What is the primary risk when a turbine hits its critical speed?

• A. Turbine will vibrate violently
• B. Turbine will overheat
• C. Turbine will accelerate uncontrollably
• D. Turbine will stall

Answer: (A)

When the rotor reaches a speed that matches one of its natural frequencies, resonance occurs. At this point, the rotating motion feeds energy into a vibration mode in step with the rotor’s natural oscillation, causing the vibration amplitude to grow rapidly. That excessive vibration places intense stress on bearings, shafts, and mounts, which can lead to fatigue, cracks, or even catastrophic failure. Engineers design to avoid operating at or near these critical speeds or use damping, stiffening, and proper balancing to control the resonance.

Overheating, uncontrolled acceleration, or stall are separate issues tied to cooling, control systems, or airflow, but they aren’t the primary danger specifically associated with hitting the rotor’s critical speed.