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Electrical machine MCQ

Electrical machine MCQ

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  • 05th May, 2021
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Electrical machine MCQ Quiz

Following are mostly asked Electrical machine MCQ test that are designed for professionals like you to crack you interviews. You can take this Electrical machine online test before appearing to you real interview. This Electrical machine quiz there are around 30+ multiple choice questions on Electrical machine with four options.

1) If field current is decreased in shunt dc motor, the speed of the motor

  • A.  remains same.
  • B.  increases.
  • C.  decreases.
  • D.  none of the above.

2) What is the mechanical power developed by a DC series motor is maximum?

  • A.  Back emf is equal to half the applied voltage.
  • B.  Back emf is equal to applied voltage.
  • C.  Back emf is equal to zero.
  • D.  None of above.

3) What is the shunt resistance component equivalent circuit obtained by no load test of an induction motor representative of ?

  • A.  windage and friction loss
  • B.  core loss only
  • C.  both 1 and 2
  • D.  Copper loss

4) In Ward-Leonard system, the lower limit of the speed imposed by

  • A.  Field resistance.
  • B.  Armature resistance.
  • C.  Residual magnetism of the generator.
  • D.  None of above.

5) Ward-Leonard control is basically a ___________ control method.

  • A.  Field control.
  • B.  Armature resistance control.
  • C.  Armature voltage control.
  • D.  Field diverter control.
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6) For very sensitive and wide speed control, the preferable control method is

  • A.  Armature control.
  • B.  Ward-Leonard control.
  • C.  Multiple voltage control.
  • D.  Field control.

7) Eddy current loss will depends on

  • A.  Frequency
  • B.  Flux density
  • C.  Thickness
  • D.  All of the above

8) Hysteresis loss will depends on

  • A.  f
  • B.  f²
  • C.  f³
  • D.  f1.6

9) Thin laminations are used in a machine in order to reduce

  • A.  Eddy current losses
  • B.  Hysteresis losses
  • C.  Both 1 and 2
  • D.  Copper losses

10) Hysteresis loop represents the area of

  • A.  copper loss
  • B.  eddy current loss
  • C.  hysteresis loss
  • D.  total iron losses

11) Commutator pitches of duplex and simplex lap windings are respectively

  • A.  4 and 2
  • B.  2 and 1
  • C.  4 ang 1
  • D.  2 and 2

12) The emf induced in the dc generator armature winding is

  • A.  AC
  • B.  DC
  • C.  AC and DC
  • D.  None of the above

13) Commutator in DC generator is used for

  • A.  collecting of current
  • B.  reduce losses
  • C.  increase efficiency
  • D.  convert AC armature current in to DC

14) A DC generator without commutator is a

  • A.  AC generator
  • B.  DC motor
  • C.  DC generator
  • D.  induction motor

15) In DC machine yoke offers

  • A.  mechanical protection to the machine
  • B.  flux path completion
  • C.  produce working flux
  • D.  both A and B

16) In a dc machine 72 number of coils are used. Find the number of commutator segments required?

  • A.  36
  • B.  37
  • C.  72
  • D.  74

17) In DC generators brushes are used for

  • A.  collecting of current without any sparkings
  • B.  collecting of voltage
  • C.  reduce eddy current loss
  • D.  convert ac armature current in to dc

18) which of the following type of brush and their application is/are correct

  • A.  carbon brush → normal ratings
  • B.  electro graphite → large ratings
  • C.  copper graphite → low voltage high current density
  • D.  all of the above

19) Which of the following bearings and their uses are correct

  • A.  ball bearings → small machines
  • B.  roller bearings → large machines
  • C.  neither 1 nor 2
  • D.  both A and B

20) Which of the following windings are necessary in case of all dc machines?

  • A.  closed winding
  • B.  lap winding
  • C.  wave winding
  • D.  open type winding

21) DC machine windings are

  • A.  full pitched
  • B.  short pitched
  • C.  either of these
  • D.  none of the above

22) Which of the following represents the commutator pitch?

  • A.  Number of conductors spanned by one coil at the back end of the armature.
  • B.  Number of conductors spanned by one coil at the front end of the armature.
  • C.  The distance between the staring of first coil and its next successive coil
  • D.  Number of commutator segments between two successive coils.

23) In a dc machine 4 pole lap winding is used. The number of parallel paths are?

  • A.  2
  • B.  4
  • C.  1
  • D.  8

24) In a dc machine 6 pole wave winding is used. The number of parallel paths are?

  • A.  6
  • B.  4
  • C.  2
  • D.  1

25) Inter pole winding is connected in-------------------------- ?

