Electrical Machines
In a DC machine

 current and emf in armature are unidirectional
 emf in armature conductors and at the terminals is alternating.
 current and emf in armature are alternating.
 current and emf at the terminals are alternating.

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Electrical Machines
A dc shunt generator, when commissioned after a major repair of the field system, failed to build Up voltage. It was because

 field system lost residual magnetism
 field resistance was higher than critical resistance
 there was a break in the armature circuit
 field winding was wrongly connected

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