Question on Separator in .csv file

Hi,

My original .csv file used comme as the separator, which could be viewed in notepad. I used excel 2013 to open it and change data format to one of the columns, then click save. after that, when I use notepad to review the file, its separator looks like 'tab'. The default separator in my control panel is comme as well. I've no idea on the reaon why the separator changed. Could any one help on me? Thanks a lot.

Regards,
V