Voltage build up in the Generator

 

• When the mechanical input power is given to the DC Generator, some emf and therefore current would be generated due to residual magnetism in the poles. 
• This current while passing through field coils, it will strengthen the magnetism of the poles which further generates emf. 
• This mutual reinforcement of field flux and emf proceeds till equilibrium condition is reached. 
• The rated terminal voltage is achieved at balanced condition.

Condition must be necessary in order to build up voltage in the generator

• There must be some residual magnetism in the poles of DC generator.
• The shunt field coils connection must be connected correctly to the armature. 
• The term – correctly – means that the flux produced by the shunt field aids residual flux. This will result in build up voltage in the DC generator. 
• If the direction of shunt field winding connection reverses, it will reduces net flux and therefore DC generator does not build up voltage.
• The direction of rotation of the armature must be such that the current produces by it always aids the residual flux.
• The shunt field resistance should be less than the critical resistance if it is excited to open circuit.

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