বৈজ্ঞানিক যন্ত্রপাতির নাম ও তার ব্যবহার...

DC MACHINES - 1

Time : 3 hours ]                                                                                                            [ Total Marks : 80
PART—A                                                                                                                                    3×10=30

Instructions :
 (1) Answer all questions.
(2) Each question carries three marks.
(3) Answer should be brief and straight to the point
and shall not exceed five simple sentences.

1. State the Fleming’s right-hand rule.
2. Define MNA and GNA.                                                                                                        1½+1½=3
3. State the functions of yoke, commutator and pole core in DC
generator.                                                                                                                                    1+1+1=3
4. What is armature reaction? List different effects of it.                                                               1+2=3
5. Derive the e.m.f. equation of a DC generator.
6. Explain the significance of back EMF.
7. Explain power stages in a DC motor.
8. State the factors that affect the speed of a DC motor.
9. State the necessity of 3-point starter.
10. What is the main difference between brake test and
Swinburne’s test?

PART—B 
                                                                                                                                                    10×5=50
Instructions : 
(1) Answer any five questions.
(2) Each question carries ten marks.

11. Explain the working of simple loop generator.

12. (a) List various losses in a DC generator.                                                                                         4
(b) A 4-pole DC generator is delivering 20 A to a load of 10W. If
the armature resistance is 50W, calculate the induced EMF
of the machine. Allow a drop of 1 V per brush.                                                                                     6

13. (a) A 4-pole DC generator has an output of 120 A at 400 V, the
wave connected armature has 980 conductors. The
brushes are advanced by 3 degrees from the neutral axis.
Find (a) ATd /pole, (b) ATc/pole.                                                                                                            6
(b) Write the advantages of parallel operation of DC generator.                                                            4

14. Explain the process of commutation with neat sketch.

15. (a) Derive the torque equation of DC motor.                                                                                   6
(b) Determine the torque established by the armature of a 4-pole DC motor having 774 conductors, two paths in parallel, 24 milliWebers of pole flux and the armature current is 50 A.                            4

16. (a) Classify DC motors.                                                                                                                    4
(b) Draw the electrical and mechanical characteristics of a DC shunt motor.                                        6

17. (a) State the function of No volt coil and overload coil in a 3-point starter.                                    6
(b) List the advantages and disadvantages of Wand Leonard methods.                                                 4

18. Explain the method of conducting Swinburne’s test with a neat
circuit diagram.