Tt pump operator cum mechanic

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NATIONAL INSTRUCTIONAL
MEDIA INSTITUTE, CHENNAI
Post Box No. 3142, CTI Campus, Guindy, Chennai - 600 032
DIRECTORATE GENERAL OF TRAINING
MINISTRY OF SKILL DEVELOPMENT & ENTREPRENEURSHIP
GOVERNMENT OF INDIA
TRADE THEORY
PUMP OPERATOR
CUM MECHANIC
2nd
Semester
SECTOR: Automobile

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Sector : Automobile
Duration : One year
Trades : Pump Operator cum Mechanic - Trade Theory
Copyright © 2014 National Instructional Media Institute, Chennai
First Edition : May 2015, Copies : 1,000
First Reprint : March 2016, Copies : 1,000
Rs. 100/-
All rights reserved.
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photocopy, recording or any information storage and retrieval system, without permission in writing from the National
Instructional Media Institute, Chennai.
Published by:
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Guindy, Chennai - 600 032.
Phone: 044 - 2250 0248, 2250 0657
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email : nimichennai@vsnl.net , nimi_bsnl@dataone.in
Website: www.nimi.gov.in

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FOREWORD
The National Instructional Media Institute (NIMI) is an autonomous body under the Directorate General of
Employment and Training (DGE&T) Ministry of Labour and Employment has been developing, producing
and disseminating Instructional Media Packages (IMPs are extensively used in the Industrial Training
Institutes/Training centres in Industries to impart practical training and develop work-skills for the trainees
and the trainers
The Ministry of Labour & Employment constituted Mentor Councils (MCs) to revampcourses run / to be
run under National Council of Vocational Training (NCVT) in 25 sectors. The MCs have representatives
from thought leaders among various stakeholders viz. one of the top ten industries in the sector innovative
entrepreneurs who have proved to be game-changers, academic/professional institutions (IITs etc.), experts
from field institutes of DGE &T, champion ITIs for each of the sectors and experts in delivering education
and training through modern methods like through use of IT, distance education etc. The technical support
to the MCs is provided by Central Staff Training and Research Institute (CSTARI), Kolkata and National
Instructional Media Institute (NIMI), Chennai. Some of the MCs are also supported by sector-wise Core
Groups which were created internally in the Ministry (in 11 sectors).
A Steering Committee to provide overall coordination and guidance to Mentor Councils has also been
constituted and has representation from the MCs, Chair positions to be endowed by the Ministry, trade
unions, and experts on distance education and training. The MCs are mandated to work towards revamping/
suggesting new courses, improving assessment systems, overall learning etc. for subjects under the
purview of the NCVT.
Accordingly NIMI with the support and assistance of MC has developed Pump Operator cum Mechanic
Trade Theory 2nd
Semester in Automobile sector to enhance the employability of ITI trainees across
the country and also to meet the industry requirement.
I have no doubt that the trainees and trainers of ITIs & Training centres in industries will derive maximum
benefit from these books and that NIMI’s effort will go a long way in improvement of Vocational Training.
I complement Director, Mentor Council members, Media Development Committee (MDC) members and
staff of NIMI for their dedicated and invaluable contribution in bringing out this publication.
ALOK KUMAR, I.A.S.,
Director General of Employment &
Training/ Joint Secretary
Ministry of Labour and Employment
Government of India
New Delhi - 110 001

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PREFACE
This National Instructional Media Institute (NIMI) was set up at Chennai by the Directorate General
of Employment and Training (DGE&T) Ministry of Labour and Employment, Government of India
with technical assistance from the Govt. of the Federal Republic of Germany. The prime objective
of this institute is to develop and disseminate instructional materials for various trades as per
the prescribed syllabi under the Craftsmen and Apprenticeship Training Schemes.
The instructional materials are developed and produced in the form of Instructional Media
Packages (IMPs). An IMP consists of Trade Theory book, Trade Practical book, Test and
Assignment book, Instructor guide, Wall Charts and Transparencies.
Hon'ble Union Minister of Finance during the budget speech 2014-2015 mentioned about
developing Skill India and made the following announcement
"A national multi-skill programme called Skill India is proposed to be launched. It would skill the
youth with an emphasis on employability and entrepreneur skills. It will also provide training and
support for traditional professions like welders, carpenters, cobblers, masons, blacksmiths,
weavers etc. Convergence of various schemes to attain this objective is also proposed."
The Ministry of Labour & Employment constituted Mentor Councils (MCs) to revamp courses
run / to be run under National Council of Vocational Training (NCVT) in 25 sectors which will give
a sustained skill based employability to the ITI trainees as the main objective of Vocational
training. The ultimate approach of NIMI is to prepare the validated IMPs based on the exercises
to be done during the course of study. As the skill development is progressive the theoretical
content on a particular topic is limited to the requirement in every stage. Hence the reader will
find a topic spread over a number of units. The test and assignment will enable the instructor to
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helps the trainee to do assignment on his own and also to evaluate himself. The wall charts and
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also helps the trainees to grasp the technical topic quickly. The instructor guide enables the
instructor to plan his schedule of instruction, plan the raw material requirement ,
Thus the availability of a complete Instructional Media Package in an institute helps the trainer
and management to impart an effective training. Hence it is strongly recommended that the
Training Institutes/Establishments should provide at least one IMP per unit. This will be small,
one time investment but the benefits will be long lasting.
The Pump Operator cum Mechanic Trade Theory 2nd
Semester in Automobile Sector is
one of the book develop by the core group members of the Mentor Councils (MCs). The 2nd
semester book includes Module 1 - Diesel Engine, Module 2 - Electrical Motor, Module 3
- Lifting Equipments, Module 4 - Bearings, Module 5 - Pumps
The Pump Operator cum Mechanic Trade Theory 2nd
Semester is the outcome of the
collective efforts of Members of Mentor Council which includes academic/professional institutions
(IITs etc.) , experts from field institutes of DGE&T, champion ITIs for each of the sectors, and
also Media Development Committee (MDC) members and staff of NIMI.
NIMI wishes that the above material (Trade Practical & Trade Theory) will fulfil to satisfy the long
needs of the Trainees and Instructor and helps the trainees for their employability in vocational
training.
NIMI would like to take this opportunity to convey sincere thanks to all the Mentor Council members and
Media Development Committee (MDC) members.
A. MAHENDIRAN
Chennai - 600 032 Director , NIMI

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ACKNOWLEDGEMENT
National Instructional Media Institute (NIMI) sincerely acknowledges with thanks for the co-operation and
contribution extended by the following Media Developers and their sponsoring organisation to bring out this IMP
(Trade Theory) for the trade of Pump Operator cum Mechanic under the Automobile Sector for Craftsman
Training Scheme. This Book is prepared as per Revised Syllabus.
MEDIADEVELOPMENTCOMMITTEEMEMBERS
Shri. A. Ramesh - Professor,
IIT,Chennai
Chairman, Mentor council.
Shri.T.C.Saravanabava - DeputyDirectorGeneral(AT),
DGE&T,NewDelhi.
Mentor, Mentor council.
Shri. K. Srinivasa Rao - JointDirectorofTraining,
NIMI,Chennai
Team Leader, Mentor council.
Shri. C. Yuvaraj - DeputyDirectorofTraining,
ATI,Chennai.
Member, Mentor council.
Shri. G. Venkatesh - Assistant Director of Training,
ATI(V),Hyderabad.
Shri. S.P. Rewaskar - Assistant Director of Training,
ATI,Hyderabad.
Shri. N. Ramesh Kumar - TrainingOfficer,
CTI,Chennai
Shri. T.N. Rudra - TrainingOfficer,
ATI,Howrah.
Shri. Akhilesh Pandey - TrainingOfficer,
ATI,Mumbai.
Shri. R. Rajesh Kanna - TrainingOfficer,
ATI,Chennai.
Shri. A. Duraichamy - Assistant Training Officer,
Govt.ITI,Coimbatore.
Shri. H.S. Kalra - Principal,
Govt.ITI,Chandigarh,Punjab.
Shri. W. Nirmal Kumar Israel - Assistant Training Officer,
Govt.ITI,Trichy.

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Shri. K. Thaniyarasu - Assistant Training Officer,
Govt.ITI,Trichy.
Shri. Dr. Abhijit KR Mandal - Consultant,
NATRIP.
Shri. V. Krishna Shankar - GeneralManager,
Ashok Leyland.
Shri. Mohan Kumar - Manager,
TAFE,Chennai.
Shri. Uma Shankar - Plant Director,
DelphiTVS
Shri.K.Ravindranath - Assistant Training Officer
Govt.ITI,Ambattur.
Member, Mentor council
Shri.N.Duraimurugan - Assistant Training Officer
Govt.ITI,Guindy.
Shri. K. Veerappan - Assistant Training Officer
Govt.ITI,Nagapattinam.
Shri. Palani Kumar - Assistant Training Officer
Govt.ITI,Pudukottai.
Shri. S.K. Patnaik - Retd. AGM,
MDCMember-NIMI.
Shri. S. Deva kumar - Retd. Principal,
MDCMember-NIMI.
NIMI records its appreciation of the Data Entry, CAD, DTP operators for their excellent and devoted services in
the process of development of this instructional material.
NIMIalsoacknowledgeswiththanks,theinvaluableeffortsrenderedbyallotherstaffwhohavecontributedforthe
developmentofthisInstructionalmaterial.
NIMI is also grateful to all others who have directly or indirectly helped in developing this IMP.

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INTRODUCTION
This manual of Trade Practical consists of 34 practical exercises to be completed by the trainees during the
2nd
semester of the following trades Pump Operator cum Mechanic in 525 Practical Working Hours. This
exercisearedesignedtoensurethatalltheskillsintheprescribedsyllabusarecovered. ThecombinedTrade
Practical syllabus have been divided in to Five Modules. The distribution of time for the practical in the Five
Modulesaregivenbelow.
Module 1 : Diesel Engine 100
Module 2 : Electrical Motor 100
Module 3 : Lifting Equipments 100
Module 4 : Bearings 50
Module 5 : Pumps 175
Total 525
The exercises in all the Five modules are arranged in proper sequence so that the trainee can learn the skills
from easy to difficult, known to unknown, simple to complex, basic to advanced. Each exercise starts with
Exercise title and the skills objectives to be achieved at the end of the exercise. Then the relevant JOB
DRAWINGandtheMaterialsizes,Materialspecification,ExerciseNo.etc.aregiven.NextthePROCEDURE
is stated which gives the step by step procedure to complete the exercise. Finally, the SKILL SEQUENCE is
given which explains the skills and techniques and precautions to be taken to do the job/exercise with safety
aspects.
Wherever possible illustrative diagrams are given in addition to explanation for easy understanding.
If a particular skill is explained in the earlier exercises, the same skill may not have been repeated again.
While developing this practical manual a sincere effort was made to prepare each exercise which will be easy
tounderstandandcarryoutevenbybelowaveragetrainee.However,thedevelopmentteamacceptthatthere
isascopeforfurtherimprovement.NIMIlooksforwardtothesuggestionsfromtheexperiencedtrainingfaculty
forimprovingthismanual.

