McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Electrical Engineering .
| 1. |
Which of the following component is usually fabricated out of silicon steel ? |
| A. | Bearings |
| B. | Shaft |
| C. | Statorcore |
| D. | None of the above |
| Answer» C. Statorcore | |
| 2. |
The frame of an induction motor is usually made of |
| A. | silicon steel |
| B. | cast iron |
| C. | aluminium |
| D. | bronze |
| Answer» B. cast iron | |
| 3. |
The shaft of an induction motor is made of |
| A. | stiff |
| B. | flexible |
| C. | hollow |
| D. | any of the above |
| Answer» A. stiff | |
| 4. |
The shaft of an induction motor is made of |
| A. | high speed steel |
| B. | stainless steel |
| C. | carbon steel |
| D. | cast iron |
| Answer» C. carbon steel | |
| 5. |
In an induction motor, no-load the slip is generally |
| A. | less than 1% |
| B. | 1.5% |
| C. | 2% |
| D. | 4% |
| Answer» A. less than 1% | |
| 6. |
In medium sized induction motors, the slip is generally around |
| A. | 0.04% |
| B. | 0.4% |
| C. | 4% |
| D. | 14% |
| Answer» C. 4% | |
| 7. |
In squirrel cage induction motors, the rotor slots are usually given slight skew in order to |
| A. | reduce windage losses |
| B. | reduce eddy currents |
| C. | reduce accumulation of dirt and dust |
| D. | reduce magnetic hum |
| Answer» D. reduce magnetic hum | |
| 8. |
In case the air gap in an induction motor is increased |
| A. | the magnetising current of the rotor will decrease |
| B. | the power factor will decrease |
| C. | speed of motor will increase |
| D. | the windage losses will increase |
| Answer» B. the power factor will decrease | |
| 9. |
Slip rings are usually made of |
| A. | copper |
| B. | carbon |
| C. | phospor bronze |
| D. | aluminium |
| Answer» C. phospor bronze | |
| 10. |
A 3-phase 440 V, 50 Hz induction motor has 4% slip. The frequency of rotor e.m.f. will be |
| A. | 200 Hz |
| B. | 50 Hz |
| C. | 2 Hz |
| D. | 0.2 Hz |
| Answer» C. 2 Hz | |
| 11. |
In Ns is the synchronous speed and s the slip, then actual running speed of an induction motor will be |
| A. | Ns |
| B. | s.N, |
| C. | (l-s)Ns |
| D. | (Ns-l)s |
| Answer» C. (l-s)Ns | |
| 12. |
The efficiency of an induction motor can be expected to be nearly |
| A. | 60 to 90% |
| B. | 80 to 90% |
| C. | 95 to 98% |
| D. | 99% |
| Answer» B. 80 to 90% | |
| 13. |
The number of slip rings on a squirrel cage induction motor is usually |
| A. | two |
| B. | three |
| C. | four |
| D. | none |
| Answer» D. none | |
| 14. |
The starting torque of a squirrel-cage induction motor is |
| A. | low |
| B. | negligible |
| C. | same as full-load torque |
| D. | slightly more than full-load torque |
| Answer» A. low | |
| 15. |
A double squirrel-cage induction motor has |
| A. | two rotors moving in oppsite direction |
| B. | two parallel windings in stator |
| C. | two parallel windings in rotor |
| D. | two series windings in stator |
| Answer» C. two parallel windings in rotor | |
| 16. |
Star-delta starting of motors is not possible in case of |
| A. | single phase motors |
| B. | variable speed motors |
| C. | low horse power motors |
| D. | high speed motors |
| Answer» A. single phase motors | |
| 17. |
The term 'cogging' is associated with |
| A. | three phase transformers |
| B. | compound generators |
| C. | D.C. series motors |
| D. | induction motors |
| Answer» D. induction motors | |
| 18. |
In case of the induction motors the torque is |
| A. | inversely proportional to (Vslip) |
| B. | directly proportional to (slip)2 |
| C. | inversely proportional to slip |
| D. | directly proportional to slip |
| Answer» D. directly proportional to slip | |
| 19. |
An induction motor with 1000 r.p.m. speed will have |
| A. | 8 poles |
| B. | 6 poles |
| C. | 4 poles |
| D. | 2 poles |
| Answer» B. 6 poles | |
| 20. |
The good power factor of an induction motor can be achieved if the average flux density in the air gap is |
| A. | absent |
| B. | small |
| C. | large |
| D. | infinity |
| Answer» B. small | |
| 21. |
An induction motor is identical to |
| A. | D.C. compound motor |
| B. | D.C. series motor |
| C. | synchronous motor |
| D. | asynchronous motor |
| Answer» D. asynchronous motor | |
| 22. |
