D.C. Machines

11. A hysteresis motor

1. is not a self-starting motor.
2. is a constant speed motor.
3. needs dc excitation.
4. can not be run in reverse speed.

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12. A motor which can conveniently be operated at lagging as well as leading power factors is the

1. squirrel cage induction motor.
2. wound rotor induction motor.
3. synchronous motor.
4. DC shunt motor.

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13. A salient pole synchronous motor is running at no loaD. Its field current is switched off. The motor will

1. come to stop.
2. continue to run at synchronous speeD.
3. continue to run at a speed slightly more than the synchronous speeD.
4. continue to run at a speed slightly less than the synchronous speeD.

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14. A series motor is best suited for driving

1. Lathes
2. Cranes and hoists
3. Shears and punches
4. Machine tools

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15. A single phase 10kVA, 50 Hz transformer with 1kV primary winding draws 0.5A and 55W, at rated voltage and frequency, on no loaD. A second transformer has a core with all its linear √2 times the corresponding dimensions of the first transformer. The core material and lamination thickness are the same in both transformers. The primary windings of both the transformers have the same number of turns. If a rated voltage of 2kV at 50Hz is applied to the primary of the second transformer, then the no load current and power, respectively, are

1. 0.7 A,77.8W
2. 0.7A,155.6 W
3. 1A,110W
4. 1A,220W

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16. A stepper motor is

1. a dc motor.
2. a single-phase ac motor.
3. a multi-phase motor.
4. a two phase motor.

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17. A synchronous machine is called as doubly excited machine because

1. It can be over excited
2. It has two sets of rotor poles
3. Both its rotor and stator are excited
4. It needs twice the normal exciting current

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18. An A.C. tachometer is just a _________ with one phase excited from the carrier frequency.

1. two-phase A.C. servomotor
2. two-phase induction motor
3. A.C. operated universal motor
4. hybrid stepper motor.

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19. An alternator is delivering rated current at rated voltage and 0.8 power-factor lagging case. If it is required to deliver rated current at rated voltage and 0.8 power-factor leading, the required excitation will be

1. less.
2. more.
3. more or less.
4. the same.

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20. An ideal dc generator has voltage regulation.

1. low
2. zero
3. positive
4. negative

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