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Module 1 : Diesel Engine
2.1.01 Types of pumps and its prime movers 1
2.1.02 DieselEngine 2
2.1.03 Starting and stopping methods of engine 5
2.1.04 Air cleaner 6
2.1.05 Fuelfilter 7
2.1.06 Oil filter 8
2.1.07 Engine lubrication system 9
2.1.08 Fuel tank and fuel pipes 11
2.1.09 Troubleshooting 12
2.1.10 Maintenanceofengine 20
Module 2: Electrical Motor
2.2.01 Safety rules pertaining to Electrician 21
2.2.02 Alternatingcurrent 27
2.2.03 3-phaseACfundamentals 28
2.2.04 D.O.L. starter 31
2.2.05 Manual star-delta switch/starter and Automatic star delta starter 33
2.2.06 Thetwo-wattmetermethodofmeasuringpower 37
2.2.07 Principle of induction motor 40
Module 3: Lifting equipments
2.3.01 Ropes 52
2.3.02 Hoisting equipment and their application 54
2.3.03 State seals and lubricants 56
2.3.04 State pipe fitting tools, pipe fittings and flange fitting technic 59
2.3.05 Keys and their applications 63
Module 4 : bearings
2.4.01 Bearings 66
2.4.02 Bushes 69
2.4.03 Belts and Couplings 70
CONTENTS
THEORY
Lesson. No. Title of the Lesson Page No.

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Lesson. No. Title of the Lesson Page No.
Module 5 : Pumps
2.5.01 Pumps 74
2.5.02 Reciprocating pumps 76
2.5.03 Valves 80
2.5.04 Centrifugal pump 83
2.5.05 Installation of pumps 89
2.5.06 Maintenance of Pumps 90
2.5.07 Submersible Pump 92
2.5.08 Troubleshooting in submersible pump 94
2.5.09 Rotary pump 96

1
Automobile Related theory for Exercise 2.1.01
Pump Operator cum Mechanic - Diesel Engine
Types of pumps and its prime movers
Objectives : At the end of this lesson you shall be able to
• history of development of pumps and prime movers
• state the leading pump manufactures.
After the advent of hand pumps, centrifugal pump
poweredbysteamenginewasdevelopedin1951. Robert
Blackmer invented the ‘Rotary vane pump in 1899. Multi
stage centrifugal pumps are developed in 1905. M/s.
Aldrick pump company developed Motor driven recipro-
cating pump in 1916. First submerible pump was devel-
oped in 1947. R. Kinney of V.S. invented ‘Jet pump’ in
1967.
Leading pump manufacturers
1. Kirloskar, 2. CRI, 3. Suguna, 4. Texmo, 5. Bestan
6. KSB, 7. ROTO, 8. Sakthi, 9. Wbil, 10. Yuken India
11. Dynamatic Tech, 12.Bemco Hydraulic, 13.‘V’ Guard
Development in pump Industry
Petrom pump sets
Small petrol engine driven pumps in the range of 1.5 to
4H.P. these pump sets relatively by cheap to buy.
As a disadvantage of the pumpset generally do not last
long. It takes much fuel and maintenance cast is high.
Diesel pump sets
Dieselenginedrivenpumpstartsfrompowerrating4.5hp
the pump sets are more extensive than petrol pumps,
heavier, more difficult to operate and repair and generally
haveacapacitythatexceedsthewaterneeds. Dieselfuel
is usually cheaper than petrol, overall fuel efficiency is
higher and life is better than petrol pump set.
Solar Thermal
Another option of using solar energy for pumping is using
solarthermalenergy. Inmostsystemsolarenergyisused
toheatamedium(gasorliquid)whichtransferthethermol
energy to an engine. Thermal energy is converted in to
mechanicalpowerthatcanbeusedtodriveawaterpump.
Wind power
Only in very few country the wind regime is reliable
enough as a source of energy for irrigated agriculture.

2
Diesel Engine
• principle of diesel and petrol engine
• differentiate between two stroke and four stroke
• differentiate between C.I. & S.I. engine
• differentiate between otto cycle & diesel cycle
• technical terms used in engine
• engine specification.
Principal of diesel and petrol engine
A heat engine is a machine, which convert heat energy in
to mechanical energy. The combustion of fuel such as
diesel and petrol generates heat. The heat is supplied to
a working substance in a suitable machines, heat energy
is converted into mechanical energy.
Differentiate between four-stroke engine and two-stroke engine
Four-stroke engine Two-stroke engine
Four operations (suction, compression, power and The four operations take place in two strokes of the
exhaust) take place in the four strokes of the piston. piston.
It gives one power stroke in the four strokes, i.e in two The power stroke takes place in every two strokes i.e.
revolutions of the crankshaft. As such three strokes are one power stroke for one revolution of the crankshaft.
idle strokes.
Due to more idle strokes and non-uniform load on the The engine has more uniform load as every time the
crankshaft, a heavier flywheel is required. piston comes down it is the power stroke. As such a
lighter flywheel is used.
The engine has more parts such as valves and its The engine has no valves and valve-operating
operating mechanism. Therefore, the engine is heavier. mechanism. Therefore, it is lighter in weight.
The engine is costlier because it has more parts. The engine is less expensive because it has a less
number of parts.
The engine efficiency is more as the charge gets The efficiency is less. A portion of the charge escapes
completely burnt out. Consequently the fuel efficiency through the exhaust port, and because of this, the fuel
is more. efficiency is less.
Differentiate between s.i.and c.i. engine
SI engine CI engine
Petrol is used as fuel. Diesel is used as fuel.
During the suction stroke air and fuel mixture is sucked During the suction stroke air alone is sucked in.
in.
Compression ratio is low. (Max. 10:1) Compression ratio is high. (Max. 24:1)

3
OTTO CYCLE
1 - 2 - Suction
2 - 3 - Compression
3 - 4 - Heat addition
4 - 5 - Power
5 - 2 - 1 - Exhaust
In otto cycle engine, combustion takes place at constant
volume.
Suction takes place at a pressure below atmospheric
pressure when piston moves from TDC to BDC. (1-2)
Compression takes place when piston moves from BDC
to TDC. (2-3)
Fuel mixture is ignited by introducing a spark at constant
volume. (3-4)
The gas expands during the power stroke (4-5), reducing
both pressure and temperature.
Heat is rejected at constant volume. (5-2)
Burnt gases exhaust when piston moves from BDC to
TDC. (2-1)
DIESEL CYCLE
1 - 2 - Suction
2 - 3 - Compression
3 - 4 - Heat addition
4 - 5 - Power
5 - 2 - 1 - Exhaust
In diesel cycle, combustion takes place at constant
pressure.
Suction takes place at pressure below atmospheric
pressure when piston moves from TDC to BDC. (1-2)
Compression takes place when piston moves BDC to
TDC. (2-3) (Both the valves closed).
Fuel is sprayed at high pressure and ignited by hot
compressed air (3-4), and this process takes place at
constant pressure.
Fuel ignites, pressure of burnt gas increases, gas ex-
pands and piston is forced from TDC to BDC. (4-5)
Heat is rejected at constant volume. (5-2)
Burnt gases exhaust when piston moves from BDC to
TDC. (2-1)
Compression pressure is low. (90 to 150 PSI) Compression pressure is high. (400 to 550 PSI)
Compression temperature is low. Compression temperature is high.
It operates under constant volume cycle (otto cycle). It operates under constant pressure cycle (diesel cycle).
Fuel is ignited by means of an electric spark. Fuel is ignited due to the heat of the highly compressed
air. Combustion takes place at constant pressure.
A carburettor is used to atomize, vaporize and meter Fuel injection pumps and atomizers are used to inject
the correct amount of fuel according to the requirement. metered quantities of fuel at high pressure according to
the requirement.
Less vibration, and hence, smooth running. More vibration, and hence, rough running and more
noisy.
Engine weight is less. Engine weight is more.
It emits carbon monoxide. (CO) It emits carbon dioxide. (CO2
)
Differentiate between Otto cycle and Diesel cycle
Automobile : Pump Operator cum Mechanic - Exercise 2.1.02

4
Basic technical terms used in relation to engines
T.D.C. (Top dead centre)
Itisthepositionofthepistonatthetopofacylinder,where
the piston changes its direction of motion from the top to
the bottom.
B.D.C.(Bottom dead centre)
It is the position of the piston at the bottom of the cylinder
where the piston changes its direction of motion from the
bottom to the top.
Stroke
The distance travelled by the piston from TDC to BDC or
BDC to TDC.
Cycle
A set of operations performed in sequence by the motion
of the piston in an engine to produce power.
Swept volume (VS)
Displacement volume of a piston.
Clearance volume (VC)
Volume of the space above the piston when it is at TDC.
Compression ratio (CR)
Ratio of compression volumes before the stroke and
after.
Where VS = swept volume
VC = clearance volume
VS+VC = total volume at BDC.
Power
Power is the rate at which work is done in a specific time.
Horsepower (HP)
It is the measurement of power in SAE. One HP is the
powerrequired toliftaloadof33000lbs,throughonefoot
in one minute.
Thermal efficiency
It is the ratio of work output to the fuel energy burnt in the
engine. This relationship is expressed in percentage.
Brake horsepower (BHP)
It is the power output of an engine, available at the
flywheel.
where N is r.p.m. of the crankshaft, and T is the torque
produced.
Indicated horse power (IHP)
It is the power developed in the engine cylinder.
where Pm is the mean effective pressure in kg./cm2
,
L is the length of the stroke in metres
A is the area of the piston in cm2
N is the No. of power strokes per minute
K is the No. of cylinders.
Frictional horsepower
It is the horsepower lost in the engine due to friction.
FHP = IHP - BHP
Mechanical efficiency
It is the ratio of power delivered (BHP) and the power
available in the engine (IHP). It is expressed in percent-
age.
Mechanical efficiency =
Volumetric efficiency
It is the ratio between the mixture drawn in the cylinder
during the suction stroke and the volume of the cylinder.
Throw
It is the distance between the centre of the crankpin to the
centre of the main journal. The piston stroke is double the
throw.
Firing order
The firing order is the sequence in which the power stroke
takes place in each cylinder in a multi-cylinder engine.
Technical specification of an engine
Engines are specified as per the following.
Type
Number of cylinders
Bore diameter
Stroke length
Capacity in cu.cm or cu.inch
Maximum engine output at specified r.p.m.
Maximum torque
Compression ratio
Firing order
Idling speed
Air cleaner (type)
Oil filter (type)
Fuel filter
Fuel injection pump
Weight of engine
Cooling system (type)
Type of fuel

