Seventh Semester
Branch: Electrical and Electronics Engineering
ELECTRICAL DRWES AND CONTROL (E)
Answer all questions.
1. Explain the importance of DC Drives. What are the methods of speed control of DC motors?
2. A highly inductive dc load requires 12 A at 150 V from a 230 V, single phase ac supply in a fully controlled bridge converter. Determine EM when a = 30°.
3. List the advantages offered by dc chopper drives over line commutated converter controlled dc drives.
4. Explain free wheeling and free wheeling with regeneration.
5. What are the various speed control techniques for induction motors?
6. Give the principle of Slip Power Recovery Scheme.
7. What is meant by flux weakening schemes of control?
8. Explain the working of a current source inverter.
9. What is a self-control mode of synchronous motors?
10. Explain the principle of Vector control.
(10 x 4 = 40 marks)
Part B
Each question carries 12 marks.
11. With neat circuit diagrams and waveforms explain the operation of a single phase fully controlled rectifier control of dc separately excited motor. Get the armature voltage for continuous conduction. Draw the speed-torque characteristics for various values of the firing angle.
Or
12. A 200 V, 875 r.p.m., 150 A separately excited dc motor has an armature resistance of 0.06 2.
It is fed from a single phase fully controlled rectifier with an ac source voltage of 220 V, 50 Hz.
Assuming continuous conduction, calculate
(a) the firing angle for rated motor torque and 750 r.p.m.
(b) Firing angle for rated motor torque and (— 500).
(c) Motor speed for a = 160° and rated torque.
13. Explain with neat circuit diagram and waveforms a three phase fully controlled dc motor drive. Get the expression for the average output voltage.
Or
14. A 230 V, 960 rpm and 200 A separately excited dc motor has an armature resistance of 0.02 . The motor is fed from a chopper which provides both motoring and braking operations. The source has a voltage of 230 V. Assuming continuous conduction,
(a) Calculate the duty ratio of chopper for motoring operations at rated torque and 350 r.p.m.;
(b) Calculate the duty ratio of chopper for braking operation at rated torque and 350 r.p.m.; and
(c) If the maximum duty ratio of chopper is limited to 0.95 and minimum permissible motor current is twice the rated, calculate the maximum permissible motor speed obtainable without — field weakening and power fed to the source.
15. Discuss the stator voltage control of induction motors. Give the various controller configurations. What are the advantages and drawbacks of phase control of induction motors?
Or
16. (a) Explain the V/f ontrol of induction motor.
(b) Explain constant torque and constant power control.
17. With neat circuit diagram explain the voltage source inverter Fed inductor motor drive. Explain the PWM control and its advantages.
Or
18. Explain with circuit diagram a current source inverter fed induction motor drive. Compare the VSI drives and CSI fed induction motor drives.
19. (a) What are the speed control schemes for synchronous motors?
(b) Explain voltage source Inverter drive with open loop control.
Or
20. (a) Compare brushless DC motor and self controlled synchronous motor drive.
(b) Explain briefly the adjustable frequency operation of synchronous motors.
[5 x 12 = 60 marks]
DOENLOAD:
http://www.4shared.com/file/137213172/4a2637b7/QUESTION_3.html
