The generator is failed to build up for the following reason:- · No residual magnetism: if there is little or no residual magnetism, because of inactivity or jarring in shipment, no voltage will be generated that can produce field current. · Field connection reversal: the voltage generated due to residual magnetism is applied to the field and current flow in such a direction as to produce lines of flux in the same direction as the residual flux. If the field connections are reversed, the lines of the flux produced by the current flow will oppose the residual flux so that the generated voltage will decrease rather than increase. · Field- circuit resistance too high: if the field current resistance is greater than the critical voltage. Then this prevents voltage buildup. · Dirty commutator: a dirty commutator does not permit good contact between brushes and the commutator. This poor contact shows up as a high resistance to
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