Electrical Engineering Lab Viva Questions :

Experiment of DC Machine:
1. What are the difference between electrical motor and generator?
2. What is the need for starters?
3. Which is the basic protective device in any circuit?
4. How to find out the fuse rating?
5. Name the different types of DC starters?
6. What is the role of Holding Coil in a DC starter?
7. Why is the armature rheostat of dc motor kept at maximum resistance position?
8. Write the e.m.f. equation of DC machine.
9. Write the torque equation of DC motor.
10. Name the parts of dc machine.
11. What is the use of commutator and brushes?
12. Draw the electrical characteristics and N/Ia characteristics of a DC shunt motor.
13. How are the ammeters and voltmeters connected in any circuit?
14. What are the methods of speed control of dc motors?
15. What is back emf? Give its significance.
16. What is the difference between self excited and separately excited machines?
17. Name the types of self excited dc machine.
18. What are the losses in dc machine?
19. How is the eddy current loss minimized in dc machine?
20. Why is armature resistance less than field resistance of dc shunt machine?
21. Why is armature resistance more than field resistance of dc series machine?
22. Why shouldn’t dc series motor started at no load?
23. What is L, F, A, N in dc starters?
24. Given 4 terminals without indication. How will you manage to find the field and
armature terminals of i) dc shunt machine ii) dc series machine.

Experiment of AC Machine:
1. What is the principle of a transformer?
2. What are the types of transformer?
3. What are the applications of transformer?
4. Why is the capacity of a transformer specified as KVA and not as KW?
5. What is the condition for maximum efficiency of a transformer?
6. Why is the efficiency of a transformer higher than that of motors?
7. What is the purpose of OC and SC tests?
8 .Why is the core of a transformer laminated?
9. What is meant by regulation?
10. Define the term transformation ratio?
11. What are the components of no load current?
12. How are the parameters referred to the HV or LV side? Explain with an example.
13. What is meant by power factor? Explain.
14. What will happen if dc supply is connected to transformer?’
15. What are the parts of transformer?
16. Why are synchronous motors not self starting? What are the methods of starting?
17. Why are single phase induction motors not self starting? Classify them according to the starting methods.
18. Why is synchronous motor referred as doubly excited machine?
19. What is slip of an induction motor?
20. Why is always the induction motor running with less than the speed of rotating
magnetic field?
21. What are the types of 3 phase induction motors?
22. Why is 3 phase induction motor referred as rotating transformer with short-circuited secondary?
23. What is the use of end rings in squirrel cage induction motor?
24. What is mutual inductance?
25. What is the principle of motor, generator and transformer?
26. How will you reverse the direction of rotation of i) dc motor ii) ac motor?
27. What is M, L, C, and V in wattmeter?
28. What is E and C in autotransformer?
29. What are the disadvantages of low power factor?
30. What are the methods of speed control of ac motors?
31. Given transformers A and B with following details:
A: η= 96% & reg: 5.8%
B: η= 94% & reg: 5.2%
Which transformer will you select? Justify your answer.
32. What do you mean by hunting?
33. What is meant by magnetizing current and active (working) component of current
with respect to transformer?
34. Give the relation between line and phase values of
i) star connected network
ii) delta connected network.
35. When can the squirrel cage machine be loaded to its fullest capacity? i) Star
connection of stator ii) delta connection of stator.
36. How can the eddy current and hysteresis loss of any machine be minimized?
37. What are the methods of electrical braking?
38. Draw the torque-slip characteristics of 3 phase induction motor and explain.
39. State the Farraday's Law of Electromagnetic Induction?
40. Explain the right hand thumb rule.
41. Draw the open and short-circuit characteristics of an alternator.