INDUSTRIAL WASTE-TO-ENERGY FACILITY (GEARBOX INSTABILITY DURING STARTUP)
- Customer: Global leader in waste management
- Location: France
- Turbine Make & Model: Thermodyne
- Rated Power: 10,000 rpm, 9.4 MW
- Driven Equipment: High-speed gearbox with alternator
- Operating Duty Cycle: Continuous operation
Problem Statement
The customer reported repeated turbine trips during startup around 2,000–3,000 rpm. Each attempt required multiple restarts before the turbine could be synchronised and taken on load.
Key points:
- The gearbox vibration sensor triggered the trips.
- The turbine itself showed no abnormal behaviour.
- Alignment had already been checked and confirmed correct.
- Despite correct alignment, the V-Box system detected significant dynamic misalignment, indicating mechanical stress on the coupling.
This recurring issue caused operational delays, uncertainty during startup, and risks to critical rotating components.
POC Objective
Since VIB360 had been installed 24 months earlier for continuous monitoring, the objective of this focused diagnostic was to:
- Determine the root cause of repeated startup trips.
- Validate whether the issue was turbine-related or originated elsewhere in the drivetrain.
- Provide a corrective recommendation to ensure reliable startup behaviour.
Measurement Setup
- Technology: WIB360 / V-Box torsional vibration monitoring
- Sensor Used: Existing turbine speed sensor
- Parameters Monitored: Torsional vibration signature, dynamic misalignment, coupling behaviour
- Operating Load at Observation: ~8 MW (during normal operation)
Key Findings
The torsional vibration analysis identified:
- High dynamic misalignment during startup, despite correct mechanical alignment.
- Misalignment-induced stress on the coupling, particularly noticeable during low-load transients.
- No abnormalities in the turbine itself—its torsional signature remained healthy.
- The behaviour pointed to instability within the high-speed gearbox bearings at low loads, causing fluctuating shaft support and triggering the gearbox vibration protection system.
This matched the repeated trip events at 2,000–3,000 rpm.
Recommended Actions
- Replace the high-speed gearbox cylindrical bearings.
- Renew the coupling to ensure proper torque transmission and alignment stability.
Action Taken by Customer
- High-speed gearbox bearings were replaced.
- Coupling was renewed.
- Additional minor maintenance activities were carried out.
- After intervention:
- No more startup trips occurred.
- All subsequent startups were smooth and efficient.
- The V-Box system has shown no further anomalies.
Benefits & Outcome
- Elimination of repeated turbine trips, improving operational reliability.
- Reduction in startup time, allowing quicker synchronisation to the grid or process.
- Restored confidence in the mechanical integrity of the turbine–gearbox train.
- Early diagnosis prevented progressive damage to coupling, gearbox bearings, and turbine shaftline.
- Avoided unnecessary turbine inspections, saving downtime and maintenance resources.
- The Vib360 system demonstrated its ability to detect faults that traditional alignment or vibration methods did not identify.
Potential Financial Impact
Estimated financial benefits include:
Avoided Direct Costs
- Avoided gearbox failure: A high-speed gearbox failure can cost €150,000–€300,000 including overhaul, parts, and labour.
- Avoided coupling damage: Replacing a coupling damaged by prolonged misalignment can cost €20,000–€50,000.
- Avoided turbine inspection downtime: Unplanned inspections may cost €10,000–€30,000 in labour and service contractor time.
Reduced Downtime
- Each failed startup can delay production by 1–3 hours.
- Conservatively, if 10–15 restarts were avoided per year, this represents:
€50,000–€150,000 in avoided lost production, depending on energy selling price or internal process value.
Total Potential Savings
A realistic aggregate range:
€200,000 – €500,000
saved through:
- Prevented mechanical failures
- Reduced downtime
- Faster startup and grid synchronisation
- Optimised maintenance decisions