electrical

DC Generator MCQ Objective Questions and Answers Page - 1

1.
 In an electromechanical energy conversion device, the developed torque depends upon A Stator field strength and torque angle B Stator field and rotor field strengths C Stator field and rotor field strengths and the torque angle D Stator field strength only Answer : C Explanation :
2.
 In electromechanical energy conversion devices (e.g generators and motors) a small air gap is left between the stator and the rotor in order to A reduce the reluctance of the magnetic path B increase flux density in the air gap C permit mechanical clearance D avoid saturation of field Answer : C Explanation :
3.
 If a current carrying coil is placed in a uniform magnetic field direction of magnetic induction, then A The net force and torque on the coil are both zero B The net force is zero but torque is finite C The net force is finite but toque is zero D The net force and torque are both finite Answer : A Explanation :
4.
 Reluctance torque in rotating machines is present , when A air gap is not uniform B reluctance seen by stator mmf varies C reluctance seen by rotor mmf varies D reluctance seen by the working mmf varies Answer : D Explanation :
5.
 A rotating electrical machine having its self inductacnes of both the stator and the stator windings, independent of rotor position will definitely not develop. A Starting torque B Synchronizing torque C Hysteresis torque D Reluctance torque Answer : B Explanation :
6.
 A circular metallic disc is placed in a vertical magnetic field of constant induction in the downward direction. If the disc is rotated in a horizontal plane, the emf induced will be A Zero B Constant independent of disc size C Increasing radially in the outward direction D Decreasing radially in the outward direction Answer : A Explanation :
7.
 The emf induced in a conductor rotating in a bipolar field is A DC B AC C DC  and  AC both D None of these Answer : B Explanation :
8.
 A  conductor is rotating within a magnetic filed. At which of the position do the peak voltages occur? A At right angles to the axis of magnetic field B Along the axis of the magnetic field C At 450 angles to the axis of magnetic field D Anywhere Answer : B Explanation :
9.
 EMF induced in a coil rotating in a uniform magnetic filed will be maximum when the A Flux linking with the coil is maximum B Rate of change of flux linkage is minimum C Rate of change of flux linkage is maximum D Rate of cutting flux by the coil sides is minimum Answer : C Explanation :
10.
 A homopolar generator usually has A High voltage and high current B Low voltage and high current C Low voltage and low current D High voltage and low current Answer : B Explanation :
11.
 In a dc generator, the ripples in the direct emf generated are  reduced by employing A Commutator with large number of segments B Equalizer rings C Carbon brushes D Graphite brushes Answer : A Explanation :
12.
 In order to ascertain whether a dc machine is lap wound or wave wound on the basis of visual observation of the armature, one should observe the A Connections to the brushes B Connections to the commutator C Connections to the field winding D Direction of end connections Answer : D Explanation :
13.
 The coil span A Must be exactly equal to pole pitch B Can never be equal to pole pitch C May or may not be exactly equal to pole pitch D None of the above Answer : C Explanation :
14.
 The  coil span A +1 B -1 C +1 or -1 D Average pitch Answer : C Explanation :
15.
 The commutator pitch for simplex wave winding is equal  to A +1 or-1 B Twice average pitch C Average pitch D Half average pitch Answer : C Explanation :
16.
 In a dc machine armature winding, the number of commutator segments is equal to the number of armature A Coils B Coil sides C Conductors D Turns Answer : A Explanation :
17.
 How many segments will be there for the commutator of a 6-pole dc machine having a simple wave wound armature with 72 slots A 73 B 72 C 71 D 70 Answer : B Explanation :
18.
 For both lap and wave windings, there are as many commutator bars as the number of A Armature conductors B Winding elements C Poles D Slots Answer : B Explanation :
19.
 In a drum type dc armature winding the back pitch and front pitch in terms of the coil sides must be A even and odd respectively B odd and even respectively C both even D both odd Answer : D Explanation :
20.
 In a dc machine, fractional pitch winding is employed to A increase generated voltage B reduce sparking C save copper D both (b) and (c) Answer : D Explanation :
21.
 In a dc machine, the armature winding is made up of number of coils distributed in large number of armature slots instead of placing all the coils into two slots to A have maximum emf at the output terminals B have maximum emf generated in the armature C have minimum heat dissipation from the armature D make the armature  dynamically balanced Answer : D Explanation :
22.
 Aluminium is not used as winding wire in dc machine armature as it A Is costlier B Is of low resistivity C Is of lower thermal conductivity D Requires large winding space Answer : D Explanation :
23.
 Short circuiting is caused in the armature winding due to A Failure of insulation between two turns of a coil B Failure of insulation between two commutator bars C Grounding of two or more turns of the same coil D Any of the above Answer : D Explanation :
24.
 In a lap wound dc generator , the equalizer rings are provided to A Neutralize the armature reaction effect B Avoid short circuiting C Avoid unequal distribution of currents at brushes D Android harmonics generated in the emf provide mechanical balancing Answer : C Explanation :
25.
