ELECTRICAL MACHINES and APPLIANCES Theory
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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) Untouchability is a Sin Untouchability is a Crime Untouchability is Inhuman 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 Page No. 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 v 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. 1 Thus the insulating materials are grouped into different classes Y, A, B, and C with temperature limits of 900 C, 1050C and 1300C for the first three classes and no specific limit Fig.1.1 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 : 1050C: Same as class Y but impregnated, plus nylon. Class E : 1200C: Polyethylene terephthalate (terylene fibre, melinex film), cellulose triacetate,