2- Why in the flux control method (field resistance control)for controlling the speed of d.c. shunt motor, the speed control is not possible below normal rated speed? 3- Why in armature voltage control method or rheostatic control method for controlling the speed of d.c. shunt motor, the speed control is not possible above normal rated speed?

2- Why in the flux control method (field resistance control)for controlling the speed of d.c. shunt motor, the speed control is not possible below normal rated speed? 3- Why in armature voltage control method or rheostatic control method for controlling the speed of d.c. shunt motor, the speed control is not possible above normal rated speed?

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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A 4 pole, (01*10)V, DC shunt motor operates on a load current (1*10)A, having wave connected armature with 200 conductors. The flux per Pole is 25 m Wb. Resistance of shunt field winding is 1 ohm and resistance of the armature is 0.15 ohm. b) what will be the factors to minimize the back emf?
Short Answer Questions 1. Why is the armature core of a DC machine laminated? 2. In small DC machine, cast iron yokes are preferred. Why? 3. What for field coils are provided in a DC machine? 4. What for brushes are employed in DC generator? 5. What is the function of armature in a DC generator? 6. What is the function of commutator in a DC machine in generator action. 7. Which are the different types of armature windings commonly used in DC machines? 8. Which is the best-suited material for commutator segments? 10. Why are the graphite or carbon brushes preferred over copper brushes for use in DC machines? 11. Write down the emf equation of a DC generator. 12. What is the principle of operation of a DC generator? Why is a commutator and brush arrangement necessary for the operation of a DC generator? 13. Describe the principle of operation and brief constructional details of a DC machine. 14. Enumerate all the parts of a DC machine. State the material and the function of each part.…
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Q2- Indicate whether the following statements are true or false and correct the false statements 1- The brushes of d.c machine always are placed at the magnetic neutral axis 2- The field current of d.c shunt generator is not affected by load current. 3-The armature voltage of d.c series generator is not affected by load current. 4- A lap winding is most suitable for higher voltage rating machines 5- In dc generator, the critical resistance can be increased by increasing its speed 6-In LAP winding the front pitch equal to (yr ye- yb). 7- The speed of d.c series motor is decreased if the armature current is decreased 8- The compensating winding carrying the field current 9- By tapping field method, the speed of d.c series motor can be controlled below rated value 10- To solve the Commutation Problem in small machines, this can be achieved by increasing the brush width
14.a. The reason for using a laminated stator core in a universal motor is toA. limit the eddy currents and the iron losses.B. limit the saturation of the magnetic circuit.C. maintain a constant level of magnetic flux.D. decrease the doc reactance of the field winding.14.b. If an induction motor has two protective housings for capacitors, it is aA. single-voltage capacitor-start motor.B. permanent-split capacitor-start motor.C. capacitor start-and-run motor.D. dual-voltage capacitor-strut motor.
Q3) A 4 pole wave wound short shunt compound DC Generator supplies a current of 100 A to a load of 10 KW through a cable of resistance Reable is hundred times the resistance of one of the armature conductor, given that the series field resistance is 0.02 ohm, shunt field resistance is 200 ohm, flux per pole is 0.035 Web, total number of armature conductors is 120, speed of generator is 600 RPM, and on load generated voltage is 110 V. Calculate armature resistance.
Electrical engineering subject of electrical machines/ I need a correct and accurate solution
Does a DC motor have to be turning in order for it to develop torque? a) yes b) no Most DC motor consist of many turns per armature loop as well as many evenly distributed loops per al mature. a) true b) false Brushes a DC motor. a) are part of the electrical circuit in b) provide a sliding electrical contact to the commutator of c) are made of a material which is softer than the commutator segments of d) all of the above
A DC series motor having a resistance of 0.4 ꭥ and runs at 2000 rpm when connected to 250 V supply and drawing a current of 20 A. (i) What resistance must be added in order to limit the speed to 4000 rpm when armature current is 5A? Assume flux varies linearly. (ii) What resistance must be added to limit the speed to 1000 rpm when armature current is 30 A? Assume that the flux at 30 A is 20% more than that at 20A. (iii) At what speed the motor will run if it is connected directly to 250 V supply when the load is such that the current drawn is 30 A?
7. A 4-pole, 500V shunt motor has 720 wave connected conductors on its armature. The full-los armature current is 60A and flux per pole is 0.03 Wb. The armature resistance is 0.020 and th contact drop per brush is 1V. then the full-load speed of the motor is -- a) 675 r.p.m. b) 690 r.p.m. c) 705 r.p.m. d) none of the previous,
2- A simple wave wound de shunt motor has the following data: Armature resistance =0.1 ohm Shunt field resistance = 100 ohm Number of poles = 2 Number of conductors = 400 Mechanical and core loss at full load = 2000 W. When the motor is connected to a 400 Volt supply and is fully loaded it draws 104 A. Calculate at a speed of 3000 rpm: i) Armature current and E.M.F ii) Flux per pole iii) Copper losses within the machine. iv) Developed torque, shaft torque and efficiency. v) Sketch the power flow diagram at full load. vi) Motor speed if an external resistance of 0.4 ohms is added to the armature circuit while the load torque remains constant.
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