Question 1

Which of the following method of speed control of D.C. machine will offer minimum efficiency ?

Accepted Answer

A) Voltage control method 
B) Field control method 
C) Armature control method 
D) All above methods 
A) Voltage control method 
B) Field control method 
C) Armature control method 
D) All above methods C

Question 2

The mechanical power developed by a shunt motor will be maximum when theratio of back e.m.f. to applied voltage is

Accepted Answer

A) 4.0 
B) 2.0 
C) 1.0 
D) 0.5 
A) 4.0 
B) 2.0 
C) 1.0 
D) 0.5 D

Question 3

Which of the following motor has the poorest speed regulation ?

Accepted Answer

A) Shunt motor 
B) Series motor 
C) Differential compound motor 
D) Cumulative compound motor 
A) Shunt motor 
B) Series motor 
C) Differential compound motor 
D) Cumulative compound motor B

Question 4

For which of the following applications a D.C. motor is preferred over an A.C. motor?

Accepted Answer

A) Low speed operation 
B) High speed operation 
C) Variable speed operation 
D) Fixed speed operation 
A) Low speed operation 
B) High speed operation 
C) Variable speed operation 
D) Fixed speed operation

Question 5

Which D.C. motor is generally preferred for cranes and hoists ?

Accepted Answer

A) Series motor 
B) Shunt motor 
C) Cumulatively compounded motor 
D) Differentially compounded motor 
A) Series motor 
B) Shunt motor 
C) Cumulatively compounded motor 
D) Differentially compounded motor

Question 6

The speed of a D.C. shunt motor can be increased by

Accepted Answer

A) increasing the resistance in 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 
A) increasing the resistance in 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

Question 7

The armature torque of the D.C. shunt motor is proportional to

Accepted Answer

A) field flux only 
B) armature current only 
C) both (a) and (b) 
D) none of the above 
A) field flux only 
B) armature current only 
C) both (a) and (b) 
D) none of the above

Question 8

The armature voltage control of D.C. motor provides

Accepted Answer

A) constant torque drive 
B) constant voltage drive 
C) constant current drive 
D) none of the above 
A) constant torque drive 
B) constant voltage drive 
C) constant current drive 
D) none of the above

Question 9

Which of the following motor is preferred for operation in highly explosive atmosphere ?

Accepted Answer

A) Series motor 
B) Shunt motor 
C) Air motor 
D) Battery operated motor 
A) Series motor 
B) Shunt motor 
C) Air motor 
D) Battery operated motor

Question 10

Sparking at the commutator of a D.C. motor may result in

Accepted Answer

A) damage to commutator segments 
B) damage to commutator insulation 
C) increased power consumption 
D) all of the above 
A) damage to commutator segments 
B) damage to commutator insulation 
C) increased power consumption 
D) all of the above

Question 11

In D.C. machines the residual magnetism is of the order of

Accepted Answer

A) 2 to 3 per cent 
B) 10 to 15 per cent 
C) 20 to 25 per cent 
D) 50 to 75 per cent 
A) 2 to 3 per cent 
B) 10 to 15 per cent 
C) 20 to 25 per cent 
D) 50 to 75 per cent

Question 12

In case of conductively compensated D.C. series motors, the compensating winding is provided

Accepted Answer

A) as separately wound unit 
B) in parallel with armature winding 
C) in series with armature winding 
D) in parallel with field winding 
A) as separately wound unit 
B) in parallel with armature winding 
C) in series with armature winding 
D) in parallel with field winding

Question 13

If the supply voltage for a D.C. motor is increased, which of the following willdecrease ?

Accepted Answer

A) Starting torque 
B) Operating speed 
C) Full-load current 
D) All of the above 
A) Starting torque 
B) Operating speed 
C) Full-load current 
D) All of the above

Question 14

Sparking, is discouraged in a D.C. motor because

Accepted Answer

A) it increases the input power con-sumption 
B) commutator gets damaged 
C) both (a) and (b) 
D) none of the above 
A) it increases the input power con-sumption 
B) commutator gets damaged 
C) both (a) and (b) 
D) none of the above

Question 15

In a differentially compounded D.C. motor, if shunt field suddenly opens

Accepted Answer

A) the motor will first stop and 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 samedirection 
D) the motor will not work and come to stop 
A) the motor will first stop and 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 samedirection 
D) the motor will not work and come to stop

Question 16

The speed of a motor falls from 1100 r.p.m. at no-load to 1050 r.p.m. at rated load.The speed regulation of the motor is

Accepted Answer

A) 2.36% 
B) 4.76% 
C) 6.77% 
D) 8.84% 
A) 2.36% 
B) 4.76% 
C) 6.77% 
D) 8.84%

Question 17

Which one of the following is not the function of pole shoes in a D.C. machine ?

