BEF - balanced earth fault. Unit protection for a delta-connected winding
REF - restricted earth fault. Unit protection for a star-connected winding
NEF - Neutral earth fault? Non-unit protection on the neutral-earth connection.
Have you tried using Google? If you search for the full name of the protection schemes instead of the abbreviated ones there is loads of information complete with diagrams which we can't match on a text-only forum.
I have seen NEF used in the UK as a check function on 132kV transformer star points, it will prevent operation of Mesh Corner DAR ( A Unit ) when it operates. I agree with ScottyUK's description of REF and BEF.