MCQOPTIONS
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MCQOPTIONS
This section includes 14 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. |
For a constant load torque, the supply voltage of a squirrel cage induction motor is reduced by a factor of 0.5, its rotor current is modified by a factor is? |
| A. | 2 |
| B. | 0.5 |
| C. | 4 |
| D. | 0.25 |
| Answer» B. 0.5 | |
| 2. |
If a 400 V, 50 hz star connected, 3-phase squirrel cage induction motor is operated from 400V and 75 Hz supply. The torque that the motor can now provide while drawing rated current from the supply will _________ |
| A. | reduce |
| B. | increase |
| C. | remains same |
| D. | increases or reduces based on the rotor resistance. |
| Answer» B. increase | |
| 3. |
A three phase induction motor is connected to 400V, 50 hz supply. If the stator to rotor turn ratio is 2, the standstill rotor induced voltage per phase is? |
| A. | 115.5 V |
| B. | 231 V |
| C. | 346 V |
| D. | 200 V |
| Answer» B. 231 V | |
| 4. |
In a three phase induction motor, voltage between the slip rings at standstill is 50 V. At full load the slip is 0.04. The voltage between slip rings at full load is? |
| A. | 2V |
| B. | 50V |
| C. | 20V |
| D. | 5V |
| Answer» B. 50V | |
| 5. |
A 3-phase induction motor is operating at slip s . If the slip is reversed, its slip at the instant will be _________ |
| A. | 2-s |
| B. | zero |
| C. | 2+s |
| D. | 1-s |
| Answer» B. zero | |
| 6. |
In an induction motor slip will be negative when the _________ |
| A. | rotor rotates at speed more than synchronous speed and in the direction of the rotation of stator field |
| B. | stator magnetic field and rotor rotate in opposite direction |
| C. | rotor rotates at speed less than synchronous speed and in the opposite direction of the rotation of stator field |
| D. | rotor rotates at speed more than synchronous speed and in the opposite direction of the rotation of stator field |
| Answer» B. stator magnetic field and rotor rotate in opposite direction | |
| 7. |
The mmf produced by the current of the three phase induction motor _________ |
| A. | is standstill with respect to stator mmf |
| B. | rotates at the speed of rotor in air gap |
| C. | rotates at slip speed with respect to stator mmf |
| D. | rotates at synchronous speed with respect to rotor |
| Answer» B. rotates at the speed of rotor in air gap | |
| 8. |
7.If the three phase supply is fed to the rotor and it is running at its normal operating conditions. Then the synchronous speed can be defined as speed at which? |
| A. | stator magnetic field rotates |
| B. | rotor magnetic field rotates |
| C. | rotor rotates |
| D. | flux is set up in the rotor |
| Answer» C. rotor rotates | |
| 9. |
If the three phase supply is fed to the stator and it is running at its normal operating conditions. Then the synchronous speed can be defined as speed at which? |
| A. | stator magnetic field rotates |
| B. | rotor magnetic field rotates |
| C. | rotor rotates |
| D. | flux is set up in the rotor |
| Answer» B. rotor magnetic field rotates | |
| 10. |
The voltage actually used to set up the working flux in the three phase induction motor is _________ |
| A. | equal to applied voltage |
| B. | less than applied voltage |
| C. | more than applied voltage |
| D. | equal to rotor induced emf. |
| Answer» B. less than applied voltage | |
| 11. |
The rotor of the induction motor must never run at synchronous speed because then the relative speed between the rotating flux and rotor will be _________ |
| A. | zero and hence torque will be zero |
| B. | zero, and torque will be maximum |
| C. | maximum and hence, torque will be zero |
| D. | maximum, and torque will also be zero |
| Answer» B. zero, and torque will be maximum | |
| 12. |
Two of the supply terminals to a three phase induction motor gets interchanges while regular scheduling work. When the machine is switched on, then it will _________ |
| A. | rotate in opposite direction |
| B. | rotate in same direction |
| C. | not start |
| D. | get heated and winding will burn |
| Answer» B. rotate in same direction | |
| 13. |
In an induction motor, when the number of stator slots is equal to an integral multiple of rotor slots? |
| A. | machine will fail to start |
| B. | machine will get heated |
| C. | high starting torque will be achieved |
| D. | discontinuity in torque slip characteristic |
| Answer» B. machine will get heated | |
| 14. |
Rotor leakage reactance for a three phase slip ring induction motor with slip s is? |
| A. | s(x2) |
| B. | (x2)/s |
| C. | x2 |
| D. | (x2)(s<sup>2</sup>) |
| Answer» B. (x2)/s | |