Electrical machine MCQ #9

1) In which transformer, the tertiary winding is used?

      (a) star-delta

      (b) star-star

      (c) delta-star

      (d) delta-delta

2) Zero sequence current can flow from a line into a transformer bank if the winding is

      (a) grounded star/delta

      (b) delta/star

      (c) delta/delta

      (d) star/grounded star

3) The harmonic currents in a power transformer does not cause increase in

      (a) copper loss

      (b) core loss

      (c) secondary voltage

      (d) magnetic interference with protective relays.

4) The magnetic current in a transformer is rich in

      (a) 13^th harmonic

      (b) 5^th harmonic

      (c) 7^th harmonic

      (d) 3^rd harmonic

ANSWER: | 1-b | 2-a | 3-c | 4-d |

5) The speed of synchronous motor can be varied by varying its

      (a) supply voltage

      (b) excitation

      (c) supply frequency

      (d) load

6) Which motor can conveniently operate at lagging as well as leading power factor?

      (a) synchronous motor

      (b) wound rotor induction motor

      (c) DC shunt motor

      (d) squirrel cage induction motor

7) Variation in dc excitation of a synchronous motor causes variation in

      (a) armature current

      (b) power factor

      (c) speed of motor

      (d) both armature current and power factor

8) The large sized induction motors are protected against overload by

      (a) high voltage fuses

      (b) thermal or magnetic relay

      (c) automatic cutouts

      (d) rewireable fuses

ANSWER: | 5-c | 6-a | 7-d | 8-b |

9) Induction generator deliver power at

      (a) unity power factor only

      (b) lagging power factor only

      (c) leading as well as lagging power factor

      (d) leading power factor only

10) Linear induction motor is used in

      (a) mechanical workshop

      (b) magnetic attraction

      (c) traction

      (d) textile mills

11) If an induction motor hums during starting up, the possible cause could be

      (a) unequal phase resistance

      (b) open circuit

      (c) inter turn short circuit on rotor

      (d) any of the above

12) The no-load current of a single-phase induction motor is around ____% of the full load current.

      (a) 10

      (b) 20

      (c) 40

      (d) 80

ANSWER: | 9-d | 10-c | 11-d | 12-c |

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