What are common causes of abnormal vibration in a running turbine?

• A. Normal operation
• B. Excess lubrication
• C. High ambient humidity
• D. Imbalance

Answer: (D)

Imbalance in the rotor is the main reason a turbine shows abnormal vibration while running. When the rotor spins, any uneven mass distribution creates centrifugal forces that pull toward one side more than the other. This produces a rhythmic vibration that increases with speed and appears at the rotation frequency (and sometimes at harmonics). Even small discrepancies from perfect balance—caused by manufacturing tolerances, blade damage, loose components, or mismatched balancing weights—can generate noticeable vibration during operation. Normal operation typically keeps vibration at a low, acceptable level, so what you’re feeling is outside that range. Excess lubrication or high ambient humidity aren’t typical root causes of rotor imbalance in a running turbine and don’t create the recurring, rotating-force pattern that balance issues do. To address it, technicians perform dynamic balancing at operating speed and inspect for damage or looseness that would alter the mass distribution.