1. Explain the constructional features of dc machine and principle of operation? [15]
2. A 6-pole d.c generator runs at 850 r.p.m and each pole has a flux of 12mwb. If there are 150 conductors in series between each pair of brushes, what is the value of generated e.m.f? [15]
3. Explain the process of commutation in d.c machine and describe the methods to improve it? [15]
4.a) Explain the process of building up of voltage in a d.c shunt generators and give conditions to be satisfied for voltage build up?
b) What are various possible causes for d.c shunt generator not building up voltage?
[10+5]
5. A short shunt compound d.c generator delivers 100A to a load at 250V. The generator delivers 100A to a load at 250V. The generator has shunt field, series field and armature resistance of 130Ω, 0.1Ω and 0.1Ω respectively. Calculate the voltage generated in armature winding. Assume 1V drop per brush. [15]
6. Sketch the speed-load characteristics of a d.c
a) Shunt motor b) Series motor c) Cumulatively compound motor.
Account for the shape of the above characteristics curves? [15]
7. A shunt generator delivers 50kw at 250V when running at 400 r.p.m. The armature and field resistance are 0.2Ω and 50Ω respectively. Calculate the speed of the machine when running as a shunt motor and taking 50kw input at 250V. Allow 1V per brush for contact drop? [15]
8.a) Draw the power flow diagram of a d.c generator and d.c motor?
b) Derive the condition for maximum efficiency? [10+5]
2. A 6-pole d.c generator runs at 850 r.p.m and each pole has a flux of 12mwb. If there are 150 conductors in series between each pair of brushes, what is the value of generated e.m.f? [15]
3. Explain the process of commutation in d.c machine and describe the methods to improve it? [15]
4.a) Explain the process of building up of voltage in a d.c shunt generators and give conditions to be satisfied for voltage build up?
b) What are various possible causes for d.c shunt generator not building up voltage?
[10+5]
5. A short shunt compound d.c generator delivers 100A to a load at 250V. The generator delivers 100A to a load at 250V. The generator has shunt field, series field and armature resistance of 130Ω, 0.1Ω and 0.1Ω respectively. Calculate the voltage generated in armature winding. Assume 1V drop per brush. [15]
6. Sketch the speed-load characteristics of a d.c
a) Shunt motor b) Series motor c) Cumulatively compound motor.
Account for the shape of the above characteristics curves? [15]
7. A shunt generator delivers 50kw at 250V when running at 400 r.p.m. The armature and field resistance are 0.2Ω and 50Ω respectively. Calculate the speed of the machine when running as a shunt motor and taking 50kw input at 250V. Allow 1V per brush for contact drop? [15]
8.a) Draw the power flow diagram of a d.c generator and d.c motor?
b) Derive the condition for maximum efficiency? [10+5]
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