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

Question 1 of 50

1. 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 cascade operation

By rotor rheostat control

Question 1 of 50

Question 2 of 50

2. 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 2 of 50

Question 3 of 50

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

Ground test

Continuity test

Polarity test

Short circuit test

Question 3 of 50

Question 4 of 50

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

Windage loss

Copper loss

Iron loss

Friction loss

Question 4 of 50

Question 5 of 50

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

Over load relay contact

Auxiliary contact

Star contact

Delta contact

Question 5 of 50

Question 6 of 50

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

Slip increases torque increases

Slip decreases torque increases

Slip increases torque decreases

Slip decreases torque decreases

Question 6 of 50

Question 7 of 50

7. 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 = Pole pitch/Winding pitch

Pitch Factor = Number of slots/Number of poles

Question 7 of 50

Question 8 of 50

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

Synchronous speed = 120P/F

Synchronous speed = 120F/P

Synchronous speed = PF/120

Synchronous speed = 120/PF

Question 8 of 50

Question 9 of 50

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

Control circuit and power circuit

Open circuit and short circuit

Closed circuit and open circuit

Short circuit and closed circuit

Question 9 of 50

Question 10 of 50

10. 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 10 of 50

Question 11 of 50

11. 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 11 of 50

Question 12 of 50

12. 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_r

N_slip = N_r - N_s

N_slip = N_s - N_r/N_s

Question 12 of 50

Question 13 of 50

13. 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

√3 times less than supply frequency

Equal to supply frequency

Question 13 of 50

Question 14 of 50

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

Inching

Sequential control

Remote control

Forward and reverse

Question 14 of 50

Question 15 of 50

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

ON remote control

Inching control

OFF remote control

Forward & reverse control

Question 15 of 50

Question 16 of 50

16. 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 = L_in + L_out/2 cm

L_m = 2/L_in+ L_out cm

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

1200 rpm

800 rpm

Question 17 of 50

Question 18 of 50

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

30 A

15 A

10 A

25 A

Question 18 of 50

Question 19 of 50

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

720°

360°

1440°

1080°

Question 19 of 50

Question 20 of 50

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

Number of slots/Total electrical degree

Total electrical degree/Number of slots

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

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

Question 20 of 50

Question 21 of 50

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

Bamboo

Empire

Cotton

Terylene

Question 21 of 50

Question 22 of 50

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

Trip at over load

Switch ON at pre set time

Switch OFF at pre set time

Change from star to delta

Question 22 of 50

Question 23 of 50

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

Internal Growler

External Growler

Tong Tester

Digital multimeter

Question 23 of 50

Question 24 of 50

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

To easy flow of varnish in the winding

To increase the insulation resistance value

To dry the varnish quickly in winding

To drive out the moisture in between winding layers

Question 24 of 50

Question 25 of 50

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

Whole coil winding

Single layer winding

Half coil winding

Double layer winding

Question 25 of 50

Question 26 of 50

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

To get high starting and running torque

To reduce the slip

To reduce the losses

To control the speed

Question 26 of 50

Question 27 of 50

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

D.O.L starter

Auto transformer starter

Automatic star/delta starter

Semi automatic star/delta starter

Question 27 of 50

Question 28 of 50

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

Runs in slow speed

Motor will not start

Over heating of motor

Vibration of shaft

Question 28 of 50

Question 29 of 50

29. 46. Which test in winding is illustrated?

Continuity test

Ground test

Short circuit test

Polarity test

Question 29 of 50

Question 30 of 50

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

Autotransformer starter

Direct on-line starter

Star delta starter

Rheostatic starter

Question 30 of 50

Question 31 of 50

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

Multimeter

Shunt type ohmmeter

Series type ohmmeter

Megger

Question 31 of 50

Question 32 of 50

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

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

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

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

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

Question 32 of 50

Question 33 of 50

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

Mandrel

Spool carrier

Wire guides

Wire feed

Question 33 of 50

Question 34 of 50

34. 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 34 of 50

Question 35 of 50

35. 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 35 of 50

Question 36 of 50

36. 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° x No. of poles

Total electrical degree = 180° / No. of poles

Total electrical degree = 180° / No. of slots

Question 36 of 50

Question 37 of 50

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

Full load speed

No load speed

Relative speed between stator and rotor

Rotating magnetic field speed

Question 37 of 50

Question 38 of 50

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

Rotor rheostat control method

Changing applied voltage method

Cascade operation method

Injecting emf in rotor circuit method

Question 38 of 50

Question 39 of 50

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

90°

180°

360°

120°

Question 39 of 50

Question 40 of 50

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

Slip rings

Brushes

Shaft

Bearings

Question 40 of 50

Question 41 of 50

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

Direct connection to rotor from supply

Due to back emf produced in stator

Direct connection from stator

By the transformer action of stator and rotor

Question 41 of 50

Question 42 of 50

42. 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

Universal motor

3 Phase slip ring induction motor

Question 42 of 50

Question 43 of 50

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

Single layer basket winding

Diamond coil winding

Involute coil winding

Double layer basket winding

Question 43 of 50

Question 44 of 50

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

Changing applied voltage

Cascade operation

Changing the number of poles

Changing applied frequency

Question 44 of 50

Question 45 of 50

45. 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%

3%

4%

5%

Question 45 of 50

Question 46 of 50

46. 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

5 to 6 times of full load current

1 to 2 times of full load current

Question 46 of 50

Question 47 of 50

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

Short circuit test

Ground test

Polarity test

Open circuit test

Question 47 of 50

Question 48 of 50

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

Double cotton covered copper wire

Single cotton covered copper wire

PVC covered copper winding wire

Super enamelled copper wire

Question 48 of 50

Question 49 of 50

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

Eddy current loss

Copper loss

Hysteresis loss

Friction loss

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 changing the number of stator poles

By rotor rheostat control

By changing the applied voltage

Question 50 of 50