During normal operation, how should operators respond if vibration rapidly increases indicating critical speed?

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

Answer: (A)

When a rotor reaches its critical speed, the natural frequency of the turbine’s rotating parts lines up with the operating speed. That alignment causes resonance, where even small inputs build up into very large oscillations. The defining result is a rapid, violent vibration of the turbine as energy is pumped into the structure at that resonance. That is why the observable outcome described is the turbine vibrating violently. Overheating, stalling, or accelerating uncontrollably come from different failure modes and aren’t the immediate symptom of crossing the critical speed. If vibration spikes, it signals resonance and the need to take protective action to move away from that speed and assess for damage.