electrical

DC Motor MCQ Objective Questions and Answers Page - 4

1.
 DC series motor is best suited for electric traction as A It develops high starting torque B It runs at very high speed at light load C It is cheaper in cost D It consumes less power Answer : A Explanation :
2.
 A dc series motor is running at rated speed without any additional resistance in series. If an additional resistance is placed in series, ther speed mof motor A Increases B Decreases C Remains unchanged D Oscillates around the rated speed Answer : B Explanation :
3.
 A dc series motor is used for an overhauling load, it can work stably if A The armature is shunted by a resistor B The field winding is reversed C A resistor is put in series with the machine D A diverter is put across the field Answer : A Explanation :
4.
 A dc shunt motor is driving a constant torque load. On inserting an additional resistance in the armature circuit, the speed of the motor will A Remain unchanged B Increase C Decrease be zero D Be zero Answer : C Explanation :
5.
 A dc may have rising speed torque characteristic due to A Very high armature circuit resistance B Very high filed circuit resistance C Very high demagnetizing armature reaction D Very low demagnetizing armature reaction Answer : C Explanation :
6.
 If the speed of a dc motor increase with load torque , then it is a A Series motor B Permanent magnet C Differentially compounded motor D Cumulatively compounded motor Answer : C Explanation :
7.
 A separately excited dc generator is feeding a dc shunt motor. If the load torque on the motor is halved approximately A Armature current of both motor and generator are halved B Armature current of motor is halved and that of the generator is unaltered C Armature current of generator is halved and that of motor is unaltered D Armature current of both motor and generator  are unaltered Answer : A Explanation :
8.
 In a dc motor , if armature current is increased, keeping field current constant, the torque developed will A Remain unchanged B Decrease in inverse proportion C Decrease in inverse proportion D Increase I proportion to the square of the armature current Answer : C Explanation :
9.
 If the supply voltage to a dc shunt motor is increased by 15% , which of the following will reduced ? A Full load current B Full load speed C Starting torque D None of the above Answer : A Explanation :
10.
 A dc shunt motor is driving a constant torque load with normal excitation. If the filed current is halved then the motor will run at A Rated speed B Half of rated speed C Double of rated speed D Slightly less than double of rated speed Answer : D Explanation :
11.
 A dc shunt motor is driving a mechanical load at rated voltage with normal excitation. If the load torque is increased to double of the normal one, the speed of the motor will A Become half B Become double C Increase slightly D Fall slightly Answer : D Explanation :
12.
 When a dc cumulative compound wound motor is loaded A Torque increases and speed decreases B Torque decreases and speed increases C Both speed and torque increase D Both speed ad torque decrease Answer : A Explanation :
13.
 A belt driven cumulative compounded dc generator  is delivering power to the dc mains. If the belt snaps then the machine will run as a A Cumulative compounded motor in the same direction B Differentially compounded motor in the same direction C Cumulative compounded motor in the opposite direction D Differentially compounded motor in the opposite direction Answer : B Explanation :
14.
 Flywheel is employed with a dc compound motor to reduce peak demand. The compound motor should be A Level compound B Differential compound C Cumulative compound D None of these Answer : C Explanation :
15.
 In a differentially compounded dc motor, if the shunt filed gets suddenly opened the motor will A first stop and then run in opposite direction as a series motor B run as a series motor, but at slower speed in the same direction C run as a series motor in the same direction at high speed D not work and come to stand still Answer : A Explanation :
16.
 When the direction of power flow in a differentially compounded motor reverses, it will operate as a A Cumulatively compounded generator B Differentially compounded generator C Series motor D Shunt motor Answer : A Explanation :
17.
 A differentially compounded dc motor with interpoles and with brushes on the neutral axis is to be driven as a generator in the same direction with the same polarity of the terminal voltage . It wi A Be a cumulatively compounded generator but the interpole coil connection are to be reverse B Be a cumulatively compounded  generator without reversing the interpole coil connections C Be a differentially compounded generator without reversing the interpole coil connection D Be a differentially compounded generator but the interpole coli connection are to be reversed Answer : B Explanation :
18.
 Running the machine at no load is inadvisable for A Dc shunt motor B Dc series motor C Induction motor D Synchronous motor Answer : B Explanation :
19.
 The dc motor suitable for applications requiring high starting torque is A Shunt B Series C Cumulative compounded D Differential compound Answer : B Explanation :
20.
 The dc motor that drawn almost same power at different loads is A Cumulative compound B Differential compound C Series D Shunt Answer : C Explanation :
21.
 A dc series motor is running with a divertor connected across in  field winding. If the divertor resistance is reduced then the speed of the motor will A Decrease B Increase C Become excessively high D Remain unaltered Answer : B Explanation :
22.
 Two dc series motors are connected in series and are driving the same mechanical load. If the motors are now connected in parallel the speed will become A One fourth B Half C Double D 4-times Answer : D Explanation :
23.
