MCQOPTIONS
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MCQOPTIONS
This section includes 12 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. |
If an emf at slip frequency is injected at an angle with existing rotor induced emf, then the ___________ |
| A. | power factor only improves |
| B. | speed changes |
| C. | power factor improves and speed changes |
| D. | power factor worsens and speed changes |
| Answer» B. speed changes | |
| 2. |
A constant torque variable power drive of induction machine has ___________ |
| A. | constant air gap flux. |
| B. | constant slip |
| C. | variable air gap flux, constant slip |
| D. | constant slip, constant air gap flux |
| Answer» E. | |
| 3. |
If a 3-phase induction motor is fed from the rotor short circuiting the stator terminals, frequency of the current flowing in the short-circuited stator is? |
| A. | slip frequency |
| B. | supply frequency |
| C. | zero |
| D. | frequency corresponding to the rotor speed |
| Answer» B. supply frequency | |
| 4. |
Torque-slip characteristic of an induction motor is linear in the smaller slip values, because ___________ |
| A. | effective rotor resistance is very large compared to reactance |
| B. | rotor resistance is equal to stator resistance |
| C. | rotor resistance is equal to rotor reactance |
| D. | rotor reactance almost equal to stator reactance |
| Answer» B. rotor resistance is equal to stator resistance | |
| 5. |
For 3-phase induction motor, as load increases from no load towards the full load then the ___________ |
| A. | power factor improves |
| B. | power factor remains same |
| C. | power factor varies linearly |
| D. | power factor increases till 40% load and then decreases |
| Answer» B. power factor remains same | |
| 6. |
Due to the line to ground fault, phase a in the induction motor phase supply gets cut, then machine ___________ |
| A. | continues to run with excessive supply current |
| B. | continues to run with reduced slip |
| C. | stalls |
| D. | all of the mentioned |
| Answer» B. continues to run with reduced slip | |
| 7. |
If one of the supply fuses blows off and gets open circuited, then for the connected induction machine continues to run with increased slip. |
| A. | True |
| B. | False |
| Answer» B. False | |
| 8. |
Choose from the below which can be obtained by the equivalent circuit of an electrical machine? |
| A. | Complete performance characteristics of the machine |
| B. | Temperature coefficients of the machine components |
| C. | Type of protection to be used in the machine |
| D. | Design parameters of the windings |
| Answer» B. Temperature coefficients of the machine components | |
| 9. |
A center ammeter connected to the rotor end circuit of a 6-pole,50 Hz, induction motor makes 45 complete oscillations in a minute. Then the rotor speed and the speed of stator field w.r.t. rotor is? |
| A. | 985, 15 |
| B. | 970, 1000 |
| C. | 985, 985 |
| D. | 985, 970 |
| Answer» B. 970, 1000 | |
| 10. |
A 3-phase slip ring IM is has its copper bars changed by the aluminium bars in the machine. With the above change ___________ |
| A. | starting torque remains same |
| B. | starting torque increase |
| C. | starting torque decrease |
| D. | maximum torque increase |
| Answer» B. starting torque increase | |
| 11. |
A 3-phase slip ring IM is has its copper bars replaced by the aluminium bars in the machine. With the above change ___________ |
| A. | starting torque increases, maximum torque remains same, smT increase |
| B. | starting torque increases, maximum torque remains same, smT remains same |
| C. | starting torque increases, maximum torque remains increases, smT increase |
| D. | starting torque decreases, maximum torque remains same, smT decrease |
| Answer» B. starting torque increases, maximum torque remains same, smT remains same | |
| 12. |
A 3-phase induction motor is fed at the stator at a frequency f. If the rotor speed is Nr and synchronous speed is Ns, then the absolute speed of the resultant flux in space is? |
| A. | Ns |
| B. | (Ns+Nr) if the flux rotates in the same same direction as the rotor |
| C. | (Ns-Nr) if the flux rotates in the same same direction as the rotor |
| D. | Nr |
| Answer» B. (Ns+Nr) if the flux rotates in the same same direction as the rotor | |