To all interested

I found a simpler solution, not knowing how prefixsegments really work, but mainly understand
from this example, is

\setupformulas[prefixsegments=chapter:section]

instead of using

\setupformulas[prefixsegments=1:100]

Both setups gives the same numbering scheme of the formula numbers.
Both setups also don't reset the formula number after a new section, it just
keeps numbering the formulas

I know I saw a code snippet which does some sort of reset, I think prefixreset or reset, but
I cannot find it anymore.