You can normally only power a powered rail up to 9 blocks, but you can build your rail up to 16 blocks and have an unpowered comparitor, repeater or observer with the emitting end facing the furthest end of the powered rail, then when you power the starting end it powers the whole line of 16. Placing a block next to that section of track causes a block update and cancels the effect, but you can log out and back in and it seems to reset the powered state to on for the full 16 rails. You can even send a mine cart on it and it doesn’t break.