5
Starting and stopping methods of diesel engine
• hand cranking
• electric cranking method.
Forstartingtheenginethefollowingdifferentmethodsare
used.
1. Hand cranking
2. Electric Motor cranking
Hand cranking
Usually small diesel engines are being started using
crank handle or rope.
Electric motor cranking
In this system a starter motor (1) is used to rotate flywheel
(3) of the engine. A battery (2) is used to supply power to
the starter motor.
Different type of stopping the engine.
1 Generallydieselenginnesarestopppingbycuttingthe
fuel supply after deducing the engine speed to the
mininum level.
2 Close the another method of stopping the diesel
engine by decompression lever. (Fig 1)

6
In this type of air cleaner, a specially treated paper
element is used to filter the intake air.
Function
The atmospheric air enters the air cleaner through the air
entrance (1) and passes through the paper element (2).
The filtered clean air goes to the carburettor via the
entrance (3).
Introduction
Atmospheric air consists of a large quantity of dirt and
dust. Uncleanedairwillcausefasterwearofanddamage
to the engine parts, so air is filtered before entering inside
the cylinder bore.
Purpose of air cleaner
-
It cleans the intake air.
-
It reduces the noise of the intake air.
-
It acts as a flame arrester during engine backfire.
Location
It is mounted either on the top of the carburettor or on the
air inlet manifold.
Types
-
Wet-type
-
Dry-type
Wet type air cleaner
The atmospheric air enters the air cleaner through the
side passage (1) and strikes on the surface of the oil (2).
Heavydustparticlesareabsorbedbytheoil. Thepartially
filteredair,alongwithoilparticles,movesupwardthrough
the filter element (3). Fine particles and oil particles are
collected by the filtering element (3). Cleaned air then
passes through the passage to the inlet manifold.
Dry type air cleaner
Air cleaner
Objectives: At the end of this lesson you shall be able to
• state the need of an air cleaner
• state the different types of air cleaners
• state the function of an air cleaner.

7
Need of fuel filter
Effective filtering of fuel, oil is most important for long
trouble free functioning of the engine. Diesel fuel while
transporting and handling has chances of getting con-
taminated by water, dirt, bacteria and wax crystals. Dirt is
the worst enemy of the fuel injection equipment. Dirt
contamination can be the result of careless filling of the
fuel tank. When fuel tank is not filled, moist air
condenses inside the metal wall of the fuel tank resulting
in water contamination of the fuel.
For these reasons a very efficient filtering system is
required to remove these impurities.
Types of fuel filter system
There are two types of fuel filtering system.
- Single filter system
- Two stage filter system
In a single filtering system one single filter assembly is
used in between feed pump and fuel pump. The single
filter in this system is capable of separating dirt from fuel.
It should be replaced periodically as per the
recommendations of the manufacturers.
In a two stage filter system, primary filter (1) is used for
filtering large solid contaminants and most of the water in
the fuel is also removed by this filter. The secondary filter
(2)is madeofapaperelement. Thisfiltercontrolsthesize
of the particles allowed to pass into the fuel injectors. It
alsoseparatesanywaterthatmighthavepassedthrough
the primary filter. An overflow valve assembly (3) is used
to send back excess fuel to fuel tank. A bleeding screw
(4) is provided to bleed the air from fuel system.
Fuel filter element
A paper element is most suitable because important
properties which determine filter quality such as pore size
and pore distribution can be effectively maintained. Gen-
erally paper filter elements are used at the secondary
stage filtration process.
Coil type paper filter inserts are wound around a tube and
neighbouring layers are glued together at the top and
bottom. This forms a pocket with the openings at the top.
In the star type paper filter inserts, the fuel flows radially
from outside to inside. The paper folds are sealed at the
top and bottom by end covers.
Cloth type filter inserts are used for primary stage filtra-
tion. In this the fuel flows radially from outside to inside.
Theclothiswoundover aperforatedtubewhoseendsare
sealed at the top and bottom by end covers.
Bleeding of the fuel system
Bleeding is the process by which air, which is present in
the fuel system, is removed. Air locking in the fuel system
will result in erratic running of the engine and may result
in stopping of the engine. Bleeding is carried out by
priming the filter. A slight loosening of the bleeding screw
allowslockedairtoescapeasbubblesalongwiththefuel.
When locked air escapes and the system is free of air, the
screw is tightened finally.
Fuel filter
• state the need of a fuel filter
• explain the types of fuel filter systems
• explain the need for bleeding the fuel system

8
Oil filter
• remove oil filter element
• check the spring tension of the bypass valve and pressure relief valve
• clean the oil filter bowl.
• check the pressure relief valve and seat
• fit a new element in the oil filter bowl
• adjust the pressure relief valve for correct pressure.
Oil filter
Full flow oil filter system
In this system all the oil passes through the filter before
reaching the main oil gallery. One bypass valve is
provided in the filter which allows oil to reach the main oil
gallery directly if the filter is chocked.
Bypass oil filter system
In this system only a part of the engine oil enters the
filter. After filtering, the oil goes to the oil sump. The
remaining oil goes directly to the main oil gallery.
Filter element
Filter elements are made of flet, cotton waste, cloth and
paper. Oil filters are replaced after certain kilometers of
running of the engine, as specified by the manufacturer.
Oil coolers
Oil coller consists of two halves(1). Passages(2) are
provided in between the cooler’s halves for oil
circulation. A ball valve(3) is provided to maintain the
required oil pressure. This is made of cast iron. The
purpose of the oil cooler is to transfer the heat from
engine oil to cooling water and cool the engine oil.
The inner wall of the oil cooler is in contact with cooling
water. The engine oil which is made to circulate through
the passages provided in the oil cooler, transfers its heat
to the cooling water circulating in engine block(4), and
the inner wall of oil cooler. This maintains the
temperature of the engine.

9
The rotor type oil pump consists of an inner driving rotor
(1), and an outer drive rotor (2) which rotates freely in the
pump housing (3) and runs eccentrically in relation to the
inner rotor.
Functions of a lubricant
The main function of a lubricant is to minimise the friction
between two moving surfaces which are in contact with
each other.
It also helps to:
- absorb heat from the moving parts due to friction
- minimise wear and tear of the components
- provide a cushioning effect between the moving parts
- clean the parts by carrying away metal chips with it
- protect parts from corrosion
- prevents blow-by of gases by providing an oil film
between the rings and the liner/bore.
Properties of a lubricant
-
It should have viscosity to suit the operating condi-
tions.
-
The viscosity should remain the same in both hot and
cold conditions.
-
Its boiling temperature should be high.
-
It should be corrosion-resistant.
-
It should not develop foam.
-
It should withstand critical operating pressure.
Components of the lubricating system
Oil pumps
The oil pump is used to pump oil from the oil sump to the
oil galleries at a certain pressure.
It is located in the crankcase and is driven by the cam-
shaft. Four types of oil pumps are used.
-
Gear type oil pump
-
Rotor type oil pump
-
Vane type oil pump
-
Plunger type oil pump
Gear type oil pump
Engine lubrication system
• state the need of lubricating an engine
• list out the properties of lubricating oils
• list out the different types of oil pumps
• state the functions of the various types of oil pumps.
In this type two gears are fixed in the pump housing (1).
The gears (2) have little clearance with the pump housing
(1). When the gears rotate a vacuum is created in the
casing. Oil is sucked through the inlet (3) and pumped to
the oil gallery through the outlet (4).
Rotor type oil pump

10
The oil is sucked into the pump at the side where the
volume between the rotor teeth increases and is pumped
out at the side where the volume decreases.

11
Function of the fuel tank
The Fuel tank is provided for storing diesel required for
running the engine. It is constructed of either pressed
sheet metal with welded seams and special coating to
prevent corrosion or fiber glass reinforced plastic
materials.
It may be round or rectangular in shape. It is mounted
above the engine assembly.
List out the Parts of the fuel tank
Filler neck and cap
Baffle
Fuel gauge sensing unit (Float)
Filter
Sediment bowl and drain plug
Function of each part of fuel tank
Filler neck is provided for pumping diesel into the fuel
tank. A cap is provided for closing the tank tightly. A vent
hole is provided either in filler neck or in cap to maintain
atmospheric pressure in the tank above the fuel.
Baffles are provided in the fuel tank to minimize the
slushing of fuel due to movement inside the tank.
Fuel gauge sensing unit is provided to know the level of
fuel available in tank. It consists of a float resting on the
surface of the diesel in the tank. The float with the help of
theelectricalsensingsystemindicatesthelevelofthefuel
available in the tank, on the dash board fuel-gauge.
Fuel tank and fuel pipes
• explain the function of the fuel tank
• list out different parts of fuel tank
• explain the function of each part of fuel tank
• explain the function of fuel pipes.
Filter is provided at the lower end of the suction pipe. It
filters heavy foreign particles.
At the bottom of the fuel tank a drain plug is provided to
collect sediments and drain it out of the tank.
Function of fuel pipe
Fuel pipe between the fuel tank and the feed pump is
called suction pipe, the pipes between F.I.P. and the
injectorsarecalledhighpressurepipes. Anoverflowpipe
is provided on fuel filter bowl and injectors to supply
excess fuel back to fuel tank.
Part of fuel tank
1. Tank 2. Filter 3. FlP.
4. Drain plug 5. Tank cap 6. Sensing unit
7. Pipe link

12
Trouble shooting
• engine does not start
• high fuel consumption
• engine overheat
• low power generation
• excessive oil comsumption
• low oil pressure
• engine noise.

