Understanding and Mitigating Transient Vibration Spikes in Steam Turbine Generators

Transient vibration spikes in steam turbine generators, particularly in a single turbine bearing, can disrupt system performance and raise safety concerns. These spikes can lead to subsequent vibration dips in downstream bearings, necessitating a comprehensive analysis to identify and mitigate the underlying causes.

Causes of Transient Vibration Spikes and Dips

Several factors can contribute to the occurrence of these vibrations and the subsequent dips. Understanding these causes is crucial for effective maintenance and operation of steam turbines.

1. Imbalance in Rotating Mass

An imbalance in the rotor or attached components can cause vibrations to propagate throughout the system. These vibrations can affect the operational stability of downstream bearings, leading to transient spikes and subsequent dips in vibration levels.

2. Bearing Wear or Damage

Wear, contamination, or damage in a single bearing can lead to uneven contact and increased vibration. The subsequent bearings may show lower vibrations as they are no longer subjected to the same level of activity or energy absorption from the damaged bearing.

3. Resonance

When the natural frequency of the turbine system aligns with the operating frequency, resonance can occur, leading to transient spikes in vibration. This can cause a momentary increase in vibrations in the affected bearing while affecting downstream bearings differently.

4. Fluid Dynamics

Changes in steam flow or pressure can create transient forces on turbine blades, leading to vibrations. A sudden change in load on the 1 bearing due to these forces can cause spikes that impact downstream components, leading to a dip in vibrations in subsequent bearings.

5. Misalignment

Misalignment of the turbine or generator can cause increased vibrations at specific bearings. A misaligned 1 bearing can generate higher vibration levels, while subsequent bearings may experience a dip in vibrations as they are not subjected to the same loading conditions.

6. Operational Transients

Operational changes such as load changes, start-stop cycles, or system disturbances can lead to transient vibrations. These events can manifest as spikes in one bearing while affecting others differently. A detailed analysis of such operational transients can help identify the root cause of the vibrations.

7. Damping Characteristics

The damping characteristics of bearings and the structure can influence the transmission of vibrations. A less effective damping in the 1 bearing may show spikes, while subsequent bearings might exhibit reduced vibrations due to better absorption of energy.

Recommendations for Analysis

Systematically investigating the following areas can help identify the root cause of transient vibration spikes and implement corrective actions to mitigate their occurrence:

Vibration Analysis

Conduct a detailed vibration analysis to pinpoint the frequency and amplitude of the spikes. This can help in identifying the source of the issue.

Thermal Imaging

Use thermal imaging to check for hotspots in the bearings, which may indicate friction or failure.

Lubrication Check

Ensure that lubrication systems are functioning properly and that there is no contamination in the lubricant.

Inspection

Perform a physical inspection of the 1 bearing and associated components to check for wear, misalignment, or damage.

Operational Review

Review operational data to correlate spikes with specific operational events or conditions.

By following these recommendations, you can systematically investigate and address the root causes of transient vibrations, ensuring the safe and efficient operation of your steam turbine generators.