of this type is shown in the Fig.1.

http://www.yourelectrichome.com/2012/08/separately-excited-generator.html

http://yourelectrichome.blogspot.com/2012/08/self-excited-generator.html

http://www.yourelectrichome.com/2012/08/separately-excited-generator.html




Shunt Generator

When the field winding is connected in parallel with the armature and the combination

across the load then the generator is called shunt generator.

The field winding has large number of turns of thin wire so it has high resistance. Let

Rsh be the resistance of the field winding.

Series Generators

When the field winding is connected in series with the armature winding while supplying the

load then the generator is called series generator. It is shown in the Fig. 1.

Field winding, in this case is denoted as S1 and S2. The resistance of series field winding

is very small and hence naturally it has less number of turns of thick cross-section wire as

shown in the Fig.

Fig. Series generator

http://www.yourelectrichome.com/2012/08/series-generators.html

http://3.bp.blogspot.com/-aCoyTzufddE/UD1QUtMFZOI/AAAAAAAAGY0/wEBNgeWdGPc/s1600/ccc190.jpeg

http://3.bp.blogspot.com/-pwNALtNukEE/UD6R4Vm-f6I/AAAAAAAAGbo/-a5yer6fHo4/s1600/ccc193.jpeg

http://4.bp.blogspot.com/-DAul-lHGZk0/UD6VTjbd2uI/AAAAAAAAGck/GACeIPdsAQc/s1600/ccc194.jpeg




Compound Generator In this type, the part of the field winding is connected in parallel with armature and part in

series with the armature. Both series and shunt field windings are mounted on the same poles.

Depending upon the connection of shunt and series field winding, compound generator is

further classified as : i) Long shunt compound generator, ii) Short shunt compound generator.

1.1 Long Shunt Compound Generator

In this type, shunt field winding is connected across the series combination of armature

and series field winding as shown in the Fig. 1.

Fig. 1 Long shunt compound generato

Short Shunt Compound Generator

In this type, shunt field winding is connected, only across the armature, excluding series

field winding as shown in the Fig. 2.

Fig. 2 Short shunt compound generator

Similar to the d.c. generators, the d.c. motors are classified depending upon the way of

connecting the field winding with the armature winding. The difference types of d.c. motors

are ;

1. Shunt motor

2. Series motors

3. Compound motors

The compound motors are further classified as ;

1. Short shunt compound

2. Long shunt compound

http://3.bp.blogspot.com/-HSee0rrbees/UD6rtS3JpRI/AAAAAAAAGdg/e80wzVcMJrU/s1600/ccc195.jpeg

http://2.bp.blogspot.com/-1J2-PwRSHGw/UD6turiFMTI/AAAAAAAAGdo/vwqQrtae1lQ/s1600/ccc196.jpeg




Applications of D.C. Motors

Applications of Various Types of Generators

Separately Excited Generators : As a separate supply is required to excite field, the use is restricted to some special

applications like electro-palting, electro-refining of materials etc.

Shunt Generators : Commonly used in battery charging and ordinary lighting purposes.

Series Generators : Commonly used as boosters on d.c. feeders, as a constant current generators for welding

generator and arc lamps.

Cumulatively Compound Generators : These are used for domestic lighting purposes and to transmit energy over long distance.

Differential Compound Generators : The of this type of generators is very rare and it is used for special application like

electric arc welding.

Types of Single Phase Induction Motors In practice some arrangement is provided in the single phase induction motors so as that the

stator flux produced becomes rotating type rather than the alternating type, which rotates in

particular direction only. So torque produced due to such rotating magnetic field is

http://www.yourelectrichome.com/2012/08/applications-of-various-types-of.html

http://www.yourelectrichome.com/2011/06/types-of-single-phase-induction-motors.html




unidirectional as there is no oppositely directed torque present. Hence under the influence of

rotating magnetic field in one direction, the induction motor becomes self starting. It rotates

in same direction as that of rotating magnetic field.