  • A.  series with armature
  • B.  series with main poles
  • C.  parallel with armature
  • D.  parallel with main poles

26) In a lap winding dc machine number of conductors are 100 and number of parallel paths are 10. Find the average pitch

  • A.  10
  • B.  100
  • C.  50
  • D.  1

27) Lap winding is prefered for which type of machines?

  • A.  low current and low voltage
  • B.  high current and high voltage
  • C.  high current and low voltage
  • D.  low current and high voltage

28) Wave winding is prefered for which of the following rating?

  • A.  low current and low voltage
  • B.  high current and high voltage
  • C.  high current and low voltage
  • D.  low current and high voltage

29) Equalizer rings are used in which of the followings?

  • A.  lap winding
  • B.  wave winding
  • C.  both 1 and 2
  • D.  none of the above

30) In a 2 pole lap winding dc machine , the resistance of one conductor is 2Ω and total number of conductors is 100. Find the total resistance

  • A.  200Ω
  • B.  100Ω
  • C.  50Ω
  • D.  10Ω

31) Dummy coils are used for

  • A.  increasing efficiency.
  • B.  reducing armature reaction.
  • C.  mechanical balancing.
  • D.  all of the above

32) A 4 pole lap wound dc generator has 4 brushes, if one of the brush is damaged, what will be the change in V, I and P ratings

  • A.  V, I and P
  • B.  V/2, I/2 and P/4
  • C.  V/2, I and P/2
  • D.  V, I/2 and P/2

33) For a dc machine shunt resistance and armature resistance values are

  • A.  high and high
  • B.  high and low
  • C.  low and low
  • D.  low and high

34) Shunt field of DC generators consists of--------number of turns and ---------- conductors respectively

  • A.  large and thick
  • B.  large and thin
  • C.  less and thick
  • D.  less and thin

35) Series field consists of--------number of turns and ---------- conductors respectively

  • A.  large and thick
  • B.  large and thin
  • C.  less and thick
  • D.  less and thin

36) What is/are the necessary conditions for voltage build up in self excited generator?

  • A.  Poles should contain residual flux.
  • B.  Field winding should be properly connected to armature winding.
  • C.  Field winding resistance should be less than critical resistance.
  • D.  All of the above.

37) No load saturation characteristics are plotted between

  • A.  no load voltage and field current
  • B.  no load voltage and armature current
  • C.  short circuit current and field current
  • D.  short circuit current and armature current

38) The effect of ------------------ on main field flux is armature reaction?

  • A.  armature mmf
  • B.  armature current
  • C.  armature flux
  • D.  all of the above

39) Armature flux is.............with respect to main field flux or main field poles?

  • A.  rotates opposite direction
  • B.  rotates same direction
  • C.  stationary
  • D.  none of the above

40) Cross magnetization effects which of the following?

  • A.  commutation
  • B.  reduction in main field flux
  • C.  reduces the terminal voltage
  • D.  both 2 and 3

41) Demagnetization effects which of the following?

  • A.  commutation
  • B.  reduction in main field flux
  • C.  reduces the terminal voltage
  • D.  both B and C

42) Brushes are always placed on--------------- , in order to achieve sparkles commutation?

  • A.  GNA
  • B.  MNA
  • C.  either GNA or MNA
  • D.  none of the above

43) Flux density under trailing pole tips in case of generator will

  • A.  increase
  • B.  decrease
  • C.  either increase or decrease
  • D.  none of the above

44) Flux density under leading pole tips in case of generator will

  • A.  increase
  • B.  decrease
  • C.  either increase or decrease
  • D.  none of the above

45) Which of the following is/are effects of armature reaction?

  • A.  increase the iron loss
  • B.  increase the maintenance and repair
  • C.  increases the design cost
  • D.  all of the above

46) Which of the following is/are the methods to reduce the armature reaction and its effects?

  • A.  pole chamfering
  • B.  pole stacking
  • C.  compensating winding
  • D.  all of the above

47) In DC machine torque depends on which of the following?

  • A.  flux (φ)
  • B.  armature current (I)
  • C.  both A and B
  • D.  speed

48) Compensating winding is placed in the

  • A.  pole shoe
  • B.  armature core
  • C.  main field
  • D.  all of the above

49) Direction of the current in the compensating winding is________ to the direction of current in the armature conductors?

  • A.  same
  • B.  exactly opposite
  • C.  either of these
  • D.  none of the above

50) Find the reactance voltage when current is changed from -2A to 2A in 4 sec and self inductance is 1H?

  • A.  0 V
  • B.  4 V
  • C.  1 V
  • D.  2 V

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