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Electrical Engineering Objective Questions { Induction Motors }

344.  An induction generator
A. takes reactive power from the mains and supplies active power to the mains
B. takes active power from the mains and gives reactive power to the mains
C. supplies both active and reactive powers to the mains
D. consumes both active and reactive powers from the mains
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345.  The approximate value of efficiency of a three-phase induction motor running at a slip 's' is given by
A. 1 + s
B. 1 + s
C.1 ? s 1 + s
D.1 ? s
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346.  Consider the following statements : The emf induced in the rotor of a 3-phase induction motor is proportional to the (I) relative velocity between stator field and rotor conductors. (2) voltage applied to the stator. (3) slip Of these statements :
A. 1, 2 and 3 are correct
B. 1 and 2 are correct
C. 2 and 3 are correct
D. 1 and 3 are correct
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347.  A single-phase induction motor with only the main winding excited would produce zero torque at
A. synchronous speed only
B. starting and synchronous speed
C. starting only
D. starting and a speed slightly below synchronous speed
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348.  A polyphase slip-ring induction machine has the stator and rotor windings wound for
A. the same number of phase but different number of pairs of poles
B. the same number of pairs of poles but different number of phases
C. the same number of phases with number of pairs of poles either equal or different
D. the same number of pairs of poles with number of phases either equal or different
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349.  The single-phase induction motor is started with
A. capacitarcP concoction
B. inductance connection
C. resistance connection
D. shaded pole arrangement
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350. Low voltage starting of induction motors is prescribed because
A. high starting current at full voltage would damage the windings
B. it facilitates smooth acceleration
C. it increases the life of the motor
D. it is mandated by electric supply authorities to prevent voltage dips at other consumer premises
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