13
High
fuel
consumption
External
leakage of
fuel
Air cleaner
clogged
Wrong
injection
timing
Defective
injector
Defective fuel
injection
pump
Worn out
valve/valve
guide
Worn out
piston/liner/
rings
Excessive
tappet
clearance
Less air
supply
Weak
compression
Less air supply/burnt
gases not going out of
cylinder completely
Incomplete
combustion fuel
High fuel consumption

14
Engine
over
heating
Radiator
cores
blocked
externally
Loose
fan belt
Faulty
water
pump
Radiator
cores blocked
internally
Hose pipe
broken/
loose
Radiator
leaking
Wrong
injection
timing
Defective
injector
Less air
supply
No water in
the radiator
Less circulation
of water
Engine over heating
Defective
F.I.P
Cylinder block
water passage
blocked /scale
formation
Water
pump’s
rpm less
Incomplete
combustion
of fuel
No water
circulation in the
cylinder block

15
Low
power
generation
Weak
compression
Low power generation
Defective
injector
Defective
F.I.P
Clogged
exhaust
manifold
Valve
leakage
Worn out
pistons/rings
/liners
Defective
feed
pump
External
leakage/
blockage
of fuel
pipe
Clogged
fuel
filter
Clogged
air
cleaner
Wrong
injection
timing
Wrong
tappet
clearance
Less supply
of fuel
Less supply
of air
Exhaust gases
not going out
of cylinder
completely
Incomplete
combustion of
fuel

16
High
oil
consumption
External
leakage of oil
High oil
level
Worn out intake valve
guides and valve stems
Worn out piston rings
and cylinder bore
Engine oil viscosity
too low
Worn out exhaust valve
guides and valves stems
Oil being
splashed in
cylinder
Oil reaching
combustion
chamber
Oil reaching
in exhaust
manifold
Excessive oil consumption

17
Low
oil
pressure
Oil pump
strainer blocked
Worn
out/damaged
gears of oil pump
Excessive backlash
between gears
Excessive
clearance
between gears
Pump delivers less
oil
Loose/cracked/
blocked strainer
pipe
Defective oil
pressure
relief valve
Defective oil
pressure
gauge
Worn out
bearings of
crankshaft
and
camshaft
Low
viscosity of
oil
Damaged
gaskets/oil
seals
Air enters in oil
pump/less oil
sucked by pump
Engine oil pressure low
Excessive
discharge of oil
through bearings
Leakage of oil
Oil level low

18
Engine
does
not
start(mechanical
causes)
Valve leakage
Worn
out/rings
/liner
Wrong
valve/injection
timing
Defective fuel
injection
pump
Defective
injector
Fuel tank
vent hole
blocked
Fuel suction pipes
cracked/blocked/
defective feed
pump
Fuel
filters/deli
‐very pipe
blocked
Engine does not start
Exhaust
manifold/
silencer
blocked
Weak
compression
Incomplete
combustion
of
fuel
No suction of
fuel from
tank
No suction of
fuel from
tank
No delivery of
fuel to F.I.P

19
Engine
noise
Excessive main bearing
clearance
Engine noise
Crank shaft main
bearing run out
Insufficient
lubrication
Ware and tear of
pisten and
cylinder bore
Excessive
tappet
clearance
Loose
connecting
rod small rod
bearing
Defective
air
clearance

20
Maintenance of engine
• explain the need of periodic maintenance of engine
• explain break down maintenance
• explain preventive maintenance.
The service life and operational economy of the engine
depends on the maintenance it receives, as the fasteners
become loose when the engine is operated. Therefore
the periodical maintenance should be carried out as
recommended by the manufacturer.
Engine oil level should be maintained to ensure proper
lubrication. Oil should be changed as recommended
along with the filter elements.
Correctwaterlevelinradiatorisrequired forcoolingofthe
engine. This will maintain the working temperature of the
engine.
Fuelfiltersshouldbechangedasrecommendedtosupply
clean fuel. Also air cleaner servicing is required to allow
air,freefromdust,sothatthewearandtearofthecylinder
is reduced.
F.I.P. and injectors should be serviced as recommended
forinjectionofcorrectquantityoffuelandforfueleconomy.
Tappet clearance should be adjusted periodically to have
complete combustion of fuel.
Thecylinderheadshouldbetightenedatspecificintervals
as recommended by the manufacturer.
Breakdown maintenance
Breakdown maintenance is carried out whenever engine
stops functioning due to some faults. This type of
maintenance is preferred where continuous operation of
engine is required and engine cannot be stopped for the
purpose of maintenance.
Preventive maintenance
Preventive maintenance is done to reduce possibility of
engine's sudden break down. For this type of
maintenance engine has to be shut-off periodically to
carry out maintenance. All engine manufacturers
recommend schedule of maintenance according to the
design of their engines.

21
Pump Operator cum Mechanic - Electrical Motor
Safety rules pertaining to Electrician
• explain the necessary of adopting the safety rules
• list the safety rules, and follow them.
Necessity of safety rules: Safety consciousness is one
of the essential attitudes required for any job. A skilled
electrician always should strive to form safe working
habits. Safeworkinghabitsalwayssavemen,moneyand
material. Unsafeworking habits always end up in loss of
production and profits, personal injury and even death.
The safety hints given below should be followed by
Electrician to avoid accidents and electrical shocks as his
job involves a lot of occupational hazards.
The listed safety rules should be learnt, remembered and
practised by every electrician. Here a electrician should
remember the famous proverb, “Electricity is a good
servant but a bad master”.
Safety rules:
– Only qualified persons should do electrical work.
– Keep the workshop floor clean, and tools in good
condition.
– Do not work on live circuits; if unavoidable, use rubber
gloves rubber mats, etc.
– Use wooden or PVC insulated handle screwdrivers
when working on electrical circuits.
– Do not touch bare conductors
– When soldering, arrange the hot soldering irons in
their stand. Never lay switched ‘ON’ or heated solder-
ing iron on a bench or table as it may cause a fire to
break out.
– Use only correct capacity fuses in the circuit. If the
capacity is less it will blow out when other load is
connected. If othe capacity is large, it gives no
protection and allows excess current to flow and
endangers men and machines, resulting in loss of
money.
– Replace or remove fuses only after switching off the
circuit switches.
– Use extension cords with lamp guards to protect
lamps against breakage and to avoid combustible
material coming in contact with hot bulbs.
– Use accessories like sockets, plugs, switches and
appliances only when they are in good condition and
besurethattheyhavethemarkofBIS(ISI).(Necessity
using BIS(ISI) marked accessories is explained under
standardisation.
– Never extend electrical circuits by using temporary
wiring.
– Stand on a wooden stool, or an insulated ladder while
repairing live electrical circuits/ appliances or replac-
ing fused bulbs. In all the cases, it is always good to
open the main switch and make the circuit dead.
– Stand on rubber mats while working/operating switch
panels, control gears etc.
– Position the ladder, on firm ground.
– While using a ladder, ask the helper to hold the ladder
against any possible slipping.
– Always use safety belts while working on poles or high
rise points.
– Never place your hands on any moving part of rotating
machine and never work around moving shafts or
pulleys of motor or generator with loose shirt sleeves
or dangling neck ties.
– Onlyafteridentifyingtheprocedureofoperation,oper-
ate any machine or apparatus.
– Runcablesorcordsthroughwoodenpartitionsorfloor
after inserting insulating porcelain tubes.
– Connections in the electrical apparatus should be
tight. Loosely connected cables will heat up and end
in fire hazards.
– Use always earth connection for all electrical appli-
ances alongwith 3-pin sockets and plugs.
– While working on dead circuits remove the fuse grips;
keep them under safe custody and also display ‘Men
on line’ board on the switchboard.
– Do not meddle with interlocks of machines/switch
gears.
– Do not connect earthing to the water pipe lines.
– Do not use water on electrical equipment.
– Discharge static voltage in HV lines/equipment and
capacitors before working on them.
Practice safe method - Rescue a person from live wires
Objectives: At the end of this exercise you shall be able to
• rescue a person from live wire
• apply respiratory resuscitation.

22
Disconnecting a person (mock victim) from a live
supply (simulated).
Observe the person (mock victim) receiving an electric
shock. Interpret the situation quickly.
Remove the victim safety from the `live` equipment by
disconnecting the supply or using one of the items of
insulating material.
Do not run to switch off the supply that is far
away.
Do not touch the victim with bare hands until
the circuit is made dead or the victim is moved
away from the equipment.
Pushorpullthevictimfromthepointofcontact
of the live equipment, without causing serious
injury to the victim.
Move the victim physically to a nearby place.
Check for the victim's natural breathing and conscious-
ness.
Take steps to apply respiratory resuscitation if the victim
is unconscious and not breathing.
Artificial respiratory resuscitation
If breathing has stopped, apply immediate artificial respi-
ration.
Loosen the tight clothing of the victim. If not possible to
loosenquickly,donotspendtoomuchtimeinthisactivity.
Remove obstructions from the mouth, if any.
Send word for professional assistance. (If no other
person is available, you stay with the victim and render
help as best as you can.)
Look for visible injury in the body and decide on the
suitable method of artificial respiration.
Have you observed ? (In this case you are told by the
instructor.)
In the case of injury/burns to chest and/or belly follow the
mouth to mouth method.
In case the mouth is closed tightly, use Schafer's or
Holgen–Nelson method.
In the case of burn and injury in the back, follow Nelson's
method.
Arrange the victim in the correct position for giving artifi-
cial respiration. Follow the steps explained, given under
skill information for each method of artificial respiration,
until the victim breathes naturally or professional help
arrives.
All action should be taken immediately.
Delayevenbyafewsecondsmaybedangerous.
Exercise extreme care to prevent injury to inter-
nal organs.
Place the mock victim in the recovery position.
Cover the victim with coat, sacks or improvise your own
method. It helps to keep the victim's body warm.
Artificial respiration - Nelson's arm - lift back - pressure method
Objective : This shall help you to
• resuscitation of a victim by the Holgen–Nelson method.
Nelson's arm-lift back-pressure method
Caution
– Remove the victim from contact with the live equip-
ment. (Ref. related theory - Electrical safety)
– Tight clothing which may interfere with the victim's
breathing must be loosened.
– Remove any foreign materials or false teeth from his
mouth, and keep the mouth open.
– Donotdelayartificialrespirationforlooseningclothes
or even if the mouth is closed tightly.
Nelson's arm-lift back pressure method must
not be used in case there are injuries to the chest
and belly.
1 Place the victim prone (that is, face down) with his
arms folded with the palms one over the other and the
head resting on his cheek over the palms. Kneel on
one or both knees near the victim's hand. Place your
hands on the victim's back beyond the line of the
armpits,withyourfingersspreadoutwardsanddown-
wards, thumbs just touching each other as in Fig 1.

23
Artificial respiration - Schafer's method
Objective: This shall help you to
• resuscitation of a victim by the Schafer's method.
3 Synchronizing the above movement rock back-
wards, slide your hands downwards along the vic-
tim's arms and grasp his upper arm just above the
elbows as shown in Fig 3. Continue to rock back-
wards.
4 As you rock back, gently raise and pull the victim's
arms towards you as in Fig 4 until you feel tension
in his shoulders. To complete the cycle, lower the
victim's arms and move your hands up to the initial
position.
2 Gently rock forward keeping the arms straight until
they are nearly vertical, and thus steadily pressing
the victim's back as in Fig 2 to force the air out of the
victim's lungs.
Other steps
1 Send for a doctor immediately.
2 Continue artificial respiration till the victim begins to
breathe naturally. Please note in some cases it may
take hours.
3 Keep the victim warm with a blanket, wrapped up hot
water bottles or warm bricks; stimulate circulation by
stroking the insides of the arms and legs towards the
heart.
4 When the victim revives, keep him lying down and do
not let him exert himself.
5 Do not give him any stimulant until he is fully con-
scious.
Schafer's method
– Do not use this method in case of injuries to victim on
the chest and belly.
– Make the equipment dead by opening the switch and
release the victim.
– If the victim is aloft, measures must be taken to
prevent him from falling or to make him fall safe.
– Do not touch the victim with bare hands until you are
sure that he is free from electrical contact..
Avoid violent operations to prevent injury to the
internal parts.
1 Lay the victim on his belly, one arm extended directly
forward, the other arm bent at the elbow and with the
face turned sideward and resting on the hand or fore-
arm as shown in Fig 1.

