Tricky D.C Motors Multiple choice Questions and Answers pdf

91.    The main disadvantage of the Ward-Leonard control method is
(a)    high initial cost
(b)    high maintenance cost
(c)    low efficiency at Hght loads
(d)    all of the above
Ans: d

92.   Regenerative method of braking is based on that
(a)    back e.m.f. is less than the applied voltage
(b)    back e.m.f. is equal to the applied voltage
(c)    back e.m.f. of rotor is more than the applied voltage
(d)    none of the above
Ans: b

93.    The hysteresis loss in a D.C. machine least depends on
(a)    Frequency of magnetic reversals
(b)    Maximum value of flux density
(c)    Volume and grade of iron
(d)    Rate of flow of ventilating air
Ans: d

94.    In a D.C. generator all of the following could be the effects of iron losses except
(a)     Loss of efficiency
(b)     Excessive heating of core
(c)    Increase in terminal voltage
(d)    Rise in temperature of ventilating air
Ans: c

95.    The losses occurring in a D.C. generator are given below. Which loss is likely to have highest proportion at rated load of the generator ?
(a)     hysteresis loss
(b)     field copper loss
(c)    armature copper loss
(d)    eddy current loss
Ans: c

96.    Which of the following loss in a D.C. generator varies significantly with the load current ?
(a)    Field copper loss
(b)    Windage loss
(c)    Armature copper loss
(d)    None of the above
Ans: c

97.    Torque developed by a D.C. motor depends upon
(a)    magnetic field
(b)    active length of the conductor
(c)    current flow through the conductors
(d)     number of conductors
(e)    radius of armature
(f)     all above factors
Ans: f

98.    D.C. shunt motors are used for driving
(a) trains
(b) cranes
(c) hoists
(d) machine tools
Ans: d

99.    In a manual shunt motor starter
(a)     over load relay is connected in series and no volt relay in parallel with the load
(6)     over load relay is connected in paral¬lel and no volt relay in series with the load
(c)    over load relay and no volt relay are both connected in series with the load
(d)    over load relay and no volt relay are both connected in parallel with the load
Ans: a

100.    Which of the following steps is likely to result in reduction of hysteresis loss in a D.C. generator ?
(a)    Providing laminations in armature core
(b)    Providing laminations in stator
(c)    Using non-magnetic material for frame
(d)    Using material of low hysteresis co-efficient for armature core material
Ans: d

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