ELECTRICAL MACHINES ANDAPPLIANCESTh

ELECTRICAL MACHINES AND
APPLIANCES
Theory
VOCATIONAL EDUCATION
Higher Secondary - Second Year
A Publication under
Government of Tamilnadu
Distribution of Free Textbook Programme
(NOT FOR SALE)
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TAMIL NADU
TEXTBOOK CORPORATION
College Road, Chennai - 600 006.
Government of Tamilnadu
First Edition – 2011
CHAIRPERSON
Dr. J. KANAKARAJ
ASSOCIATE PROFESSOR
DEPT. OF ELECTRICAL & ELECTRONICS ENGINEERING
PSG COLLEGE OF TECHNOLOGY
COIMBATORE – 641 004
AUTHORS
Ms. A. Sumathi Mr.R. Krishnakumar
Associate Professor Assistant Professor(Senior Grade)
Dept. of Electrical & Electronics Engg. Dept. of Electrical & Electronics Engg.
PSG College of Technology PSG College of Technology
Coimbatore – 641 004 Coimbatore – 641 004
Mr P. Balasubramanian Mr.K.S. Sampath Nagarajan
Vocational Instructor (Spl. Grade) Vocational Instructor (Spl. Grade)
Municipal Boys Hr.Sec School Govt. Hr.Sec School
Pollachi - 642 001 Parava kottai - 614 015
Coimbatore District. Thiruvarur District.
This book has been prepared by the Directorate of School Education on behalf of the
Government of Tamilnadu
This book has been printed on 60 G.S.M. Paper
Printed by Offset of:
ii
HIGHER SECONDARY – VOCATIONAL COURSE
ELECTRICAL MACHINES AND APPLIANCES
SECOND YEAR – THEORY SYLLABUS
1. Winding Insulating Materials
Introduction – Electrical properties – Classification – Characteristics – Application areas insulation
materials – plastics – insulating varnishes - Types of Insulating varnishes
2. Winding Wire
Introduction – Properties – Characteristics – Choice of Conductor material – Enamelled wire –
Grades – Properties – Types & shapes of winding wires – Gauge plate
3. Details of winding
Coil details – shapes of slot – slot insulation – coil formation – Stator (stationary) winding –
Rotor (rotating) winding – DC Armature winding - Lap winding – wave winding – whole coil
winding – half coil winding – concentrated winding – distributed winding - single layer winding –
double layer winding – single phase winding – three phase winding – concentric winding –
chain winding.
4. Development of winding – AC machines
Single phase windings – Lap winding – wave winding – concentric winding – Three phase
winding – single layer winding – double layer winding.
5. Development of winding – DC machines
General procedure – Double Layer simplex Lap winding – Double layer duplex Lap winding –
Double Layer simplex wave winding.
6. Rewinding and Testing of Electric Motors
Methods of Rewinding – Testing the new winding – Testing of Armature – Insulation resistance
test - Growler test - Drop test.
7. Instruments and Testing
Introduction – Voltage tester screwdriver – Continuing Test – Insulation test – Measurement of
Power for DC & AC Circuits.
8. Electrical Cooking Appliances
Introduction – Types – Construction – Electric Toaster – Types – Automatic and Non-Automatic.
9. Electric Iron Box
Types – Non-Automatic – Automatic – Construction and Working – Comparision – Trouble
Shooting – Steam Iron Box.
iii
10. Water Heaters & Coffee makers
Water Heater – Function – Types – Electric Kettle – Immersion water heater – Construction
and working – storage water heaters – Non pressure type – pressure type – construction and
working – repairs & remedies – Coffee maker – types – construction and working of percolator
type.
11. Electric Mixer & Egg beaters
Electric Maker – Function – Construction – General Operating Instruction – Caution – Cleaning
– Repairs and Remedies – Egg beaters – Hand operated crank type – Electric type – Construction.
12. Vacuum Cleaner and washing machine
Vacuum Cleaner – Function – Principle – Main components – features – types - working –
accessories - Filters – Repairing.
Washing Machine – Function – Types – Semi and Fully Automatic – Top and Front loading –
washing technique – working cycle – construction and working of washing machine – comparison
of Top and front loading machines – Problems and Remedies.
13. Electric Fan & Hair Drier
Electric Fan – Function – Terminology – Construction and Working of Ceiling & table fans –
Exhaust Fan – General Fault and Remedy.
Hair Drier – Function – Types – Construction and working – safety features – repairs & remedies.
14. Centrifugal Pump :
Introduction – Constructional features – working – friction lead – static suction head – static
delivery lead –automatic operation of pump – Trouble shooting.
