Objective type Q & A

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Q A

01. The number of poles, when the frequency is 50Hz and speed of the motor is 500 rpm?

😐 5

😐 10

😐 12

😐 24

02. Which of the following induction motor has the highest starting torque?

😐 Squirrel cage induction motor

😐 Slip ring induction motor

😐 Same in both induction motors

😐 Same in both induction motors

03.Which of the following motors is /are widely used?

😐 Squirrel cage induction motor

😐 Slip ring induction motor

😐 Either of these

😐 Either of these

04.Which of the following component is usually fabricated out of silicon steel?

😐 Bearings

😐 Shaft

😐 stator core

😐None of the above

05.The shaft of an induction motor is made of

😐 stiff

😐 flexible

😐 hollow

😐any of the above

06.The power factor of squirrel cage induction motor is

😐 low at light loads only

😐 low at heavy loads only

😐 both A and B

😐low at rated load only

07.The frame of an induction motor is usually made of

😐 silicon steel

😐 cast iron

😐 aluminium

😐bronze

08.The synchronous speed of a motor with 6 poles and operating at 50 Hz frequency is ___.

😐 1500

😐 1000

😐 3000

😐750

09.The shaft of an induction motor is made of

😐 high speed steel

😐 stainless steel

😐 carbon steel

😐cast iron

10.The power consumption, in case of centrifugal loads (like pump, fan, blower etc.), proportional to ____.

😐 speed

😐 square of speed

😐 cube of speed

😐not applicable

11.In an induction motor, no-load the slip is generally

😐 less than 1%

😐1.5%

😐 2%

😐4%

12.The efficiency figures for energy efficient motors (in comparison with standard efficiency motor) can be generally higher by____%.

😐1%

😐3-7%

😐10% and above

😐8-10%

13. In medium sized induction motors, the slip is generally around

😐0.04%

😐0.4%

😐4%

😐14%

14. The speed of an AC motor depends on ____.

😐 Frequency

😐No. of poles

😐both (a) and (b)

😐None of the above

15.In squirrel cage induction motors, the rotor slots are usually given slight skew in order to

😐reduce windage losses

😐 reduce eddy currents

😐reduce accumulation of dirt and dust

😐reduce magnetic hum

16. The speed of the motor can be varied by ___.

😐Changing supply frequency

😐Changing no. of poles

😐Using multi speed windings

😐All the above

17. The efficiency of an induction motor can be expected to be nearly

😐60 to 90%

😐80 to 90%

😐95 to 98%

😐99%

18. Reduction in supply voltage by 10% will change the torque of the motor by ___.

😐38%

😐19%

😐9.5%

😐no change

19. The number of slip rings on a squirrel cage induction motor is usually

😐two

😐three

😐four

😐none

20. Which of the following information available on name plate of a motor?

😐KW Rating

😐RPM

😐Frame Size

😐all the above

21. The starting torque of a squirrel-cage induction motor is

😐low

😐 negligible

😐same as full-load torque

😐slightly more than full-load torque

22.Rotor rheostat control method of speed control is used for

😐squirrel-cage induction motors only

😐slip ring induction motors only

😐both (a) and (b)

😐none of the above

23. Size of a high-speed motor as compared to low-speed motor for the same KW rating

😐Bigger

😐Smaller

😐Same Size

😐None of the above

24. In induction motor the unit of slip is

😐rpm

😐metre per second.

😐radian.

😐unit less.

25. The starting torque of a 3-phase induction motor can be increased by increasing

😐the rotor reactance

😐the rotor resistance

😐the stator resistance

😐 None of the above

26. Which types of following motors are most efficient?

😐TEFC

😐SPDP

😐Both

😐 None

27. . What determines the thermal loading on the motor?

😐 Duty/Load cycle

😐Temperature of the winding

😐Age of the motor

😐 Ambient conditions

28. Unbalance in voltages at motor terminals is caused by ____.

😐 Supplying single phase loads disproportionately

😐Use of different sizes of cables

😐 Both (a) & (b)

😐 None of the above

29 . A double squirrel-cage induction motor has

😐 two rotors moving in opposite direction

😐two parallel windings in stator

😐two parallel windings in rotor

😐 two series windings in stator

30 . With decrease in speed of the motor, the required capacitive kVAr.

😐 Increases

😐Decreases

😐Does not change

😐 None of the above

31 .What is the primary function of a capacitor in an electrical circuit?

😐 To increase voltage

😐 To control current flow

😐To store and release electrical energy

😐To generate heat answer

32 . Star-delta starting of motors is not possible in case of

😐single phase motors

😐 variable speed motors

😐 low horse power motors

😐high speed motors

33 . The speed of the motor can be varied by ___.

😐Changing supply frequency

😐Changing no. of poles

😐Using multi speed windings

😐All the above

34.An induction motor with 1000 r.p.m. speed will have

😐8 poles

😐6 poles

😐4 poles

😐2 poles

35.The good power factor of an induction motor can be achieved if the average flux density in the air gap is

😐absent

😐small

😐large

😐infinity

36.Which of the following are ill suited for energy efficient motors application?

😐Pumps

😐 Fans

😐Punch Presses

😐All the above

37.Stepless speed control of induction motor is possible by which of the following methods?

