Silly movie.
The park would have been a spectacular success if they'd hired an actual engineer to design their systems.
"Say, I've got a great idea! Let's put a Tyrannosaur in a cage that stops working if the power goes out!"
"Somebody throw that idiot out the window."
Very large animals are not that spry, despite what animators in our time have shown. An elephant, for example, cannot jump. A simple "pit/moat" type enclosure, with narrow windows in the walls for ground-level observation, would have held a Tyrannosaur quite well with or without power.