Electrical Machines
Autotransformer makes effective saving on copper and copper losses, when its transformation ratio is equal to

  greater than one.
  very low
  approx to one.
  less than one.

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Electrical Machines
If the applied voltage of a certain transformer is increased by 50% and the frequency is reduced by 50%, the maximum flux density will (assuming that the magnetic circuit remains unsaturated)

 changes to 1.5 times the original value
 remain the same as the original
 changes to three times the original value
 changes to 0.5 times the original value

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