The injected e.m.f. in the rotor of induction motor must have |
| A. | zero frequency |
| B. | the same frequency as the slip fre-quency |
| C. | the same phase as the rotor e.m.f. |
| D. | high value for the satisfactory speed control |
| Answer» B. the same frequency as the slip fre-quency | |
| 23. |
Which of the following methods is easily applicable to control the speed of the squirrel-cage induction motor ? |
| A. | By changing the number of stator poles |
| B. | Rotor rheostat control |
| C. | By operating two motors in cascade |
| D. | By injecting e.m.f. in the rotor circuit |
| Answer» A. By changing the number of stator poles | |
| 24. |
The crawling in the induction motor is caused by |
| A. | low voltage supply |
| B. | high loads |
| C. | harmonics develped in the motor |
| D. | improper design of the machine |
| Answer» C. harmonics develped in the motor | |
| 25. |
The auto-starters (using three auto transformers) can be used to start cage induction motor of the following type |
| A. | star connected only |
| B. | delta connected only |
| C. | (a) and (b) both |
| D. | none of the above |
| Answer» C. (a) and (b) both | |
| 26. |
The torque developed in the cage induction motor with autostarter is |
| A. | k/torque with direct switching |
| B. | K x torque with direct switching |
| C. | K2 x torque with direct switching |
| D. | k2/torque with direct switching |
| Answer» C. K2 x torque with direct switching | |
| 27. |
When the equivalent circuit diagram of doouble squirrel-cage induction motor is constructed the two cages can be considered |
| A. | in series |
| B. | in parallel |
| C. | in series-parallel |
| D. | in parallel with stator |
| Answer» B. in parallel | |
| 28. |
It is advisable to avoid line-starting of induction motor and use starter because |
| A. | motor takes five to seven times its full load current |
| B. | it will pick-up very high speed and may go out of step |
| C. | it will run in reverse direction |
| D. | starting torque is very high |
| Answer» A. motor takes five to seven times its full load current | |
| 29. |
Stepless speed control of induction motor is possible by which of the following methods ? |
| A. | e.m.f. injection in rotor eueuit |
| B. | Changing the number of poles |
| C. | Cascade operation |
| D. | None of the above |
| Answer» B. Changing the number of poles | |
| 30. |
Rotor rheostat control method of speed control is used for |
| A. | squirrel-cage induction motors only |
| B. | slip ring induction motors only |
| C. | both (a) and (b) |
| D. | none of the above |
| Answer» B. slip ring induction motors only | |
| 31. |
In the circle diagram for induction motor, the diameter of the circle represents |
| A. | slip |
| B. | rotor current |
| C. | running torque |
| D. | line voltage |
| Answer» B. rotor current | |
| 32. |
For which motor the speed can be controlled from rotor side ? |
| A. | Squirrel-cage induction motor |
| B. | Slip-ring induction motor |
| C. | Both (a) and (b) |
| D. | None of the above |
| Answer» B. Slip-ring induction motor | |
| 33. |
If any two phases for an induction motor are interchanged |
| A. | the motor will run in reverse direction |
| B. | the motor will run at reduced speed |
| C. | the motor will not run |
| D. | the motor will burn |
| Answer» A. the motor will run in reverse direction | |
| 34. |
An induction motor is |
| A. | self-starting with zero torque |
| B. | self-starting with high torque |
| C. | self-starting with low torque |
| D. | non-self starting |
| Answer» C. self-starting with low torque | |
| 35. |
The maximum torque in an induction motor depends on |
| A. | frequency |
| B. | rotor inductive reactance |
| C. | square of supply voltage |
| D. | all of the above |
| Answer» D. all of the above | |
| 36. |
In three-phase squirrel-cage induction motors |
| A. | rotor conductor ends are short-circuited through slip rings |
| B. | rotor conductors are short-circuited through end rings |
| C. | rotor conductors are kept open |
| D. | rotor conductors are connected to insulation |
| Answer» B. rotor conductors are short-circuited through end rings | |
| 37. |
In a three-phase induction motor, the number of poles in the rotor winding is always |
