Electrical Machines
In Ward-Leonard system, the lower limit of the speed imposed by

 Field resistance.
 Residual magnetism of the generator.
 None of above.
 Armature resistance.

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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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