Electrical Machines - Dec 2015

Electronics Engineering (Semester 4)

TOTAL MARKS: 60
TOTAL TIME: 2 HOURS (1) Question 1 is compulsory.
(2) Attempt any three from the remaining questions.
(3) Use suitable data wherever required.
(4) Figures to the right indicate full marks.

Solve any three.

1 (a) Draw the block diagram and explain V/F control using converter inverter scheme for 3 phase induction motor.(5 marks) 1 (b) State the application areas of brushless DC motor.(5 marks) 1 (c) What is the principle of operation of variable reluctance motor.(5 marks) 1 (d) A 230V D.C. motor has an armature circuit resistance 0.8Ω if the full load armature current is 40A and no load armature current is 6A find the change in back emf fro no load to full load.(5 marks) 1 (e) Which are methods employed to make the single phase induction motor self starting.(5 marks) 2 (a) Explain with neat sketches the armature reaction in dc machine.(7 marks) 2 (b) A 6 pole lap wound shunt motor has 500 conductors, the armature and shunt filed resistance are 06Ω and 30Ω respectively find the speed of the motor if it takes 110A from a dc supply of 100V. Flux per pole is 30 mwb.(8 marks) 3 (a) Draw and explain torque speed characteristics of 3 phase induction motor.(8 marks) 3 (b) Explain construction and working principle of 3 phase squirrel cage induction motor.(7 marks) 4 (a) Explain the double field revolving theory in single phase induction motor.(8 marks) 4 (b) Explain construction working and control requirements of switched reluctance motor.(7 marks) 5 (a) A 800W, 115V, 60Hz capacitor start motor draws 13.8A from the supply at rated load if the efficiency is 70% and rated speed is 1800 rpm.
Calculate
i) Input power at rated load
ii) Power factor at rated load
iii) Rated motor horse power(8 marks) 5 (b) State the advantages of brushless DC motor and explain any one brushless DC motor.(7 marks)

Write a short note on.

6 (a) Different speed control methods of DC shunt motor(5 marks) 6 (b) Star-delta starter of 3 phase induction motor(5 marks) 6 (c) Explain in detail permanent magnet synchronous motor.(5 marks)