B.E./B.Tech. DEGREE EXAMINATION, NOVEMBER/DECEMBER 2011.
Electrical and Electronics Engineering
EE 2302 — ELECTRICAL MACHINES — II
Time : Three hours Maximum : 100 marks
Answer ALL questions.
PART A — (10 × 2 = 20 marks)
1. What do you mean by single layer and double layer winding?
2. What are the various function of damper winding provided with alternator?
3. What is a synchronous capacitor?
4. What are V–curves?
5. Why are the rotor slots of a 3 phase induction motors skewed?
6. Define slip of induction motor.
7. State the effect of rotor resistance on starting torque.
8. What are the various method of speed control of 3 phase induction motor?
9. What type of motor is used for ceiling fan?
10. State the application of shaded pole motor.
PART B — (5 × 16 = 80 marks)
11. (a) (i) Derive from first principle, the EMF of 3 phase alternator. (8)
(ii) The following open circuit and short circuit test are made on a 6000 kVA, 6600 V, star connected, 2 pole, 60 Hz turbine driven alternator. If I = 125 A, at open circuit terminal voltage = 8200 V. With armature short circuited I = 125 A. IL = 800 A (line). At the rated load and upf armature loss is 1.5% of out put. Determine the percentage regulation at rated load and 0.8 p.f. lag. (8)
(b) (i) Explain how will you determine the d and q axis reactance of a synchronous machine in your laboratory. (8)
(ii) For the salient synchronous machine, derive the expression for power developed as a function of load angle. (8)
12. (a) Explain V–curve and inverted V curve. (16)
(b) Explain effect of changing field current excitation at constant load. (16)
13. (a) (i) Explain with neat sketches the principle of a 3 Phase induction motor. (8)
(ii) A 6 pole, 50 Hz, 3-Phase, induction motor running on full load develops a useful torque of 160 N m. When the rotor emf makes 120 complete cycle per minute. Calculate the shaft power input. If the mechanical torque lost in friction and that for core loss is 10 N m, complete.
(1) The copper loss in the rotor windings.
(2) The input the motor.
(3) The efficiency.
The total stator loss in given to be 800 W. (8)
(b) (i) Explain top slip characteristic of 3 phase induction motor. (8)
(ii) Develop the equivalent circuit for a 3 phase induction motor. (8)
14. (a) Describe with a neat sketch, the principle and working of a star delta starter and autotransformer starter of a 3 phase induction motor. (16)
(b) Explain, with a neat sketch, slip power recovery scheme of 3 phase induction motor. (16)
15. (a) Explain with a neat diagram the following types of single phase induction motor.
(i) Split phase induction run motor.
(ii) Capacitor start induction run motor, and also draw the slip torque characteristics. (16)
(b) Describe the constructional features & principle of operation of hysterisis motor and AC Series motor. (16)