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

Question 1 of 50

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

360°

90°

120°

180°

Question 1 of 50

Question 2 of 50

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

Copper loss

Windage loss

Friction loss

Iron loss

Question 2 of 50

Question 3 of 50

3. 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_slip = N_s - N_r/N_s

Question 3 of 50

Question 4 of 50

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

Wire guides

Wire feed

Mandrel

Spool carrier

Question 4 of 50

Question 5 of 50

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

Generate maximum flux

Produce more uniform rotor field and torque

Reduce the stray losses

Maintain the rotor speed constant

Question 5 of 50

Question 6 of 50

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

L_m = L_out - L_in/2 cm

L_m = 2/L_in+ L_out cm

L_m = 2/L_out - L_in cm

L_m = L_in + L_out/2 cm

Question 6 of 50

Question 7 of 50

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

Sequential control

Inching

Remote control

Forward and reverse

Question 7 of 50

Question 8 of 50

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

Ground test

Polarity test

Continuity test

Short circuit test

Question 8 of 50

Question 9 of 50

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

Ground test

Polarity test

Short circuit test

Open circuit test

Question 9 of 50

Question 10 of 50

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

Whole coil winding

Single layer winding

Half coil winding

Double layer winding

Question 10 of 50

Question 11 of 50

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

2 to 3 times of full load current

4 to 5 times of full load current

1 to 2 times of full load current

5 to 6 times of full load current

Question 11 of 50

Question 12 of 50

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

Cascade operation method

Changing applied voltage method

Injecting emf in rotor circuit method

Rotor rheostat control method

Question 12 of 50

Question 13 of 50

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

Diamond mesh shaped coil winding

Distributed coil winding

Concentric coil winding

Mesh shaped coil winding

Question 13 of 50

Question 14 of 50

14. 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 14 of 50

Question 15 of 50

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

Super enamelled copper wire

PVC covered copper winding wire

Double cotton covered copper wire

Single cotton covered copper wire

Question 15 of 50

Question 16 of 50

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

OFF remote control

ON remote control

Inching control

Forward & reverse control

Question 16 of 50

Question 17 of 50

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

1440 rpm

1000 rpm

800 rpm

1200 rpm

Question 17 of 50

Question 18 of 50

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

Diamond coil winding

Single layer basket winding

Double layer basket winding

Involute coil winding

Question 18 of 50

Question 19 of 50

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

Pitch Factor = Pole pitch/Winding pitch

Pitch Factor = Number of slots/Number of poles

Pitch Factor = Winding pitch/Pole pitch

Pitch Factor = Number of poles/Number of slots

Question 19 of 50

Question 20 of 50

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

DOL starter

Semi automatic star delta starter

Auto transformer starter

Fully automatic star delta starter

Question 20 of 50

Question 21 of 50

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

Autotransformer starter

Direct on-line starter

Star delta starter

Rheostatic starter

Question 21 of 50

Question 22 of 50

22. 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_s - N_r)/N_s) x 100

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

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

Question 22 of 50

Question 23 of 50

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

Total electrical degree = 180° / No. of poles

Total electrical degree = 180° / No. of slots

Total electrical degree = 180° x No. of slots

Total electrical degree = 180° x No. of poles

Question 23 of 50

Question 24 of 50

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

Changing the number of poles

Changing applied voltage

Cascade operation

Changing applied frequency

Question 24 of 50

Question 25 of 50

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

Full load speed

Relative speed between stator and rotor

Rotating magnetic field speed

No load speed

Question 25 of 50

Question 26 of 50

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

To dry the varnish quickly in winding

To drive out the moisture in between winding layers

To easy flow of varnish in the winding

To increase the insulation resistance value

Question 26 of 50

Question 27 of 50

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

Allow for continuous over loading

Protect against dead short circuit

Protect from heavy load

Protect against high voltage

Question 27 of 50

Question 28 of 50

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

360°

1440°

1080°

720°

Question 28 of 50

Question 29 of 50

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

Megger

Multimeter

Shunt type ohmmeter

Series type ohmmeter

Question 29 of 50

Question 30 of 50

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

2

1

3

4

Question 30 of 50

Question 31 of 50

31. 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 31 of 50

Question 32 of 50

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

Synchronous speed = 120/PF

Synchronous speed = PF/120

Synchronous speed = 120P/F

Synchronous speed = 120F/P

Question 32 of 50

Question 33 of 50

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

Universal motor

3 Phase slip ring induction motor

Permanent capacitor motor

3 Phase single squirrel cage induction motor

Question 33 of 50

Question 34 of 50

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

Number of slots/Total electrical degree

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

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

Total electrical degree/Number of slots

Question 34 of 50

Question 35 of 50

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

To reduce the slip

To control the speed

To reduce the losses

To get high starting and running torque

Question 35 of 50

Question 36 of 50

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

Switch ON at pre set time

Switch OFF at pre set time

Change from star to delta

Trip at over load

Question 36 of 50

Question 37 of 50

37. 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%

5%

3%

2%

Question 37 of 50

Question 38 of 50

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

Slip increases torque decreases

Slip decreases torque increases

Slip decreases torque decreases

Slip increases torque increases

Question 38 of 50

Question 39 of 50

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

Eddy current loss

Hysteresis loss

Friction loss

Copper loss

Question 39 of 50

Question 40 of 50

40. 46. Which test in winding is illustrated?

Ground test

Polarity test

Short circuit test

Continuity test

Question 40 of 50

Question 41 of 50

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

Empire

Cotton

Terylene

Bamboo

Question 41 of 50

Question 42 of 50

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

Closed circuit and open circuit

Control circuit and power circuit

Open circuit and short circuit

Short circuit and closed circuit

Question 42 of 50

Question 43 of 50

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

Slip rings

Bearings

Brushes

Shaft

Question 43 of 50

Question 44 of 50

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

Star contact

Over load relay contact

Auxiliary contact

Delta contact

Question 44 of 50

Question 45 of 50

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

Due to back emf produced in stator

By the transformer action of stator and rotor

Direct connection to rotor from supply

Direct connection from stator

Question 45 of 50

Question 46 of 50

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

Auto transformer starter

Automatic star/delta starter

Semi automatic star/delta starter

D.O.L starter

Question 46 of 50

Question 47 of 50

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

Vibration of shaft

Runs in slow speed

Motor will not start

Over heating of motor

Question 47 of 50

Question 48 of 50

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

External Growler

Tong Tester

Digital multimeter

Internal Growler

Question 48 of 50

Question 49 of 50

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

15 A

30 A

25 A

10 A

Question 49 of 50

Question 50 of 50

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

By changing applied frequency

By rotor rheostat control

By changing the applied voltage

By changing the number of stator poles

Question 50 of 50