Thursday, September 10, 2020

Chapter 6 : DC Machines- Page 10

Chapter 6 : DC Machines

91. In Ward Leonard method of speed control, the lower limit of speed is caused bY
A. residual magnetism of the generation
B. core losses of motor
C. mechanical losses of motor and generator together
D. all of the above


... Answer is (A)

 

 
 

92. In a permanent magnet de motor which of the following methods of speed control can not be used?
A. armature voltage variation
B. armature resistance control
C. field current variation
D. all of these

... Answer is (C)

 
 
 

93. Usually wide and very sensitive speed control is required in case of
A. reciprocating pumps
B. colliery winders
C. centrifugal blowers
D. lathe machines

... Answer is (B)

 

 
 

94. In rheostatic method of braking, the braking torque is proportional to
A. N
B. N
²
C. 1/N
D. 1/N²

  ... Answer is (A)

 

 
 
95. Regenerative breaking in shunt motors is used when
A. the load is variable
B. the load is constantly decreasing
C. the load has overhauling characteristics
D. the load also acts as a braking force
 
  ...
Answer is (C)

 
 
 

96. The most economical method of electrical braking of a dc motor is
A. regenerative braking
B. dynamic braking with self excitation
C. dynamic braking with separate excitation
D. plugging

  ... Answer is (A)

 

 
 

97. For nonreversing dc drives, it is preferred to employ
A. regenerative braking
B. dynamic braking with separate excitation
C. dynamic braking with self excitation
D. plugging

  ... Answer is (B)


 
 

98. Which of the following dc motor is used for intermittent high torque load
A. dc series motors
B. dc shunt motor
C. differential compound motor
D. cumulative compound motor

... Answer is (D)

 
 

99. DC series motor are best suited for traction because

A. torque is proportional to the square of the armature current and speed is proportional to the torque
B. torque is proportional to square of the armature current and speed is inversely proportional to the torque
C. torque and speed both are proportional to the square of the armature current
D. none of these
 
  ... Answer is (B)

 
 

100. Which dc motor should not be used for centrifugal pumps?(MORE PAGES WILL BE UPDATED SOON)
A. shnt motor
B. series motor
C. cumulatively compound motor
D. differentially compound motor

  ... Answer is (C)

 

 

Page 10 of  17

Pages   1  2  3  4  5  6  7 8  9  10  11 12 13 14 15 16 17                      
Share:

0 comments:

Post a Comment

Email Subscription

Blog Archive