| ELECTRICAL MACHINES |
| PAPER NO. 2 |
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IC-203 ELECTRICAL MACHINES (B.Tech 3rd Semester,2121) Time : 3 Hours Maximum Marks : 60 NOTE:- This paper consist of Three Sections. Section A is compulsory. Do any Four questions from Section B and any two questions from Section C Section-A Marks : 20 1(a) List probable causes of failure of excitation of self-exited d.c. shunt generator. (b) Sketch shell type core construction of a 3-phase transformer. (c) Draw phaser diagram for a lagging power factor of an auto-transformer. (d) Write expression for calculating rotor frequency of a 3-phase induction motor. (e) Draw connection diagram of a capacitor start and capacitor run single-phase induction motor. (f) Name the motor generally employed for demestic grinder-mixer and justify your choice. (g) Draw basic diagram of a four pole stepper motor having a permanent magnet rotor. (h) Explain effect of short pitching on performance of an alternator. (i) Explain purpose of providing damper winding in synchronous machines. (j) Differentiate between salient pole and cylinderical rotor construction of a synchronous machine. Section-B Marks:5 Each 2. Explain plugging method of braking d.c. motors. 3. Draw exact equilent circuit of a single phase transfermer and name various components used therein. 4. Draw the torque-slip curve of a 3-phase induction motor and explain any one method used for obtaining high starting torque. 5. Define Synchronous Rectance. How is it determined experimentally. 6. Explain construction of a general purpose servomotor with the help of a diagram. Section-C Marks : 10 Each 7. Prove with the help of double revolving field theory that single-phase induction motors have net torque zero when only one winding is exited by a single-phase supply. Give any one method to make self-starting. 8. A given 3 MVA, 50 Hz, 11 kV, 3-phase, star connected alternator when supplying 100 A at zero p.f. leading has a line to line voltage of 12,370 V, when the load is removed, the terminal voltage falls down to 11,000 V. Predict the regulation of the alternator when supplying full load at 0.8 p.f. load. Assume an effective resistance of 0.4 ohm per phase. 9. A 100 kVA, 6600/330 V, 50 Hz, single-phase transformer took 10 A and 346 W, at 100 V during a short circuit test, the figures referring to the high voltage side. Calculate the voltage to be applied to the h.v. side on fall load at 0.8 p.f. logging when the secondary terminal voltage is 330 V. |
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