ELECTRICIAN 2nd YEAR MODULE – AC. Three Phase Motor ONLINE TEST

Question 1 of 50

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

No load speed

Relative speed between stator and rotor

Rotating magnetic field speed

Full load speed

Question 1 of 50

Question 2 of 50

2. 18. What is the electrical degree of 6 pole stator of motor?

720°

360°

1440°

1080°

Question 2 of 50

Question 3 of 50

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

Reduce the stray losses

Maintain the rotor speed constant

Produce more uniform rotor field and torque

Generate maximum flux

Question 3 of 50

Question 4 of 50

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

3 Phase slip ring induction motor

Universal motor

3 Phase single squirrel cage induction motor

Permanent capacitor motor

Question 4 of 50

Question 5 of 50

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

30 A

10 A

25 A

15 A

Question 5 of 50

Question 6 of 50

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

Trip at over load

Change from star to delta

Switch ON at pre set time

Switch OFF at pre set time

Question 6 of 50

Question 7 of 50

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

By rotor rheostat control

By changing the applied voltage

By changing applied frequency

By changing the number of stator poles

Question 7 of 50

Question 8 of 50

8. 27. How the voltage is received in the rotor of induction motor?

Direct connection from stator

Direct connection to rotor from supply

Due to back emf produced in stator

By the transformer action of stator and rotor

Question 8 of 50

Question 9 of 50

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

Cascade operation

Changing the number of poles

Changing applied voltage

Changing applied frequency

Question 9 of 50

Question 10 of 50

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

Open circuit and short circuit

Short circuit and closed circuit

Control circuit and power circuit

Closed circuit and open circuit

Question 10 of 50

Question 11 of 50

11. 14. What is the name of the coil winding?

Distributed coil winding

Diamond mesh shaped coil winding

Concentric coil winding

Mesh shaped coil winding

Question 11 of 50

Question 12 of 50

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

3 times less than supply frequency

√3 times less than supply frequency

3 times more than supply frequency

Equal to supply frequency

Question 12 of 50

Question 13 of 50

13. 17. Name the part marked as 'X' of the winding machine?

Spool carrier

Mandrel

Wire feed

Wire guides

Question 13 of 50

Question 14 of 50

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

5 to 6 times of full load current

1 to 2 times of full load current

2 to 3 times of full load current

4 to 5 times of full load current

Question 14 of 50

Question 15 of 50

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

Copper loss

Windage loss

Friction loss

Iron loss

Question 15 of 50

Question 16 of 50

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

Cascade operation method

Rotor rheostat control method

Changing applied voltage method

Injecting emf in rotor circuit method

Question 16 of 50

Question 17 of 50

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

To drive out the moisture in between winding layers

To easy flow of varnish in the winding

To dry the varnish quickly in winding

To increase the insulation resistance value

Question 17 of 50

Question 18 of 50

18. 12. What is the name of the part marked as 'X'?

Slip rings

Bearings

Shaft

Brushes

Question 18 of 50

Question 19 of 50

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

Fully automatic star delta starter

Semi automatic star delta starter

Auto transformer starter

DOL starter

Question 19 of 50

Question 20 of 50

20. 39. Which test in winding is essential before giving supply?

Ground test

Short circuit test

Polarity test

Open circuit test

Question 20 of 50

Question 21 of 50

21. 11. What is the phase displacement between windings in 3 phase motor?

120°

180°

90°

360°

Question 21 of 50

Question 22 of 50

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

Hysteresis loss

Eddy current loss

Friction loss

Copper loss

Question 22 of 50

Question 23 of 50

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

By changing the applied frequency

By cascade operation

By injecting emf in rotor circuit

By rotor rheostat control

Question 23 of 50

Question 24 of 50

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

Slip increases torque decreases

Slip increases torque increases

Slip decreases torque decreases

Slip decreases torque increases

Question 24 of 50

Question 25 of 50

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

Single cotton covered copper wire

Double cotton covered copper wire

Super enamelled copper wire

PVC covered copper winding wire

Question 25 of 50

Question 26 of 50

26. 23. What is the formula to calculate the mean circumference of the coil?

