Prevent infection by adding alcohol

Can i add alcohol to carboy during fermentation to avoid any infection ? is alcohol effective to prevent infection ?

In a word: no. The alcohol level that is necessary to thwart bacterial growth will screw up your fermentation. And yes, alcohol is effective in preventing infection...before you get to the fermenter; you can use alcohol to clean your utensils...etc. (but bleach at 10ppm works just as well, and it is cheaper), but never add alcohol to the wort, starter, fermenter, grain, extract in an attempt to sanitize/avoid infection.

Cheers,
PikledBill