 In dc shunt motors , at start the filed excitation is kept at maximum value in order to A Reduce starting torque B Increase acceleration duration C Reduce armature heating D Avoid voltage dip in the supply mains Answer : C Explanation :
24.
 A dc shunt motor has external resistance of Ra and Rf in the armature and filed circuits respectively Armature current at starting can be reduced by keeping A Rf maximum and Ra minimum B Ra maximum and Rf maximum C Ra minimum and Rf maximum D Ra maximum and Rf minimum Answer : D Explanation :
25.
 Direct on line (DOL) starters are not suitable for starting large dc motors, because A The starting current will be enormously high, which will cause large voltage drop in the supply m B The motor may not start C The motor may run away D The starting torque become low Answer : A Explanation :
26.
 A DOL starter is employed fro starting motors of ratings up to A 3.75kW B 7.5kW C 1.5kW D 25kW Answer : A Explanation :
27.
 In a dc shunt motor, the three point starter A Limits the starting current to a  safer value B Provides overload protection C Provides no volt protection D All of the above Answer : D Explanation :
28.
 The dc motor starter handle should be moved A Very slowly in steps B Smoothly in steps C Quickly D With a jerk to final position Answer : B Explanation :
29.
 A 4-point starter is used to start and control the speed of a A dc shunt motor with armature resistance control B dc shunt motor with field weakening control C dc series motor D dc compound motor Answer : B Explanation :
30.
 The dynamic braking is generally used with ____dc motors A Series B Shunt C Compound D All Answer : D Explanation :
31.
 Which D.C motor is generally preferred for cranes and hoists? A Series motor B Shunt motor C Cumulatively compounded motor D Differentially compounded motor Answer : A Explanation :
32.
 Three-point starter can be used for A Series motor only B Shunt motor only C Compound motor only D Both shunt and compound motor Answer : D Explanation :
33.
 Sparking is discouraged in a D.C motor because A It increases the input power consumption B Commutator get damaged C Both (a) and (b) D None of the above Answer : B Explanation :
34.
 Speed control by Ward Leonard method gives uniform speed variation A In one direction B In both direction C Below normal speed only D Above normal speed only Answer : B Explanation :
35.
 Flywheel is used with D.C compound motor to reduce the peak damaged by the motor, compound motor will have to be A Level compounded B Under compounded C Cumulatively compounded D Differentially compounded Answer : C Explanation :
36.
 Following motor is used where high starting torque and wide speed range control is required A Single phase capacitor start B Induction motor C Synchronous motor D D.C motor Answer : D Explanation :
37.
 In a differentially compounded D.C motor, if the shunt field suddenly opens A The motor will first stop then run in opposite direction as series motor B The motor will work as series motor and run at slow speed in the same direction C The motor will work as series motor and run at high speed in the same direction D The motor will not work and come to stop Answer : A Explanation :
38.
 Which of the following motor has the poorest speed regulation? A Shunt motor B Series motor C Differential compound motor D Cumulative compound motor Answer : B Explanation :
39.
 Buses, trains. Trolleys, hoists, cranes require high starting torque and therefore make use of A D.C series motor B D.C shunt motor C Induction motor D All of the motors Answer : A Explanation :
40.
 As the load is increased the speed of the D.C shunt motor will A Reduce slightly B Increase slightly C Increases proportionately D Remains unchanged Answer : A Explanation :
41.
 The armature torque of the D.C shunt motor is proportional to A Field flux only B Armature current only C Both (a) and (b) D None of the above Answer : B Explanation :
42.
 Which of the following method of speed control of D.C machine will offer minimum efficiency? A Voltage control method B Field control method C Armature control method D All of the above Answer : C Explanation :
43.
 Usually wide and sensitive speed control is desired in case of A Centrifugal pumps B Elevators C Steel rolling mills D Colliery winders Answer : D Explanation :
44.
 The speed of a motor falls from 1100 r.p.m at no-load at rated load. The speed regulation of the motor is A 2.36% B 4.76% C 6.77% D 8.84% Answer : B Explanation :
45.
 The armature voltage control of D.C motor provides A Constant torque drive B Constant voltage drive C Constant current drive D None of the above Answer : A Explanation :
46.
 As there is no back e.m.f at the instant of starting a D.C motor, in order to prevent a heavy current from flowing through the armature circuit A A resistance is connected in series with armature B A resistance is connected parallel to the armature C Armature is temporarily open circuited D A high value resistor is connected across the field winding Answer : A Explanation :
47.
 The speed of a D.C shunt motor can be increased by A Increasing the resistance in the armature circuit B Increasing the resistance in field circuit C Reducing the resistance in the field circuit D Reducing the resistance in the armature circuit Answer : B Explanation :
48.
 If Ia be the armature current, then speed of a D.C shunt motor is A Independent of Ia B Proportional to Ia C Varies Ia² D Varies as 1/Ia Answer : A Explanation :