| A. | zero |
| B. | more than the number of poles in stator |
| C. | less than number of poles in stator |
| D. | equal to number of poles in stator |
| Answer» D. equal to number of poles in stator | |
| 38. |
DOL starting of induction motors is usually restricted to |
| A. | low horsepower motors |
| B. | variable speed motors |
| C. | high horsepower motors |
| D. | high speed motors |
| Answer» A. low horsepower motors | |
| 39. |
The speed of a squirrel-cage induction motor can be controlled by all of the following except |
| A. | changing supply frequency |
| B. | changing number of poles |
| C. | changing winding resistance |
| D. | reducing supply voltage |
| Answer» C. changing winding resistance | |
| 40. |
The 'crawling" in an induction motor is caused by |
| A. | high loads |
| B. | low voltage supply |
| C. | improper design of machine |
| D. | harmonics developed in the motor |
| Answer» D. harmonics developed in the motor | |
| 41. |
The power factor of an induction motor under no-load conditions will be closer to |
| A. | 0.2 lagging |
| B. | 0.2 leading |
| C. | 0.5 leading |
| D. | unity |
| Answer» A. 0.2 lagging | |
| 42. |
The 'cogging' of an induction motor can be avoided by |
| A. | proper ventilation |
| B. | using DOL starter |
| C. | auto-transformer starter |
| D. | having number of rotor slots more or less than the number of stator slots (not equal) |
| Answer» D. having number of rotor slots more or less than the number of stator slots (not equal) | |
| 43. |
If an induction motor with certain ratio of rotor to stator slots, runs at 1/7 of the normal speed, the phenomenon will be termed as |
| A. | humming |
| B. | hunting |
| C. | crawling |
| D. | cogging |
| Answer» C. crawling | |
| 44. |
Slip of an induction motor is negative when |
| A. | magnetic field and rotor rotate in opposite direction |
| B. | rotor speed is less than the syn-chronous speed of the field and are in the same direction |
| C. | rotor speed is more than the syn-chronous speed of the field and are in the same direction |
| D. | none of the above |
| Answer» C. rotor speed is more than the syn-chronous speed of the field and are in the same direction | |
| 45. |
Size of a high speed motor as compared to low speed motorfor the same H.P. will be |
| A. | bigger |
| B. | smaller |
| C. | same |
| D. | any of the above |
| Answer» B. smaller | |
| 46. |
A 3-phase induction motor stator delta connected, is carrying full load and one of its fuses blows out. Then the motor |
| A. | will continue running burning its one phase |
| B. | will continue running burning its two phases |
| C. | will stop and carry heavy current causing permanent damage to its winding |
| D. | will continue running without any harm to the winding |
| Answer» A. will continue running burning its one phase | |
| 47. |
A 3-phase induction motor delta connected is carrying too heavy load and one of its fuses blows out. Then the motor |
| A. | will continue running burning its one phase |
| B. | will continue running burning its two phase |
| C. | will stop and carry heavy current causing permanent damage to its winding |
| D. | will continue running without any harm to the winding |
| Answer» C. will stop and carry heavy current causing permanent damage to its winding | |
| 48. |
Low voltage at motor terminals is due to |
| A. | inadequate motor wiring |
| B. | poorely regulated power supply |
| C. | any one of the above |
| D. | none of the above |
| Answer» C. any one of the above | |
| 49. |
In an induction motor the relationship between stator slots and rotor slots is that |
| A. | stator slots are equal to rotor slots |
| B. | stator slots are exact multiple of rotor slots |
| C. | stator slots are not exact multiple of rotor slots |
| D. | none of the above |
| Answer» C. stator slots are not exact multiple of rotor slots | |
| 50. |
Slip ring motor is recommended where |
| A. | speed control is required |
| B. | frequent starting, stopping and reversing is required |
| C. | high starting torque is needed |
| D. | all above features are required |
| Answer» D. all above features are required | |
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