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Register Number SATHYABAMA UNIVERSITY (Established under section 3 of UGC Act,1956) Course & Branch :B.E - P-EEE Title of the Paper : Electrical Machines – II Sub. Code : 614PT202 (2009-2010) Date :16/11/2012 Max. Marks:80 Time : 3 Hours Session :AN _______________________________________________________________________________________________________________________________ 1. PART - A (10 x 2 = 20) Answer ALL the Questions What are the conditions to be satisfied for successful parallel operation of alternators? 2. List the difference between salient pole and cylindrical rotor synchronous machines. 3. What are the causes if a synchronous motor fails to start? 4. What is V and Inverted V curve .Why it is called so. 5. What are the different speed control methods available for 3 phase slip ring Induction motor? 6. Name any two starters used for induction motors. 7. What will be reasons if a single phase Induction motor fails to start and hums loudly? 8. State any two applications of Universal motor. 9. Write the expression for 3-phase torque of a permanent magnet synchronous motor. 10. What is two-phase servomotor? PART – B Answer All the Questions (5 x 12 = 60) 11. Discuss the data required for estimating the regulation of alternator by potier method .Explain how regulation is calculated for various power factor. (or) 12. Find the synchronous impedance and reactance of an alternator in which a given field current produces an armature current of 200 A on short circuit and a generated e.m.f of 50 V on open circuit. The armature resistance is 0.1 ohm. To what induced voltage must the alternator be excited if it is to deliver a load of 100 A at a pf of 0.8 lagging, with a terminal voltage of 200 V. 13. Explain the effect of varying excitation upon the armature current and power factor of the synchronous motor for a constant output with phasor diagram. (or) 14. (a) A 500, 1 Phase synchronous motor gives a net output mechanical power of 7.46 KW and operates at 0.9 pf lagging. Its effective resistance is 0.8 ohm. If the iron and friction losses are 500 W and excitation losses are 800 W, estimate the armature current .calculate the commercial efficiency. (b) A 75 KW,3 phase star connected ,50 Hz ,440v cylindrical rotor synchronous motor operates at rated condition with 0.8 pf leading. The motor efficiency excluding field and stator losses, is 95% and Xs =2.5 ohm. Calculate 1.mechanical power developed 2.armature current 3.Back e.m.f 4.power angle 5.Maximum or pull out torque of the motor. 15. Draw the circle diagram for a 5.6 KW, 400V, 3 phase, 4 pole, and 50HZ slip ring induction motor from the following data: No load test: 400 V, 6A, cos φ0=0.087. Short circuit test: 100V, 12A, 720W. The ratio of primary to secondary terms is 2.62.Stator resistance per phase is 0.67 OHM and that of the rotor is 0.185 OHM .Calculate i) The full load current ii) Full load slip iii) Full load power factor iv) Maximum power and v)Maximum Torque. (or) 16. Explain the construction, types and rotating magnetic principle of 3 phase Induction motor. 17. Explain the construction, principle, characteristics applications of split phase type induction motor. (or) 18. Explain the construction, principle, characteristics applications of reluctance type induction motor. and and 19. Explain the construction & principle of operation of permanent magnetic synchronous motor. (or) 20. Draw the speed torque characteristics and phasor diagrams of permanent magnetic synchronous motor and explain.