Free Printable Electrician 3rd sem AC 3 phase Motor

1.

What is the formula to calculate the slip speed (Nslip) of 3 phase squirrel cage induction motor?

a)

$N_{slip}=N_s-N_r$

b)

$N_{slip}=N_r-N_s$

c)

$N_{slip}=\frac{N_s-N_r}{N_r}$

d)

$N_{slip}=\frac{N_s-N_r}{N_s}$

2.

Which operation the control circuit is used?

a)

Remote control

b)

Inching

c)

Sequential control

d)

Forward and reverse

3.

What is the type of control circuit?

a)

Inching control

b)

ON remote control

c)

OFF remote control

d)

Forward & reverse control

4.

Which formula is used to calculate the total electrical degree in stator of an A.C motor?

a)

Total electrical degree = 180° / No. of slots

b)

Total electrical degree = 180° x No. of slots

c)

Total electrical degree = 180° / No. of poles

d)

Total electrical degree = 180° x No. of poles

5.

What is the name of the A.C motor starter?

a)

DOL starter

b)

Auto transformer starter

c)

Semi automatic star delta starter

d)

Fully automatic star delta starter

6.

What is the formula to find synchronous speed of a A.C 3 phase induction motor?

a)

$Synchronous\ speed=\frac{120F}{P}$

b)

$Synchronous\ speed=\frac{120P}{F}$

c)

$Synchronous\ speed=\frac{120}{PF}$

d)

$Synchronous\ speed=\frac{PF}{120}$

7.

What is the fuse rate to run a 10 HP three phase induction motor at full load?

a)

10 A

b)

15 A

c)

25A

d)

30A

8.

What is the name of the contact marked as X?

a)

Star contact

b)

Delta contact

c)

Auxiliary contact

d)

Over load relay contact

9.

What is the type of A.C motor stator winding?

a)

Single layer basket winding

b)

Double layer basket winding

c)

Involute coil winding

d)

Diamond coil winding

10.

Which formula is used to calculate percentage slip of an AC 3 phase induction motor?

a)

$\frac{N_S-N_R}{N_S}\times100$

b)

$\frac{N_R-N_S}{N_S}\times100$

c)

$\frac{N_S-N_R}{N_R}\times100$

d)

$\frac{N_R-N_S}{N_R}\times100$

11.

What is the phase displacement between windings in 3 phase motor?

a)

90°

b)

120°

c)

180°

d)

360°

12.

What is the name of the part marked as X?

a)

Shaft

b)

Brushes

c)

Bearings

d)

Slip rings

13.

What is the name of AC coil winding?

a)

Half coil winding

b)

Whole coil winding

c)

Single layer winding

d)

Double layer winding

14.

What is the name of the coil winding?

a)

Concentric coil winding

b)

Distributed coil winding

c)

Mesh shaped coil winding

d)

Diamond mesh shaped coil winding

15.

Which speed is called as synchronous speed in 3 phase induction motor?

a)

No load speed

b)

Full load speed

c)

Rotating magnetic field speed

d)

Relative speed between stator and rotor

16.

What is the name of the starter symbol?

a)

D.O.L starter

b)

Auto transformer starter

c)

Automatic star/delta starter

d)

Semi automatic star/delta starter

17.

What is the electrical degree of 6 pole stator of motor?

a)

360°

b)

720°

c)

1080°

d)

1440°

18.

Calculate the number of coils per phase per pair of poles of 3 phase motor having 2 pole, 24 slots,12 coils?

a)

1

b)

2

c)

3

d)

4

19.

What is the name of the starter symbol?

a)

Star delta starter

b)

Rheostatic starter

c)

Direct on-line starter

d)

Autotransformer starter

20.

What is the formula to calculate pitch factor?

a)

$Pitch\ factor=\frac{Pole\ pitch}{Winding\ pitch}$

b)

$Pitch\ factor=\frac{Winding\ pitch}{Pole\ pitch}$

c)

$Pitch\ factor=\frac{Number\ of\ slots}{Number\ of\ poles}$

d)

$Pitch\ factor=\frac{Number\ of\ poles}{Number\ of\ slots}$

21.

