The table mapping an ability score to a modifier covers Ability Scores from 1 to 30.
A previous question established that it is indeed possible to attain an Ability Score of 1 due to effects lowering a character score below its nominal value.
This question wishes to explore the other end of the spectrum:
Is it possible for a character to attain a Strength Score of 30?
Another question established that 30 is the absolute cap: there is no way to go over 30. It is mentioned that monsters and gods could have an Ability Score of 30, but not that a character could.