Electrical Machines
A simple method of increasing the voltage of a DC generator is to

 increase the source frequency.
 increase the number of turns in field coil.
  increase the speed of shaft rotation.
 increase the number of turns in armature coil.

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Electrical Machines
A dc shunt generator, when driven without any excitation, showed an open circuit voltage of 12 V. When the field winding was excited, the voltage dropped to zero. It happened because

 there was no residual magnetism in the field circuit
 field winding was wrongly connected
 field resistance was higher than critical resistance
 there was a break in the armature circuit

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