Most Synchronous Motors

11. A synchronous motor connected to infinite bus-bars has at constant full load, 100% excitation and unity power factor. On changing the excitation only, the armature current will have

1. no change of power factor
2. lagging power factor with over-excitation
3. leading power factor with under-excitation
4. leading power factor with over-excitation

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12. A synchronous motor develops maximum power when load angle is

1. 45°
2. 60°
3. 90°
4. 120°

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13. A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because

1. synchronous motor has no slip
2. stator supply is not required to produce magnetic field
3. mechanical load on the rotor remains constant
4. synchronous motor has large airgap

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14. A synchronous motor installed at the receiving end substation operates with such an excitation that it takes power at lagging power factor. Now if the applied voltage of the synchronous motor goes down, the power factor of the synchronous motor will

1. remain same
2. go down
3. improve
4. none of the above

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15. A synchronous motor is running on a load with normal excitation. Now if the load on the motor is increased

1. power factor as well as armature current will decrease
2. power factor as well as armature current will increase
3. power factor will increase but armature current will decrease
4. power factor will decrease and armature current will increase

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16. A synchronous motor is running with normal excitation. When the load is increased, the armature current drawn by it increases because

1. speed of the motor is reduced
2. power factor is decreased
3. Eb (back e.m.f.) becomes less than V (applied voltage)
4. Er (net resultant voltage) in armature is increased

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17. A synchronous motor running with normal excitation adjusts to load increases essentially by increase in

1. back e.m.f.
2. armature current
3. power factor
4. torque angle

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18. A synchronous motor which works on a leading power factor and does not drive a mechanical load is called as

1. static condenser
2. condenser
3. synchronous condenser
4. none of the above

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19. A synchronous motor will always stop when

1. supply voltage fluctuates
2. load in motor varies
3. excitation winding gets disconnected
4. supply voltage frequency changes9885859805

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20. A synchronous motor working at leading power factor can be used as

1. voltage booster
2. phase advancer
3. noise generator
4. mechanical synchronizer

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