Thus depending upon the methods of producing rotating stator magnetic flux, the single

phase induction motors are classified as,

1. Split phase induction motor

2. Capacitor start induction motor

3. Capacitor start capacitor run induction motor

4. Shaded pole induction motor

Applications of single phase induction motors

Split phase motors have low starting current and moderate starting torque. These are used for

easily started loads like fans, blowers, grinders, centrifugal pumps, washing machines, oil

burners, office equipments etc. These are available in the range of 1/120 to 1/2 kW.

Capacitor starts induction motors have high starting torque and hence are used for hard

starting loads. These are used for compressors, conveyors, grinders, fans, blowers,

refrigerators, air conditions etc. These are most commonly used motors. The capacitor start

capacitor run motors are used in celling fans, blowers and air-circulations. These motors are

available upto 6 kW.

Shaded pole induction motor are cheap but have very low starting torque, low power factor

and low efficiency. These motors are commonly used for the small fans, by motors,

advertising displays, film projectors, record players, gramophones, hair dryers, photo copying

machines etc.

Light: Light is defined as the radiant energy from a hot body causing visual sensation upon the

human eye.

Concept of Lumen:

It is defined as the total quantity of light energy radiated or emitted per second from a

luminous body in the form of light waves




Different types of Lamps:

Filament(incandescent) bulb:

An incandescent bulb works on the principle of incandescence, a general term meaning light

produced by heat.

In an incandescent type of bulb, an electric current is passed through a thin metal filament,

heating the filament until it glows and produces light. Incandescent bulbs typically use a

tungsten filament because of tungsten’s high melting point. A tungsten filament inside a light

bulb can reach temperatures as high as 4,500 degrees Fahrenheit.

A glass enclosure, the glass “bulb”, prevents oxygen in the air from reaching the hot

filament.Without this glass covering and the vacuum it helps create, the filament would

overheat and oxidize in a matter or moments.

After the electricity has made its way through the tungsten filament, it goes down another

wire and out of the bulb via the metal portion at the side of the socket. It goes into the lamp or

fixture and out a neutral wire.

Fluorescent (Tube) lamp:

1. When power is applied to a tube light circuit, this voltage is not sufficient to ionize the gas

inside the main tube.

2.However, this power generates an electric potential across the contacts of small tube of

starter.

3.This electric field is large enough to ionize the gas inside the small tube and hence a current

flow in the two contacts through the ionized gas.

4.The heat generated due to the flow of current expands the bi-metallic plate towards the

other plate and within a few tenths of seconds, it touches the other plate. During the short the

voltage falls to zero. The bimetallic strip cools and pops back open, opening the circuit. In the

ballast the transformer had a magnetic field, when the circuit is cut the magnetic field

collapses and forms an 'inductive kick' from the ballast. Suddenly this kick of high voltage is




sent through the lamp and this starts the arc. If it didn't work, if the lamp is still too cold, then

the starter switch will light again and repeat the process.

Now the gas of the main tube gets ionized and current starts flowing through it. Thus the bi-

metallic plate of starter cools down re-opening the gap between the two contacts. This gap

will remain open until the tube light will start next time.

LED Bulb:

LEDs are diodes. A diode has a P-N junction across which charge carriers like electrons and

holes pass when current flows through the diode. When forward biased, the electrons from N

region flows to the P region and holes from P region towards N region. Some of the electrons

recombine with the holes at the junction and their energy is radiated outward. By proper

design using suitable materials like indium phosphide or gallium arsenide, we can create a

junction that radiates maximum energy as visible light. This is Light Emittng Diode.

The wavelength of the radiation and hence the colour of the light depends on the materials

used.

To create white light, the junction is designed to emit ultraviolet light. A coat of fluorescent

material absorbs this UV radiation and re-radiates it as white light.

Star rating of home appliances: These days, most major electrical appliances for the kitchen are sold with energy efficiency

labels (also called MEPS labels, short for Minimum Energy Performance Standards).

Refrigerators, ovens, microwaves and dishwashers are all required to carry a label that shows

a star rating, indicating an appliance's overall efficiency.

