## electrical

### DC Generator MCQ Objective Questions and Answers Page - 4

1.
 The commutator of a dc motor serves the purpose of A Changing friction B Converting dc into ac C Reducing friction D Avoiding arc at the brushes Answer : B Explanation :
2.
 In a dc machine, the brushes are physically placed in the A Polar axis and electrically connected to the coils lying in the interpolar axis B Polar axis electrically connected to the coils lying in the polar axis C Interpolar axis and electrically connected to the coils lying in polar axis D Interpolar axis and electrically connected to the coils lying in interpolar axis Answer : A Explanation :
3.
 In dc machines , the armature windings are placed on the rotor because of the necessity for A Electromechanical energy conversion B Generation of voltage C Commutation D Development of torque Answer : C Explanation :
4.
 Wave winding is employed in a dc machine of A High current and low voltage rating B Low current and high voltage rating C High current and high voltage rating D Low current and low voltage rating Answer : B Explanation :
5.
 If two 8 –pole dc machines of identical armatures are wound, one with lap winding and the other with wave winding , then A Wave wound machine will have more rated current and more voltage B Lap would machine will have more rated voltage and more current C Lap wound machine will have more rated voltage and less current D Wave wound machine will have more rated voltage and less current Answer : D Explanation :
6.
 The armature resistance in case of lap wound armature having Z conductors  each conductor of length  /  metres, x-sectional area a m2, resistivity and P poles will be A
7.
 In lap winding , the number of brushes is always _______the number of poles A Double B Same as C Half D None of these Answer : B Explanation :
8.
 A P-Pole lap wound dc machine had an armature current Ia. The conductor current in the armature winding is A $I_{a}$ B $I_{a}/P$ C $PI_{a}$ D None of above Answer : B Explanation :
9.
 A lap wound dc machine has 400 conductors and 8 poles. The voltage induced per conductor is 2V. The machine generates a voltage of A 100 V B 200 V C 400 V D 800 V Answer : A Explanation :
10.
 A 4 pole generator with 16 coils has a two layer lap winding. The pole pitch is A 32 B 16 C 8 D 4 Answer : C Explanation :
11.
 When the shunt field of a dc compound generator is connected across both the series filed and armature . Such a connection is known as A Short shunt B Long shunt C Cumulative compounding D Differential compounding Answer : B Explanation :
12.
 The series field of a short shunt dc generator is excited by ___________ A Armature B Shunt field C Load D
13.
 The slight curvature at the lower end of the OCC of a self-excited dc generator is due to A Magnetic inertia B Residual flux C High speed D High field resistance Answer : B Explanation :
14.
 The fall in speed of a dc generator due to increase in load can be corrected by A Cooling the armature B Increasing the excitation C Reducing the load voltage D Increasing the input to the prime mover Answer : D Explanation :
15.
 The magnetic field which initially induces emf in the armature in a self excited dc generator is because of A Permanent magnets B Armature rotation C Residual magnetism D None of the above Answer : C Explanation :
16.
 A generator may losse residual magnetism due to A Heating B Vibration C Over excitation D Any of these Answer : A Explanation :
17.
 In dc generators the residual magnetism is of the order of A 2.5% B 10% C 15% D 25% Answer : A Explanation :
18.
 In comparison to self excited generator, a separately excited generator A Is more reliable B Is amenable to better voltage regulation C Has exciting current independent of load characteristic has all of the above features D Has all of the above features. Answer : D Explanation :
19.
 The voltage at the terminals of a dc series generator running at rated rpm and no load will be A More than the rated voltage B Full rated voltage C A very small voltage D Zero Answer : C Explanation :
20.
 A dc series generator is provided with divertor an is delivering its rated current. If the divertor switch is opened, the terminal voltage will A Remain constant B Decrease C Increase D None of these Answer : C Explanation :
21.
 A 4 pole , 25 kW, 200 V wave wound dc shunt generator the current in each parallel path will be A 62.5 A B 125 A C 31.25 A D 250 A Answer : A Explanation :
22.
 A dc shunt generator is supplying load of 1.8 kW at 200 V . Its armature and filed resistances are 0.4Ω and 200 Ω respectively . What is the generated emf  ? A 190 V B 196 V C 204 V D 210 V Answer : C Explanation :
23.
 If the field circuit resistance of a dc shunt generator exceeds its critical value, the generator A Fails to build up B Build up a very light  voltage C Exceeds its current capacity D Produces power beyond its rating Answer : A Explanation :
24.
 A shunt generator has a critical field resistance of 200 Ω at a speed of 800 rpm. If the speed of the generator is increased to 1,000 rpm what is the change in the critical field resistance of th A Decreases to 160 Ω B Remains the same at 200 Ω C Increase to 250 Ω D Increase to 312.5 Ω Answer : C Explanation :
25.
