MCQOPTIONS
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MCQOPTIONS
This section includes 23 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. |
The hydroelectric plants in the industry are best suited with _________ |
| A. | closed circuit air cooling |
| B. | hydrogen gas |
| C. | direct water |
| D. | all of the mentioned |
| Answer» B. hydrogen gas | |
| 2. |
A peaky voltage supply is given to the 3 phase power transformer of the connection power system. These results in _________ |
| A. | reduction in iron losses |
| B. | reduction in copper losses |
| C. | increase in iron losses |
| D. | reduction in noise |
| Answer» B. reduction in copper losses | |
| 3. |
A three phase induction motor is connected to the infinite bus operating at the normal conditions. There occurs an unbalancing in the supply, leading to _________ |
| A. | unequal heating losses |
| B. | stopping of motor |
| C. | increase in lower |
| D. | none of the mentioned |
| Answer» B. stopping of motor | |
| 4. |
If one of the phases of RYB supply gets broken, then the temperature rise of the induction motor _________ |
| A. | remains same as before |
| B. | reduces as compared to the normal operating temperature |
| C. | reduces to temperature rise of corresponding single phase induction motor |
| D. | increases |
| Answer» B. reduces as compared to the normal operating temperature | |
| 5. |
If one of the phases of the supply breaks down, then the connected three phase induction motor _________ |
| A. | continues to run as a single phase induction motor, provided load does does not increase beyond 57.7% |
| B. | stops operating after few seconds |
| C. | continues to run as single phase induction motor |
| D. | continues to run as two phase induction motor |
| Answer» B. stops operating after few seconds | |
| 6. |
For squirrel cage and slip ring induction motor, cooling methods is efficient in _________ |
| A. | squirrel cage induction motor |
| B. | slip ring induction motor |
| C. | both of the motors |
| D. | none of the mentioned |
| Answer» B. slip ring induction motor | |
| 7. |
In dc machine iron losses cause _________ |
| A. | heating in core |
| B. | loss in efficiency |
| C. | rise in temperature of ventilating air |
| D. | all of the mentioned |
| Answer» B. loss in efficiency | |
| 8. |
If two series motors are identically coupled. One is running as motor while other as generator. For this combination, the iron losses and frictional losses are found identical for _________ |
| A. | identical speed and excitation |
| B. | identical speed |
| C. | identical rating and construction |
| D. | none of the mentioned |
| Answer» B. identical speed | |
| 9. |
For the given traction application using a dc series motor for a starting time t is applied. If this method is replaced by a series-parallel control, giving 50% time for each series and parallel. The saving in the starting energy of _________ |
| A. | 25% |
| B. | zero |
| C. | 50% |
| D. | 75% |
| Answer» B. zero | |
| 10. |
If the rotor circuit resistance is increased in an induction motor, maximum torque will occur at _________ |
| A. | lower speed |
| B. | higher speed |
| C. | same speed |
| D. | none of the mentioned |
| Answer» B. higher speed | |
| 11. |
What is the synchronous watt? |
| A. | the torque under which synchronous speed would develop a power of 1 W or power input to rotor in watts |
| B. | shaft output in watts at sub synchronous speed |
| C. | input power to stator at synchronous speed |
| D. | unit rating of synchronous machine |
| Answer» B. shaft output in watts at sub synchronous speed | |
| 12. |
The rotor power input of 3-phase induction motor is 15 kW at a slip of 5%. The mechanical power developed at the shaft is? |
| A. | 14.25 kW |
| B. | 7.5 kW |
| C. | 4 kW |
| D. | 700 W |
| Answer» B. 7.5 kW | |
| 13. |
Iron loss in the rotor is negligible. This is due to _________ |
| A. | very low frequency of emf induced in the rotor |
| B. | very low emf induced in the rotor |
| C. | very low flux density in rotor parts |
| D. | laminated core |
| Answer» B. very low emf induced in the rotor | |
| 14. |
The losses that occur in induction motor are _________ |
| A. | stator copper loss |
| B. | rotor iron loss |
| C. | rotor copper loss |
| D. | all of the mentioned |
| Answer» B. rotor iron loss | |
| 15. |
In a three-phase induction motor, the starting torque is maximum when? |
| A. | r2 = x2 |
| B. | r2 = 1/x2 |
| C. | r2 = (x2)<sup>2</sup> |
| D. | r2 = 1 pu |
| Answer» B. r2 = 1/x2 | |
| 16. |
In a 3-phase slip ring induction motor high starting torque is achieved by _________ |
| A. | increasing supply voltage |
| B. | increasing supply frequency |
| C. | connecting a capacitor across the motor terminals |
| D. | connecting a star connected resistance across slip ring terminals of motor |
| Answer» E. | |
| 17. |
For achieving high starting torque and high operating efficiency an induction motor should have _______ rotor circuit resistance and _______ circuit resistance under operating condition. |
| A. | high, low |
| B. | low, high |
| C. | low, low |
| D. | high, high |
| Answer» B. low, high | |
| 18. |
The starting torque of the squirrel-cage induction motor is _________ |
| A. | slightly more than full load torque |
| B. | slightly less than full load torque |
| C. | equal to full load torque |
| D. | zero |
| Answer» B. slightly less than full load torque | |
| 19. |
A 3-phase, 6-pole, 50 Hz induction motor has a full load speed of 960 rpm with its slip rings short-circuited. The motor drives the constant load. If the speed is reduced to 400 rpm, then ohmic losses will be? |
| A. | 15 |
| B. | 1/15 |
| C. | 5 |
| D. | 1/5 |
| Answer» B. 1/15 | |
| 20. |
A 3-phase, 6-pole, 50 Hz induction motor has a full load speed of 960 rpm with its slip rings short circuited. The motor drives the constant load. If the speed is reduced to 800 rpm, then ohmic losses will be? |
| A. | 5 times that at full load |
| B. | 0.2 times as that at full load |
| C. | 15 times as that at full load |
| D. | same as that at full load |
| Answer» B. 0.2 times as that at full load | |
| 21. |
A 3-phasle, 6-pole, 50 Hz induction motor has a full load speed of 960 rpm with its slip rings short circuited. The motor drives the constant load. If the speed is reduced to 800 rpm, then ohmic losses will _________ |
| A. | reduce |
| B. | increase |
| C. | reduce first then becomes constant |
| D. | remains same |
| Answer» B. increase | |
| 22. |
Insertion of external resistance in the squirrel cage induction motor _________ the current ________ the starting current. |
| A. | reduces, increases |
| B. | increases, reduces |
| C. | increases, increases |
| D. | reduces, reduces |
| Answer» B. increases, reduces | |
| 23. |
Insertion of external resistance in the squirrel cage induction motor _________ |
| A. | increases torque |
| B. | decreases torque |
| C. | increases torque for some seconds and then decreases |
| D. | does not affect |
| Answer» B. decreases torque | |