Accepted Answer

A) To reduce eddy current loss 
B) To support the field coils 
C) To spread out flux for better unifor-mity 
D) To reduce the reluctance of the mag-netic path 
A) To reduce eddy current loss 
B) To support the field coils 
C) To spread out flux for better unifor-mity 
D) To reduce the reluctance of the mag-netic path

Question 18

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 though the armature circuit

Accepted Answer

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 fieldwinding 
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 fieldwinding

Question 19

Usually wide and sensitive speed control is desired in case of

Accepted Answer

A) centrifugal pumps 
B) elevators 
C) steel rolling mills 
D) colliery winders 
A) centrifugal pumps 
B) elevators 
C) steel rolling mills 
D) colliery winders

Question 20

Flywheel is used with D.C. compound motor to reduce the peak demand by the motor, compound motor will have to be

Accepted Answer

A) level compounded 
B) under compounded 
C) cumulatively compounded 
D) differentially compounded 
A) level compounded 
B) under compounded 
C) cumulatively compounded 
D) differentially compounded

Which of the following method of speed control of D.C. machine will offer minimum efficiency ?

The mechanical power developed by a shunt motor will be maximum when theratio of back e.m.f. to applied voltage is

Which of the following motor has the poorest speed regulation ?

For which of the following applications a D.C. motor is preferred over an A.C. motor?

Which D.C. motor is generally preferred for cranes and hoists ?

The speed of a D.C. shunt motor can be increased by

The armature torque of the D.C. shunt motor is proportional to

The armature voltage control of D.C. motor provides

Which of the following motor is preferred for operation in highly explosive atmosphere ?

Sparking at the commutator of a D.C. motor may result in

In D.C. machines the residual magnetism is of the order of

In case of conductively compensated D.C. series motors, the compensating winding is provided

If the supply voltage for a D.C. motor is increased, which of the following willdecrease ?

Sparking, is discouraged in a D.C. motor because

In a differentially compounded D.C. motor, if shunt field suddenly opens

The speed of a motor falls from 1100 r.p.m. at no-load to 1050 r.p.m. at rated load.The speed regulation of the motor is

Which one of the following is not the function of pole shoes in a D.C. machine ?

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 though the armature circuit

Usually wide and sensitive speed control is desired in case of

Flywheel is used with D.C. compound motor to reduce the peak demand by the motor, compound motor will have to be

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Exam 8: D.C Motors and Speed Control

Which of the following method of speed control of D.C. machine will offer minimum efficiency ?

The mechanical power developed by a shunt motor will be maximum when theratio of back e.m.f. to applied voltage is

Which of the following motor has the poorest speed regulation ?

For which of the following applications a D.C. motor is preferred over an A.C. motor?

Which D.C. motor is generally preferred for cranes and hoists ?

The speed of a D.C. shunt motor can be increased by

The armature torque of the D.C. shunt motor is proportional to

The armature voltage control of D.C. motor provides

Which of the following motor is preferred for operation in highly explosive atmosphere ?

Sparking at the commutator of a D.C. motor may result in

In D.C. machines the residual magnetism is of the order of

In case of conductively compensated D.C. series motors, the compensating winding is provided

If the supply voltage for a D.C. motor is increased, which of the following willdecrease ?

Sparking, is discouraged in a D.C. motor because

In a differentially compounded D.C. motor, if shunt field suddenly opens

The speed of a motor falls from 1100 r.p.m. at no-load to 1050 r.p.m. at rated load.The speed regulation of the motor is

Which one of the following is not the function of pole shoes in a D.C. machine ?

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 though the armature circuit

Usually wide and sensitive speed control is desired in case of

Flywheel is used with D.C. compound motor to reduce the peak demand by the motor, compound motor will have to be

Transformer Fundamentals and Operation

Transformer Technology and Design

Transformer: Resistance, Oil, Relays, Harmonics, and Core Properties

Transformers: Efficiency, Design, and Testing

Transformers: Voltage Regulation, Efficiency, and Protection

Transformer and D.C Motor

D.C Motors and Starters

D.C Motors and Controls

D.C Motors and Generators

D.C Machine and Generator Laminations, Commutation, and Components

D.C Generators and Commutators

D.C Generator Operation and Construction

D.C Generators

Direct Current Generators and Parallel Operation

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