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Electrical Machines

Electrical Machines
Motors for fans and pumps are selected in the rpm range

  375 to 500.
  1440 to 2880.
  500 to 720.
  720 to 920.

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Electrical Machines
Unbalance 3 - Φ stator currents cause

  double frequency currents in the rotor.
  heating of rotor.
All of these
  vibrations.

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Electrical Machines
φA DC shunt machine generates 250 V on open circuit at 1000 RPM. Armature resistance is 0.5 Ω, field resistance 250 Ω. When running as a motor takes 4 A at 250 V. Calculate the speed when running as a motor taking 40 A at 250 V. Armature reaction weakens the field by 4%.

 960 RPM
 940 RPM
 970 RPM
 920 RPM

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Electrical Machines
A dc series motor driving and electric train faces a constant power load. It is running at rated speed and rated voltage. If the speed has to be brought down to 0.25 p.u. the supply voltage has to be approximately brought down to

  0.75 p.u
  0.5 p.u
  0.125 p.u
  0.25 p.u

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Electrical Machines
In dc machines, the armature windings are placed on the rotor because of the necessity for

 generation of voltage
 development of torque
 electromechanical energy conversion
 commutation

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Electrical Machines
Belt conveyors offer _______________ starting torque.

  medium.
  zero.
  high.
  low.

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MORE MCQ ON Electrical Machines

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