For which types of D.C. motor, dynamic braking is generally used ?
For which types of D.C. motor, dynamic braking is generally used ?
A. Shunt motors
B. Series motors
C. Compound motors
D. All of the above
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The main disadvantage of the Ward-Leonard control method is______________?
The main disadvantage of the Ward-Leonard control method is______________?
A. high initial cost
B. high maintenance cost
C. low efficiency at Hght loads
D. all of the aboveIn Ward-Leonard control the lower limit of speed is imposed by________?
In Ward-Leonard control the lower limit of speed is imposed by________?
A. residual magnetism of the generator
B. core losses of motor
C. mechanical losses of motor and generator together
D. all of the aboveAs 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____________________?
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____________________?
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 windingWhich of the following load normally needs starting torque more than the rated torque?
Which of the following load normally needs starting torque more than the rated torque?
A. Blowers
B. Conveyors
C. Air compressors
D. Centrifugal pumpsIn which of the following applications D.C. series motor is invariably tried?
In which of the following applications D.C. series motor is invariably tried?
A. Starter for a car
B. Drive for a water pump
C. Fan motor
D. Motor operation in A.C. or D.CThe starting resistance of a D.C. motor is generally_______________?
The starting resistance of a D.C. motor is generally_______________?
A. low
B. around 500 Q
C. 1000 Q
D. infinitely large