Turbine technology | Monitoring and diagnostics
Data resolution reduces over time, although eccentricity data serves as a backup to mitigate this. Updates: – System uses eccentricity as a redundancy for 1X displacement data in case of resolution loss.
Monitoring enhancements required Blade cracking is minimally monitored due to shrouded HP and IP blades.
Full NDT inspections, including shroud and tenon crack testing, are now standard for HP and IP rotors in prolonged operation. SETPOINT system upgrades for unit 2: – event-based waveform storage replaces time-based intervals;
Figure 7. Unit 3 IP turbine section being moved to replace the unit 2 IP section
Three missing blade packages on the rotor and extensive rubbing wear across multiple stages. A 90° arc of missing blades in the second-row top stationary blades.
Metal debris and severe damage to stationary blades in the casing bottom half, with blade fragments measuring no larger than 5 mm. Immediate repair of the IP turbine was not feasible due to the necessity for extensive re- blading of both the rotor and stationary blade diaphragms. With no spare blades available and the original manufacturer no longer in business, the only viable solution was to replace the faulty unit 2 IP turbine with unit 3’s IP section (Figure 7), which had fewer operating hours. To expedite the process, the replacement was conducted without opening the IP section for inspection or removing the unit 2 HP turbine section lid.
Repair and lessons learned The replacement of the defective unit 2 IP turbine section with the unit 3 spare IP section was followed by immediate testing (Figure 8). The unit was returned to service within demanding time constraints and with limited repair options. Below are listed key lessons learned and improvements implemented:
Need for improved data visibility in the control room
Operators lacked sufficient vibration data to assess if a manual shutdown was necessary. Quick actions by the Operator and Predictive Maintenance Engineer prevented further damage. Key issues: – 1X velocity and displacement data were not visible in the DCS.
– BP velocity data was available but not in alarm mode.
– Eccentricity data, effective in condition detection, was unavailable after 600 RPM. Updates: – Eccentricity now displays continuously on DCS trends across all units.
– 1X and 2X alarms will trigger unit 2 shutdown using SETPOINT’s state monitoring once installed.
Need to enhance diagnostic processes IP turbine blade failures affected HP section vibration, necessitating multiple measurements for accurate diagnostics. Eccentricity and 1X displacement proved most reliable for detecting and localising blade damage.
Diagnostic challenges: – 1X velocity readings were misleading as opposing broken blade packages cancelled imbalance effects. Updates: – Eccentricity monitoring is enabled at all speeds across all units for enhanced diagnostics.
Need to address monitoring system limitations
Compass system stores time waveform and spectral data at fixed intervals, potentially missing significant events.
– data integration with the PI system; – state-based monitoring with acceptance regions and alarms;
– full-spectrum analysis for rub diagnostics; – programmable relay voting and detailed event logging.
The improvements listed above aim to optimise monitoring, diagnostics, and preventive measures for enhanced turbine performance and reliability.
Managing ageing equipment: the critical factor
Unit 2 has been operating smoothly since the repair, and this is expected to continue with the implemented changes.
While this case study demonstrates a quick and successful resolution, many thermal power stations with ageing turbo-generating units face similar risks, often leading to extended downtime in the absence of spare parts.
Maintenance requirements vary by plant, but one critical factor remains universal: effective machine protection, condition monitoring, and diagnostic tools are essential for managing ageing equipment.
Figure 8. DCS plot during runup showing HP and IP turbine section BP vibration and eccentricity after replacing the defective IP section. The IP shaft eccentricity, 31.396 μm, is much lower than before (56.60 μm). The BP vibration (0.069 to 1.113 mm/s) is also much lower than before (5.604 to 6.540 mm/s)
20 | July/August 2025|
www.modernpowersystems.com
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