Electrical Machines Questions and Answers – DC Motors
DC Motor Starting
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How does the speed build up takes place in a dc motor with time?
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For a dc machine , its commutator has a diameter of 50 c rotating at 1000 rpm. For a brush width of 1 cm, the time commutation taken by the machine will be
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A starting resistance is inserted at the starting in an induction motor as well as dc motor.
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Considering a human handed control system for the dc motor speed control, if the resistance wire cut out too slowly, then
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The directonline starter is used to start a small dc motor because it limits initial current drawn by armature circuit.
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The post effects of the armature reaction is
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Following are the observations due to large starting current in dc motor.
(i) Sparking at brushes
(ii) Mechanical shock at shaft
(iii) Source current fluctuations
(iv) Burning of the field winding
(i) Sparking at brushes
(ii) Mechanical shock at shaft
(iii) Source current fluctuations
(iv) Burning of the field winding
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The effect of fringing increases as we
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Which of the following express the starting current nature of the dc motor.
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Thyristor controlled starter is preferred over DOL starter due to
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A dc machine is run at rated speed in forward direction and then in backward direction. It is observed that, speeds of the rotation are different, then it leads to the conclusion of
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For a 7.46 kW, 200 V dc shunt motor with full load efficiency of 85% has armature resistance of 0.25 ohms. Calculate the value of starting resistance in ohms for a current 1.5 times of the full load current.
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If the students give a forward shift of 10Â° to the dc generator, then it
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The shunt motor starters that can be used is/are
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A 100 hp, 250 V, 350 A shunt dc motor with an armature resistance of 0.05 ohms. To limit maximum starting current to twice the rated of its value, what will be the number of stages of starting resistances?
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