What is the primary function of the turbine overspeed trip?

• A. Opens the sentinel valve
• B. Prevents the turbine from exceeding the maximum rated speed
• C. Alerts the operator of excessive turbine RPM
• D. Adjusts steam flow to keep the speed at set point

Answer: (B)

Turbine overspeed protection is about preventing dangerous rotation speeds. When the turbine starts to run too fast, the overspeed trip automatically acts to shut things down, typically by stopping steam input (and often closing the main steam path) so the speed drops back below the limit. This automatic shutdown protects the rotor, bearings, and other components from the excessive centrifugal forces and heat that could cause serious damage or failure.

So the primary function is to prevent the turbine from exceeding the maximum rated speed. It isn’t about alerting the operator or continuously adjusting steam flow to hold a set speed—that’s the governor’s job. The overspeed trip is a safety mechanism that triggers automatic shutdown when speed goes beyond safe limits.