1.a) Discuss the principle of operation of d.c machine as a motor and as a generator?
b) Derive the expression of emf generated in case of generator from the first principles?
[10+5]
2. An 8-pole lap-wound d.c generator armature has 960 conductors, a flux of 40mwb and a speed of 400 r.p.m. Calculate the e.m.f generated on open circuit. If the same armature is wave wound, at what speed must it be driven to generate 400V? [15]
3.a) What do you understand by demagnetizing and cross magnetizing effects of armature reaction in a d.c machine?
b) Define commutation. Explain the process of commutation in d.c generators with neat sketches? [9+6]
4. Explain the process of building up of voltage in d.c shunt generator? What is its significance? How O.C.C. is being drawn for shunt generator? [15]
5. A 25kw, 250V dc shunt generator has armature and field resistance of 0.06Ω and 100Ω respectively. Determine the total armature power developed when working
a) as generator delivering 25kw output
b) as motor taking 25kw input. [15]
6. Discuss the different methods of speed control of d.c motor with neat circuit diagram.
[15]
7. A 4-pole, 250-V, wave-connected shunt motor gives 10kw when running at 1000 r.p.m and drawing armature and field currents of 60A and 1A respectively. It has 560 conductors. Its armature resistance is 0.2Ω. Assuming a drop of 1V per brush. Determine
a) total torque b) useful torque c) useful flux per pole
d) rotational losses e) efficiency [15]
8. Describe the Swinburne’s test with the help of a neat diagram to find out the efficiency of d.c machine. What are the main advantages and disadvantages of this test? [15]
b) Derive the expression of emf generated in case of generator from the first principles?
[10+5]
2. An 8-pole lap-wound d.c generator armature has 960 conductors, a flux of 40mwb and a speed of 400 r.p.m. Calculate the e.m.f generated on open circuit. If the same armature is wave wound, at what speed must it be driven to generate 400V? [15]
3.a) What do you understand by demagnetizing and cross magnetizing effects of armature reaction in a d.c machine?
b) Define commutation. Explain the process of commutation in d.c generators with neat sketches? [9+6]
4. Explain the process of building up of voltage in d.c shunt generator? What is its significance? How O.C.C. is being drawn for shunt generator? [15]
5. A 25kw, 250V dc shunt generator has armature and field resistance of 0.06Ω and 100Ω respectively. Determine the total armature power developed when working
a) as generator delivering 25kw output
b) as motor taking 25kw input. [15]
6. Discuss the different methods of speed control of d.c motor with neat circuit diagram.
[15]
7. A 4-pole, 250-V, wave-connected shunt motor gives 10kw when running at 1000 r.p.m and drawing armature and field currents of 60A and 1A respectively. It has 560 conductors. Its armature resistance is 0.2Ω. Assuming a drop of 1V per brush. Determine
a) total torque b) useful torque c) useful flux per pole
d) rotational losses e) efficiency [15]
8. Describe the Swinburne’s test with the help of a neat diagram to find out the efficiency of d.c machine. What are the main advantages and disadvantages of this test? [15]
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