Why does a synchronous generator have no EMF at zero field current unlike DC machines?

[ranju]

Homework Statement

Is there no residual magnetism in case of synchronous machines? Actually I had this doubt because of the OCC of alternator as when the field current is zero the generated value of the machine is also zero unlike the dc machines..why is it so??

Homework Equations

The Attempt at a Solution

The OCC of a synchronous machine is plotted between the generated emf and field current ast rated speed .[/B]

 

[NascentOxygen]

The exciter (DC generator) can be designed to have residual magnetism, to make the machine self-excited and eliminate the slip-rings of separately excited.

 

[ranju]

this doesn't answer my q. I was asking about if synchronous generator have residual magnetism?