Electrical Machines
In large sized DC machines the compensating windings are provided to

  neutralize voltage induced in coil due to fluctuation of l
 compensate for the decrease in speed due to increase of load.
 reduce eddy current losses by providing local short circuits.
None of these

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

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