The idea behind these ratings is to make it as easy as possible for people to be able to

compare the real-world performance and efficiency of the products they're buying without

having to rely on manufacturers' claims or their own subjective calculations.




How do energy star ratings work?

The star system and labelling scheme is an easy way to figure out how energy efficient

different appliances will be when compared to other appliances of the same kind.

Under the current system, appliances with up to six stars are known as 'efficient' appliances,

while any more stars than that is enough for the appliance to win a "super efficient" label (see

picture). The maximum efficiency rating is a ten star rating, and appliances can also receive

half-star ratings (e.g. 5 1/2 stars).

In addition to the star ratings, each label will also list the overall estimated energy

consumption of the appliance in kWh, over the period of one year. Using this number, you

should be able to get a reasonable idea of how much the appliance will cost to run over the

course of a year.




CHAPTER 05

WIRING AND POWER BILLING

Different Types of Electrical Wiring Systems

The types of internal wiring usually used are

Cleat wiring

Wooden casing and capping wiring

CTS or TRS or PVC sheath wiring

Lead sheathed or metal sheathed wiring

Conduit wiring

There are additional types of conduit wiring according to Pipes installation (Where steel and

PVC pipes are used for wiring connection and installation).

Surface or open Conduit type

Recessed or concealed or underground type Conduit

1. Cleat Wiring

This system of wiring comprise of ordinary VIR or PVC insulated wires (occasionally,

sheathed and weather proof cable) braided and compounded held on walls or ceilings by

means of porcelain cleats, Plastic or wood. Cleat wiring system is a temporary wiring system

therefore it is not suitable for domestic premises. The use of cleat wiring system is over

nowadays.

Advantages of Cleat Wiring:

It is simple and cheap wiring system

Most suitable for temporary use i.e. under construction building or army camping

As the cables and wires of cleat wiring system is in open air, Therefore fault in cablescan

be seen and repair easily.

Cleat wiring system installation is easy and simple.

Customization can be easily done in this wiring system e.g. alteration and addition.

Inspection is easy and simple.

Disadvantages of Cleat Wiring:

Appearance is not so good.

Cleat wiring can’t be use for permanent use because, Sag may be occur after sometime of

the usage.

In this wiring system, the cables and wiring is in open air, therefore,

oil, Steam, humidity, smoke, rain, chemical and acidic effect may damage the cables and

wires.

https://www.electricaltechnology.org/2015/06/cable-faults-how-to-locate-faults-in-cables.html




it is not lasting wire system because of the weather effect , risk of fire and wear & tear.

it can be only used on 250/440 Volts on low temperature.

There is always a risk of fire and electric shock.

it can’t be used in important and sensitive location and places.

It is not lasting, reliable and sustainable wiring system.

2. Casing and Capping wiring

Casing and Capping wiring system was famous wiring system in the past but, it is considered

obsolete this days because of Conduit and sheathed wiring system. The cables used in this

kind of wiring were either VIR or PVC or any other approved insulated cables.

The cables were carried through the wooden casing enclosures. The casing is made up of a

strip of wood with parallel grooves cut length wise so as to accommodate VIR cables. The

grooves were made to separate opposite polarity. the capping (also made of wood) used to

cover the wires and cables installed and fitted in the casing.

Advantages of Casing Capping Wiring:

It is cheap wiring system as compared to sheathed and conduit wiring systems.

It is strong and long-lasting wiring system.

Customization can be easily done in this wiring system.

If Phase and Neutral wire is installed in separate slots, then repairing is easy.

Stay for long time in the field due to strong insulation of capping and casing..

It stays safe from oil, Steam, smoke and rain.

No risk of electric shock due to covered wires and cables in casing & capping.

Disadvantages Casing Capping Wiring:

There is a high risk of fire in casing & capping wiring system.

Not suitable in the acidic, alkalies and humidity conditions

Costly repairing and need more material.

Material can’t be found easily in the contemporary

White ants may damage the casing & capping of wood.

