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Electrical Engineering Objective Questions { Induction Motors }

85. The magnetising current drawn by induction motors and transformers is the cause of their power factor.
A. leading
B. lagging
C. unity
D. zero
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86.  A 3-phase slip-ring induction motor is always started with
A. a starting winding
B. squirrel cage winding
C. no external resistance in rotor circuit
D. full external resistance in rotor circuit
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87. The synchronous speed of a 3-phase induction motor is given by the formula
A. Ns =120f
B. Ns ?120f
C. Ns = 120 f P
D. Ns = 120
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88.  Out of the following methods of starting a 3-phase induction motor, which one requires six stator terminals?
A. Direct-on-line
B. Star-delta
C. Auto-transformer
D. Rotor rheostat
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89. If single-phasing occurs on the running position in an induction motor, the motor will
A. fail to carry load
B. produce peculiar noise
C. draw unbalanced and excessive currents
D. not start
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90. The fractional slip of an induction motor is the ratio
A. rotor copper loss/rotor output
B. rotor copper loss/rotor input
C. rotor copper loss/stator copper loss
D. stator copper loss/stator input
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91.  Each of the following statements regarding stator flux of an induction motor is trueexcept
A. it induces e.m.f. in the rotor bars
B. its magnitude depends on the motor load
C. it is constant in magnitude
D. it revorve around the stator at syn chronous speed
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