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EEE, Iiird YEAR, Vth - SEMESTER K.S.R. COLLEGE OF ENGINEERING, TIRUCHENGODE – 637 215 (Autonomous) Department of Electrical & Electronics Engineering SUBJECT: 16EE511 ELECTRICAL MACHINES – II (Regulation: 2016) (Two Mark Questions with Answers) B.E. – EEE, IIIrd YEAR, Vth - SEMESTER Prepared by Dr.M.Ramasamy Associate Professor / EEE K.S.R. College of Engineering KSRCE/EEE 1 ELECTRICAL MACHINES - II SYLLABUS KSRCE/EEE 2 ELECTRICAL MACHINES - II KSRCE / QM / 7.5.1 /EEE/41 K.S.R COLLEGE OF ENGINEEIRNG (AUTONOMOUS),TIRUCHENGODE - 637 215 DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING LESSON PLAN III YEAR - EEE (JUNE 2019 - NOV 2019) Subject: Electrical Machines - II Year / Sem: III / V Regulation: 2016 Staff Name: Dr.M.Ramasamy Lecture Teaching Topic Hours Source Page No. Hour Aid UNIT - I THREE PHASE INDUCTION MOTOR L01 Constructional details, Types of rotors 1 BB R - 4 1245 L02 Principle of operation, Slip 1 BB R - 4 1244,1254 L03 Equivalent Circuit 1 BB R - 4 1302 L04 Torque Equations 1 BB R - 3 1256 L05 Slip - Torque Characterstics 1 BB R - 4 1264 L06 Need for Starter, Types of Starters 1 BB R - 4 1329 L07 Rotor Resistance Starter 1 BB R - 4 1330 L08 Autotransformer Starter 1 BB R - 4 1331 Star - Delta Starter, Crawling and Cogging, L09 1 BB R - 4 1335, 1342 Double Cage Rotors Total 09 UNIT - II PERFORMANCE ANALYSIS AND SPEED CONTROL OF THREE PHASE INDUCTION MOTOR L10 Loss and Efficiency 1 BB R - 3 47 L11 Load Test 1 BB R - 3 109 L12 No load and Blocked Rotor Tests 1 BB R - 4 1315 L13 Circle Diagram 1 BB R - 4 1314 L14 Separation of no load losses 1 BB T - 1 614 L15 Speed Control by Change of Voltage 1 BB R - 4 1349 L16 Speed Control: Change of Poles and Slip 1 BB R - 4 1350 L17 Slip Power Recovery Schemes 1 BB T - 1 647 L18 Tutorial 1 BB R - 4 Notes Total 09 UNIT - III SINGLE PHASE INDUCTION MOTORS L19 Constructional Details 1 BB R - 4 1368 L20 Double Revolving Field Theory 1 LCD R - 4 1369 L21 Equivalent Circuit 1 LCD R - 4 1373 L22 Starting Methods and Applications 2 BB R - 4 1377 L23 Working Principle of Reluctance motor 1 BB R - 4 1394 KSRCE/EEE 3 ELECTRICAL MACHINES - II Lecture Teaching Topic Hours Source Page No. Hour Aid L24 Working Principle of Repulsion motor 1 BB R - 4 1385 L25 Working Principle of Stepper motor 1 BB R - 4 1536 L26 Working Principle of Universal motor 1 BB R - 4 1390 L27 Tutorial 1 BB R - 4 - Total 09 UNIT - IV ALTERNATOR L28 Constructional Details, Types of Rotors 1 LCD R - 4 1403, 1404 L29 EMF Equation, Synchronous Reactance, 1 BB R - 4 1415, 1425 Armature Reaction, Voltage Regulation: EMF L30 1 BB R - 4 1427, 1423 Method L31 MMF and ZPF Methods 1 BB R - 4 1439, 1444 L32 Synchronizing & Parallel Operation 1 BB R - 4 1456 Synchronizing Power, Change of Excitation 1460 L33 1 BB R - 4 & Mechanical Input 1469 L34 Blondel’s theory 1 BB R - 4 1450 L35 Determination of Xd & Xq using Slip Test 1 BB R - 4 1425 L36 Alternator on Infinite Busbar 1 BB R - 4 1461 Total 12 UNIT - V SYNCHRONOUS MOTOR L37 Principle of Operation 1 LCD R - 4 1490 L38 Torque Equation 1 BB R - 4 1501 L39 Starting Methods 1 BB R - 4 1529 L40 Operation on Infinite Busbars 1 BB R - 4 1493 L41 V and Inverted V curves 1 BB R - 4 1527 Power Input and Power Developed L42 1 BB R - 4 1494 Equations Current loci for constant Power Input, L43 constant excitation and Constant Power 1 BB R - 4 1494 Developed L44 Hunting, Synchronous Condenser 1 BB R - 4 1528 L45 Applications 1 BB R - 4 1531 Total 11 BB - Black Board; LCD - Projector Text Books: 1. D.P. Kothari and I.J. Nagrath, Electric Machines, Tata McGraw Hill Publishing Company Ltd, 2010. 2. P.S. Bhimbhra, Electrical Machinery, Khanna Publishers, 2003. KSRCE/EEE 4 ELECTRICAL MACHINES - II Reference Books: 1. A.E. Fitzgerald, Charles Kingsely Jr, Stephen D.Umans, Electric Machinery, McGraw Hill Book Company, 2003. 2. K. Murugesh Kumar, Electric Machines, Vikas publishing house Pvt Ltd, 2002. 3. J.B. Gupta, Theory and Performance of Electrical Machines, S.K.Kataria and Sons, 2002. 4. B.L.Theraja and A.K.Theraja, A Text Book of Electrical Technology, S.Chand Publishing, 2010. KSRCE/EEE 5 ELECTRICAL MACHINES - II UNIT – I INDUCTION MOTOR (Course Outcome – 1) 1. What are the types of rotors used in the induction motor? (Remembering) (i) Squirrel cage rotor. (ii) Slip ring (or) wound rotor. 2. What are the two types of 3 phase induction motor? (Remembering) There are two types of 3-phase induction motor based on the type of rotor used: (i) Squirrel cage induction motor. (ii) Slip ring induction motor. 