 The factor that is not responsible for drop in terminal voltage of a dc shunt generator on load is A Commutation B Armature reaction C Armature resistance drop D Filed weakening due to (b) and (c) Answer : A Explanation :
26.
 In a dc shunt generator , the voltage build up is generally restricted due to A Armature heating B Insulation restriction C Saturation of iron D Speed limitation Answer : C Explanation :
27.
 An ideal dc generator has a regulation of _____ per cent A Zero B 10 C 25 D 100 Answer : A Explanation :
28.
 The  terminal voltage of an over compounded dc generator A Decreases with  the increase in load current B Increases with the increase in load current C Remain constant at all load currents D None of the above Answer : B Explanation :
29.
 In a dc compound generator , “flat compound” characteristic required for certain application, may be obtained by connecting a variable resistance: A Across the series filed B In series with the series filed C In parallel with the shunt filed D In series with the shunt field. Answer : A Explanation :
30.
 The armature core of a DC generator is usually made of A Silicon steel B Copper C Non-ferrous material D Cast-iron Answer : A Explanation :
31.
 Dc generator generates A AC voltage in the armature B Dc voltage in the armature C AC superimposed over DC D None of the above Answer : A Explanation :
32.
 Satisfactory commutation of DC machines requires A Brushes should be of proper grade and size B Brushes should smoothly run in the holders C Smooth, concentric commutator properly undercut D All of the above Answer : D Explanation :
33.
 Open circuited armature coil of a DC machine is A Identified by the scarring of the commutator segment to which open circuited coil is connected B Indicated by a spark completely around the commutator C Both (a) and (b) D None of the above Answer : C Explanation :
34.
 In a DC machine, fractional pitch winding is used A To increases the generated voltage B To reduce sparking C To save the copper because of shorted end connections D Due to (b) and (c) above Answer : D Explanation :
35.
 Dc series generator is used A To supply traction load B To supply industrial load at constant voltage C As a booster to maintain constant voltage at the load end of the feeder D For none of the above purpose Answer : C Explanation :
36.
 Following DC generator will be in a position to build up without any residual magnetism in the poles A Series generator B Shunt generator C Compound generator D Self-excited generator Answer : D Explanation :
37.
 Interpole flux should be sufficient to A Neutralise the commutating self-induced e.m.f. B Neutralise the armature reaction flux C Neutralise both the armature reaction flux as well as commutating e.m.f. induced in the coil D Perform none of the above functions Answer : C Explanation :
38.
 DC generator generally preferred for charging automobile batteries is A Series generator B Shunt generator C Long shunt compound generator D Any of the above Answer : B Explanation :
39.
 In a DC generator the number of mechanical degrees and electrical degrees will be the same when A RPM is more than 300 B RPM is less than 300 C Number of poles is 4 D Number of poles is 2 Answer : D Explanation :
40.
 Permeance is the reciprocal of A Flux density B Reluctance C Ampere-turns D Resistance Answer : B Explanation :
41.
 In DC generators the polarity of the interpoles A Is the same as that of the main pole ahead B Is the same as that of the immediately preceding pole C Is opposite to that of the main pole ahead D Is neutral as these poles do not play part in generated e.m.f. Answer : A Explanation :
42.
 The e.m.f. generated in a DC generator is directly proportional to A Flux/pole B Speed of armature C Number of poles D All of the above Answer : D Explanation :
43.
 In a DC generator the magnetic neutral axis coincides with the geometrical neutral axis, when A There is no load on the generator B The generator runs on full load C The generator runs on overload D The generator runs on designed speed Answer : A Explanation :
44.
 In a DC generator in order to reduce sparking at brushes, the self-induced e.m.f. in the coil is neutralised by all of the following except A Interpoles B Dummy coils C Compensating winding D Shifting of axis of brushes Answer : B Explanation :
45.
 In DC generators on no-load, the air gap flux distribution in space is A Sinusoidal B Triangular C Pulsating D Flat topped Answer : D Explanation :
46.
 A shunt generator running at 1000 rpm has generated e.m.f. as 200 V. if the speed increases to 1200 rpm, the generated e.m.f. will be nearly A 150 V B 175 V C 240 V D 290 V Answer : C Explanation :
47.
 The purpose of providing dummy coils in a generator is A To reduce eddy current losses B To enhance flux density C To amplify voltage D To provide mechanical balance for the rotor Answer : D Explanation :
48.
 In a shunt generator the voltage build up is generally restricted by A Speed limitation B Armature heating C Insulation restrictions D Saturation of iron Answer : D Explanation :