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MCQs

Total Questions : 631 | Page 7 of 64 pages
Question 61. The magnetising current of a transformer is usually small because it has
  1.    small air gap
  2.    large leakage flux
  3.    laminated silicon steel core
  4.    fewer rotating parts
 Discuss Question
Answer: Option A. -> small air gap
Question 62. Which of the following insulating materials can withstand the highest temperature safely?
  1.    Cellulose
  2.    Asbestos
  3.    Mica
  4.    Glass fibre
 Discuss Question
Answer: Option C. -> Mica
Question 63. In case of 3-phase induction motors, plugging means
  1.    pulling the motor directly on line without a starter
  2.    locking of rotor due to harmonics
  3.    starting the motor on load which is more than the rated load
  4.    interchanging two supply phases for quick stopping
 Discuss Question
Answer: Option D. -> interchanging two supply phases for quick stopping
Question 64. The main reason for generation of harmonics in a transformer could be
  1.    fluctuating load
  2.    poor insulation
  3.    mechanical vibrations
  4.    saturation of core
 Discuss Question
Answer: Option D. -> saturation of core
Question 65. When secondary of a current transformer is open-circuited its iron core will be
  1.    hot because of heavy iron losses taking place in it due to high flux density
  2.    hot because primary will carry heavy current
  3.    cool as there is no secondary current
  4.    none of above will happen
 Discuss Question
Answer: Option A. -> hot because of heavy iron losses taking place in it due to high flux density
Question 66. Spacers are provided between adjacent coils
  1.    to provide free passage to the cooling oil
  2.    to insulate the coils from each other
  3.    both (A) and (B)
  4.    none of the above
 Discuss Question
Answer: Option A. -> to provide free passage to the cooling oil
Question 67. A shell-type transformer has
  1.    high eddy current losses
  2.    reduced magnetic leakage
  3.    negligibly hysteresis losses
  4.    none of the above
 Discuss Question
Answer: Option B. -> reduced magnetic leakage
Question 68. In Ns is the synchronous speed and s the slip, then actual running speed of an induction motor will be
  1.    Ns
  2.    s.N.
  3.    (l-s)Ns
  4.    (Ns-l)s
 Discuss Question
Answer: Option C. -> (l-s)Ns
Question 69. Power transformers are generally designed to have maximum efficiency around
  1.    no-load
  2.    half-load
  3.    near full-load
  4.    10% overload
 Discuss Question
Answer: Option C. -> near full-load
Question 70. Distribution transformers are generally designed for maximum efficiency around
  1.    90% load
  2.    Zero load
  3.    25% load
  4.    50% load
 Discuss Question
Answer: Option D. -> 50% load

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