Synchronous Machines: Larger Air Gap Aids Sinusoidal MMF

[ranju]

Homework Statement

I studied that a larger air gap in alternators aids in sinusoidal mmf distribution ..I didn't get this as larger air gap should deteriorate the wave..but here it is opposite..?? Is it right ?? [/B]

Homework Equations

The Attempt at a Solution

One point can be said that larger air gap improves the stability limit of synchronous machines ..[/B]

 

[rude man]

In general, a larger air gap puts more of the loop mmf in the gap and less in the highly unstable, non-linear and unpredictable metal. The air gap reluctance is a very stable L/μ₀A with L = gap length and A = gap area. It's approximate since it ignores fringing effects but it's very stable and linear with flux, so avoiding harmonic generation. There will of course be a commensurate loss of flux for a given mmf.