Page 660 - Basic Electrical Engineering

As a motor, the machine will draw 100 A from the supply out of which 2 A
will go to the field circuit.

Therefore, I = 100 − 2 = 98 A
a
E = V − I R = 220 − 98 × 0.1 = 210.2 V
a
a
m

or,

7.16 REVIEW QUESTIONS

A. Short Answer Type Questions

1. Draw a next sketch of a dc machine and name the component parts.
2. What is the function of the following parts of a dc machine: (i) field poles; (ii) armature; (iii)
brush and commutator; (iv) shaft?
3. Explain the function of brush and commutator in a dc machine for generating action.
4. With a simple example show how lap winding and wave windings are made.
5. Deduce the EMF equation for a dc machine.
6. Describe various methods of speed control of dc motors.
7. Explain why dc motors should require starters.
8. Draw the connection diagram of a dc motor starter.
9. Draw characteristics of dc series motors and mention applications.
10. State the various losses that occur in a dc machine.
11. What is hysteresis loss and eddy current loss?
12. Derive the torque equation for a dc motor.
13. Draw the connection diagrams for dc shunt, series, and compound motors.
14. Explain the working principle of a dc generator.
15. How can you determine the efficiency of a dc machine without actually loading the machine?
16. Why do we use laminated sheets for the armature and the field cores?
17. How can you change the direction of rotation of a dc motor?
18. Why is it advisable not to start a dc series motor without having any load on it?
19. Why do we connect the coils of the armature in series parallel?
20. What are the various losses in a dc machine. Which losses are called constant losses and why?
21. How can you determine the efficiency of a dc machine without actually loading the machine?