How pole pitch is measured in terms of slots in AC winding?

a)

$\frac{Total\ electrical\ \deg ree}{Number\ of\ slots}$

b)

$\frac{\ Number\ of\ slots}{Total\ electrical\ \deg ree}$

c)

$\frac{No.\ of\ slots\ in\ the\ stator\ }{No.\ of\ poles}$

d)

$\frac{\ No.\ of\ poles\ }{No.\ of\ slots\ in\ the\ stator}$

22.

What is the formula to calculate the mean circumference of the coil?

a)

$L_m=\frac{L_{out}-L_{in}}{2}\ \ \ cm$

b)

$L_m=\frac{L_{out}+L_{in}}{2}\ \ cm$

c)

$L_m=\frac{2}{L_{out}-L_{in}}\ \ cm$

d)

$L_m=\frac{2}{L_{out}+L_{in}}\ \ cm$

23.

What is the synchronous speed of a A.C 3 phase induction motor having 6 poles at a frequency of 50 Hertz?

a)

800 rpm

b)

1000 rpm

c)

1200 rpm

d)

1440 rpm

24.

Calculate the percentage slip in a 3 phase induction motor having 6 poles with a frequency of 50 Hertz rotating with actual speed of 960 rpm?

a)

2%

b)

3%

c)

4%

d)

5%

25.

What is the rotor frequency of a 3 phase squirrel cage induction motor at the time of starting?

a)

Equal to supply frequency

b)

3 times less than supply frequency

c)

3 times more than supply frequency

d)

√3 times less than supply frequency

26.

How the voltage is received in the rotor of induction motor?

a)

Direct connection from stator

b)

Due to back emf produced in stator

c)

Direct connection to rotor from supply

d)

By the transformer action of stator and rotor

27.

Which method is applied to control the speed of 3 phase squirrel cage induction motor from its rotor side?

a)

Cascade operation

b)

Changing applied voltage

c)

Changing applied frequency

d)

Changing the number of poles

28.

Which loss of 3 phase induction motor is determined by blocked rotor test?

a)

Copper loss

b)

Friction loss

c)

Hysteresis loss

d)

Eddy current loss

29.

Why pre heating is necessary for motors before varnishing in rewinding process?

a)

To dry the varnish quickly in winding

b)

To easy flow of varnish in the winding

c)

To increase the insulation resistance value

d)

To drive out the moisture in between winding layers

30.

Which type of test is conducted using internal growler in AC motor winding?

a)

Ground test

b)

Polarity test

c)

Continuity test

d)

Short circuit test

31.

Which device is used to test startor winding short and open fault?

a)

Tong Tester

b)

Internal Growler

c)

External Growler

d)

Digital multimeter

32.

What is the purpose of using thermal cutout in addition to fuse in A.C motor circuit?

a)

Protect from heavy load

b)

Protect against high voltage

c)

Allow for continuous over loading

d)

Protect against dead short circuit

33.

Which type of motor is used to provide high starting torque at variable speed?

a)

Universal motor

b)

Permanent capacitor motor

c)

3 Phase slip ring induction motor

d)

3 Phase single squirrel cage induction motor

34.

What is the relation between torque and slip in an A.C induction motor?

a)

Slip increases torque decreases

b)

Slip increases torque increases

c)

Slip decreases torque increases

d)

Slip decreases torque decreases

35.

What is effect of A.C induction motor if rotor bar is in open circuit?

a)

Vibration of shaft

b)

Motor will not start

c)

Runs in slow speed

d)

Over heating of motor

36.

Which type of wire is used for rewinding of A.C 3 phase motors?

a)

Super enamelled copper wire

b)

PVC covered copper winding wire

c)

Single cotton covered copper wire

d)

Double cotton covered copper wire

37.

Which material is used as wedges in winding process?

a)

Empire

b)

Cotton

c)

Bamboo

d)

Terylene

38.

Which test in winding is essential before giving supply?

a)

Ground test

b)

Polarity test

c)

Open circuit test

d)

Short circuit test

39.

Why the rotor bars are mounted in a slightly skewed position in 3 phase motor?

a)

Generate maximum flux

b)

Reduce the stray losses

c)

Maintain the rotor speed constant

d)

Produce more uniform rotor field and torque

40.

Which loss is determined by no load test of 3 phase induction motor?

a)

Iron loss

b)

Copper loss

c)

Friction loss

d)

Windage loss

41.

Which method of speed control two variable speeds only obtained in 3 phase motor?

a)

By rotor rheostat control

b)

By changing applied frequency

c)

By changing the applied voltage

d)

By changing the number of stator poles

42.

