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Reg. No. : ..................................... Name : ..........................................
Third Semester B.Tech. Degree Examination, November 2009 (2008 Scheme) Branch : Applied Electronics & Instrumentation 08.306 : ELECTRICAL MACHINES & DRIVES (A) Time : 3 Hours
Max. Marks : 100 PART – A
Answer all questions : 1. Mention the functions of yoke, armature, commutator and brushes in a dc generator. 2. Derive from fundamentals the e.m.f equation of a dc generator. 3. Explain the working principle of a transformer. 4. Draw the vector diagram when the transformer on lagging load. Explain. 5. What is the principle of operation of an alternator ? 6. What is the regulation is an alternator ? 7. Explain the starting method of slipring Induction motor. 8. Derive the torque equation of an induction motor. 9. Explain the Double field revolving theory. 10. What are the advantages of electric drives ?
(10Ă—4=40 Marks)
P.T.O.
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PART – B Answer any two questions from each Module. Module – I 11. Derive the torque equation of a dc motor. 12. The armature resistance of a 200V shunt motor is 0.4 Ω and no load current of 2A when loaded and taking an armature current of 50A, the speed is 1200 rpm. Find the no load speed. 13. Draw the equivalent circuit of a transformer. Explain.
(2×10=20 Marks)
Module – II 14. Explain the principle of operation of synchronous motor. 15. Derive an expression for the running torque of an induction motor. 16. A 3-phase slipring Induction motor with star connected rotor has an induced emf of 120 volts between sliprings at standstill with normal voltage applied to the stator. The rotor winding has a resistance per phase of 0.3 ohm and standstill leakage reactance per phase of 1.5 ohm calculate (i) the rotor current / phase when running short circuted with 4% slip and (ii) the slip and rotor current per phase when the rotor is developing maximum torque. (2×10=20 Marks) Module – III 17. Why single phase Induction motor is not self starting ? What are the different methods of starting of single phase Induction motor ? 18. Explain the working principle of shaded pole motor with suitable diagram. 19. Derive the basic performance equations for a separately excited dc motor and draw the characteristics of a separately excited dc motor. (2×10=20 Marks)
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