15. Maintenance of Rotating Machines
Introduction – Types of maintenance – preventive maintenance schedule – Fitting and removing
of a bearing - Maintenance of bearing – Balancing – Preventive maintenance of electric
equipments – General procedure for overhaul of motors – Maintenance of AC Motors ––
Insulation resistance of a motor - Defects in brushes, brush gear - Trouble shooting chart –
defects in commutator – Degreasing – Varnish application - Vacuum Impregnation.
16. Maintenance of Transformers :
Introduction – Action taken for rise in oil temperatures and falling of oil level – methods of drying
out of transformers – Time of drying out operation - Qualities for Transformer oil – methods of
purifying and drying out of transformer oil – Checking of dielectric strength of transformer oil –
action taken for transformer failure - periodical overhaul.
iv
CONTENTS
1. Winding Insulating Materials 1
2. Winding wire 15
3. Details of winding 24
4. Development of Winding - AC machines 36
5. Development of Winding - DC machines 64
6. Rewinding and Testing of Electric motors 75
7. Instruments and Testing 89
8. Electrical Cooking Appliances 97
9. Electric Iron Box 102
10. Water Heaters and Coffee Makers 109
11. Electric mixer and Egg Beaters 118
12. Vacuum cleaner and Washing machines 124
13. Electric Fan and Electric hair drier 138
14. Centrifugal Pump 152
15. Maintenance of Roatating machines 160
16. Maintenance of Transformers 179
Page No.
v

1
1. WINDING INSULATING MATERIALS
1.1 INTRODUCTION
The Electrical insulating materials are defined as materials which offer a very large resistance
to flow of current, and for that reason they are used to keep the current in its proper path along
the conductor. This is evident when we touch an electric machine when it is under operation.
We don’t receive any electric shocks, because of the insulation. Breakdown of insulation results
in short circuiting of the coils, causing electric currents to flow in unintended paths. This may
also cause, electric shocks to humans operating the machinery and also damage the machines.
Requirements of a good insulating materials involve physical properties, reliability, cost,
availability, adaptability to machining operations etc. Electrical insulation and dielectric materials
includes various forms of materials that surround and protect electrical conductors and prevent
unwanted current flow, leakage. Electrical specifications include electrical resistivity, dielectric
strength, and dielectric constant.
1.2 ELECTRICAL PROPERTIES
Electrical Resistivity : It is the electrical resistance (ohm-cm) to the flow of current through it.
Its value should be very high. Resistivity is the inverse of conductivity.
Dielectric Strength : Dielectric strength is the maximum voltage gradient that the material can
withstand before electrical breakdown occurs. This value specified as ‘kV/mm’ should be very
high even for very thin films.
1.3 CLASSIFICATION OF INSULATING MATERIALS : The insulating materials are classified
in the following two ways : 1. Classification according to substances and materials.
2. Classification according to temperature.
Classification according to substances and materials :
(i) Solid Insulating Materials [Inorganic and organic]
Mica, wood, slate, glass, porcelain, rubber, cotton, silk, rayon, terylene, paper and
cellulose materials etc.
(ii) Liquid Insulating Materials [Oils and Varnishes]
Refined hydrocarbon minerals oils, Linseed oil, spirit and synthetic varnishes, etc.
(iii) Gaseous Insulating Materials
Dry air, carbon dioxide, argon, nitrogen, etc.
Classification according to temperature : The insulating materials are classified mainly based
on the thermal limit. The performance of the insulation depends on its operating temperature.
The higher the temperature, the higher will be the rate of its chemical degrading, and hence the
lower will be its useful life as shown in fig.1.1. If a reasonably long life of insulation is expected,
its operating temperature must be maintained low. Therefore, it is necessary to determine the
limits of temperature for the insulation, which will ensure safe operation over its expected life.
2
Thus the insulating materials are grouped into different classes Y, A, B, and C with
temperature limits of 900 C, 1050
C and 1300C for the first three classes and no specific limit
fixed for class C. Class Y and A cover the various organic materials without and with impregnation
respectively, while classes B and C cover inorganic materials, respectively with and without a
binder. With the existence of newer insulating materials, namely, the plastics and silicones,
during the middle of this century, a need was felt to reorganize the classification of the insulating
materials. This calssification is shown in fig.1.2. This led IEC (International Electro technical
Commission) to come up with the new categories:
Class Y : 900
C: Paper, cotton, silk, natural rubber, polyvinyl chloride, etc. without impregnation.
(formerly O)
Class A : 1050
C: Same as class Y but impregnated, plus nylon.
Class E : 1200
C: Polyethylene terephthalate (terylene fibre, melinex film), cellulose triacetate,
polyvinyl acetate enamel.
Class B : 1300
C: Mica, fiberglass (alkali free alumino borosilicate), bituminized asbestos,
bakelite, polyester enamel.
Class F : 1550 C: As class B but with alkyd and epoxy based resins, polyurethane.
Class H : 1800
C: As clas