Electrical Machines
The residual magnetism of a self-excited dc generator is lost. To build up its emf again

 the armature connection must be reversed
 the field winding connection must be reversed
 the field winding must be replaced
 field winding must be excited by low voltage dc supply

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

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

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