MU Electronics Engineering (Semester 7)
Total marks: --
Total time: --
INSTRUCTIONS
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary
1 (a) List the advantages of dc chopper drives over line commutated converter controlled dc drives.
5 marks
1 (b) Explain how semiconverter provides better power factor compared to full converter when both are working as rectifier with RL load.
5 marks
1 (c) What are advantages of flyback converter compared to forward converter?
5 marks
1 (d) Compare between current source and voltage source inverters.
5 marks
2 (a) Draw and explain the operation of speed control of a DC series motor fed by a single phase semiconverter for the continuous motor current. Draw also the associated voltage and current waveforms.
5 marks
2 (b) A 220 V, 1500 rpm, 10 A separately expired dc motor has an armature resistance of 1 ohm. It is fed from a single phase fully controlled bridge rectifier with an ac source voltage of 230, 50Hz. Assuming continuous load current compute:
i) Motor speed at firing angle of 30° and torque of 5 NM.
ii) Developed torque at firing angle of 45° and speed of 1000rpm.
5 marks
3 (a) Explain the operation of dual converter with circulating current. What are the advantages and disadvantages of the same?
5 marks
3 (b) With neat circuit diagram explain the working of load commulated chopper with relevant voltage and current waveforms. Show voltage variation across each pair of SCRs as a function of time.
5 marks
4 (a) Explain the working of McMurry bridge inverter using circuit diagram and appropriate waveforms.
5 marks
4 (b) Explain the operation of Induction Motor for two different cases when fed by current source inverter.
i) Operation at and below rated frequency
ii) Operation above rated frequency.
5 marks
5 (a) Discuss the stator voltage control scheme of induction motor, Also draw and explain the speed torque curves.
5 marks
5 (b) Explain the working of parallel inverter employing feedback diodes. Draw the voltage and current waveforms. What care should be taken to avoid commutation failure.
5 marks
6 (a) Using block diagrams discuss different configurations of UPS.
5 marks
6 (b) Draw and explain the operation of flyback converter with relevant waveforms.
5 marks
7 (a) Effect of source inductance of performance of converter.
5 marks
7 (b) Harmonic reduction in inverters.
5 marks
7 (c) Selection of battery in UPS.
5 marks