Electrical Machines
A slip ring Induction motor runs at 290 rpm at full load, when connected to 50 Hz supply. Determine the number of poles and slip.

  P = 50, s = 4.43 %.
  P = 20, s = 3.33 %.
  P = 60, s = 0.96 %.
  P = 40, s = 5.79 %.

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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)

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

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