date conversion on import

  When loading from csv file to table I have a field that stores it's date in this format dd-mon-yy

example:
21-Aug-18

 How can I using derived column get in this date format to load to a datetime SQL field?

 yyyy-mm-dd

 what I'm already checking in Derived column:
 (LEN([Column 27]) == 10 ? (DT_DATE)([Column 27]) : NULL(DT_DATE))

Thanks.