Thursday, September 10, 2015
It is a collection of most frequently asked Interview Question On DC Machines in various examinations like GATE,DRDO,BARC...etc.
Electrical Questions from DC Motors,generators.Write an online test on latest Interview questions,Interview preparation.
Here You Get Important Electrical Interview Objective Questions ,MCQswith Answers
Electrical Questions from DC Motors,generators.Write an online test on latest Interview questions,Interview preparation.
Here You Get Important Electrical Interview Objective Questions ,MCQswith Answers
Electrical Machines - DC Machines Objectives,MCQs:
[Q-1]The basic requirement of a d.c. armature winding is that it must be
(a) a closed one
(b) a lap winding
(c) a wave winding
(d) either (b) or (c)
(b) a lap winding
(c) a wave winding
(d) either (b) or (c)
[Q-2]The sole purpose of a commutator in a dc generator is to
(a) Increase output voltage
(b) Reduce sparking at brushes
(c) Provide smoother output
(d) Convert the induced ac into dc
(e) None of the above.
[Q-3] The voltage regulation of an over compound dc generator is always
(a) Positive
(b) Negative
(c) Zero
(d) High
[Q-4] A wave winding must go at least ............ around the armature before it closes back where it started.
(a) once
(b) twice
(c) thrice
(d) four times
[Q-5] In small DC machines, armature slots are sometimes not made axial but are skewed, results in
(a) Quieter operation
(b) Slight decrease in losses
(c) Saving of copper
(d) Both a and b
(e) None of the above
Ans: Protects from magnetic locking.
[Q-6]The d.c. armature winding in which coil sides are a pole pitch apart is called ............ winding.
(a) multiplex
(b) fractional-pitch
(c) full-pitch
(d) pole-pitch
[Q-7]For making coil span equal to a pole pitch in the armature winding of a d.c. generator, the back pitch of the winding must equal the number of
(a) commutator bars per pole
(b) winding elements
(c) armature conductors per path
(d) armature parallel paths.
[Q-8]The critical resistance of the dc generator is the resistance of
(a) Armature
(b) Field
(c) Load
(d) Brushes
(e) None of the above.
[Q-9]The primary reason for making the coil span of a d.c. armature winding equal to a pole pitch is to
(a) obtain a coil span of 180ยบ (electrical)
(b) ensure the addition of e.m.fs. of consecutive turns
(c) distribute the winding uniformly under different poles
(d) obtain a full-pitch winding.
[Q-10]In a 4-pole, 35 slot d.c. armature, 180 electrical-degree coil span will be obtained when coils occupy ............ slots.
(a) 1 and 10
(b) 1 and 9
(c) 2 and 11
(d) 3 and 12
[Q-11]For standing a DC motor a starter is required because
(a)it limits the starting current to a safe value.
(b)It starts the motor.
(c)it limits the speed of the motor.
(d)None of the above.
[Q-12]When two DC series motors are connected in parallel, the resultant speed is
(a)Zero.
(b)Normal speed.
(c)Less than normal speed.
(d)More than normal speed.
[Q-13]To get the speed of DC motor is more than normal without wastage of electrical energy _____________ is used.
(a)Rheostatic control.
(b)Ward Leonard control.
(c)Any of above method.
(d)None of above.
[Q-14]The armature of a d.c. generator has a 2-layer lap-winding housed in 72 slots with six conductors/slot. What is the minimum number of commutator bars required for the armature?
(a) 72
(b) 432
(c) 216
(d) 36
[Q-15]The sole purpose of a commutator in a d.c. Generator is to
(a) increase output voltage
(b) reduce sparking at brushes
(c) provide smoother output
(d) convert the induced a.c. into d.c.
[Q-16]In a dc generator, the generator, the generated emf is directly proportional to the
(a) Field current
(b) Pole flux
(c) Number of armature parallel paths
(d) Number of dummy coils
(e) None of the above
[Q-17]For a 4-pole, 2-layer, d.c., lap-winding with 20 slots and one conductor per layer, the number of commutator bars is
(a) 80
(b) 20
(c) 40
(d) 160
[Q-18]A 4-pole, 12-slot lap-wound d.c. armature has two coil-sides/slot. Assuming single turn coils and progressive winding, the back pitch would be
(a) 5
(b) 7
(c) 3
(d) 6
[Q-19]A DC shunt motor is operating at no load. If the armature is shunted by a resistance, its speed will
(a)Increase.
(b)Decrease.
(c)Remain the same.
(d)Be unpredictable.
[Q-20]The armature voltage control is considered suitable for a DC motor driven at constant
(a)Speed.
(b)Power.
(c)Torque.
(d)Current.
[Q-21]If in the case of a certain d.c. armature, the number of commutator segments is found either one less or more than the number of slots, the armature must be having a simplex ............ winding.
(a) wave
(b) lap
(c) frog leg
(d) multi element.
[Q-22]Lap winding is suitable for ............ current,............ voltage d.c. generators.
(a) high, low
(b) low, high
(c) low, low
(d) high, high.
[Q-23]The essential condition for stable parallel operation of two dc generators having similar characteristics is that they should have
(a) Same kilowatt output ratings
(b) Dropping voltage characteristics
(c) Same percentage regulation
(d) Same no load and full load speed
(e) None of the above
[Q-24]An ideal dc generator has .......... voltage regulation.
(a) Low
(b) Zero
(c) Positive
(d) Negative
(e) None of the above
[Q-25]Which generator has poorest voltage regulation
(a) Series
(b) Compound
(c) Shunt
(d) High
(e) None of the above