3. Batten Wiring (CTS or TRS)

Single core or double core or three core TRS cables with a circular oval shape cables are used

in this kind of wiring. Mostly, single core cables are preferred. TRS cables are chemical

proof, water proof, steam proof, but are slightly affected by lubricating oil. The TRS cables

are run on well seasoned and straight teak wood batten with at least a thickness of 10mm.

The cables are held on the wooden batten by means of tinned brass link clips (buckle clip)

already fixed on the batten with brass pins and spaced at an interval of 10cm for horizontal

runs and 15cm for vertical runs.

Advantages of Batten Wiring

Wiring installation is simple and easy

cheap as compared to other electrical wiring systems

Paraphrase is good and beautiful

Repairing is easy




strong and long-lasting

Customization can be easily done in this wiring system.

less chance of leakage current in batten wiring system

Disadvantages of Batten Wiring

Can’t be install in the humidity, Chemical effects, open and outdoor areas.

High risk of firs

Not safe from external wear & tear and weather effects (because, the wires are openly

visible to heat, dust, steam and smoke.

Heavy wires can’t be used in batten wiring system.

Only suitable below then 250V.

Need more cables and wires.

4. Lead Sheathed Wiring

The type of wiring employs conductors that are insulated with VIR and covered with an outer

sheath of lead aluminum alloy containing about 95% of lead. The metal sheath given

protection to cables from mechanical damage, moisture and atmospheric corrosion.

The whole lead covering is made electrically continuous and is connected to earth at the point

of entry to protect against electrolytic action due to leaking current and to provide safety in

case the sheath becomes alive. The cables are run on wooden batten and fixed by means of

link clips just as in TRS wiring.

5. Conduit Wiring There are two additional types of conduit wiring according to pipe installation

1. Surface Conduit Wiring

2. Concealed Conduit Wiring

5.1 Surface Conduit Wiring

If conduits installed on roof or wall, It is known as surface conduit wiring. in this wiring

method, they make holes on the surface of wall on equal distances and conduit is installed

then with the help of rawal plugs.

5.2 Concealed Conduit wiring

If the conduits is hidden inside the wall slots with the help of plastering, it is called concealed

conduit wiring. In other words, the electrical wiring system inside wall, roof or floor with the

help of plastic or metallic piping is called concealed conduit wiring. obliviously, It is

the most popular, beautiful, stronger and common electrical wiring system nowadays.

In conduit wiring, steel tubes known as conduits are installed on the surface of walls by

means of pipe hooks (surface conduit wiring) or buried in walls under plaster and VIR or

PVC cables are afterwards drawn by means of a GI wire of size if about 18SWG.




Layout of household electrical wiring (single line

diagram):

Basic protective devices used in house

hold wiring.:-

Fuses, MCBs, RCDs, and RCBOs are all devices used to protect users and equipment from

fault conditions in an electrical circuit by isolating the electrical supply. With fuses and

MCBs only the live feed is isolated; with RCDs and RCBOs both the live and neutral feeds

are isolated.

Fuses

A fuse is a very basic protection device which is destroyed (i.e. it 'blows')

and breaks the circuit should the current exceed the rating of the fuse. Once the fuse has

blown, it needs to be replaced.

In older equipment, the fuse may just be a length of appropriate fuse wire fixed between two

terminals (normally screw terminals). These are becoming rarer as electrical installations are

updated - the presence of such fuses usually indicates that it is about time that the installation

is updated.




Modern fuses are generally incorporated within sealed ceramic cylindrical body (or cartridge)

and the whole cartridge needs to be replaced.

Cartridge fuses are used in older type consumer units, fused sockets, fused plugs etc.

Miniature Circuit Breaker (MCB)

An MCB is a modern alternative to fuses used in Consumer Units (Fuse

Boxes). They are just like switches which switch off when an overload is detected in the

circuit. The advantage of MCBs over fuses is that if they trip, they can be reset - they also

offer a more precise tripping value.