😐e.m.f. injection in rotor eueuit

😐Changing the number of poles

😐Cascade operation

😐None of the above

38.For which motor the speed can be controlled from rotor side ?

😐Squirrel-cage induction motor

😐Slip-ring induction motor

😐 Both (a) and (b)

😐None of the above

39. Five percent increase in supply frequency will change the synchronous speed by _____.

😐-5%

😐 +5%

😐 -10%

😐 +10%

40. Which of the following needs to be measured after rewinding of motor?

😐No load current

😐winding resistance

😐 air gap

😐all the above

41. In three-phase squirrel-cage induction motors

😐rotor conductor ends are short-circuited through slip rings

😐rotor conductors are short-circuited through end rings

😐rotor conductors are kept open

😐rotor conductors are connected to insulation

42. Output power requirements of constant torque loads vary with _____.

😐Speed

😐voltage

😐Current

😐power factor

43. Which of the following is an AC motor?

😐Slip ring motor

😐 Synchronous motor

😐 Squirrel cage Induction

😐all of the above

44. DOL starting of induction motors is usually restricted to

😐low horsepower motors

😐variable speed motors

😐high horsepower motors

😐high speed motors

45. The speed of a squirrel-cage induction motor can be controlled by all of the following Except

😐changing supply frequency

😐changing number of poles e

😐changing winding resistance

😐reducing supply voltag

46. The power factor of an induction motor under no-load conditions will be closer to

😐0.2 lagging

😐0.2 leading

😐0.5 leading

😐unity

47. Stray losses in an induction motor generally are ____ .

😐proportional to the square of the stator current

😐 proportional to the square of the rotor current

😐 proportional to the rotor current

😐 inversely proportional to the square of rotor current

48. Which of the following information available on name plate of a motor?

😐HP rating

😐RPM

😐Frame model

😐all the above

49. A 3-phase slip ring motor has

😐double cage rotor

😐wound rotor

😐short-circuited rotor

😐any of the above

50. In three-phase induction motors sometimes copper bars are placed deep in the rotor to

😐improve starting torque

😐reduce copper losses

😐improve efficiency

😐improve power factor

51. In a three-phase induction motor

😐power factor at starting is high as compared to that while running

😐power factor at starting is low as compared to that while running

😐power factor at starting in the same as that while running

😐all the above

52. A change of 4% of supply voltage to an induction motor will produce a change of approximately

😐4% in the rotor torque

😐8% in the rotor torque

😐12% in the rotor torque

😐16% in the rotor torque

53. An induction motor can run at synchronous speed when

😐it is run on load

😐direction

😐it is run on voltage higher than the rated voltage

😐e.m.f. is injected in the rotor circuit

54. The torque developed by a 3-phase induction motor least depends on

😐rotor current

😐rotor power factor

😐rotor e.m.f.

😐shaft diameter

55. In an induction motor if air-gap is increased

😐the power factor will be low

😐windage losses will be more

😐bearing friction will reduce

😐copper loss will reduce In an induction motor

56. In induction motor, percentage slip depends on

😐supply frequency

😐supply voltage

😐copper losses in motor

😐none of the above

57. The torque of an induction motor is

😐directly proportional to slip

😐inversely proportional to slip

😐proportional to the square of the slip

😐none of the above

58. The induction motor shaft should be

😐Hollow

😐Stiff

😐Flexible

😐 Any of these

59. Induction motors normally use die cast aluminum rotor because aluminum is

😐Cheaper in cost

😐Lighter in weight

😐Easy to cast owing to its low melting point and is easily available

😐Of low resistivit

60. The squirrel cage induction motors are provided with blades in order to

😐Facilitate cooling of rotor

😐Balance the rotor dynamically

😐Eliminate noise

😐None of these

61. The rotor winding for a 3-phase slip ring induction motor having delta connected stator must be connected in

😐 Delta

😐Star

😐Delta or star according to need

😐None of these

62.In a 3-phase slip ring induction motor, brushes are connected to

😐External star connected resistors

😐DC supply

😐3 – Phase AC supply

😐Equalizing coils

63.Uneven gap in an induction motor is likely to cause

😐Heating of motor

😐Unbalancing of motor shaft

😐Both (a) and (b)

😐None of these

64.A wound rotor induction motor can be distinguished from squirrel cage induction motor by

😐Presence of slip rings

😐Size of frame

😐Shaft diameter

😐Any of the above

65.The 3-phse induction motor with rotor circuit open will

😐Run normally

😐Get overheated

😐 Not run

😐 Make noise

66.If any two leads from slip rings are interchanged in a 3-phase induction motor the motor will

😐 Continue running in the same direction as before

😐Run in a direction opposite to previous one

😐 Not run

😐Get damaged

67.The direction of rotation of a 3-phase induction motor can be reversed by

😐 Transposing any two leads from supply

😐Transposing any two leads from slip rings

😐 Transposing all the three leads from the supply

😐Disconnecting any one phase

69.For driving high inertia loads best type of induction motor suggested is

😐 slip ring type

😐squirrel cage type

😐any of the above

😐none of the above

70.A squirrel cage induction motor is not selected when

😐 initial cost is the main consideration

😐maintenance cost is to be kept low

😐 higher starting torque is the main consideration

😐all above considerations are involved