 In a lap wound dc generator haivn P poles and Z conductors the maximum number of equalizer rings will be A Z/P B 2Z/P C Z/2P D Z/4P Answer : A Explanation :
26.
 Number of tappings to each equalizer ring is equal to number of A Poles B Pole pairs C Parallel paths D Commutator segments Answer : B Explanation :
27.
 A frog leg winding is used in a dc machine to eliminate A The sue of equalizers in lap winding B The sue of compensating winding C The sue of compensating winding D Reactance voltage produced due to commutation Answer : A Explanation :
28.
 A 250 V dc generator is run at rated speed with no excitation . The open circuit voltage will be A Zero B Very small, say about 2 or 3 V C About 100 V D 250 V Answer : B Explanation :
29.
 At a certain speed and flux, the voltage generated by dc generator is 230 volts. If the speed is increased by 20% and the flux is simultaneously reduced by 10% , the voltage will be A Increase by 10 % B Reduced by 20% C Increased by 8% D Decreased by 8% Answer : C Explanation :
30.
 The function of compensating winding is to neutralize A Reactance voltage generated as a consequence of commutation B Cross magnetizing the effect of armature reaction C Demagnetizing effect of armature reaction D All the above. Answer : C Explanation :
31.
 Laminations of core are generally made of A Cast iron B Carbon C Silicon steel D Stainless steel Answer : C Explanation :
32.
 Which of the following could be lamina-proximately the thickness of laminations of a DC machine? A 0.005 mm B 0.05 mm C 0.5 mm D 5 mm Answer : C Explanation :
33.
 The armature of DC generator is laminated to A Reduce the bulk B Provide the bulk C Insulate the core D Reduce eddy current loss Answer : D Explanation :
34.
 The resistance of armature winding depends on A Length of conductor B Cross-sectional are of the conductor C Number of conductors D All of the above Answer : D Explanation :
35.
 The field coils of DC generator are usually made of A Mica B Copper C Cast iron D Carbon Answer : B Explanation :
36.
 The commutator segments are connected to the armature conductors by means of A Copper lugs B Resistance wires C Insulation pads D Brazing Answer : A Explanation :
37.
 In a commutator A Copper is harder than mica B Mica and coper are equally hard C Mica is harder than copper D None of the above Answer : C Explanation :
38.
 In DC generators the pole shoes are fastened to the pole core by A Rivets B Counter sunk screws C Brazing D Welding Answer : B Explanation :
39.
 According to Fleming’s right-hand rule for finding the direction of induced e.m.f., when middle finger points in the direction of induced e.m.f., forefinger will point in the direction of A Motion of conductor B Lines of force C Either of the above D None of the above Answer : B Explanation :
40.
 Fleming’s right-hand rule regarding direction of induced e.m.f., correlates A Magnetic flux, direction of current flow and resultant force B Magnetic flux, direction of motion and the direction of e.m.f., induced C Magnetic field strength, induced voltage and current D Magnetic flux, direction of force and direction of motion of conductor Answer : B Explanation :
41.
 While applying Fleming’s right-hand rule to find the direction of induced e.m.f., the thumb points towards A Direction of induced e.m.f. B Direction of flux C Direction of motion of the conductor if forefinger points in the direction of generated e.m.f. D Direction of motion of the conductor, if forefinger points along the lines of flux Answer : D Explanation :
42.
 The bearings used to support the rotor shafts are generally A Ball bearings B Bush bearings C Magnetic bearings D Needle bearings Answer : A Explanation :
43.
 In DC generators, the cause of rapid brush wear may be A Severe sparking B Rough commutator surface C Imperfect contact D Any of the above Answer : D Explanation :
44.
 In lap winding, the number of brushes is always A Double the number of poles B Same as the number of poles C Half the number of poles D Two Answer : B Explanation :
45.
 For a DC generator when the number of poles and the number of armature conductors is fixed, then which winding will give the higher e.m.f.? A Lap winding B Wave winding C Either of (a) and (b) above D Depends on other features of design Answer : B Explanation :
46.
 In a four-pole DC machine A All the four poles are north poles B Alternate poles are north and south C All the four poles are south poles D Two north poles follow two south poles Answer : B Explanation :
47.
 Copper brushes in DC machine are used A Where low voltage and high currents are involved B Where high voltage and small currents are involved C In both of the above cases D In none of the above cases Answer : A Explanation :
48.
 A separately excited generator as compared to a self-excited generator A Is amenable to better voltage control B Is more stable C Has exciting current independent of load current D Has all above features Answer : D Explanation :
49.
 In case of DC machines, mechanical losses are primary function of A Current B Voltage C Speed D None of above Answer : C Explanation :
50.
 Iron losses in a DC machine are independent of variations in A Speed B Load C Voltage D Speed and voltage Answer : B Explanation :