1.a) Explain how ac voltage is converted to dc voltage in a generator?
b) Explain clearly the necessities of commutator arrangement in dc generators?
c) Derive the expression of emf generated in case of dc machine. [15]
2. A 4-pole generator has an induced emf of 262V when driven at a speed of 400rpm. The armature is lap wound and has 652 conductors, its resistance being 0.15Ω. The bore of the pole shoe is 42cm diameter; the pole subtends an angle of 600 and is 20cm long. Calculate the flux density in the air gap. [15]
3. What is armature reaction? Describe the effects of armature reaction on the operation of d.c machine. How armature reaction is minimized? [15]
4. Distinguish between self excited and separately excited d.c generators. How is self-excited d.c generators classified? Give their connection diagram? [15]
5. A shunt generator gives a full-load output of 30kw at a terminal voltage of 200V. The armature and shunt field resistance are 0.05Ω and 50Ω respectively. The iron and friction losses are 1000w. Calculate
a) generated e.m.f b) copper losses c) efficiency [15]
6. Explain what is meant by back e.m.f. Explain the principle of torque production in d.c motor and also derive the expression of torque? [15]
7. A d.c shunt machine, connected to 250V, has an armature resistance of 0.12Ω and resistance of the field circuit is 100Ω. Find the ratio of the speed as a generator to the speed as a motor, the line current in each case being 80A. [15]
8. Explain Hopkinson’s test and corresponding circuit diagram and procedure for efficiency calculation as motor and generator? [15]
b) Explain clearly the necessities of commutator arrangement in dc generators?
c) Derive the expression of emf generated in case of dc machine. [15]
2. A 4-pole generator has an induced emf of 262V when driven at a speed of 400rpm. The armature is lap wound and has 652 conductors, its resistance being 0.15Ω. The bore of the pole shoe is 42cm diameter; the pole subtends an angle of 600 and is 20cm long. Calculate the flux density in the air gap. [15]
3. What is armature reaction? Describe the effects of armature reaction on the operation of d.c machine. How armature reaction is minimized? [15]
4. Distinguish between self excited and separately excited d.c generators. How is self-excited d.c generators classified? Give their connection diagram? [15]
5. A shunt generator gives a full-load output of 30kw at a terminal voltage of 200V. The armature and shunt field resistance are 0.05Ω and 50Ω respectively. The iron and friction losses are 1000w. Calculate
a) generated e.m.f b) copper losses c) efficiency [15]
6. Explain what is meant by back e.m.f. Explain the principle of torque production in d.c motor and also derive the expression of torque? [15]
7. A d.c shunt machine, connected to 250V, has an armature resistance of 0.12Ω and resistance of the field circuit is 100Ω. Find the ratio of the speed as a generator to the speed as a motor, the line current in each case being 80A. [15]
8. Explain Hopkinson’s test and corresponding circuit diagram and procedure for efficiency calculation as motor and generator? [15]
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