Why slip ring induction motor is fitted with wound rotor?

a)

To reduce the slip

b)

To control the speed

c)

To reduce the losses

d)

To get high starting and running torque

43.

What is the function of timer in automatic star delta starter?

a)

Trip at over load

b)

Switch ON at pre set time

c)

Change from star to delta

d)

Switch OFF at pre set time

44.

Which instrument is used to measure insulation resistance of a 3 phase induction motor?

a)

Megger

b)

Multimeter

c)

Shunt type ohmmeterr

d)

Series type ohmmeter

45.

Which test in winding is illustrated?

a)

Polarity test

b)

Ground test

c)

Continuity test

d)

Short circuit test

46.

What is the starting current of an A.C 3 phase induction motor?

a)

1 to 2 times of full load current

b)

2 to 3 times of full load current

c)

4 to 5 times of full load current

d)

5 to 6 times of full load current

47.

Which method is used to control the speed of 3 phase induction motor from stator side?

a)

By cascade operation

b)

By rotor rheostat control

c)

By injecting emf in rotor circuit

d)

By changing the applied frequency

48.

What is the speed control method of 3 phase induction motor?

a)

Cascade operation method

b)

Rotor rheostat control method

c)

Changing applied voltage method

d)

Injecting emf in rotor circuit method

49.

What are the two functional circuits incorporated with a three phase motor starter?

a)

Open circuit and short circuit

b)

Closed circuit and open circuit

c)

Control circuit and power circuit

d)

Short circuit and closed circuit

50.

Which is the main property of leatheroid paper insulation?

a)

Non moisturized material

b)

Highly non-hygroscopic

c)

Very good for class F insulation

d)

Better ageing and dielectric strength

51.

Which type of insulating material is selected for binding the coils and over hangs?

a)

Cotton sleeves

b)

Empire sleeves

c)

Terylene thread

d)

Fibre glass tape

52.

Which insulation is used for cuffing in AC winding?

a)

Fibre glass tape

b)

Leatheroid paper

c)

Empire fiber glass tape

d)

Fabric based adhesive tape

53.

What refers coil in AC winding?

a)

Number of turns connected in series

b)

Number of turns connected in parallel

c)

Number of turns under two similar poles

d)

Number of turns under two dissimilar poles

54.

Which type of AC winding the number of coil/pole/phase is more than one at different pitches?

a)

Involute coil winding

b)

Diamond coil winding

c)

Flat loop over lapped winding

d)

Flat loop non-over lapped winding

55.

Calculate the number of coils /phase/ pole for a 3 phase double layer distributed winding for a motor having 36 slots, 36 coils and 4 poles?

a)

3 coils /phase/ pole

b)

6 coils / phase/pole

c)

9 coils / phase/pole

d)

12 coils/ phase/ pole

56.

What is the type of rewinding process?

a)

Hand winding

b)

Skein winding

c)

Former winding

d)

Machine winding

57.

Which type of starter is used to start and run the 3 phase slip ring induction motor?

a)

Direct on-line starter

b)

Rotor rheostat starter

c)

Auto transformer starter

d)

Manual star-delta starter

58.

What is the function of collar?

a)

Provides insulation around field

b)

Provides insulation for coil tapping

c)

Helps tightening material for flange

d)

Provides insulation for heat transfer from coil

59.

Which type of winding wire is used to wind submersible pump motors?

a)

PVC covered type

b)

Terylene thread type

c)

Super enamelled type

d)

Double cotton covered type

60.

What is the reason of long chord winding is avoided in AC motors?

a)

Low efficiency

b)

Low starting torque

c)

More winding wire required

d)

Less heat dissipation

61.

Which type of winding has more space for cooling?

a)

Between overhanging coils

b)

Between overhanging coil and rotor

c)

Between overhanging coils and yoke

d)

Between overhanging coil and wedge

62.

Where the panel boards are used?

a)

Industrial motor drives

b)

Domestic wiring circuits

c)

3 phase domestic wiring

d)

Load distribution for AC & DC supply

63.

Determine the torque in newton metres produced by a 7.5 HP squirrel cage motor rotating at 1440 rpm?

a)

21.63 Nm

b)

24.4 Nm

c)

33.05 Nm

d)

36.6 Nm

64.

