MCQOPTIONS
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MCQOPTIONS
This section includes 120 Mcqs, each offering curated multiple-choice questions to sharpen your Electrical Machines knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
Auto transformer method of starting has most acceptable method for the starting of the induction motor due to __________ |
| A. | maximum torque |
| B. | maximum reduction of inrush current |
| C. | variable tapping |
| D. | all of he mentioned |
| Answer» B. maximum reduction of inrush current | |
| 2. |
For the application requiring high starting torque and minimum starting current, the most suitable starting method will be? |
| A. | Auto transformer starting method |
| B. | Reactance starting method |
| C. | DOL method |
| D. | Star-Delta method |
| Answer» B. Reactance starting method | |
| 3. |
A 3-phase, 4-pole, 50 Hz induction motor is uses DOL method of starting. It is later replaced by auto transformer method of starting with a tapping ratio of ‘x’, then the starting torque will be? |
| A. | x *Tfl |
| B. | x^2 *Tfl |
| C. | 1/x *Tfl |
| D. | no change in the starting current |
| Answer» B. x^2 *Tfl | |
| 4. |
A 3-phase, 4-pole, 50 Hz induction motor is uses DOL method of starting. It is later replaced by auto transformer method of starting with a tapping ratio of ‘x’, then the starting current reduces by? |
| A. | x |
| B. | x^2 |
| C. | 1/x |
| D. | no change in the starting current |
| Answer» C. 1/x | |
| 5. |
Series reactor method of starting has main disadvantage of lowering the starting power. This can be overcome by __________ |
| A. | using series resistance |
| B. | using parallel reactor |
| C. | using parallel resistance |
| D. | using series reactor |
| Answer» B. using parallel reactor | |
| 6. |
Series reactor method of starting has main disadvantage of __________ |
| A. | lowering the starting power |
| B. | increasing the starting current |
| C. | increasing starting torque |
| D. | all of the mentioned |
| Answer» B. increasing the starting current | |
| 7. |
A 3-phase, 4-pole, 50 Hz induction motor is uses DOL method of starting. It is later replaced by reactance method of starting with a fraction of ‘x’, then the starting torque reduces by? |
| A. | x |
| B. | x^2 |
| C. | 1/x |
| D. | no change in the starting current |
| Answer» C. 1/x | |
| 8. |
A 3-phase, 4-pole, 50 Hz induction motor is uses DOL method of starting. It is later replaced by reactance method of starting with a fraction of ‘x’, then the starting current reduces by? |
| A. | x |
| B. | x^2 |
| C. | 1/x |
| D. | no change in the starting current |
| Answer» B. x^2 | |
| 9. |
External methods of induction motor starting is employed to __________ |
| A. | Reduce the voltage |
| B. | Reduce the current |
| C. | Improve efficiency |
| D. | All of the mentioned |
| Answer» B. Reduce the current | |
| 10. |
The method which employs raising of the voltage while induction motor starting is? |
| A. | Only A |
| B. | A, B |
| C. | Only B |
| D. | Neither A nor BView Answer |
| Answer» E. | |
| 11. |
The method which employs reduction of the voltage while induction motor starting is? |
| A. | Only A |
| B. | A, B |
| C. | Only B |
| D. | Neither A nor BView Answer |
| Answer» B. A, B | |
| 12. |
Starting methods applicable to both squirrel-cage and slip ring induction motors is/are __________ |
| A. | A, B |
| B. | A, B, C |
| C. | B, C |
| D. | A, CView Answer |
| Answer» B. A, B, C | |
| 13. |
For a 4-pole, 50 Hz induction motor has starting current as 5 times to that of the full load current working at a speed of 1450rpm. The ratio of starting to full load torque will be? |
| A. | 0.83 |
| B. | 0.17 |
| C. | 0.67 |
| D. | 1 |
| Answer» B. 0.17 | |
| 14. |
Full voltage starting of induction motor may cause __________ |
| A. | dip in the voltages |
| B. | high inrush current |
| C. | high losses |
| D. | all of the mentioned |
| Answer» B. high inrush current | |
| 15. |
Starters are required in the induction motor because __________ |
| A. | of high starting current |
| B. | they are not self starting |
| C. | torque produced is very low at starting to overcome inertia |
| D. | all of the mentioned |
| Answer» B. they are not self starting | |
| 16. |
Voltage induce in the induction motor is highest at __________ |
| A. | starting |
| B. | standstill |
| C. | rated speed |
| D. | any of the mentioned |
| Answer» B. standstill | |
| 17. |
The number of slip rings on a squirrel cage induction motor is usually |
| A. | Two |
| B. | Three |
| C. | Four |
| D. | None |
| Answer» E. | |
| 18. |
The shaft of an induction motor is made of |
| A. | High speed steel |
| B. | Stainless steel |
| C. | Carbon steel |
| D. | Cast iron |
| Answer» D. Cast iron | |
| 19. |
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» E. | |
| 20. |
Insertion of reactance in the rotor circuit |
| A. | Reduces starting torque as well as maximum torque |
| B. | Increases starting torque as well as maximum torque |
| C. | Increases starting torque but maximum torque remains unchanged |
| D. | Increases starting torque but maximum torque decreases |
| Answer» B. Increases starting torque as well as maximum torque | |
| 21. |
The purpose of using short-circuit gear is |
| A. | To short circuit the rotor at slip rings |
| B. | To short circuit the starting resistances in the starter |
| C. | To short circuit the stator phase of motor to form star |
| D. | None of the above |
| Answer» B. To short circuit the starting resistances in the starter | |
| 22. |
In an induction motor, no-load the slip is generally |
| A. | Less than 1 % |
| B. | 1.5 % |
| C. | 2 % |
| D. | 4 % |
| Answer» B. 1.5 % | |
| 23. |
Size of a high speed motor as compared to low speed motor for the same H.P. will be |
| A. | Bigger |
| B. | Smaller |
| C. | Same |
| D. | Any of the above |
