Choose the correct answer from the given alternatives
i) Slip ring induction motor has (a) Low starting torque (b)
Medium starting torque (c) High starting torque (d) None of these
ii) In an induction motor, rotor speed is always (a) Less
than the stator speed (b) More the stator speed (c) Equal to the stator speed
(d) None of these
iii) Slip ring induction motor are employed for (a) Speed
control (b) High starting torque (c) Both (a) and (b) (d) None of these.
iv) The direction of rotating magnetic field produced by the
stator of 3-ph induction motor can be changed (a) The sequence of supply to
stator terminal is changed (b) a variable frequency voltage may be applied to
stator terminals (c) the supply voltage is changed (d) supply to any one phase
is disconnected
v) The pitch factor for a two-third short-pitch coil is (a)
0.5 (b) 0.66 (c) 0.866 (d) 0.707
vi) The span for a
full-pitch cost wound for six poles is (a) 180° Mechanical(b)90 Mechanical (c)
60° Mechanical (d) 45° Mechanical
vii) The stator core
of a synchronous machine is made up of laminated sheet to (a) increase the magnetic
of flux produced (b) make the machine lighted in weight (c) Minimize the eddy
current loss (d) Minimize the hysteresis loss.
viii) Synchronous motors are to be used in situation where
(a) the load is constant (b) the load is to be driven at high speed (c) the
load is to be driven at constant speed (d) the starting torque required very high.
ix) The direction of rotation of an ordinary shaded pole
single phase induction motor (a) can be reversed by reversing the supply
connection (b) cannot be reversed (c) can be reversed by open-circuiting the
shading ring (d) short circuiting the shading rings.
x)The stator and rotor cores of an Induction motor are made
up of magnetic material (a) to keep construction cost low (b) to reduce
magnetising current (c) to make the parts strong (d) because the reluctance of
magnetic material high.
xi)The ratio among rotor input, rotor output and rotor
copper losses of a 3-ph induction motor running at a slip 's' is (a) 1 :(1-s) :s
(b) I: s :(1-s) (c) s :1 :(1-s) (d) (1-s): s: l.
xii) The starting toque of a 3-phase induction is ____ supply voltage (a)
Independent of (b) directly proportional to (c) Directly proportional to square
of (d) none of the above.
xiii) When the rotor circuit resistance of poly phase
induction motor is increased (a) the starting torque increases, (b) the maximum
value of torque decreases, (c) the slip at which maximum torque occurs remain
unchanged, (d) none of the above
xiv) The power input
in block rotor test performed on a three phase induction motor is approximately
equal to (a) hysteresis loss in the core, (b) eddy current loss in the core.(c)
copper loss in the winding, (d) friction and windage loss
xv) A delta connected 400 V, 50 Hz, three phase induction
motor when started direct-on-line takes a starting current of 60 A. When motor
is started through a star-delta starter, the starting current will be (a) 10 A,
(b) 15 A, (c) 20 A, (d) 30 A
xvi) When load of the alternator is increased, the terminal
voltage increases if the load power factor is (a) unity, (b) zero, (c) lagging.
(d) leading
xvii) If the prime mover of an alternator supplying load to
an infinite bus is suddenly shut down, it will (a) continue to run as an
alternator in the same direction, (b) stop. (c) continue to run as an
synchronous motor in the same direction, (d) continue to run as an synchronous
motor in the reverse direction.
xviii) An infinite bus-bar should maintain (a) infinite
frequency and infinite voltage, (b) constant frequency and constant voltage,
(c) constant frequency and variable voltage, (d) variable frequency and
constant voltage.
xix) A commercial alternator has (a) rotating armature and
stationary field, (b) both armature and field rotating. (c) stationary armature
rotating field, (d) both armature and field stationary
xx) Variation of power factor of synchronous motor is
achieved by (a) changing field excitation, (b) changing input voltage. (c)
changing speed, (d) changing load.
xxi)The single phase induction motor (capacitor start
capacitor run) basically is (a) single phase motor, (b) dc series motor, (c)
a.c. series motor, (d) two phase motor
xxii)The ratio among rotor input, rotor output and rotor
copper losses of a 3-ph induction motor running at a slip's (a) 1 :(1-s) :s (b) I: s :(1-s) (c) s :1
:(1-s) (d) (1-s): s: l.
xxiii) A star delta starter is equivalent to an
auto-transformer starter with tapping of (a) 86.6%, (b) 57.7%, (c) 57%. (d) 58%
xxiv) If a 3-ph
induction motor runs at super synchronous speed and the machine is self-excited
then it (a) draws reactive power from the main. (b) draws real power from the
main(c) feeds reactive power to the main.
xxv) The power factor
of a 3-ph induction motor is (a) low at heavy loads only. (b) low at light
loads only. (c) low at both heavy & light loads, (d) low at rated loads only
xxvi) The inner cage
of a double cage induction motor consists of (a) high inductance and low
resistance, (b) high inductance and high resistance, (c) low inductance and low
resistance,(d) low inductance and high resistance
xxvii) If the prime
mover of an alternator supplying load to an infinite bus is suddenly shut down,
it will (a) continue to run as an alternator, (b) stop, (c) continue to run as
an synchronous motor in the same
direction. (d) continue to run as an synchronous motor in the reverse direction
xxviii) The armature reaction of an alternator will be
cross-magnetising if the power factor of the load is (a) unity, (b) less than
unity. (c) zero leading. (d) 0 8 lagging
xxxi) Variation of
power factor of a synchronous motor is achieved by (a) changing input voltage,
(b) changing speed, (c) changing field excitation. (d) changing load
xxx) If the power remains same the higher voltage alternator
is (a) larger in size, (b) costlier, (c) cheaper, (d) smaller in size
xxxi) Damper winding is provided in a synchronous motor (a)
to produce starting torque,(b) to increase speed. (c) to produce starting
torque & prevent hunting, (d) to prevent hunting
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