What is overspeed protection and how does it operate?

• A. It monitors exhaust temperature and adjusts fuel accordingly.
• B. A safety system that detects RPM exceeding maximum and reduces or cuts fuel or trips the engine to prevent damage.
• C. It provides constant RPM irrespective of load.
• D. It increases fuel to maintain RPM when the engine overspeeds.

Answer: (B)

Overspeed protection is a safety function that watches the turbine’s rotor speed and prevents it from exceeding the maximum safe speed. It uses sensors to monitor RPM, and when the speed reaches or surpasses the preset limit, it acts quickly to protect the machine. The typical action is to reduce or cut fuel flow, or to trip the engine so it shuts down, bringing the speed back down before the rotating parts suffer damage. This protection is essential because overspeed can cause blade and bearing damage, rotor instability, and other catastrophic failures.

It’s different from temperature control or a normal speed governor. Temperature protection handles high exhaust gas temperatures, not speed itself, and a governor tries to hold a target RPM under normal loading. Overspeed protection serves as a backup safety mechanism that intervenes when control systems fail or abnormal conditions push speed beyond safe limits. It does not work by increasing fuel; that would drive the speed higher and worsen the risk.