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Electrical Engineering Objective Questions { Induction Motors }

351.  While plugging a 3-phase induction motor, if one supply terminal gets disconnected, then the motor will
A. Continue to run in the same direction
B. stop
C. start rotating in the opposite direction at the same speed
D. start rotating in the opposite direction at reduced speed
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352.  The stator of a 415V, 50Hz, 6-pole, 970 rpm, 3-phase slipring induction motor is fed with normal voltage. The rotor with slip rings open-circuited is rotated at 500 rpm along the normal direction of its rotation. The frequency of the voltage across slip rings will be
A. 1.5 Hz
B. 25 Hz
C. 26.5 Hz
D. 75 Hz
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353. The given figure shows typical torque-speed curves of the following induction motors A. Ordinary cage B. Double cage C. Deep bar rotor D. Slip ring motor 1 The correct matching of the motors and torque-speed curves is Codes :
A. 2,3,4,1
B. 3,2,1,4
C. 4,2,1,3
D. 4,1,2,3
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354.  Consider the following statements about the operation of a three-phase induction motor running at full load : If one of the supply line fuse blows off, the motor will stall. 2. continue to run with increased slip, 3. continue to run with normal supply current 4. continue to run with excessive supply current Of these statements
A. 1 alone is correct
B. 3 alone is correct
C. 2 and 3 are correct
D. 2 and 4 are correct
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355.  The phenomenon of crawling is usually not formed in slip-ring because these motors have
A. no space harmonics
B. high resistance rotor windings
C. no zig-zag leakage
D. comparatively large air-gap
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356.  Consider the following statements : As a 3-phase induction motor is loaded from noload to rated load,I. there is an improvement in the power factor.2. the torque increases almost in proportion to slip.3. the air-gap flux falls shorply. 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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357.  In a 3-phase induction motor, if the angular speed of the stator field is w and, the actual angular speed of the rotor is wr, and the stator induced emf is given by es = N1 wKws Qisin wt, (N1 being the stator turns/phase), the rotor emf with N2 as the rotor/turns phase will be (Kws = stator winding factor and Kwr =rotor winding factor)
A. er = N2 co Kwr sin cot
B. er = N2 cor Kwr sin cort
C. er = N2 (co? cod Kcorcp sin (co ? cor)t
D. er = N2 (Co + cod Kmr(1) sin (w + (Or)t
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