Electrical Machines
In a DC generator if field winding attains the critical resistance

 machine will generate maximum voltage.
 machine will generate maximum power.
 field winding will burn.
 the voltage generated will be zero.

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

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