J ECM267D. C. Motorskercise Problems on D.C. Motors1. A 440 voits d.c. shunt motor has an armature resistance of 0.5 N and field resistance of 180 2Determine back e.m.f when giving an E output of 7.46 kW at 85% efficiency. (Ans. : 431.25 V)2. A 240 V d.c. shunt motor has an armature resistance of 0.2 2 The rated fuli load current is80 A. Calculate the current at the instant of starting if the motor is started direct on line andexpress it in terms of the full load current. Calculate the value of starting resistance to limit the(Ans. : 1200 A, 0.133 2)starting current to 150% of rated current.3. A d.c. shunt machine has rating of 10 kW, 500 V. The armature resistance is 0.1 Q Calculatethe induced e.m.f. if machine is made to run as i) Generator ii) Motor. (Ans. : 502.5 V, 499.85 V)4. A d.c. shunt motor connected to a 230 V supply takes a line current of 12 A, at some load. IfR, = 10 and R,- 230 2 calculate the back e.m.f.5. A 4 pole, 250 V, series motor has a wave connected armature with 1254 conductors. The fluxper pole is 22 mWb when motor is taking 50 A. Armature and fleld resistance are 0.2 and 0.2Q respectively. Calculate its speed.6. Determine the total torque developed in a 250 V, 4 pole d.c. shunt motor with lap winding,accomodated in 60 slots, each containing 20 conductors. The armature current is 50 A and theflux per pole is 23 mWb.7. A 250 V, d.c. shunt motor takes 6 A line current on no load and runs at 1000 r.p.m. The fieldresistance is 250 2 and armature resistance is 0.2 Q If the full load line current is 26 A,calculate(Ans. : 219 V)(Ans. : 250.1 r.p.m.)(Ans. :219.5 N-m)full load speed assuming constant flux.(Ans. : 984 r.p.m.)8. A 4 pole, d.c. shunt motor takes 22.5 A from a 250 V supply. R, = 0.5 N and R = 125 2.The armature is wave wound with 300 conductors. If the flux per pole is 0.02 Wb, calculatei) Speed li) Torque developed i) Gross power developed.(Ans. : 1199 r.p.m, 39.1 N-m, 4.915 kW)9. A 250 V d.c. shunt motor has no load speed 1200 r.p.m. The line current being 5 A. Whenfully loaded line current is 30 A. Shunt field resistance is 250 ohms and armature resistance is0.5 ohms. Find the speed of the motor on full load and its speed regulation.(Ans. : 1139.51 r.p.m., 5.3 %)10. A 4 pole, 250 V d.c. series motor has a wave connected armature with 496 conductors.Calculate i) Gross torque ii) Shaft torque i) Efficiency iu) Armature resistance. Assume flux perpole 22 mWb, the armature current of 50A, the speed N = 462 r.p.m., R, = 0.14 n and(Ans. : i) 173.66 N-m ii) 161.621 N-m iii) 86.92 % iv) 0.1896 Q)11. A 460 V, d.c. series motor runs at 500 r.p.m. taking a current of 40 A. calculate the speed ifmotor takes a current of 30 A. Total resistance of the motor across the terminals is 0.8 2(Ans. : 679.127 r.p.m.)mechanical losses are 810 W.Assume flux proportional to field current.niversity Questions1. A 250 V, 4 pole, d.c. shunt has armature resistance of 0.12 Q and fieid resistance of 125 ithas 960 lap connected conductors and a flux of 20 milli-Wb per pole. if the input current is 30A, estimate :- i) Speed and torque developed and i) % efficiency, if constant losses are 10% ofoutput power of the motor.2. Sketch and explain, giving reasons, the speed-torque characteristics of d.c. shunt, series andcumulative compound motor.3. A 250 V d.c. shunt motor runs at 1000 r.p.m, and taking 20 A current in the armature whichhas a resistance of 0.5 2. Estimate : - 1) Extra resistance to be added in the armature circuit toreduce speed to 500 r.p.m. i) Speed of motor with increased load raising armature current to30 A with resistance in i) included in the circuit of the armature.(Мay-99)(May-99)(May-99)J 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.(May-99)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 fluxlpole if motor runs at1250 r.p.m. while taking 30 A armature current.(Dec.-99).

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1. A 440 volts d.c. shunt motor has an armature resistance of 0.5 Q and field resistance of 180 2. Determine back e.m.f when giving an E output of 7.46 kW at 85% efficiency. (Ans. : 431.25 V) 2 A 240 V de chunt notor har an grmnture recietance of 020 The rated full lood current je

1. A 440 volts d.c. shunt motor has an armature resistance of 0.5 Q and field resistance of 180 2. Determine back e.m.f when giving an E output of 7.46 kW at 85% efficiency. (Ans. : 431.25 V) 2 A 240 V de chunt notor har an grmnture recietance of 020 The rated full lood current je

Introductory Circuit Analysis (13th Edition)

13th Edition

ISBN:9780133923605

Author:Robert L. Boylestad

Publisher:Robert L. Boylestad

Chapter1: Introduction

Section: Chapter Questions

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