24
2 Kneel astride the victim, so that his thighs are
betweenyourkneesandwithyourfingersandthumbs
positioned as in Fig 1.
3 With the arms held straight, swing forward slowly so
that the weight of your body is gradually brought to
bear upon the lower ribs of the victim to force the air
out of the victim's lungs as shown in Fig 2.
4 Now swing backward immediately removing all
pressure from the victim's body as shown in Fig 3,
and thereby allowing the lungs to fill with air.
5 After two seconds, swing forward again and repeat
the cycle twelve to fifteen times a minute.
heart.
3 Continue artificial respiration till the victim begins to
breathe naturally. Beware it may take hours even.
5 Do not give him any stimulant until he is fully
conscious.
Caution
Tight clothing which may interfere with the victim's
breathing must be loosened; all foreign matter, such
as false teeth, tobacco, pan, etc. should be removed
from his mouth. Delay by even a few seconds may be
dangerous.
– Loosen tight clothing which may interfere with the
victim's breathing.
– Make sure that the airways (nose and mouth) are
clear. Remove loose dentures or other obstructions
from the mouth.
– Do not delay artificial respiration for loosening the
clothes. Delay even by a few seconds may be
dangerous.
Other steps
1 Send for a doctor immediately.
Artificial respiration - mouth to mouth method
Objective: This shall help you to
• perform resuscitation of a victim by mouth to mouth method.
Mouth-to-mouth method of artificial respiration
– Free the victim from the live equipment before com-
mencing artificial respiration.
1 Lay the victim flat on his back and place a roll of
clothing under his shoulders to ensure that his head
is thrown well back. (Fig 1)
Tilt the victim's head back so that the chin points
straight upward. (Fig 2)

25
4 Blow into the victim's mouth (gently in the case of
an infant) until his chest rises. Remove your mouth
and release the hold on the nose, to let him exhale,
turning your head to hear the out-rush of air. The first
8 to 10 breaths should be as rapid as the victim
responds, thereafter the rate should be slow down to
about 12 times a minute (20 times for an infant).
If air cannot be blown in, check the position of
the victim's head and jaw and recheck the
mouth for obstructions, then try again more
forcefully. If the chest still does not rise, turn
the victim's face down and strike his back
sharply to dislodge obstructions.
2 Grasp the victim's jaw as shown in Fig 3, and raise
it upward until the lower teeth are higher than the
upper teeth; or place fingers on both sides of the jaw
near the ear lobes and pull upward. Maintain the
jaw position throughout the artificial respiration to
prevent the tongue from blocking the air passage.
Sometimes air enters the victim's stomach as
evidenced by a swelling stomach. Expel the
air by gently pressing the stomach during the
exhalation period.
Mouth to nose method: If the victim's mouth will not
open, or has a blockage you cannot clear, use the fingers
of one hand to keep the victim's lips firmly shut, seal
your lips around the victim's nostrils and breathe
into him. Check to see if the victim's chest is rising
and falling. (Fig 5)
Cardiac arrest: In cases where the heart has stopped
beating, you must act immediately.
You should check if :
• the carotid pulse in the neck can be felt. (Fig 6)
• the casualty is blue around the lips.
• the pupils of his eyes are widely dilated.
Quick action is essential.
• Lay the victim on his back on a firm surface.
• Kneel alongside, facing the chest and locate the
lower part of the breastbone. (Fig 7).
3 Take a deep breath and place your mouth over the
victim's mouth as shown in Fig 4 making airtight
contact. Pinch the victim's nose shut with the thumb
and forefinger. If you dislike direct contact, place a
porous cloth between your mouth and the victim's.
For an infant, place your mouth over its mouth and
nose. (Fig 4).

26
• Place the palm of one hand on the centre of the lower
part of the breastbone, keeping your fingers off the
ribs. Cover the palm with your other hand and lock
your fingers together. (Fig 8)
• Keeping your arms straight, press sharply down on
the lower part of the breastbone; then release the
pressure. (Fig 9)
• Move back to the victim's mouth to give two breaths
(mouth-to-mouth resuscitation). (Fig 4)
• Continue with another 15 compressions of the heart,
followed by a further two breaths of mouth-to-mouth
resuscitation, and so on, checking for the pulse at
frequent intervals.
• As soon as the heartbeat returns, stop the
compre-ssions immediatelybutcontinuewithmouth-
to-mouth resuscitation until natural breathing is fully
restored.
• Place the victim in the recovery position. Keep him
warm and get medical help quickly. (Fig 10)
• Repeat this 15 times at a rate of atleast once per
second.
• Check the carotid pulse.
Other aids
1 Send him (or) victim for a doctor immediately.
heart.
3 Continue artificial respiration till the viticm begins to
breathe naturally. It may take hours.
5 Do not give him any stimulant until he is fully con-
scious.

27
Direct current (DC): Electric current can be defined as
the flow of electrons in a circuit. Based on the electron
theory, electrons flow from the negative (-) polarity to the
positive (+) polarity of a voltage source.
Direct current (DC) is the current that flows only in one
direction in a circuit. (Fig 1) The current in this type of
circuit is supplied from a DC voltage source. Since the
polarity of a DC source remains fixed, the current pro-
duced by it flows in one direction only.
Dry cells are commonly used as a DC voltage source.
Both the voltage and polarity of the dry cell are fixed.
When connected to a load, the current produced flows in
one direction at some steady or constant value.
Adirectcurrentflowneednotnecessarilybeconstant,but
it must travel in the same direction at all times. There are
several types of direct current, and all of them depend
upon the value of the current in relation to time. (Fig 2)
A constant DC current shows no variation in value over a
period of time. Both varying and pulsating DC currents
have a changing value when plotted against time. The
pulsatingDCcurrentvariationsareuniform,andrepeatat
regular intervals.
Alternating current (AC): An alternating current (AC)
circuit is one in which the direction and amplitude of the
currentflowchangeatregularintervals.Thecurrentinthis
type of circuit is supplied from an AC voltage source. The
polarity of an AC source changes at regular intervals
resulting in a reversal of the circuit current flow.
Alternating current usually changes in both value and
direction. The current increases from zero to some maxi-
mum value, and then drops back to zero as it flows in one
direction. This same pattern is then repeated as it flows in
the opposite direction. The wave-form or the exact man-
ner in which the current increases and decreases is
determined by the type of AC voltage source used. (Fig 3)
Alternating current generator: Alternating current is
used wherever a large amount of electrical power is
required. Almost all of the electrical energy supplied for
domestic and commercial purposes is alternating cur-
rent. AC voltage is used because it is much easier and
cheaper to generate, and when transmitted over long
distances, the power loss is low.
AC equipment is generally more economical to maintain
and requires less space per unit of power than the DC
equipment.
Alternating current can be generated at higher voltages than
DC, with fewer problems of heating and arcing.
The basic method of obtaining AC is by the use of an AC
generator.Agenerator isamachinethatusesmagnetism
to convert mechanical energy into electrical energy.
Alternating current
• define alternating current and direct current
• explain the difference between alternating current and direct current
• list the advantages and disadvantages of alternating current.

28
3-Phase AC fundamentals
• state and describe single phase and three phase system
• state one of the advantages of the 3-phase system over a single phase system
Introduction
When a piece of electrical equipment is plugged into the
socket of a normal alternating current supply (e.g. a ring
main circuit), it is connected between the terminal of one
phase and the neutral wire. (Fig 1)
Thus a normal domestic alternating current circuit may
also be described as a single-phase circuit.
Similarly,athree-phasepowerconsumerisprovidedwith
the terminals of three phases. (Fig 2)
One great advantage of a three-phase AC supply is that
it can produce a rotating magnetic field when a set of
stationarythree-phasecoilsisenergizedfromthesupply.
This is the basic operating principle for most modern
rotating machines and, in particular, the three-phase
induction motor.
Further,lightingloadscanbeconnectedbetweenanyone
of the three phases and neutral.
Review: Further to the above two advantages the follow-
ing are the advantages of polyphase system over single
phase system.
• 3-phase motors develop uniform torque whereas sin-
gle phase motors produce pulsating torque only
• Most of the 3-phase motors are self starting whereas
single phase motors are not
• For a given size the power out put is high in 3-phase
motors whereas in single phase motors the power
output is low.
• 3-phase motor like squirrel cage induction motor is
robust in construction and more are less maintenance
free.
Systems of connection in 3-phase AC
Objective: At the end of this lesson you shall be able to
• explain the star and delta systems of connection.
Methods of 3-phase connection: If a three-phase load
is connected to a three-phase network, there are two
basic possible configurations. One is `star connection'
(symbol Y) and the other is `delta connection' (symbol D).
Star connection: In Fig 1 the three-phase load is shown
asthreeequalmagnituderesistances. Fromeachphase,
at any given time, there is a path to the terminal points U,
V, W of the equipment, and then through the individual
elements of the load resistance. All the elements are
connected to one point N: the `star point'. This star point
is connected to the neutral conductor N. The phase
currents iU
, iV
, and iW
flow through the individual elements,
and the same current flows through the supply lines, i.e.
in a star connected system, the supply line current (IL
) =
phase current (IP
).

