Electrical Machines
In travelling cranes for hoisting and lowering which type of motor is preferred?

  Synchronous motor.
  DC series motor.
  Single phase induction motor.
  AC slip ring motor.

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Electrical Machines
With the increase in speed of DC motor

  Back emf increase but line current falls.
 Both back emf as well as line current fall.
 Back emf falls and line current increase.
 Both back emf as well as line current increase.

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Electrical Machines
Skewing of the rotor in a 3 - Φ squirrel cage induction motor reduces

  noise, parasitic torque, starting torque and pull out torque.
  noise and pullout torque, but increase parasitic and starting torque.
  noise, parasitic and starting torque, but increase pull out torque.
  noise and parasitic torque, but increase starting and pull-out torque.

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Electrical Machines
For a given torque, reducing diverter resistance of a DC series motor causes

 increase in speed but armature currnet remains the same.
 decrease in speed but armature current remains the same.
 increase in speed demanding more armature current.
 decrease in speed demanding less armature current.

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