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

132 thoughts on “50 TOP MOST ELECTRICAL MACHINES VIVA Questions and Answers – EEE

  1. sir please send the electrical and electronics basic interview questions and answers with pdf to an my mail

  2. Sir can you provide me all the questions and answer in PDF format.if so please send at my mail.I have interview in lecturer.also send me the power system question and answer.

  3. Sir please send all viva questions related to electrical engineering(Electrical machines,control system,circuit Theory,transmission and distribution,power system) to the mail id kharunprasadgmail.com. please reply sir.

  4. Sir plz send me also interiview related question and answer related from machine,power system,measurement and also basic electrical subjects
    thanku sir

  5. Dear sirs please send me below questions answers

    1) Design a suitable double –layer lap winding for a 6-pole dc armature with 18 slots and two coil sides per slot. Give values of front-pitch, brack–pitch and commutator pitch. Draw the developed diagram and show the positions of brushes.

    2) A dc shunt motor is being operated from300Vmains.Its no-load speed is 1200rpm.When fully loaded it delivers a torque of 400 N m and its speed drops to 1100rpm.Find its speed and power output when delivering the same torque; if operated with an armature voltage of 600 V. Excitation is assumed unchanged, i.e. motor fields still excited at 300VState any assumption you are required to make.

    3) Calculate the efficiency of a 500V shunt motor when taking 700A from the following data taken when the motor was hot: motor stationary, voltage drop in the armature winding 15V.when the armature current was 510Afield current is 9 A at a normal voltage. Motor running at normal speed unloaded the armature current was 22.5Awhen the applied voltage was 550V; allow 2 V for brush contact drop and 1%of the rated output of 400kw for stray-load losses
    4) Two star-connected generators are connected in a parallel and supply a balanced load of 1500kva at 11kV line voltage and 0.8lagging power factor. The Synchronous reactnces of the two machines respectively are: 35 ohms and 40 ohms. The prime mover governors of the two machines are adjusted so as to equally share the power load The phase current in one machine is 43A at a lagging power factor Calculate:
    a) The phase current in the second machine
    b) The induced emf of each machine
    c) The power factor at which each machine operates.

    5) Calculate the ratio of transformation of an autotransformer starter for a 25 Kw, 400V,
    3-phase induction motor if the starting torque is to be 75% of full-loaded torque.
    Assume the slip at full-load to be 3.5% and short circuit current to be six times full-
    load current. Ignore magnetizing current of the transformer and of the motor.

    6) For a 2 phase servomotor with a high resistance rotor find approximate expression for forward and backward torques in terms of phase voltages (differing 90 degree in phase) and motor speed. Assume the stator impedance and rotor reactance to be negligible.

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