If a turbine runs for extended periods at critical speed, what is the likely consequence?

When a turbine operates for extended periods at its critical speed, it experiences excessive vibrations and oscillations. This can lead to a situation where the turbine shaft is subjected to mechanical stresses that exceed its design limits. The critical speed is where the natural frequency of the turbine aligns with the operating frequency, resulting in resonance.

The resonance effect can amplify the vibrations significantly, which may cause physical deformation or failure of the turbine shaft due to fatigue cracking or breakage. In severe cases, this can lead to catastrophic failure, resulting in permanent damage to the shaft and potentially affecting adjacent components of the turbine system. The integrity of the turbine shaft is crucial for safe and efficient operation, and operating at critical speed jeopardizes this integrity.

In contrast, while the heating of the bearings and shortened oil lifespan can result from increased friction and wear due to vibrations, these consequences stem from how well the turbine is maintained and operated, rather than being direct results of operating at critical speed itself. Increased efficiency is not typically associated with critical speed, as it represents a point of instability rather than optimal performance.