| Answer» C. Same | |
| 24. |
In a squirrel cage motor the induced e.m.f. is |
| A. | Dependent on the shaft loading |
| B. | Dependent on the number of slots |
| C. | Slip times the stand still e.m.f. induced in the rotor |
| D. | None of the above |
| Answer» D. None of the above | |
| 25. |
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» C. Running torque | |
| 26. |
In a three-phase induction motor |
| A. | Power factor at starting is high as compared to that while running |
| B. | Power factor at starting is low as compared to that while running |
| C. | Power factor at starting in the same as that while running |
| D. | None of these |
| Answer» C. Power factor at starting in the same as that while running | |
| 27. |
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» E. | |
| 28. |
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. | Both (A) and (B) |
| D. | None of the above |
| Answer» D. None of the above | |
| 29. |
The shape of the torque/slip curve of induction motor is |
| A. | Parabola |
| B. | Hyperbola |
| C. | Rectangular parabola |
| D. | Straight line |
| Answer» D. Straight line | |
| 30. |
In a star-delta starter of an induction motor |
| A. | Resistance is inserted in the stator |
| B. | Reduced voltage is applied to the stator |
| C. | Resistance is inserted in the rotor |
| D. | Applied voltage per stator phase is 57.7% of the line voltage |
| Answer» E. | |
| 31. |
Insertion of resistance in the stator of an induction motor |
| A. | Increases the load torque |
| B. | Decreases the starting torque |
| C. | Increases the starting torque |
| D. | None of the above |
| Answer» C. Increases the starting torque | |
| 32. |
When the equivalent circuit diagram of double 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» C. In series-parallel | |
| 33. |
The starting torque of a 3 phase squirrel cage induction motor is |
| A. | Twice the full load torque |
| B. | 1.5 times the full load torque |
| C. | Equal to full load torque |
| D. | Any of the above |
| Answer» C. Equal to full load torque | |
| 34. |
Step-less 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» C. Cascade operation | |
| 35. |
The speed characteristics of an induction motor closely resemble the speed-load characteristics of which of the following machines |
| A. | D.C. series motor |
| B. | D.C. shunt motor |
| C. | Universal motor |
| D. | None of the above |
| Answer» C. Universal motor | |
| 36. |
In three-phase induction motors sometimes copper bars are placed deep in the rotor to |
| A. | Improve starting torque |
| B. | Reduce copper losses |
| C. | Improve efficiency |
| D. | Improve power factor |
| Answer» B. Reduce copper losses | |
| 37. |
What will happen if the relative speed between the rotating flux of stator and rotor of the induction motor is zero? |
| A. | The slip of the motor will be 5% |
| B. | The rotor will not run |
| C. | The rotor will run at very high speed |
| D. | The torque produced will be very large |
| Answer» C. The rotor will run at very high speed | |
| 38. |
The torque of a rotor in an induction motor under running condition is maximum |
| A. | At the unit value of slip |
| B. | At the zero value of slip |
| C. | At the value of the slip which makes rotor reactance per phase equal to the resistance per phase |
| D. | At the value of the slip which makes the rotor reactance half of the rotor |
| Answer» D. At the value of the slip which makes the rotor reactance half of the rotor | |
| 39. |
Short-circuit test on an induction motor cannot be used to determine |
| A. | Windage losses |
| B. | Copper losses |
| C. | Transformation ratio |
| D. | Power scale of circle diagram |
| Answer» B. Copper losses | |
| 40. |
The circle diagram for an induction motor cannot be used to determine |
| A. | Efficiency |
| B. | Power factor |
| C. | Frequency |
| D. | Output |
| Answer» B. Power factor | |
| 41. |
A pump induction motor is switched on to a supply 30% lower than its rated voltage. The pump runs. What will eventually happen? It will |
| A. | Stall after sometime |
| B. | Stall immediately |
| C. | Continue to run at lower speed without damage |
| D. | Get heated and subsequently get damaged |
| Answer» E. | |
| 42. |
In an induction motor if air-gap is increased |
| A. | The power factor will be low |
| B. | Windage losses will be more |
| C. | Bearing friction will reduce |
| D. | Copper loss will reduce in an induction motor |
| Answer» B. Windage losses will be more | |
| 43. |
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» C. Rotor conductors are kept open | |
| 44. |
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» B. Rotor rheostat control | |
| 45. |
It is advisable to avoid line starting of induction motor and use starter because |
| A. | It will run in reverse direction |
| B. | It will pick up very high speed and may go out of step |
| C. | Motor takes five to seven times its full load current |
| D. | Starting torque is very high |
| Answer» D. Starting torque is very high | |
| 46. |
A 500 kW, 3-phase, 440 volts, 50 Hz, A.C. induction motor has a speed of 960 r.p.m. on full load. The machine has 6-poles. The slip of the machine will be |
| A. | 0.01 |
| B. | 0.02 |
| C. | 0.03 |
| D. | 0.04 |
| Answer» E. | |
| 47. |
Low voltage at motor terminals is due to |
| A. | Inadequate motor wiring |
| B. | Poorly regulated power supply |
| C. | Any one of the above |
| D. | None of the above |
| Answer» D. None of the above | |
| 48. |
A 3-phase slip ring motor has |
| A. | Double cage rotor |
| B. | Wound rotor |
| C. | Short-circuited rotor |
| D. | Any of the above |
| Answer» C. Short-circuited rotor | |
| 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» D. None of the above | |
| 50. |
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» B. Variable speed motors | |