L_m = 2/L_in+ L_out cm

L_m = L_out - L_in/2 cm

L_m = 2/L_out - L_in cm

L_m = L_in + L_out/2 cm

Question 26 of 50

Question 27 of 50

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

Double layer basket winding

Single layer basket winding

Involute coil winding

Diamond coil winding

Question 27 of 50

Question 28 of 50

28. 38. Which material is used as wedges in winding process?

Empire

Cotton

Terylene

Bamboo

Question 28 of 50

Question 29 of 50

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

Short circuit test

Ground test

Continuity test

Polarity test

Question 29 of 50

Question 30 of 50

30. 25. 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?

2%

4%

3%

5%

Question 30 of 50

Question 31 of 50

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

2

3

4

1

Question 31 of 50

Question 32 of 50

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

1200 rpm

800 rpm

1440 rpm

1000 rpm

Question 32 of 50

Question 33 of 50

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

No. of poles/No. of slots in the stator

Total electrical degree/Number of slots

No. of slots in the stator/No. of poles

Number of slots/Total electrical degree

Question 33 of 50

Question 34 of 50

34. 13. What is the name of AC coil winding?

Single layer winding

Half coil winding

Whole coil winding

Double layer winding

Question 34 of 50

Question 35 of 50

35. 16. What is the name of the starter symbol?

Auto transformer starter

D.O.L starter

Automatic star/delta starter

Semi automatic star/delta starter

Question 35 of 50

Question 36 of 50

36. 1. What is the formula to calculate the slip speed (N_slip) of 3 phase squirrel cage induction motor?

N_slip = N_r - N_s

N_slip = N_s - N_r/N_r

N_slip = N_s - N_r/N_s

N_slip = N_s - N_r

Question 36 of 50

Question 37 of 50

37. 10. Which operation the control circuit is used?

Remote control

Forward and reverse

Inching

Sequential control

Question 37 of 50

Question 38 of 50

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

Synchronous speed = 120F/P

Synchronous speed = 120P/F

Synchronous speed = 120/PF

Synchronous speed = PF/120

Question 38 of 50

Question 39 of 50

39. 2. What is the type of control circuit?

ON remote control

Forward & reverse control

OFF remote control

Inching control

Question 39 of 50

Question 40 of 50

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

Shunt type ohmmeter

Megger

Multimeter

Series type ohmmeter

Question 40 of 50

Question 41 of 50

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

Slip = ((N_r - N_s)/N_r) x 100

Slip = ((N_r - N_s)/N_s) x 100

Slip = ((N_s - N_r)/N_s) x 100

Slip = ((N_s - N_r)/N_r) x 100

Question 41 of 50

Question 42 of 50

42. 21. What is the formula to calculate pitch factor?

Pitch Factor = Number of slots/Number of poles

Pitch Factor = Pole pitch/Winding pitch

Pitch Factor = Number of poles/Number of slots

Pitch Factor = Winding pitch/Pole pitch

Question 42 of 50

Question 43 of 50

43. 43. Why slip ring induction motor is fitted with wound rotor?

To control the speed

To reduce the slip

To reduce the losses

To get high starting and running torque

Question 43 of 50

Question 44 of 50

44. 20. What is the name of the starter symbol?

Rheostatic starter

Star delta starter

Direct on-line starter

Autotransformer starter

Question 44 of 50

Question 45 of 50

45. 32. Which device is used to test stator winding short and open fault?

Tong Tester

External Growler

Digital multimeter

Internal Growler

Question 45 of 50

Question 46 of 50

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

Runs in slow speed

Over heating of motor

Vibration of shaft

Motor will not start

Question 46 of 50

Question 47 of 50

47. 7. What is the name of the contact marked as 'X'?

Over load relay contact

Star contact

Delta contact

Auxiliary contact

Question 47 of 50

Question 48 of 50

48. 46. Which test in winding is illustrated?

Short circuit test

Ground test

Continuity test

Polarity test

Question 48 of 50

Question 49 of 50

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

Total electrical degree = 180° x No. of slots

Total electrical degree = 180° / No. of poles

Total electrical degree = 180° x No. of poles

Total electrical degree = 180° / No. of slots

Question 49 of 50

Question 50 of 50

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

Protect against high voltage

Allow for continuous over loading

Protect against dead short circuit

Protect from heavy load

Question 50 of 50