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MCQs

Total Questions : 395 | Page 35 of 40 pages
Question 341. . When the rotor speed, in a synchronous machine, become more than the synchronous speed during hunting, the damper bars develop
  1.    inductor motor torque
  2.    induction generator torque
  3.    synchronous motor torque
  4.    d.c. motor torque
 Discuss Question
Answer: Option B. -> induction generator torque
Question 342. . As important advantage of a synchronous motor over wound round induction motor is that
  1.    its power factor may be varied at will
  2.    its speed in independent of supply frequency
  3.    its speed may be controlled more easily
  4.    none of the above
 Discuss Question
Answer: Option A. -> its power factor may be varied at will
Question 343. . Which of the following motors will be used in electric clocks?
  1.    D.C. shunt motor
  2.    D.C. series motor
  3.    A.C. induction motor
  4.    A.C. synchronous motor
 Discuss Question
Answer: Option A. -> D.C. shunt motor
Question 344. 4.  If in a synchronous motor, driving a given mechanical load and drawing current at a leading power factor from constant voltage supply its field excitation is increased, its power factor
  1.    will become more
  2.    will become less
  3.    will remain unchanged
  4.    none of the above
 Discuss Question
Answer: Option B. -> will become less
Question 345. 0. Armature of a synchronous mechine is kept fixed because
  1.    of reducing number of slip rings on the rotor
  2.    armature is associated with large power as compared to the field circuits
  3.    of difficulty of providing high voltage insulation or rotor
  4.    all of the above reasons
 Discuss Question
Answer: Option D. -> all of the above reasons
Question 346. 1.  If excitation of a synchronous motor running with a constant load is decreased from its normal value, ignoring effects of armature reaction, it leads to
  1.    increase in both armature current and power factor angle
  2.    increase in back e.m.f. but decrease in armature current
  3.    increase in both armature current and power factor which is lagging
  4.    increase in torque angle but decrease in back e.m.f.
 Discuss Question
Answer: Option A. -> increase in both armature current and power factor angle
Question 347. 3. The power factor of a synchronous motor is better than that of induction motor because
  1.    stator supply is relieved of responsibility of producing magnetic field
  2.    mechanical load on the motor can be adjusted
  3.    synchronous motor runs at synchronous speed
  4.    synchronous motor has large air gap
 Discuss Question
Answer: Option A. -> stator supply is relieved of responsibility of producing magnetic field
Question 348. 2. Stability of a synchronous machine
  1.    decreases with increases in its excitation
  2.    increases with increase in it excitation
  3.    remains unaffected with increase in excitation
  4.    any of the above
 Discuss Question
Answer: Option B. -> increases with increase in it excitation
Question 349. 5.  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 ex
  2.    power factors is decreased
  3.    Eb (back e.m.f.) becomes less than V (applied voltage)
  4.    Er (net resultant voltage) in armature is increased
 Discuss Question
Answer: Option B. -> power factors is decreased
Question 350. 6.  If one-phase of a 3-phase synchronous motor is short-circuited, motor
  1.    will refuse to start
  2.    will overheat in spots
  3.    will not come upto speed
  4.    will fail to pull into step
 Discuss Question
Answer: Option A. -> will refuse to start

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