Why they prefer synchronous(PM) generators instead of DFIG (Double fed induction generator) in condition monitoring for wind turbine generators? plz can anyone tell me...

 

The PM doesn't require additional excitation voltage for power generation.

You dont want to use the power you are generating to generate the power.

 

Actually why condition monitoring has to be done on wind turbines what is the primary reason?

 

Usually to be sure something can be done in case of winds that are too fast for the turbine. You can load down the generator to slow the blades to keep damage from off balance blades and bearings that cannot handle the RPMs.

This link may offer some insight:
http://www.plant-maintenance.com/articles/ConMon21stCentury.shtml

 

please can anyone help me i'm doing a project

 

As long as you are reviewing the literature - http://machinedesign.com/article/hydraulic-wind-turbines-0420

 

what are the main differences between DFIG and syncronous generator?

 

can any one tell me why condition monitoring is done on wind turbine blades is there any specific technique is used?