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

Question 1 of 50

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

1080°

1440°

720°

360°

Question 1 of 50

Question 2 of 50

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

L_m = L_in + L_out/2 cm

L_m = L_out - L_in/2 cm

L_m = 2/L_in+ L_out cm

L_m = 2/L_out - L_in cm

Question 2 of 50

Question 3 of 50

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

Distributed coil winding

Mesh shaped coil winding

Concentric coil winding

Diamond mesh shaped coil winding

Question 3 of 50

Question 4 of 50

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

3

2

1

4

Question 4 of 50

Question 5 of 50

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

Star contact

Auxiliary contact

Delta contact

Over load relay contact

Question 5 of 50

Question 6 of 50

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

Synchronous speed = 120/PF

Synchronous speed = 120P/F

Synchronous speed = 120F/P

Synchronous speed = PF/120

Question 6 of 50

Question 7 of 50

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

Eddy current loss

Copper loss

Hysteresis loss

Friction loss

Question 7 of 50

Question 8 of 50

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

Shunt type ohmmeter

Series type ohmmeter

Multimeter

Megger

Question 8 of 50

Question 9 of 50

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

Direct on-line starter

Autotransformer starter

Star delta starter

Rheostatic starter

Question 9 of 50

Question 10 of 50

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

1000 rpm

1200 rpm

800 rpm

1440 rpm

Question 10 of 50

Question 11 of 50

11. 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_r

N_slip = N_r - N_s

N_slip = N_s - N_r/N_s

N_slip = N_s - N_r

Question 11 of 50

Question 12 of 50

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

By injecting emf in rotor circuit

By changing the applied frequency

By rotor rheostat control

By cascade operation

Question 12 of 50

Question 13 of 50

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

180°

120°

90°

360°

Question 13 of 50

Question 14 of 50

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

DOL starter

Fully automatic star delta starter

Semi automatic star delta starter

Auto transformer starter

Question 14 of 50

Question 15 of 50

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

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

Number of slots/Total electrical degree

Total electrical degree/Number of slots

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

Question 15 of 50

Question 16 of 50

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

Internal Growler

Digital multimeter

Tong Tester

External Growler

Question 16 of 50

Question 17 of 50

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

Generate maximum flux

Maintain the rotor speed constant

Produce more uniform rotor field and torque

Reduce the stray losses

Question 17 of 50

Question 18 of 50

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

3 Phase single squirrel cage induction motor

Universal motor

Permanent capacitor motor

3 Phase slip ring induction motor

Question 18 of 50

Question 19 of 50

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

ON remote control

Forward & reverse control

OFF remote control

Inching control

Question 19 of 50

Question 20 of 50

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

Cotton

Empire

Bamboo

Terylene

Question 20 of 50

Question 21 of 50

21. 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 21 of 50

Question 22 of 50

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

30 A

25 A

15 A

10 A

Question 22 of 50

Question 23 of 50

23. 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_r) x 100

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

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

Question 23 of 50

Question 24 of 50

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

Closed circuit and open circuit

Short circuit and closed circuit

Control circuit and power circuit

Open circuit and short circuit

Question 24 of 50

Question 25 of 50

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

No load speed

Full load speed

Relative speed between stator and rotor

Rotating magnetic field speed

Question 25 of 50

Question 26 of 50

26. 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 frequency

Cascade operation

Changing applied voltage

Question 26 of 50

Question 27 of 50

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

3 times more than supply frequency

√3 times less than supply frequency

Equal to supply frequency

3 times less than supply frequency

Question 27 of 50

Question 28 of 50

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

Total electrical degree = 180° / No. of slots

Total electrical degree = 180° x No. of slots

Total electrical degree = 180° x No. of poles

Total electrical degree = 180° / No. of poles

Question 28 of 50

Question 29 of 50

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

Whole coil winding

Double layer winding

Half coil winding

Single layer winding

Question 29 of 50

Question 30 of 50

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

Pitch Factor = Number of slots/Number of poles

Pitch Factor = Number of poles/Number of slots

Pitch Factor = Pole pitch/Winding pitch

Pitch Factor = Winding pitch/Pole pitch

Question 30 of 50

Question 31 of 50

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

Sequential control

Forward and reverse

Remote control

Inching

Question 31 of 50

Question 32 of 50

32. 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?

3%

4%

5%

2%

Question 32 of 50

Question 33 of 50

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

To control the speed

To reduce the slip

To get high starting and running torque

To reduce the losses

Question 33 of 50

Question 34 of 50

34. 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 34 of 50

Question 35 of 50

35. 46. Which test in winding is illustrated?

Continuity test

Polarity test

Ground test

Short circuit test

Question 35 of 50

Question 36 of 50

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

Wire guides

Mandrel

Wire feed

Spool carrier

Question 36 of 50

Question 37 of 50

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

Continuity test

Short circuit test

Ground test

Polarity test

Question 37 of 50

Question 38 of 50

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

Protect against dead short circuit

Allow for continuous over loading

Protect against high voltage

Protect from heavy load

Question 38 of 50

Question 39 of 50

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

By rotor rheostat control

By changing applied frequency

By changing the number of stator poles

By changing the applied voltage

Question 39 of 50

Question 40 of 50

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

Double cotton covered copper wire

Super enamelled copper wire

Single cotton covered copper wire

PVC covered copper winding wire

Question 40 of 50

Question 41 of 50

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

Vibration of shaft

Motor will not start

Over heating of motor

Runs in slow speed

Question 41 of 50

Question 42 of 50

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

Direct connection from stator

Direct connection to rotor from supply

By the transformer action of stator and rotor

Due to back emf produced in stator

Question 42 of 50

Question 43 of 50

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

1 to 2 times of full load current

4 to 5 times of full load current

5 to 6 times of full load current

2 to 3 times of full load current

Question 43 of 50

Question 44 of 50

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

Slip rings

Bearings

Shaft

Brushes

Question 44 of 50

Question 45 of 50

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

Short circuit test

Ground test

Polarity test

Open circuit test

Question 45 of 50

Question 46 of 50

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

Single layer basket winding

Double layer basket winding

Diamond coil winding

Involute coil winding

Question 46 of 50

Question 47 of 50

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

Windage loss

Iron loss

Friction loss

Copper loss

Question 47 of 50

Question 48 of 50

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

Switch ON at pre set time

Change from star to delta

Trip at over load

Switch OFF at pre set time

Question 48 of 50

Question 49 of 50

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

Slip decreases torque increases

Slip increases torque decreases

Slip decreases torque decreases

Slip increases torque increases

Question 49 of 50

Question 50 of 50

50. 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 50 of 50