Machine Parts

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 e

How can the problem be remedied : No residual magnetism, reversed field connection and high resistance of field circuit are responsible for the failure of build up process of a dc generator. The factors are explained below: No residual magnetism:    For the starting build up process requires some residual magnetism in the magnetic circuit then no voltage will be generated that can produce current flow through field circuit. Reversed field connection:    The voltage induced inside the coil of field circuit due to residual magnetism that can permit the flow of current. For the following direction of this flux will be created and the direction of this flux will be same direction as the residual flux. If the field connections are reversed the lines of flux produced by current flow will oppose the residual flux, as a result generate voltage will decrease rather than increase. So voltage build up process failed. Field circuit resistance too high:   A field

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