Multiple choice questions on dc motor # 8

                   
                        Hi friends, this is post about objectives of electrical engineering with emphasis on dc motor check out and comment...

1) The speed of a dc shunt motor can be raised above its rated value by
A) inserting an additional resistance in the armature circuit
B) inserting an additional resistance in the field circuit
C) reducing the applied voltage
D) using either of the above methods

Ans:B

2) The speed of dc shunt motor supplying a load at its rated speed can be reduced by
A) connecting an additional resistance in the armature circuit
B) connecting an additional resistance in the field circuit
C) increasing the applied voltage
D) any of the above methods

Ans:A

3) For same power output rating and full load speed , the motor that will have poorest starting torque, is
A) cumulatively compound
B) differential compound
C) series
D) shunt

Ans:B

4) 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

Ans:C

5) The field flux method of speed control of dc shunt motor is generally used for which one of the following?
A) constant hp drive below the base speed
B) constant torque drive above the base speed
C) constant torque drive below the base speed
D) constant hp drive above the base speed

Ans:D

6) 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 at cost
D) it consumes less power

Ans:A

7) When an electric train is moving down a hill, the dc motor will operate as a dc
A) series motor
B) series generator
C) shunt motor
D) shunt generator

Ans:B

8) In a dc series motor, if armature current is reduced to 70% of its original value, the torque of the motor will be reduced by
A) 49%
B) 51%
C) 50%
D) 70%

Ans:B

9) A differentially compounded dc motor is running at rated speed. If the series field winding of the motor gets short-circuited, the speed of the motor will
A) remain unaltered
B) increase
C) decrease
D) be zero

Ans:C

10) Which of the following dc motors will have highest percentage increase of input current, for the same percentage increase in torque?
A) series
B) shunt
C) cumulative compound
D) All equal

Ans:B

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