Which type of handle design of rotary switch is illustrated?

a)

Knob

b)

Lever

c)

Coin slot

d)

Key operation

65.

What is the purpose of using rotor resistance starter to start 3 phase slip ring induction motor?

a)

Reduce rotor voltage

b)

Reduce rotor current

c)

Increase the torque

d)

Reduce the power loss

66.

Which method of speed control is only applicable for 3 phase slipring induction motor?

a)

Cascade operation method

b)

Rotor rheostat speed control

c)

Changing the applied frequency method

d)

Changing the number of stator poles method

67.

What is the name of the winding?

a)

Skew winding

b)

Skein winding

c)

Involute coil winding

d)

Diamond coil winding

68.

What is the name of 3 phase motor winding, if the coil pitch is less than pole pitch?

a)

Full pitch winding

b)

Whole coil winding

c)

Long chorded winding

d)

Short chorded winding

69.

Which is the demerit of 3 phase concentric winding?

a)

More space is required

b)

A stepped former is required

c)

More difficult to shape the coils uniformly

d)

It is not easy to make the end connection

70.

Calculate the phase displacement in terms of slots for a 3 phase, 36 slots, 12 coils, 4 pole stator winding?

a)

3 slots

b)

4 slots

c)

6 slots

d)

8 slots

71.

Which type of AC motor winding having the number of coil/pole/phase is more than one arranged in different slots?

a)

Basket winding

b)

Concentric winding

c)

Distributed winding

d)

Concentrated winding

72.

Which type of testing of winding is illustrated?

a)

Polarity test

b)

Resistance test

c)

Short circuit test

d)

Voltage drop test

73.

Why external resistance is included in the rotor circuit at starting through 3 phase slipring induction motor starter?

a)

To get high running torque

b)

To get high starting torque

c)

To reduce the load current

d)

To get increased speed at starting

74.

What is the effect of motor, if the rotor windings in slipring induction motor is open circuited at starting?

a)

Will not run

b)

Runs at slow speed

c)

Runs at very high speed

d)

Runs but not able to pull load

75.

What happens to a 3 phase induction motor if one phase fails during running?

a)

Motor runs normally

b)

Motor stop instantaneously

c)

Motor runs slowly, finally it burns

d)

Motor runs with irregular speed

76.

What is the effect on 3 phase induction motor if one phase is cut-off during running with load?

a)

Motor stops at once

b)

Motor will run normally

c)

Motor runs with humming noise with slow speed

d)

Motor will run slow speed but winding will be burnt out shortly

77.

What is the defect in AC 3 phase induction motor runs at low speed if loaded?

a)

Wrong motor connection

b)

Wrong starter connection

c)

Open circuit in rotor winding

d)

Partially shorted stator winding

78.

Which fault condition thermal overload relay protects A.C induction motor?

a)

Short circuit

b)

Open circuit

c)

Over current

d)

Under voltage

79.

What happens to the rotor of a 3 phase induction motor if its speed attains to synchronous speed?

a)

Rotor speed reduces

b)

Rotor speed increases

c)

Rotor speed remains same

d)

Rotor bars get damaged

80.

What is the effect of open circuit in rotor of an induction motor?

a)

Motor does not start

b)

Over heating in motor

c)

Excess vibration of shaft

d)

Motor runs with very low speed

81.

What is the reason for frequent blowing of fuse after motor running some time?

a)

Improper earthing

b)

Over loading of motor

c)

Heavy voltage fluctuation

d)

Poor insulation in winding

82.

What happens to a 3 phase induction motor, if one phase fails during starting?

a)

Motor runs and stop immediately

b)

Motor runs in slow speed continuously

c)

Motor runs and draws more current

d)

Motor continues to run with irregular speed

83.

Which is the cause for the 3 phase motor starter with single phase preventer trips frequently?

a)

Incorrect fuse ratings

b)

Unbalanced line voltage

c)

Incorrect settings of OLR

d)

Improper phase sequence

84.

What indication denotes the shorted coil defect in 3 phase motor stator winding while testing with internal growler by keeping hacksaw blade?

a)

Hacksaw blade gets over heated

b)

Rapid vibration of hacksaw blade

c)

Hacksaw blade repels against the slots

d)

Attracted by the winding turns on the slot

Electrician 3rd sem AC 3 phase Motor

Total questions: 84

Worksheet time: 42mins

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