29
In the phasor diagram (Fig 2)
VL
= VUV
= VUN
Cos 30o
+ VNV
Cos 30o
But Cos 30o
=
3
2
.
Thus as VUN
= VVN
= VP
VL
= 3 VP
.
This same relationship is applied to VUV
, VVW
and VWU
.
In a three-phase star connection, the line volt-
age is always 3 times the phase-to-neutral
voltage. The factor relating the line voltage to
the phase voltage is 3 .
Example 1: What is the line voltage for a three-phase,
balancedstar-connectedsystem,havingaphasevoltage
of 240V?
VL
= 3 VP
= 3 x 240
= 415.7V.
Delta connection: There is a second possible arrange-
ment for connecting a three-phase load in a three-phase
network. This is the delta or mesh connection (D).(Fig 3)
The load impedances form the sides of a triangle. The
terminals U, V and W are connected to the supply lines of
the L1
, L2
and L3
.
In contrast to a star connection, in a delta
connection the line voltage appears across
each of the load phases.
The potential difference for each phase, i.e. from a line to
the star point, is called the phase voltage and
designated as VP
. The potential difference across any
two lines is called the line voltage VL
. Therefore, the
voltage across each impedance of a star connection
is the phase voltage VP
. The line voltage VL
appears
across the load terminals U-V, V-W and W-U and desig-
nated as VUV
, VVW
and VWU
in the Fig 1. The line voltage
in a star-connected system will be equal to the phasor
sum of the positive value of one phase voltage and the
negativevalueoftheotherphasevoltagethatexistacross
the two lines.
Thus
VL
= VUV
= (phasor VUN
) (phasor VVN
)
= phasor VUN
+ VVN
.
The voltages, with symbols VUV
, VVW
and VWU
are, there-
fore, the line voltages.
The phase currents through the elements in a delta
arrangement are composed of IUV
, IVW
and IWU
. The
currentsfromthesupplylinesareIU
,IV
andIW
,andoneline
current divides at the point of connection to produce two
phase currents.
On the other hand, the line currents IU
, IV
and IW
are now
compounded from the phase currents. A line current is
always given by the phasor sum of the appropriate
phase currents. The line current IU
is the phasor sum of
the phase currents IUV
and IUW
.
Hence, IU
= IUV
Cos 30o
+ IIUW
Cos 30o
But Cos 30o
=
3
2
.
Thus IL
= 3 Iph
Thus, for a balanced delta connection, the ratio of the line
current to the phase current is 3 .
Thus, line current = 3 x phase current.

30
Neutral: In a three-phase star connection, the star point
isknownasneutralpoint,andtheconductorconnectedto
the neutral point is referred as neutral conductor.
Earthing of neutral conductor: Supply of electrical
energy to commercial and domestic consumers is an
important application of three-phase electricity. For `low
voltage distribution' - in the simplest case, i.e. supply of
light and power to buildings.
Neutral in 3-phase system
• explain the current in neutral of a 3-phase star connection
• state the method of producing artificial neutral in a 3-phase delta connection
• state the method of earthing the neutral.
A neutral conductor is required for measuring phase
voltage, energy, power to connect indicating lamps, etc.
Anartificialneutralforconnectingindicatinglampscanbe
formedbyconnectingtheminstar.(Fig1) Artificialneutral
for instruments can be formed by connecting additional
resistors in star. (Fig 2)

31
D.O.L. starter
• state the specification of a D.O.L. starter, explain its operation and application
• explain the necessity of a back-up fuse and its rating according to the motor rating.
Introduction : The D.O.L. starter consists of the fixed
contacts, movable contacts, no-volt coil, overload relay
and start button which is in green colour and a stop but-
ton in red colour with a locking arrangement. Analyse the
D.O.L. starter available in the workshop. The main pur-
pose of the contactor is to make and break the motor
circuit. These contacts in the contactor suffer maximum
wear, due to frequent use and hence these contacts are
made of silver alloy material.
A no-volt coil acts as under-voltage release mechanism
disconnecting supply to the motor when the supply volt-
age fails or is lower than the stipulated value. Thus the
motor will be disconnected from supply under these con-
ditions. The no-volt coil magnetic system consists of a
laminated iron core for minimising the eddy current and
hysterisis losses. Shading rings are provided on the pole
faces of the magnetic core to reduce the hum level and
chattering which is present due to A.C. supply.
A thermal overload relay unit is provided for the protec-
tion of the motor. This unit consists of a triple pole, bime-
tallic relay housed in a sealed bimetallic enclosure. This
is provided with a current setting arrangement. After trip-
ping on overload, the relay has to be reset by pressing
the stop button. The relay can be reset only after bimetalic
strips get cooled sufficiently.
A D.O.L. starter is one in which a contactor with no-volt
relay, ON and OFF buttons, and overload relay are
incorporated in an enclosure.
Construction and operation: A push-button type, direct
on-line starter, which is in common use, is shown in Fig 1.
It is a simple starter which is inexpensive and easy to
install and maintain.
There is no difference between the complete contactor
circuit explained in Exercise 12 and the D.O.L.starter,
except that the D.O.L. starter is enclosed in a metal or
PVC case, and in most cases, the no-volt coil is rated for
415Vandistobeconnectedacrosstwophasesasshown
in Fig 1. Further the overload relay can be situated
between CTP switch and contactor,or between the con-
tactor and motor as shown in Fig 1, depending upon the
starter design.
Specification of D.O.L. starters: While giving specifica-
tion, the following data are to be given.
D.O.L. STARTER
Phases - single or three.
Voltage 230 or 415V.
Current rating 10, 16, 32, 40, 63, 125 or 300 amps.
No-voltcoilvoltageratingACorDC12,24,36,48,110,
230/250, 360, 380 or 400/440 volts.
Number of main contacts 2, 3 or 4 which are normally
open.
Number of auxiliary contacts 2 or 3. 1 NC + 1 NO or 2
NC + 1 NO respectively.
Push-button - one `ON' and one `OFF' buttons.
Overload from setting – amp-to-amp. Enclosure -
metal sheet or PVC.
Applications: InaninductionmotorwithaD.O.L.starter,
the starting current will be about 6 to 7 times the full load
current. As such, D.O.L. starters are recommended to be
used only up to 3 HP squirrel cage induction motors, and
up to 1.5 kW double cage rotor motors.
Necessity of back-up fuses: Motor starters must never
be used without back-up fuses. The sensitive thermal
relay mechanism is designed and calibrated to provide
effectiveprotectionagainstoverloadsonly.Whensudden
short circuits take place in a motor circuit, the overload
relays, due to their inherent operating mechanism, take a
longer time to operate and open the circuit. Such delays
will be sufficient to damage the starter motor and

32
connected circuits due to heavy in-rush of short circuit
currents. This could be avoided by using quick-action,
high-rupturing capacity fuses which, when used in the
motor circuit, operate at a faster rate and open the circuit.
Hence H.R.C. diazed (DZ) type fuses are recommended
for protecting the installation as well as the thermal
overload relay of the motor starter against short circuits.
In case of short circuits, the back-up fuses melt and open
the circuit quickly. A reference table indicating fuse rat-
ings for different motor ratings is given.
Itisrecommendedthattheuseofsemi-enclosed,rewirable,
tinned copper fuses may be avoided as for as possible.
The given full load currents apply in the case of
single phase, capactor-start type motors, and in
thecaseof3-phase,squirrelcagetypeinduction
motors at full load having average power factor
and efficiency. The motors should have speeds
not less than 750 r.p.m.
Fusesuptoandincluding63AareDZtypefuses.
Fuses from 100 A and above are IS type fuses
(type HM).
Table of relay ranges and back-up fuses for motor protection
Sl. Motor ratings Motor ratings Relay range Nominal back-up
No. 240V 1-phase 415V 3-phase A fuse recommended
hp kW Full load hp kW Full load a c
current current
1 0.05 0.04 0.175 0.15 - 0.5 1A
2 0.05 0.04 0.1 0.075 0.28 0.25 - 0.4 2A
3 0.25 0.19 0.70 0.6 - 1.0 6A
4 0.125 0.11 0.50 0.37 1.2 1.0 - 1.6 6A
5 0.5 0.18 2.0 1.0 0.75 1.8 1.5 - 2.5 6A
6 0.5 0.4 3.6 1.5 1.1 2.6 2.5 - 4.0 10A
7 2.0 1.5 3.5 2.5 - 4.0 15A
8 0.75 0.55 2.5 1.8 4.8 4.0 - 6.5 15A
9 3.0 2.2 5.0 4.0 - 6.5 15A
10 1.0 0.75 7.5 5.0 3.7 7.5 6.0 - 10 20A
11 2.0 1.5 9.5 7.5 5.5 11.0 9.0 - 14.0 25A
12 3.0 2.25 14 10.0 7.5 14 10.0 - 16.0 35A

33
Manual star-delta switch/starter and Automatic star delta starter
• state the necessity of a star-delta starter for a 3-phase squirrel cage induction motor
• draw and explain the construction, connection and working of a star-delta switch and starter
• specify the back-up rating of the fuse in the motor circuit
• list of application of automatic star delta starter
• read the line diagram of automatic star delta starter
• describe the procedure of setting over load relays on star delta starter.
Necessity of star-delta starter for 3-phase squirrel
cage motor: If a 3-phase squirrel cage motor is started
directly, it takes about 5-6 times the full load current for a
few seconds, and then the current reduces to normal
valueoncethespeedacceleratestoitsratedvalue.Asthe
motor is of rugged construction and the starting current
remains for a few seconds, the squirrel cage induction
motor will not get damaged by this high starting current.
However with large capacity motors, the starting current
willcausetoomuchvoltagefluctuationsinthepowerlines
and disturb the other loads. On the other hand, if all the
squirrel cage motors connected to the power lines are
started at the same time, they may momentarily overload
the power lines, transformers and even the alternators.
Because of these reasons, the applied voltage to the
squirrel cage motor needs to be reduced during the
starting periods, and regular supply could be given when
the motor picks up its speed.
Followingarethemethodsofreducingtheappliedvoltage
to the squirrel cage motor at the start.
– Star-delta switch or starter
– Auto-transformer starter
– Step-down transformer starter
Star-delta starter: A star-delta switch is a simple ar-
rangement of a cam switch which does not have any
additionalprotectivedeviceslikeoverloadorunder-voltage
relayexceptfuseprotectionthroughcircuitfuses,whereas
the star-delta starter may have overload relay and under
voltage protection in addition to fuse protection. In a
star-delta switch/starter, at the time of starting, the squir-
rel cage motor is connected in star so that the phase
voltageisreducedto 3
1 timesthelinevoltage,andthen
when the motor picks up its speed, the windings are
connected in delta so that the phase voltage is the same
as the line voltage. To connect a star-delta switch/starter
to a 3-phase squirrel cage motor, all the six terminals of
the three-phase winding must be available.
As shown in Fig 1a, the star-delta switch connection
enables the 3 windings of the squirrel cage motor to be
connected in star, and then in delta. In star position, the
line supply L1
, L2
and L3
are connected to the beginning of
windings U1
, W1
and V1
respectively by the larger links,
Manual star-delta starter: Fig 2 shows the conventional
manual star-delta starter. As the insulated handle is
spring-loaded, it will come back to OFF position from any
position unless and until the no-volt (hold-on ) coil is
energised. When the hold-on coil circuit is closed through
the supply taken from U2
and W2
, the coil is energised and
itholdstheplunger,andtherebythehandleisheldindelta
position against the spring tension by the lever plate
mechanism. When the hold-on coil is de-energised the
plunger falls and operates the lever plate mechanism so
as to make the handle to be thrown to the off position due
to spring tension. The handle also has a mechanism (not
whereas the short links, which connect V2
U2
and W2
, are
shorted by the shorting cable to form the star point. This
connection is shown as a schematic diagram. (Fig 1b)
When theswitchhandleischangedovertodeltaposition,
the line supply L1
, L2
and L3
are connected to terminals U1
V2
, W1
U2
and V1
W2
respectively by the extra large links
to form a delta connection. (Fig 1c)

