Monitoring and diagnostics | Turbine technology
Figure 3. Compass trend plots from the second startup (27 May 2024) following LP turbine blade inspection. On the left, BP vibrations (also visible in the DCS (as shown in right hand side of Figure 4), reveal high vibration levels in the HP and IP turbine sections. On the right, 1x velocity vibration magnitudes from the HP, IP, and LP turbine bearing pedestal accelerometers (not available in the DCS) are displayed, with the data in an alarm state
Displacement sensors and accelerometers
The AVEVA PI system serves as the company- wide data historian, storing process and vibration data locally at Huntly and on a mirrored corporate PI server.
Genesis Energy employs PI ProcessBook and PI Vision for data analysis, using these tools to detect anomalies that warrant further investigation.
Vibration data from monitoring systems is integrated into the distributed control system (DCS) and stored in the PI system, except for data from the SETPOINT VC-8000 system on unit 1, which is directly logged into the PI system. This case study highlights how advanced monitoring and diagnostics systems enabled Genesis Energy to resolve a significant operational challenge efficiently. The case study presented here focuses on unit 2, though all four turbo-generator units at the power station share identical configurations. Each unit comprises a high-, intermediate-, and low-pressure steam turbine section (HP, IP, and LP) (see Figure 2). The turbine rotors are rigid, meaning they operate below the first critical speed (rotor resonance). While the units have functioned reliably over the years, occasional issues have arisen related to the natural frequency of the flexible steel foundations near the generator turbine shaft running speed.
Monitoring strategy
Figure 2 outlines the sensor installation points and measurements for the turbo-generator units (excluding overspeed measurements). Tables 1 and 2 summarise deployment of displacement sensors and accelerometers for the steam turbine and generator components. Due to the flexibility of the bearing pedestals caused by the steel support structure foundation, special precautions are in place for condition monitoring.
During runup (29–2850 RPM), BP (bearing pedestal) vibration alarms are set to 50 mm/s, with 1X and 2X velocity vibration alarms profiled for runup values to prevent unnecessary alerts from natural frequency resonances. If a 1X or 2X velocity vibration alert occurs during runup, it triggers a speed hold or runback within the critical speed range, while a danger alarm will trip the unit.
For speeds above 2850 RPM, bearing pedestal accelerometer-based protection is configured for BP vibration only.
Monitoring system
In 2011, the Compass Classic monitoring systems on Units 2 and 4 were upgraded to the Compass 6000/VC-6000 system (Figure 1). Unit 1 was upgraded in 2021 to the SETPOINT system, which can automatically store data in the PI system, including vibration time waveform data.
These monitoring systems offer protection and condition monitoring for the steam turbine, generator, exciter, bearing vibration, and thrust position of the main boiler feed pumps driven by a steam turbine on each unit.
Tables 1 and 2 show that some vibration data — such as BP vibration, eccentricity, differential expansion, casing expansion, and axial position — is exported to the DCS for display and trending. Units will trip if specific danger alarm thresholds are exceeded:
Differential expansion or axial position breach.
During run-up, 1X or 2X velocity vibration danger alarms trigger shutdowns. Above 2850 RPM, a BP vibration danger alarm along with another BP bearing vibration in alert status will trip the unit (voting logic in the DCS).
Below 600 RPM, an eccentricity danger alarm will trip the unit.
Other vibration measurements are accessed via the Compass system for condition monitoring and diagnostics and include plots for velocity vibration, displacement waveforms, orbit, spectra, waterfall, Bode/polar, average shaft centreline, and amplitude or phase changes over time.
Shut down due to vibrations On 16 May 2024, unit 2 was returned to service following an LP turbine blade inspection
Figure 4. Compass trend plot on the left showing 1X radial displacement magnitude of the turbine bearings from the first and second startup. The DCS plot (right) shows the bearing pedestal vibration and turbine shaft eccentricity during the same startups
www.modernpowersystems.com | July/August 2025 | 17
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