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

Question 1 of 50

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

By the transformer action of stator and rotor

Direct connection to rotor from supply

Due to back emf produced in stator

Direct connection from stator

Question 1 of 50

Question 2 of 50

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

Full load speed

Relative speed between stator and rotor

No load speed

Rotating magnetic field speed

Question 2 of 50

Question 3 of 50

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

Over load relay contact

Star contact

Auxiliary contact

Delta contact

Question 3 of 50

Question 4 of 50

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

By injecting emf in rotor circuit

By cascade operation

By rotor rheostat control

By changing the applied frequency

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?

25 A

15 A

10 A

30 A

Question 5 of 50

Question 6 of 50

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

Involute coil winding

Single layer basket winding

Diamond coil winding

Double layer basket winding

Question 6 of 50

Question 7 of 50

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

Shunt type ohmmeter

Series type ohmmeter

Multimeter

Megger

Question 7 of 50

Question 8 of 50

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

1080°

1440°

720°

360°

Question 8 of 50

Question 9 of 50

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

Maintain the rotor speed constant

Reduce the stray losses

Generate maximum flux

Produce more uniform rotor field and torque

Question 9 of 50

Question 10 of 50

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

Polarity test

Open circuit test

Short circuit test

Ground test

Question 10 of 50

Question 11 of 50

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

Inching

Remote control

Forward and reverse

Sequential control

Question 11 of 50

Question 12 of 50

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

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

Total electrical degree/Number of slots

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

Number of slots/Total electrical degree

Question 12 of 50

Question 13 of 50

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

Protect against high voltage

Protect from heavy load

Allow for continuous over loading

Protect against dead short circuit

Question 13 of 50

Question 14 of 50

14. 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?

4%

3%

2%

5%

Question 14 of 50

Question 15 of 50

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

360°

120°

180°

90°

Question 15 of 50

Question 16 of 50

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

Auto transformer starter

Fully automatic star delta starter

Semi automatic star delta starter

DOL starter

Question 16 of 50

Question 17 of 50

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

Half coil winding

Double layer winding

Whole coil winding

Single layer winding

Question 17 of 50

Question 18 of 50

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

To easy flow of varnish in the winding

To drive out the moisture in between winding layers

To increase the insulation resistance value

To dry the varnish quickly in winding

Question 18 of 50

Question 19 of 50

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

Pitch Factor = Number of poles/Number of slots

Pitch Factor = Winding pitch/Pole pitch

Pitch Factor = Number of slots/Number of poles

Pitch Factor = Pole pitch/Winding pitch

Question 19 of 50

Question 20 of 50

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

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

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

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

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

Question 20 of 50

Question 21 of 50

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

Control circuit and power circuit

Short circuit and closed circuit

Open circuit and short circuit

Closed circuit and open circuit

Question 21 of 50

Question 22 of 50

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

L_m = 2/L_out - L_in cm

L_m = L_out - L_in/2 cm

L_m = 2/L_in+ L_out cm

L_m = L_in + L_out/2 cm

Question 22 of 50

Question 23 of 50

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

By changing the applied voltage

By changing the number of stator poles

By changing applied frequency

By rotor rheostat control

Question 23 of 50

Question 24 of 50

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

Copper loss

Friction loss

Windage loss

Iron loss

Question 24 of 50

Question 25 of 50

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

Rheostatic starter

Direct on-line starter

Autotransformer starter

Star delta starter

Question 25 of 50

Question 26 of 50

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

Tong Tester

External Growler

Digital multimeter

Internal Growler

Question 26 of 50

Question 27 of 50

27. 46. Which test in winding is illustrated?

Short circuit test

Ground test

Continuity test

Polarity test

Question 27 of 50

Question 28 of 50

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

N_slip = N_s - N_r

N_slip = N_s - N_r/N_s

N_slip = N_r - N_s

N_slip = N_s - N_r/N_r

Question 28 of 50

Question 29 of 50

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

To reduce the losses

To control the speed

To get high starting and running torque

To reduce the slip

Question 29 of 50

Question 30 of 50

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

Concentric coil winding

Diamond mesh shaped coil winding

Mesh shaped coil winding

Distributed coil winding

Question 30 of 50

Question 31 of 50

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

Auto transformer starter

D.O.L starter

Semi automatic star/delta starter

Automatic star/delta starter

Question 31 of 50

Question 32 of 50

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

4

1

3

2

Question 32 of 50

Question 33 of 50

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

Brushes

Shaft

Bearings

Slip rings

Question 33 of 50

Question 34 of 50

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

Ground test

Short circuit test

Continuity test

Polarity test

Question 34 of 50

Question 35 of 50

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

Slip increases torque increases

Slip decreases torque increases

Slip decreases torque decreases

Slip increases torque decreases

Question 35 of 50

Question 36 of 50

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

Inching control

Forward & reverse control

OFF remote control

ON remote control

Question 36 of 50

Question 37 of 50

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

Cascade operation method

Changing applied voltage method

Rotor rheostat control method

Injecting emf in rotor circuit method

Question 37 of 50

Question 38 of 50

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

Equal to supply frequency

√3 times less than supply frequency

3 times more than supply frequency

3 times less than supply frequency

Question 38 of 50

Question 39 of 50

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

Switch OFF at pre set time

Trip at over load

Change from star to delta

Switch ON at pre set time

Question 39 of 50

Question 40 of 50

40. 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 40 of 50

Question 41 of 50

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

Synchronous speed = PF/120

Synchronous speed = 120/PF

Synchronous speed = 120F/P

Synchronous speed = 120P/F

Question 41 of 50

Question 42 of 50

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

Changing applied voltage

Changing applied frequency

Changing the number of poles

Cascade operation

Question 42 of 50

Question 43 of 50

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

Wire guides

Mandrel

Wire feed

Spool carrier

Question 43 of 50

Question 44 of 50

44. 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

1000 rpm

800 rpm

1440 rpm

Question 44 of 50

Question 45 of 50

45. 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 45 of 50

Question 46 of 50

46. 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 poles

Total electrical degree = 180° / No. of slots

Total electrical degree = 180° / No. of poles

Total electrical degree = 180° x No. of slots

Question 46 of 50

Question 47 of 50

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

Permanent capacitor motor

3 Phase single squirrel cage induction motor

3 Phase slip ring induction motor

Universal motor

Question 47 of 50

Question 48 of 50

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

4 to 5 times of full load current

5 to 6 times of full load current

1 to 2 times of full load current

2 to 3 times of full load current

Question 48 of 50

Question 49 of 50

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

Friction loss

Copper loss

Eddy current loss

Hysteresis loss

Question 49 of 50

Question 50 of 50

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

Cotton

Bamboo

Terylene

Empire

Question 50 of 50