Complex sentence: At the same time (or with some delay, for example 2 to 11 seconds, to prevent the diesel engine from starting at every incident), the diesel engine takes over from the flywheel to drive the electrical generator to make the electricity required.
Split into simpler sentences: At the same time (or with some delay to prevent the diesel engine from starting at every incident) the diesel is started up. Depending on the system design, after 2--11 seconds the diesel engine takes over from the flywheel to drive the electrical generator to make the electricity required.