Residual Current Device (RCD)Modern alternatives (better) to Earth Leakage Circuit

Breakers and fuses in the Consumer Unit. RCDs are tripped if they detect a small current

imbalance between the Live and Neutral wires above the trip value - this is typically

30mA.RCDs can be wired to protect a single or a number of circuits - the advantage of

protecting individual circuits is that if one circuit trips, it will not shut down the whole house,

just the protected circuit.RCDs are available in at least 4 basic configurations:

1. As hard wired in units, where both the inputs and outputs are wired

into the unit - ideal for a workshop etc where all the sockets within can be protected.

Each individual circuit taken from the RCD is protected by a MCB of an appropriate

value.

2. As protected outlets - normally a protected socket can be fitted as a

direct replacement for a standard, no protected outlet socket.




3. As a plug-in unit which can convert any socket into to a protected

circuit - this gives good flexibility as, for example, a lawn mower or a hedge trimmer

can be plugged in at different times. However, as the individual appliance could still

be plugged into an unprotected socket, you need to remember to fit the

4. As a plug for wiring on to the lead of an individual appliance, this

does make it less flexible than the plug-in unit above but it does ensure that the piece

of equipment is always protected. One very usefully use to to fit it to the end of an

extension cable, then whatever you plug into the extension lead is protected.

Residual Current Breaker with Overload protection (RCBO)

A RCBOs combines the functions of a MCB and a RCD in one unit. They

are used to protect a particular circuit, instead of having a single RCD for the whole building.

Generally these are used more often in commercial building than domestic ones.




Energy consumed in a small electrical

installation:

Electrical energy:

The energy consumed by an appliance for a time period t is given by the product of the

power(P) ratings (in kw) and time(T) (in hour) .

E=P*T

It’s unit is kwh, 1kwh is known as 1 unit

1hp(Horse power)=746 watt

Problem:

Calculate the electricity bill amount for a month of April, if 4 bulbs of 40 W for 5 h, 4

tubelights of 60 W for 5 h, a TV of 100 W for 6 h, a washing machine of 400 W for 3 h are

used per day. The cost per unit is Rs 1.80.

Solutions:

Electric energy consumed per day by 4 bulbs = 4x40 x5 = 800Wh

Electric energy consumed per day by 4 lights = 4x60x5 =1200 Wh

Electric energy consumed per day by TV = 100x6 = 600 Wh

Electric energy consumed per day by washing machine = 400x3 =1200 Wh

.’. Total electric energy consumed by all electric appliances

= (800+ 1200 + 600+ 1200)Wh = 3800 Wh = 3.8 kWh =3.8 units

Total electric energy consumed in the month of April (30 days) = 3.8 x 30 = 114units

Cost of one unit = Rs. 1.80

Cost of 114 units = 114 x 1.80 = 205.20

.:. Electricity bill amount = Rs 205.20




CHAPTER 06

MEASURING INSTRUMENTS

Introduction: The measurement of a given quantity is the result of comparison between the quantity to be

measured and a definite standard. The instruments which are used for such measurements are

called measuring instruments. The three basic quantities in the electrical measurement are

current, voltage and power. The measurement of these quantities is important as it is used for

obtaining measurement of some other quantity or used to test the performance of some

electronic circuit or components etc.

The necessary requirements for any measuring instruments are

1- With the introduction of the instrument in the circuit, the circuit conditions should not be

altered.

2- The power consumed by the instruments for their operation should be as small as possible.

The instruments which measure the current flowing in the circuit is called ammeter while

the instrument which measures the voltage across any two points of a circuit is called

voltmeter.

Torques in instruments: In case of measuring instruments, the effect of unknown quantity is converted into a

mechanical force which is transmitted to the pointer which moves over a calibrated scale. The

moving system of such instrument is mounted on a pivoted spindle. For satisfactory operation

of any indicating instrument, following system must be present in an instrument.

1) Deflecting system producing deflecting torque Td

2) Controlling system producing damping torque Tc

3) Damping system producing damping torque.

