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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

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

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

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

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

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

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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