34
The motor also could be stopped by operating the stop
button which in turn de-energises the hold-on coil.
Back-up fuse protection: Fuse protection is necessary
inthestar-deltastartedmotorcircuitagainstshortcircuits.
In general, as a thumb rule for 415V, 3-phase squirrel
cage motors, the full load current can be taken as 1.5
timestheH.P.rating.Forexample,a10HP3-phase415V
motor will have approximately 15 amps as its full load
current.
Toavoidfrequentblowingofthefuseandatthesametime
for proper protection, the fuse wire rating should be 1.5
timesthefullloadcurrentratingofthemotor.Hencefor10
HP,15ampsmotor,thefuseratingwillbe23amps,orsay
25 amps.
Automatic star-delta starter
Applications : The primary application of star-delta mo-
tors is for driving centrifugal chillers of large central air-
conditioning units for loads such as fans, blowers, pumps
orcentrifuges,andforsituationswhereareducedstarting
torque is necessary. A star-delta motor is also used
where a reduced starting current is required.
In star-delta motors all the winding is used and there are
no limiting devices such as resistors or auto-transform-
ers. Star-delta motors are widely used on loads having
high inertia and a long acceleration period.
Overload relay settings : Three overload relays are
provided on star-delta starters. These relays are used so
thattheycarrythemotorwindingcurrent. Thismeansthat
the relay units must be selected on the basis of the
winding current, and not the delta connected full load
current. The motor name-plate indicates only the delta
connected full load current, divide this value by 1.73 to
obtainthewindingcurrent. Usethiswindingcurrentasthe
basis for selecting and setting the motor winding protec-
tion relay.
Operation : Figure 1 shows the line diagram of the power
circuit and the control circuit of the automatic star-delta
starter. Pressing the start button S-energises the star
contactor K3
. (Current flowsthroughK4
TNCterminals15
&16andK2
NCterminals11&12). OnceK3
energisesthe
K3
NOcontactcloses(terminals23&24)andprovidepath
for the current to close the contactor K1
. The closing of
contactor K1
establishes a parallel path to start button via
K1
NO terminals 23 & 24.
shown in Fig) which makes it impossible for the operator
to put the handle in delta position in the first moment. It is
only when the handle is brought to star position first, and
thenwhenthemotorpicksupspeed,thehandleispushed
to delta position.
The handle has a set of baffles insulated from each other
and also from the handle. When the handle is thrown to
star position, the baffles connect the supply lines L1
, L2
and L3
to beginning of the 3-phase winding W1
, V1
and U1
respectively. At the same time the small baffles connect
V2
, W2
and U2
through the shorting cable to form the star
point. (Fig 2b)
Whenthehandleisthrowntodeltaposition,thelargerend
of the baffles connect the main supply line L1
, L2
and L3
to
the winding terminals W1
U2
, V1
W2
and U1
V2
respectively
to form the delta connection. (Fig 2c)
The overload relay current setting could be adjusted by
the worm gear mechanism of the insulated rod. When the
load current exceeds a stipulated value, the heat devel-
oped in the relay heater element pushes the rod to open
thehold-oncoilcircuit,andtherebythecoilisde-energised,
and the handle returns to the off position due to the spring
tension.

35

36
Figure 4 shows the connections established while the
motor is running in delta with the contactors K1
and K2
closed.
Delta contact closes.
Troubleshooting of motor starter
In case the motor does not start even though the start
button is pressed, observe whether the stop button is
locked with a metallic locking piece provided near the
stop button. Release it and press the start button, then
observe the functioning of the motor. Even then if the
motor does not start check up the 3 phase supply. If the
supply is found available at the incoming terminals of the
starter, then switch off the supply and rectify the defect in
the starter. This is only trouble shooting of a motor starter.

37
The two-wattmeter method of measuring power
Objectives: At the end of this lesson you shall be able to:
• measure 3-phase power using two single phase wattmeter
• explain the `two-wattmeter' method of measuring power in a three-phase, three-wire system
Power in a three-phase, three-wire system is normally
measuredbythe`two-wattmeter'method. Itmaybeused
with balanced or unbalanced loads, and separate con-
nections to the phases are not required. This method is
not, however, used in four-wire systems because current
may flow in the fourth wire, if the load is unbalanced and
the assumption that IU
+ IV
+ IW
= 0 will not be valid.
The two wattmeters are connected to the supply system
as shown in Fig 1. The current coils of the two wattmeters
are connected in two of the lines, and the voltage coils are
connected from the same two lines to the third line. The
total power is then obtained by adding the two readings:
PT
= P1
+ P2
.
Consider thetotalinstantaneouspowerinthesystemPT
=
P1
+ P2
+ P3
where P1
, P2
and P3
are the instantaneous
values of the power in each of the three phases.
PT
= VUN
iU
+ VVN
i V
+ VWN
IW
Since there is no fourth wire, iU
+iV
+iW
= 0; iV
= (iU
+ iW
).
PT
= VUN
iU
VVN
(iU
+iW
) + VWN
iW
= iU
(VUN
VVN
) + iW
(VWN
VUN
)
= iU
VUV
+ iW
VWV
Now iU
VUV
is the instantaneous power in the first wattme-
ter, and iW
VWV
is the instantaneous power in the second
wattmeter. Therefore, the total mean power is the sum of
the mean powers read by the two wattmeters.
Itispossiblethatwiththewattmetersconnectedcorrectly,
one of them will attempt to read a negative value because
of the large phase angle between the voltage and current
for that instrument. The current coil or voltage coil must
then be reversed and the reading given a negative sign
when combined with the other wattmeter readings to
obtain the total power.
Atunitypowerfactor,thereadingsoftwowattmeterwillbe
equal. Total power = 2 x one wattmeter reading.
When the power factor = 0.5, one of the wattmeter's
reading is zero and the other reads total power.
When the power factor is less than 0.5, one of the
wattmeters will give negative indication. In order to read
the wattmeter, reverse the pressure coil or current coil
connection. The wattmeter will then give a positive
reading but this must be taken as negative for calculating
the total power.
When the power factor is zero, the readings of the two
wattmeters are equal but of opposite signs.
Measurement of energy in single phase circuits
• describe the construction and working principle of single phase energy meters.
Necessity of energy meter: The electrical energy sup-
pliedbytheElectricityboardshouldbebilled,basedonthe
actual amount of energy consumed. We need a device to
measure the energy supplied to a consumer. Electrical
energy is measured in kilowatt hours in practice. The
meter used for this is an energy meter.
In AC, an induction type of energy meter is universally
used for measurement of energy in domestic and indus-
trial circuits.
Principle of a single phase induction type energy
meter: The operation of this meter depends on the
induction principle. Two alternating magnetic fields pro-
duced by two coils induce current in a disc and produce a
torque to rotate it (disc). One coil (potential coil) carries
current proportional to the voltage of the supply and the
other(currentcoil)carriestheloadcurrent.(Fig1) Torque
is proportional to the power as in wattmeter. The watt-
hourmetermusttakebothpowerandtimeintoconsidera-
tion. The instantaneous speed is proportional to the
powerpassingthroughit. Thetotalnumberofrevolutions
in a given time is proportional to the total energy that
passes through the meter during that period of time.
Parts and functions of an energy meter: The parts of
the induction type single phase energy meter are as
shown in Fig 1.

38
Ironcore:Itisspeciallyshapedtodirectthemagneticflux
in the desired path. It directs the magnetic lines of force,
reduces leakage flux and also reduces magnetic reluc-
tance.
Potential coil (voltage coil): The potential coil is con-
nected across the load and is wound with many turns of
fine wire. It induces eddy current in the aluminium disc.
Current coil: The current coils, connected in series with
load, are wound with a few turns of thick wire, since they
must carry the full load current.
Disc: The disc is the rotating element in the meter, and is
mounted on a vertical spindle which has a worm gear at
one end. The disc is made of aluminium and is positioned
in the air gap between the potential and current coil
magnets.
Spindle: The spindle ends have hardened steel pivots.
Thepivotissupportedbyajewelbearing. Thereisaworm
gear at one end of the spindle. As the gear turns the dials,
they indicate the amount of energy passing through the
meter.
Permanent magnet/brake magnet: The permanent
magnet restrains the aluminium disc from racing at a high
speed. It produces an opposing torque that acts against
the turning torque of the aluminium disc.
Functioning of energy meters: The rotation of the
aluminium disc in Fig 2 is accomplished by an electro-
magnet, which consists of a potential coil and current
coils. The potential coil is connected across the load. It
induces an eddy current in the aluminium disc. The eddy
current produces a magnetic field which reacts with the
magnetic field produced by the current coils to produce a
driving torque on the disc.
Insulation tester (Megohmmeter)
• state the necessity of insulation tester
• state the types of insulation tester
• state the main parts of an insulation tester (magneto-generator type)
• state the working principle of an insulation tester (magneto-generator type)
• state the ranges of magneto-generator type insulation tester
• explain the constructional features of transitarized insulation tester
• state the I.S. recommended voltage ratings of insulation tester
• state the safety precautions to be observed while using an insulation tester
• state the uses of an insulation tester.
Necessity of megohmmeter: Ordinary ohmmeters and
resistancebridgesarenotgenerallydesignedtomeasure
extremely high values of resistance. The instrument
designed for this purpose is the megohmmeter. (Fig 1) A
megohmmeter is commonly known as MEGGER.
Types of insulation testers: There are two types of
insulation testers as stated below.
– Magneto-generator type
– Transistorised type
Magneto-generatortypeInsulationtester:Inthistester,
the testing voltage is produced by a magneto-generator
when the handle is cranked at a speed of 160 r.p.m.
approximately,whereasthetransistorisedinsulationtester
isincorporatedwithcellswhichpowerthetester.However
a testing voltage in the order of 250V to 5000 V DC is
produced by internal circuitry.

