PU ECM269D. C. Motors23. A 220 V d.c. shunt motor akes an armature current of 30 A on certain load. Its armatureresistance is 0.8 ohm. Find the resistance to be connected in series with the armature to halvethe speed, if the load torque is proportional ta the square of the speed.(May-2001)24. What is back e.m.f.? Explain the significance of a back e.m.f.(Dec-2001)25. Why can a d.c. series motor not be started on no-load ?(Dec-2001)26. A 4 pole, d.c. motor has lap connected armature winding. Theflux per pole is 30 mWb. Thenumber of armature conductors is 250. When connected to 230 V d.c. supply it draws anarmature current of 40 amp. Calculate the back e.m.f. and the speed with which motor isrunning. Assume armature resistance is 0.6 2(Dec-2001)27. What are the types of a d.c. motor ? Draw various characteristics and give applications of eachmotor.(Dec-2001)28. A 300 V d.c. shunt motor is taking 50 Amp. Resistance of the shunt field and the armature are150 and 0.03 respectively. Motor is running with a speed of 1000 r.p.m. If now anadditional resistance of 0.25 n is added in series with the armature, calculate the new value ofspeed. Assume load constant.29. Write a short note on three point starter.30. A 220 d.c. shunt motor has armature and field resistance of 0.5 ohm and 110 ohms respectively.While running at 500 r.p.m. motor draws line curent of 32 A from 220 V supply. If the speedof the motor is to be raised to 750 r.p.m., what value of additional resistance must be includedin shunt field circuit ? Assume linear magnetization characteristics. Also the load torque remains(Dec-2001)(Dec-2001)constant.(May-2003) (Hint : Refer Ex. 4.28. Ans. : 62.1096 2)31. A 400 V d.c. series motor takes 100 A on full load and runs at 1000 r.p.m. The armature andseries field resistance are 0.2 ohm and 0.1 ohm respectively. If a field divertor of 0.2 ohm isconnected in parallel with series field winding, what would be the speed of the motor, if motoris developing full load torque again. Assume unsaturated magnetic circuit.32. Write a short note on four point D.C. shunt motor starter.(May-2003)(May-2003)33. Write a short note on mechanical characteristics of DC series motor and its applications.(May-2003)34. From first principle derive the torque equation for a D.C. motor and draw the torque-current,speed-current and torque-speed characteristics of a shunt motor, using torque equation orotherwise.(Dec-2003)35. Explain the methods of speed control using diverter, both for D.C. shunt as well as seriesmotors. Draw the necessary circuit diagrams.(Dec-2003)36. A 250 V d.c. shunt motor runs at 800 r.p.m. driving a constant torque load, taking current of25 A from 250 V supply. If the speed is to be raised to 1000 r.p.m. now, what value ofexternal resistance should be inserted in field winding of the motor ? The field resistance andarmature resistance are 250 ohms and 1 ohm respectively. Assume the unsaturated magneticcircuit.(Dec-2003) (Hint : Refer Ex. 4.28. Ans. : 72.4181 2)37. When running at 800 r.p.m. a series motor takes 30 A current from 250 V supply. Calculate thespeed of the motor and current taken by it when a resistance equal to series field windingresistance is used as a shunt across series field winding and the torque is raised by 50%. Thearmature and series field winding resistances are 0.2 ohm and 0.1 ohm respectively. Assumeflux to be proportional to current.(Dec-2003)38. Write a short note on D.C. shunt motor starters.(Dec-2003)

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23. A 220 V d.c. shunt motor akes an armature current of 30 A on certain load. Its armature resistance is 0.8 ohm. Find the resistance to be connected in series with the armature to halve the speed, if the load torque is proportional ta the square of the speed. (May-2001)

23. A 220 V d.c. shunt motor akes an armature current of 30 A on certain load. Its armature resistance is 0.8 ohm. Find the resistance to be connected in series with the armature to halve the speed, if the load torque is proportional ta the square of the speed. (May-2001)

Introductory Circuit Analysis (13th Edition)

13th Edition

ISBN:9780133923605

Author:Robert L. Boylestad

Publisher:Robert L. Boylestad

Chapter1: Introduction

Section: Chapter Questions

Problem 1P: Visit your local library (at school or home) and describe the extent to which it provides literature...

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