Why a self excited shunt generator will not build up voltage?

Reasons for not building up voltage of a self excited shunt generator:

· No residual magnetism: The start of the build up process requires some residual magnetism in the magnetic circuit of a generator. 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 reversed: The voltage generated due to residual magnetism is applied to the field and current flows 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 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 circuit resistance is greater than the critical resistance then this prevents voltage build up.

· Open field circuit connection: The effects of an open circuit are apparent. The field-circuit resistance is much greater than the critical value, hence the generator will not build up.