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Electrical Engineering Objective Questions { DC Motors }



106. In Ward Leonard method of speed control, the minimum number of machines needed is
A. one
B. two
C. three
D. four

107. Ward Leonard method of speed control is basically useful where usually
A. a small range of very sensitive speed control is required
B. a wide range of less sensitive speed control is required
C. a wide range of sensitive speed control is required
D. a narrow range of less sensitive speed control is required

108. 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

109. 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

110. In Ward Leonard method of speed control, the direction of rotation of the motor is usually reversed by reversing the connections of the generator field terminals reversing the connection of the generator armature terminals reversing the connection of the motor armature terminals none of these
A.13
B.(3)81.6
C. B2
D.83

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

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

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