39
Construction: The megohmmeter consists of (1) a
small DC generator, (2) a meter calibrated to measure
high resistance, and (3) a cranking system. (Fig 2)
A generator commonly called a magneto is often de-
signedtoproducevariousvoltages.Theoutputmaybeas
low as 500 volts or as high as 1 megavolt. The current
supplied by the megohmmeter is in the order of 5 to 10
milliamperes. The meter scale is calibrated: either in kilo-
ohms (kW) or in megohms(MW).
Working principle: (Fig 2) The permanent magnets
supply the flux for both the generator and the metering
device. The voltage coils are connected in series across
the generator terminals. The current coil is arranged so
that it will be in series with the resistance to be measured.
Theunknownresistanceisconnectedbetweenthetermi-
nals L and E.
When the armature of the magnet is rotated, an emf is
produced. This causes the current to flow through the
current coil and the resistance being measured. The
amount of current is determined by the value of the
resistance and the output voltage of the generator. The
torque exerted on the meter movement is proportional to
the value of current flowing through the current coil.
The current through the current coil, which is under the
influenceofthepermanentmagnet,developsaclockwise
torque. The flux produced by the voltage coils reacts with
the main field flux, and the voltage coils develop a coun-
ter-clockwise torque. For a given armature speed, the
current through the voltage coils is constant, and the
strength of the current coil varies inversely with the value
ofresistancebeingmeasured.Asthevoltagecoilsdeflect
counter-clockwise, they move away from the iron core
and produce less torque. A point is reached for each
valueofresistanceatwhichthetorquesofthecurrentand
voltage coils balance, providing an accurate measure-
ment of the resistance. Since the instrument does not
haveacontrollingtorquetobringthepointertozero,when
the meter is not in use, the position of the pointer may be
anywhere on the scale.
The speed at which the armature rotates does not affect
the accuracy of the meter, because the current through
both the circuits changes to the same extent for a given
change in voltage. However, it is recommended to rotate
the handle at the slip speed to obtain steady voltage.
Because megohmmeters are designed to measure
very high values of resistance, they are frequently
used for insulation tests.

40
Principle of induction motor
• explain briefly the method of producing a rotating field
• state the principle of a 3-phase induction motor.
The three-phase induction motor is used more exten-
sively than any other form of electrical motor, due to its
simple construction, trouble-free operation, lower cost
and a fairly good torque speed characteristic.
Principle of 3-phase induction motor: It works on the
sameprincipleasaDCmotor,thatis,thecurrent-carrying
conductors kept in a magnetic field will tend to create a
force. However, the induction motor differs from the DC
motor in fact that the rotor of the induction motor is not
electricallyconnectedtothestator,butinducesavoltage/
current in the rotor by the transformer action, as the stator
magnetic field sweeps across the rotor. The induction
motor derives its name from the fact that the current in the
rotor is not drawn directly from the supply, but is induced
by the relative motion of the rotor conductors and the
magnetic field produced by the stator currents.
The stator of the 3-phase induction motor is similar to that
of a 3-phase alternator, of revolving field type. The
three-phase winding in the stator produces a rotating
magneticfieldinthestatorcoreasitwillbeexplainedlater.
The rotor of the induction motor may have either shorted
rotor conductors in the form of a squirrel cage or in the
form of a 3-phase winding to facilitate the circulation of
current through a closed circuit.
Let us assume that the stator field of the induction motor
is rotating in a clockwise direction as shown in Fig 1. This
makes for the relative motion of the rotor in an anticlock-
wise direction as shown in Fig 1. Applying Fleming's right
hand rule, the direction of emf induced in the rotor will be
towards the observer as shown in Fig 2. As the rotor
conductors have a closed electric path, due to their
shorting, a current will flow through them as in a
short-circuited secondary of a transformer.
The magnetic field produced by the rotor currents will be
inacounter-clockwisedirectionasshowninFig2accord-
ing to Maxwell's Corkscrew rule. The interaction between
the stator magnetic field and the rotor magnetic field
results in a force to move the rotor in the same direction
as that of the rotating magnetic field of the stator, as
At higher speeds of the rotor nearing to synchronous
speeds, the relative speed between the rotor and the
rotating magnetic field of the stator reduces and results in
a smaller induced emf in the rotor. Theoretically, if we
assume that the rotor attains a speed equal to the syn-
chronousspeedoftherotatingmagneticfieldofthestator,
there will be no relative motion between the stator field
and the rotor, and thereby no induced emf or current will
be there in the rotor. Consequently there will not be any
torque in the rotor. Hence the rotor of the induction motor
cannot run at a synchronous speed at all. As the motor is
loaded, the rotor speed has to fall to cope up with the
mechanical force; thereby the relative speed increases,
and the induced emf and current increase in the rotor
resulting in an increased torque.
To reverse the direction of rotation of a rotor: The
direction of rotation of the stator magnetic field depends
upon the phase sequence of the supply. To reverse the
direction of rotation of the stator as well as the rotor, the
phase sequence of the supply is to be changed by
changing any two leads connected to the stator.
shown in Fig 3. As such the rotor follows the stator field in
the same direction by rotating at a speed lesser than the
synchronous speed of the stator rotating magneticfield.

41
Rotating magnetic field from a three-phase stator:
The operation of the induction motor is dependent on the
presence of a rotating magnetic field in the stator. The
statoroftheinductionmotorcontainsthree-phasewindings
placed at 120 electrical degrees apart from each other.
These windings are placed on the stator core to form
non-salient stator field poles. When the stator is ener-
gized from a three-phase voltage supply, in each phase
winding will set up a pulsating field. However, by virtue of
the spacing between the windings, and the phase differ-
ence, the magnetic fields combine to produce a field
rotating at a constant speed around the inside surface of
the stator core. This resultant movement of the flux is
called the `rotating magnetic field', and its speed is
called the `synchronous speed'.
The manner, in which the rotating field is set up, may be
described by considering the direction of the phase cur-
rents at successive instants during a cycle. Fig 4a shows
a simplified star-connected, three-phase stator winding.
The winding shown is for a two-pole induction motor. Fig
4bshowsthephasecurrentsforthethree-phasewindings.
Thephasecurrentswillbe120electricaldegreesapartas
showninFig4b.Theresultantmagneticfieldproducedby
the combined effect of the three currents is shown at
increments of 60° for one cycle of the current.
Using the same reasoning as above for the current wave
positions 3, 4, 5, 6 and 7, it will be seen that for each
successive increment of 60 electrical degrees, the result-
ant stator field will rotate a further 60° as shown in Fig 5.
Note that from the resultant flux from position (1) to
position (7), it is obvious that for each cycle of applied
voltage the field of the two-pole stator will also rotate one
revolution around its core.
From what is stated above it will be clear that the rotating
magnetic field could be produced by a set of 3-phase
stationary windings, placed at 120° electrical degrees
apart, and supplied with a 3-phase voltage.
Thespeedatwhichthefieldrotatesiscalledsynchronous
speed, and, it depends upon the frequency of supply and
the number of poles for which the stator is wound.
Hence
Ns
= Synchronous speed in r.p.m.
=
where`P'isthenumberofpolesinthestator,and`F'isthe
frequency of the supply.
At position (1) in Fig 4b, the phase current IR
is zero, and
hence coil R will be producing zero flux. However, the
phase current IB
is positive and Iy
is negative.
Consideringtheinstantaneouscurrentdirectionsofthese
threephasewindings,asshowninFig4batposition1,we
can indicate the current direction in Fig 5(1).
For convenience the +ve current is shown as +ve sign,
and the -ve current is shown as dot (•) sign. Accordingly
Y2
and B1
are shown as positive and Y1
and B2
are shown
asnegative.UsingMaxwell'scorkscrewrule,theresulting
flux by these currents will produce a flux as shown in Fig
5(1). The arrow shows the direction of the magnetic field
and the magnetic poles in the stator core.
At position 2, as shown by Fig 5(2), 60 electrical degrees
later, the phase current IB
is zero, the current IR
is positive
and the current IY
is negative. In Fig 5a the current is now
observedtobeflowingintotheconductorsatthecoil ends
R1
and Y2
, and out of the conductors at coil R2
and Y1
.
Therefore, as shown in Fig 5c(2), the resultant magnetic
poles are now at a new position in the stator core. In fact
the poles in position 2 have also rotated 60° from position
(1).

42
Construction of A3-phase squirrel cage induction motor
• describe the construction of a 3-phase, squirrel cage induction motor
• describe the construction of double squirrel cage motor and its advantage
• explain slip, speed, rotor frequency, rotor copper loss, torque and their relationship.
Three-phase induction motors are classified according to
their rotor construction. Accordingly, we have two major
types.
– Squirrel cage induction motors
– Slip ring induction motors.
Squirrel cage motors have a rotor with short-circuited
bars whereas slip ring motors have wound rotors having
three windings, either connected in star or delta. The
terminals of the rotor windings of the slip ring motors are
brought out through slip-rings which are in contact with
stationary brushes.
Development of these two types of induction motors is
due to the fact that the torque of the induction motor
depends upon the rotor resistance. Higher rotor resist-
ance offers higher starting torque but the running torque
will be low with increased losses and poor efficiency. For
certain applications of loads where high starting torque
and sufficient running torque are the only requirements,
the rotor resistance should be high at the time of starting,
and low while the motor is running. If the motor circuit is
leftwithhighresistance,therotorcopperlosswillbemore,
resulting in low speed and poor efficiency. Hence it is
advisable to have low resistance in the rotor while in
operation.
Both these requirements are possible in slip-ring motors
by adding external resistance at the start and cutting it off
while the motor runs. As this is not possible in squirrel
cage motors, the above requirements are met by devel-
opingarotorcalleddoublesquirrelcagerotorwherethere
will be two sets of short circuited bars in the rotor.
Stator of an induction motor: There is no difference
between squirrel cage and slip-ring motor stators.
The induction motor stator resembles the stator of a
revolving field, three-phase alternator. The stator or the
stationary part consists of three-phase winding held in
place in the slots of a laminated steel core which is
enclosed and supported by a cast iron or a steel frame as
shown in Fig 1. The phase windings are placed 120
electrical degrees apart, and may be connected in either
starordeltaexternally,forwhichsixleadsarebrought out
to a terminal box mounted on the frame of the motor.
When the stator is energised from a three-phase voltage
it will produce a rotating magnetic field in the stator core.
Rotor of a squirrel cage induction motor: The rotor of
the squirrel cage induction motor shown in Fig 2 contains
no windings. Instead it is a cylindrical core constructed of
steel laminations with conductor bars mounted parallel to
theshaftandembeddednearthesurfaceoftherotorcore.
These conductor bars are short circuited by an end-ring
at either end of the rotor core. On large machines, these
conductor bars and the end-rings are made up of copper
with the bars brazed or welded to the end rings as shown
in Fig 3. On small machines the conductor bars and
end-rings are sometimes made of aluminium with the
bars and rings cast in as part of the rotor core.
The rotor or rotating part is not connected electrically to
the power supply but has voltage induced in it by trans-
former action from the stator. For this reason, the stator
is sometimes called the primary, and the rotor is referred
to as the secondary of the motor. Since the motor oper-
ates on the principle of induction; and as the construction

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