PU ECM268D. C. Motors4. Explain the need, salient features and working with the help of a neat circuit diagram showingNVC and OLC protections of d.c. shunt motor, 3-point starter.5. Explain the draw speed-current and torque-speed characteristics of a d.c. series motor. Describeany two applications on the basis of characteristics.6. A 250 V d.c. shunt motor takes a load current of 50 A and runs at 1000 r.p.m. calculate : )no-load speed of the motor if no-load current is 5 A. i) % change in flux/pole if motor runs at1250 r.p.m. while taking 30 A armature current.Assume R, = 0.2 ohms and R = 125 ohms7. Write a short note on 4 point d.c. shunt motor starter(May-99)(Dec.-99)(Dec.-99)(Dec.-99)8. Write a short note on any two methods of speed control of d.c. series motor.9. A 250 V, d.c. shunt motor takes a current of 4 A from 250 V mains when running at no-load.The resistance of armature circuit is 1 Q and that of the field circuit is 250 Q Calculate:(i) The efficiency of motor when it draws a current of 20 A from the mains.(ii) The armature current for which the efficiency is a maximum(iii) The value of maximum efficiency.(Dec.-99)(May-2000)(Мay-2000)10. Explain the speed control of d.c. shunt motor.11. A 230 V d.c. shunt motor takes an armature current of 20 A on a certain load. Resistance ofarmature is 0.52. Find the resistance required in series with the armature to halve the speed ifthe load torque is proportional to the square of the speed.12. Draw and explain the characteristics of d.c. series motor.13. Explain 3 point starter used in a d.c. motor.14. A 230 V shunt motor takes 5 A on no-load and runs at 750 r.p.m. Its shunt field and armatureresistances are 115 2 and 0.25 n respectiveły. Calculate the speed of the motor when loadedand taking a current of 55 A. Assume that the flux becomes weak by 4 percent under loadcondition.(Мay-2000)(May-2000)(May-2000)(Dec.-2000)15. What are the types of d.c. motor ? Draw various characteristics and give applications of each(Dec.-2000)motor.16. A 500 V d.c. series motor has armature and series field resistance of 0.06 N and 0.02respectively and takes a current of 50 A at a speed of 500 r.p.m. What resistance should beconnected in series with armature to reduce speed to 350 r.p.m. ? Load torque at new speed is75% of its previous value. Assume flux to be proportional to the load current.(Dec.-2000)17. Write a short note on speed control of d.c. series motor.18. Draw speed-torque and torque-armature current characteristics of d.c. shunt and series motors.State one application of each motor with justification.19. Draw a neat labelled diagram showing the intemal connections of a four point starter used ford.c. shunt motor.In what way is a four point starter superior to a three point starter ?20. A 200 V, 6 połe, d.c. shunt motor has 600 lap-connected armature conductors. Its armatureresistance is 0.1 ohm and shunt field resistance is 100 ohm: Assuming the flux pole as 0.06 Wb,calculate the speed of the motor when it draws 20 A from the supply.21. Enlish speed control methods of d.c. shunt motor. Draw corresponding speed variation graphs.Also, state the maximum and minimum limits of speeds attainable safely using these methods.(Dec.-2000)(May-2001)(May-2001) 2(May-2001)22. Explain the method of controlling the speed of a d.c. series motor using a field diverter.(May-2001)

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4. Explain the need, salient features and working with the help of a neat circuit diagram showing NVC and OLC protections of d.c. shunt motor, 3-point starter. (May-99) Expl