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

Question 1 of 50

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

L_m = L_out - L_in/2 cm

L_m = L_in + L_out/2 cm

L_m = 2/L_in+ L_out cm

L_m = 2/L_out - L_in cm

Question 1 of 50

Question 2 of 50

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

Inching control

Forward & reverse control

ON remote control

OFF remote control

Question 2 of 50

Question 3 of 50

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

By changing the number of stator poles

By changing the applied voltage

By rotor rheostat control

By changing applied frequency

Question 3 of 50

Question 4 of 50

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

Pitch Factor = Number of poles/Number of slots

Pitch Factor = Number of slots/Number of poles

Pitch Factor = Pole pitch/Winding pitch

Pitch Factor = Winding pitch/Pole pitch

Question 4 of 50

Question 5 of 50

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

Star contact

Delta contact

Over load relay contact

Auxiliary contact

Question 5 of 50

Question 6 of 50

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

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

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

Question 6 of 50

Question 7 of 50

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

By the transformer action of stator and rotor

Direct connection from stator

Direct connection to rotor from supply

Due to back emf produced in stator

Question 7 of 50

Question 8 of 50

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

PVC covered copper winding wire

Double cotton covered copper wire

Single cotton covered copper wire

Super enamelled copper wire

Question 8 of 50

Question 9 of 50

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

Short circuit and closed circuit

Closed circuit and open circuit

Open circuit and short circuit

Control circuit and power circuit

Question 9 of 50

Question 10 of 50

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

Slip rings

Bearings

Brushes

Shaft

Question 10 of 50

Question 11 of 50

11. 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

Maintain the rotor speed constant

Reduce the stray losses

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

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

Number of slots/Total electrical degree

Total electrical degree/Number of slots

Question 12 of 50

Question 13 of 50

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

Auto transformer starter

Semi automatic star delta starter

Fully automatic star delta starter

DOL starter

Question 13 of 50

Question 14 of 50

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

Slip decreases torque decreases

Slip decreases torque increases

Slip increases torque increases

Slip increases torque decreases

Question 14 of 50

Question 15 of 50

15. 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 15 of 50

Question 16 of 50

16. 46. Which test in winding is illustrated?

Ground test

Continuity test

Polarity test

Short circuit test

Question 16 of 50

Question 17 of 50

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

Semi automatic star/delta starter

D.O.L starter

Auto transformer starter

Automatic star/delta starter

Question 17 of 50

Question 18 of 50

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

Eddy current loss

Friction loss

Hysteresis loss

Copper loss

Question 18 of 50

Question 19 of 50

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

Full load speed

Rotating magnetic field speed

No load speed

Relative speed between stator and rotor

Question 19 of 50

Question 20 of 50

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

Cascade operation method

Injecting emf in rotor circuit method

Changing applied voltage method

Rotor rheostat control method

Question 20 of 50

Question 21 of 50

21. 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 21 of 50

Question 22 of 50

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

To reduce the losses

To reduce the slip

To get high starting and running torque

To control the speed

Question 22 of 50

Question 23 of 50

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

Forward and reverse

Remote control

Inching

Sequential control

Question 23 of 50

Question 24 of 50

24. 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 24 of 50

Question 25 of 50

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

Megger

Series type ohmmeter

Shunt type ohmmeter

Multimeter

Question 25 of 50

Question 26 of 50

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

Wire guides

Wire feed

Mandrel

Spool carrier

Question 26 of 50

Question 27 of 50

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

Double layer winding

Whole coil winding

Half coil winding

Single layer winding

Question 27 of 50

Question 28 of 50

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

2

4

3

1

Question 28 of 50

Question 29 of 50

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

Cascade operation

Changing applied voltage

Changing the number of poles

Changing applied frequency

Question 29 of 50

Question 30 of 50

30. 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 30 of 50

Question 31 of 50

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

1080°

1440°

360°

720°

Question 31 of 50

Question 32 of 50

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

Single layer basket winding

Involute coil winding

Double layer basket winding

Diamond coil winding

Question 32 of 50

Question 33 of 50

33. 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 less than supply frequency

3 times more than supply frequency

Question 33 of 50

Question 34 of 50

34. 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° / No. of poles

Total electrical degree = 180° x No. of poles

Question 34 of 50

Question 35 of 50

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

Star delta starter

Autotransformer starter

Rheostatic starter

Direct on-line starter

Question 35 of 50

Question 36 of 50

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

Short circuit test

Continuity test

Ground test

Polarity test

Question 36 of 50

Question 37 of 50

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

Switch ON at pre set time

Change from star to delta

Switch OFF at pre set time

Trip at over load

Question 37 of 50

Question 38 of 50

38. 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%

2%

5%

3%

Question 38 of 50

Question 39 of 50

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

Ground test

Polarity test

Open circuit test

Short circuit test

Question 39 of 50

Question 40 of 50

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

Mesh shaped coil winding

Distributed coil winding

Concentric coil winding

Diamond mesh shaped coil winding

Question 40 of 50

Question 41 of 50

41. 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 41 of 50

Question 42 of 50

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

Tong Tester

External Growler

Digital multimeter

Internal Growler

Question 42 of 50

Question 43 of 50

43. 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_s

N_slip = N_s - N_r/N_r

N_slip = N_s - N_r

N_slip = N_r - N_s

Question 43 of 50

Question 44 of 50

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

Empire

Cotton

Bamboo

Terylene

Question 44 of 50

Question 45 of 50

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

360°

120°

180°

90°

Question 45 of 50

Question 46 of 50

46. 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 46 of 50

Question 47 of 50

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

2 to 3 times of full load current

5 to 6 times of full load current

4 to 5 times of full load current

1 to 2 times of full load current

Question 47 of 50

Question 48 of 50

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

Friction loss

Iron loss

Copper loss

Windage loss

Question 48 of 50

Question 49 of 50

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

Protect from heavy load

Protect against high voltage

Allow for continuous over loading

Protect against dead short circuit

Question 49 of 50

Question 50 of 50

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

Over heating of motor

Motor will not start

Vibration of shaft

Runs in slow speed

Question 50 of 50