Electrical Machines
Field winding of a DC series motor is usually provided with thick wire

 in order to reduce eddy current to provide large flux.
 as it carries large load current.
 to reduce the insulation of materials.
 to provide large flux.

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

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