Electrical Machines
The low voltage winding of a 400/230 V single phase 50 Hz transformer is to be connected to keep the magnetization current at the same level in both the cases the voltage at 25 Hz should be

 115 V
 460 V
 230 V
 65 V

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Electrical Machines
If the frequency of input voltage of a transformer is increased keeping the magnitude of voltage unchanged, then

 Ph will increase but Pe will decrease
 both hysteresis loss(Ph) and eddy current loss(Pe) will increase
 Pe will increase but Ph will decrease
 Ph will decrease but Pe will remain same

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