3. What is meant by rotating transformer? (or) What is the principle used in induction motor? (Remembering) Conversion of electric power into mechanical power takes place in the rotating part of an Electric motor. In D.C. motor, the electrical power is conducted directly to the armature (i.e. rotating part) through brushes and commutators. Hence, in this sense, a D.C. motor can be called a conduction motor. However, in A.C. motors, the rotor does not receive electric power by conduction but by induction in exactly the same way as the secondary of a 2- winding transformer receives its power from primary. That is why such motors are called induction motors. In fact, induction motors can be treated as a rotating transformer i.e. in one which primary winding is stationary but the secondary is free to rotate. 4. What are the losses present in the Induction motor? (Remembering) i. Stator copper loss. ii. Stator iron loss. iii. Rotor copper loss. iv. Windage loss & friction loss. 5. What is the condition for maximum starting torque? Also write the corresponding torque equation at starting condition? (Remembering) The condition for maximum torque at the starting condition is, R2 = X2. 3 2 E 2 R2 The torque equation is given by, TST = 2 2Ns 2 R2 X 2 Where, R2 = rotor resistance, X2 = rotor reactance, E2 = Rotor induced e.m.f at standstill, Ns = synchronous speed. 6. What is the condition for maximum running torque? Also write the corresponding torque equation at running condition? (Understanding) The condition for maximum torque at the running condition is, R2 = S X2 The torque equation at running condition is, 2 3 sE2 R2 T = 2 2 . 2Ns R2 (SX 2 ) 7. How the starting torque can be improved in slip ring induction motor? (Understanidng) The starting torque of a slip ring induction motor is increased by improving its power factor by adding external resistance in the rotor circuit from the star- connected rheostat. The rheostat resistance being progressively cut out as the motor gathers speed because torque equation is given as, T = k Ф I2 cos 2 Where, 2 = power factor angle between rotor e.m.f and rotor current, R Cos = 2 . 2 2 R2 X 2 Hence by increasing R2 the power can be improved and hence the starting torque of induction motor can be improved. KSRCE/EEE 6 ELECTRICAL MACHINES - II 8. What is ‘slip’ in an induction motor? (Remembering) The induction motor speed is always less than the speed of synchronous speed of revolving flux. The difference in speed between synchronously revolving flux and the rotor speed is called slip speed. The ratio between the slip speed and synchronous speed of induction motor is called slip. It is denoted by‘s’. N N Slip, S = s . N s % slip, %S = 100 %. The motor speed is given by, N = Ns (1-S) Rpm. 9. How can you separate No-load losses in an induction motor? (Understanding) The No-load losses are divided as: (i) Iron loss (or) core loss. (ii) Mechanical loss (or) rotational loss. (iii) Friction loss. In an induction motor, slip ring induction motor is taken. The rotor circuit is opened and 3-phase supply is given to stator. Now the wattmeter are connected to stator side of induction motor reads Iron loss (or) core loss. Now the rotor circuit of induction motor is short circuited. When rated voltage is applied, the induction motor starts to rotate and the wattmeter readings will read the rotational losses. 10. Why induction motors are called asynchronous? (Understanding) Because their rotors can never run with the synchronous speed. The rotor does not catch-up the stator flux 11. What is synchronous speed? (Remembering) The speed at which the stator field rotates is called synchronous speed and it depends upon the frequency of supply and number of poles for which the stator is wound. Ns = synchronous speed in rpm. = 120 f / p. f = frequency of supply. p = Number of poles in the stator. 12. What is the rotor frequency in induction motor? (Remembering) When a rotor is at standstill, the frequency of the rotor current is the same as that of the supply frequency. But when the rotor is rotating its frequency depends upon slip-speed. Assume the frequency of the rotor current to be fr , at any slip speed, then, 120 f r Ns – N = ------------- (1) p But synchronous speed, 120 f Ns = ----------------- (2) p (1) % (2) f r N s N S f N s (Or) fr = f S Rotor frequency, fr = f S 13. What are the advantages of the slip-ring induction motor over squirrel cage Induction motor? (Remembering) It is possible to speed control by regulating rotor resistance.
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