The engine overspeed systems are part of the design of all turbine engines so that any runaway is stopped before the engine speeds up so much that it comes apart. In older engine designs, the protection system was mechanical, in newer aircraft (virtually all by now) it is electronic, and predicts the failure state by using both trhe actual N2 speed and the rate of increase of the N2 speed. Thus it triggers at lower N2 if the turbine is accelerating.