Deflecting System

In most of the indicating instruments the mechanical force proportional to the quantity to be

measured is generated. This force or torque deflects the pointer. The system which produces

such a deflecting torque is called deflecting system and the torque is denoted as The

deflecting torque overcomes,

1) The inertia of the moving system

2) The controlling torque provided by controlling system.

3) The damping torque provided by damping system.

The deflecting system uses on of the following effects produced by current or voltage, to

produce deflecting torque.

http://www.yourelectrichome.com/2013/12/deflecting-system.html




Controlling System

This system should provided a force so that current or any other electrical quantity will

produce deflection of the pointer proportional to its magnitude. The important functions of

this system are,

1) It produces a force equal and opposite to the deflecting force in order to make the

deflection of pointer at a definite magnitude. If this system is absent, then the pointer will

swing beyond its final steady positions for the given magnitude and deflection will become

indefinite.

2) It brings the moving system back to zero position when the force which causes the

movement of the moving system is removed. It will never come back to its zero position in

the absence of controlling system.

Controlling torque is generally provided by springs. Sometimes gravity control is also

used.

Damping System

The deflecting torque provides some deflection and controlling torque acts in the opposite

direction to that of deflection torque. So before coming to the rest, pointer always oscillates

due to inertia, about the equilibrium position. Unless pointer rests, final reading cannot be

obtained. So to bring the pointer to rest within short time, damping system is required. The

system should provide a damping torque only when the moving system is in motion.

Damping torque is proportional to velocity of the moving system but it does not depend on

operating current. It must not affect controlling torque or increase the friction.

The quickness with which the moving system settles to the final steady position depends

on relative damping.

Permanent Magnet Moving Coil

Instruments (PMMC) The permanent magnet moving coil instruments are most accurate type for d.c.

measurements. The action of these instruments is based on the motoring principle. When a

current carrying coil is placed in the magnetic field produced by permanent magnet, the coil

experiences a force and moves. As the coil is moving and the magnet is permanent, the

instrument is called permanent magnet moving coil.

http://www.yourelectrichome.com/2013/12/controlling-system.html

http://www.yourelectrichome.com/2014/05/damping-system.html

http://www.yourelectrichome.com/2014/05/permanent-magnet-moving-coil.html

http://www.yourelectrichome.com/2014/05/permanent-magnet-moving-coil.html




Fig. 1. Construction of PMMC instrument

The moving coil is either rectangular or circular in shape. it has number of turns of fine

wire. The coil is suspended so that it is free to turn about its vertical axis. The coil is placed in

uniform, horizontal and radial magnetic field of a permanent magnet in the shape of a horse-

shoe. The iron core is spherical if coil is circular and is cylindrical if the coil is rectangular.

Due to iron core, the deflecting torque increases, increasing the sensitivity of the instrument.

The controlling torque is provided by two phosphor bronze hair springs.

The damping torque is provided by eddy current damping. It is obtained by movement of

the aluminium former, moving the magnetic field of the permanent magnet.

The pointer is carried by the spindle and it moves over a graduated scale. The pointer has

light weight so that it can deflect rapidly. The mirror is placed below the pointer to get the

accurate reading by removing the parallax. The weight of the instrument is normally counter

balanced by the weights situated diametrically opposite and rigidly connected to it. The scale

markings of the basic d.c. PMMC instruments are usually linearly spaced as the deflecting

torque and hence the pointer deflection and directly proportional to the current passing

through the coil.

The top view of PMMC instrument is shown in the Fig. 2.

http://2.bp.blogspot.com/-x8aM_DuVnUs/U3KTwPw8n_I/AAAAAAAANMs/2EJRH60iIoA/s1600/p1.png




Fig. 2 PMMC instrument

In a practical PMMC instrument, a Y shaped member is attached to the fixed end of the

front control spring. An eccentric pin through the instrument case engages the Y shaped

member so that the zero position of the pointer can be adjusted from outside.

