DC Motors Question and Answer


21. For constant torque drive which speed control method is preferred ?

  1. Field control
  2. Armature voltage control
  3. Shunt armature control
  4. Mechanical loading system

22. For starting a D.C. motor a starter is required because

  1. it limits the speed of the motor
  2. it limits the starting current to a safe value
  3. it starts the motor
  4. none of the above

23. For the same H.P. rating and full load speed, following motor has poor starting torque

  1. shunt
  2. series
  3. differentially compounded
  4. cumulativelycompounded

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

  1. Low speed operation
  2. High speed operation
  3. Variable speed operation
  4. Fixed speed operation

25. For which types of D.C. motor, dynamic braking is generally used ?

  1. Shunt motors
  2. Series motors
  3. Compound motors
  4. All of the above

26. Hopkinsons test on D.C. machines is conducted at

  1. no-load
  2. part load
  3. full-load
  4. overload

27. If a D.C. motor designed for 40°C ambient temperature is to be used for 50°C ambient temperature, then the motor

  1. of lower H.P. should be selected
  2. of higher H.P. should be selected
  3. can be used for 50°C ambient temperature also
  4. is to be derated by a factor recom-mended by manufacturer and select the next higher H.P. motor

28. If a D.C. motor is connected across the A.C. supply it will

  1. run at normal speed
  2. not run
  3. run at lower speed
  4. burn due to heat produced in the field winding by .eddy currents

29. If a D.C. motor is to be selected for conveyors, which rriotor would be preferred ?

  1. Series motor
  2. Shunt motor
  3. Differentially compound motor
  4. Cumulative compound motor

30. If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens

  1. this will make armature to take heavy current, possibly burning it
  2. this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
  3. nothing will happen to motor
  4. motor will come to stop
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