Electrical Engineering VIVA Questions



Electrical Machines VIVA Questions and Answers

1.What is the power factor of a transformer at no load?

2.What is the normal phase difference between the voltage and the no-load current in a transformer?

3.What are the essential parts of a transformer?

4.What is the name of the winding to which supply is given?

5.What is the name of the winding from which the supply is taken for load connections?
Secondary winding.

6.Which material is used for the core of a transformer and why?

7.What is the use of iron core in a transformer?

8.How is magnetic leakage reduced?

9.Why are iron cores in transformers made laminated?

10.What determines the thickness of the lamination or stamping?

11.Why are the laminations insulated from each other?

12.What is stacking factor? What is its approximate value?

13.What is called grain-oriented laminations?

14.What is the permissible maximum flux density in transformer core?

15.What is the phase relationship between the primary and secondary voltages of a transformer?

16.What is turn ratio of a transformer?

17.What is voltage ratio of a transformer?

18.What current flows in the transformer primary when its secondary is open?

19.What is the formula for calculating no-load current?

20.Why is the frequency not changed during transformation of electrical energy in a transformer?

21.What is the emf equation of a transformer?

22.What are the two basic types of transformers?

23.What are the types of transformers according to the arrangement of iron cores?

24.What magnetic circuit is formed in Berry-type constructions and why?

25.What is called limb of a transformer?

Electrical Machines VIVA Questions and Answers

26.Why are LT windings placed near the core?

27.What are the types of windings according to the construction?

28.What is the difference between cylindrical-type and sandwich-type winding?

29.What are the types of transformers ?

30 .What do you mean by step-up and step-down transformers?

31.What is an ideal transformer?

32.What do you mean by power transformer?

33.What do you mean by distribution transformers?

34.What do you mean by lighting transformer?

35.How does a transformer contribute towards the widespread popularity of AC system over DC?

36.The required thickness of lamination in a transformer decreases when

37.Oil in transformers is used to –

38.The windings of a transformer are divided into several coils because

39.The size and construction of bushings in a transformer depend upon the

40.What is the resistance of the field winding of a d.c. shunt generator kept low?

41.What do you understand by external characteristics of a d.c. generator?

42.What will happen if the d.c. machine is operated below rated speed?

43.What is the most important precaution in any experiment with d.c. shunt motor?

44.What range of speed can you get with the field control method of speed control of d.c. shunt motor?

45.What range of speed can you get with the armature control method of speed control of d.c. shunt motor?

46.Does the direction of rotation of d.c. shunt motor would get reversed if the armature current and field current both are reversed?

47.If the rated speed of a d.c. shunt motor is1440 r.p.m, which method of speed control would you suggested to obtain a speed of 1500 r.p.m?

48.What will happen if the d.c. shunt motor opened accidentally running on no-load has its shunt field winding?

49.What is the most essential condition for the voltage build up for a d.c. shunt generator?

50. A d.c. shunt motor is found suitable to drive fans because they require


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