1.1 Torque Equation

The equation for the developed torque can be obtained from the basic low of the

electromagnetic torque. The deflecting torque is given by,

Td = NBAI

where Td = deflecting torque in N-m

B = flux density in air gap, Wb/m2

N = number of turns of the coil

A = Effective coil area m2

I = Current in the moving coil, amperes

Td = GI

where G = NBA = constant

The controlling torque is provided by the springs and is proportional to the angular

deflection of the pointer.

Tc = kθ

where Tc = controlling torque

K = spring constant, Nm/rad or Nm/deg

θ = angular deflection

for the final steady state position,

Td = Tc

GI = Kθ

θ = (G/K) I

I = (K/G)θ

Note: Thus the deflection is directly proportional to the current passing through the coil.

The pointer deflection can therefore be used to measure current.

http://3.bp.blogspot.com/-WneZNVrv54Y/U3KUGWFnOTI/AAAAAAAANM0/fzo-uXFVwBo/s1600/p2.png




As the direction of the current through the coil changes, the direction of the deflection of

the pointer is also changes. Hence such instrument are well suited for the d.c. measurements.

Moving Iron Instruments The moving iron instruments are classified as:

i) Moving iron attraction type instruments and

ii) Moving iron repulsion type instruments

1.1 Moving iron attraction type instruments

The basic working principle of these instruments is very simple that a soft iron piece if

brought near the magnet gets attracted by the magnet.

The construction of the attraction type instrument is shown in the Fig.1.

Fig. 1 Moving iron attraction type instruments

It consists of a fixed coil C and moving iron piece D. The coil is flat and has a narrow

slot like opening. The moving iron is a flat disc which eccentrically mounted. on the spindle.

The spindle is supported between the jewel bearings. The spindle caries a pointer which

moves over a graduated scale. The number of turns of the fixed coil are dependent on the

range of the instrument. For passing current through the coil only few turns are required.

The controlling torque is provided by the springs but gravity control may also ne used for

vertically mounted panel type instruments.

The damping torque is provided by the air friction. A light aluminium piston is attached

to the moving system. It moves in a fixed chamber. The chamber is closed at one end. It can

also provided with the help of van attached to the moving system.

The operating magnetic field in moving iron instruments is very weak. Hence eddy

current damping is not used since it require a permanent magnet which would affect or

distort the operating field.

1.2 Moving Iron Repulsion Type Instrument

These instruments have two vanes inside the coil, the one is fixed and other is movable.

When the current flows in the coil, both the vanes are magnetised with like polarities induced

on the same side. Hence due to repulsion of like polarities, there is a force of repulsion

between the two vanes causing the movement of the moving van. The repulsion type

instruments are the most commonly used instruments.

http://www.yourelectrichome.com/2014/05/moving-iron-instruments.html

http://2.bp.blogspot.com/-dwt_cpKhnWs/U3OZf_vzK6I/AAAAAAAANNo/yK-d9OWD31Y/s1600/m1.png




Connection diagram of Ammeter, voltmeter:

Connection diagram of wattmeter (single phase):

The wattmeter is an instrument for measuring the electric power in watts of any given circuit.

The internal construction of a wattmeter is such that it consists of two coils. One of the coil is

in series and the other is connected in parallel. The coil that is connected in series with the

circuit is known as the current coil and the one that is connected in parallel with the circuit is

known as the voltage coil.




This is shown in given circuit diagram. This is basic construction of any wattmeter.

Connection diagram of Energy meter:




DISCLAIMER

COPYRIGHT IS NOT RESERVED BY AUTHORS. AUTHORS ARE NOT RESPONSIBLE

FOR ANY LEGAL ISSUES ARISING OUT OF ANY COPYRIGHT DEMANDS AND/OR

REPRINT ISSUES CONTAINED IN THIS MATERIALS. THIS IS NOT MEANT FOR ANY

COMMERCIAL PURPOSE & ONLY MEANT FOR PERSONAL USE OF STUDENTS

FOLLOWING SYLLABUS. READERS ARE REQUESTED TO SEND ANY TYPING

ERRORS CONTAINED, HEREIN.

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