Gas Turbine Trips: Common Causes and How Plants Reduce Them

Why turbines trip

The protection system monitors speed, temperatures, pressures, vibration, flame and many other signals. When a value crosses a trip limit, the system shuts off fuel and brings the unit down safely. Some faults cause an alarm first, giving operators time to act; others trip immediately because the risk of damage is too high.

Trips can come from genuine equipment problems, from faulty instruments that report false values or from external events such as grid faults. Separating these causes is the first step in reducing trips.

Combustion problems and flame-out

If the flame becomes unstable or goes out, flame detectors signal a loss of flame and the unit trips to prevent unburnt fuel from accumulating. Causes include fuel supply disturbances, incorrect combustion tuning, worn fuel nozzles and, in low emissions combustors, operation close to lean limits.

Regular combustion tuning and inspections keep the flame stable. Our article on gas turbine combustion explains how combustors work and why tuning matters.

Vibration

High vibration on bearings or the casing indicates imbalance, misalignment, rubbing, bearing wear or loose components. Vibration trips protect the rotor from serious damage. Sudden changes in vibration deserve immediate investigation, while slow trends can be planned into maintenance.

Faulty vibration probes or wiring can also cause false trips. Checking the instrument chain before assuming a mechanical problem saves time and avoids unnecessary inspections.

Exhaust temperature spread

Thermocouples around the exhaust measure temperature at many points. A large difference between them, called spread, may indicate a failed combustor, blocked fuel nozzle or damaged hot section part. High spread can trigger an alarm or a trip.

Failed thermocouples produce false spread readings, so maintaining the thermocouple set is part of avoiding unnecessary trips. Trends in spread over time are a valuable early warning of hot section problems.

Lube oil and bearings

Low lube oil pressure, high bearing temperature or high oil temperature trip the unit to protect the bearings. Causes include pump failure, blocked filters, cooler problems, oil contamination and low oil level.

Routine oil analysis, filter changes and checks on pumps and coolers prevent most of these trips. Backup pumps should be tested regularly so they start when needed.

Fuel gas pressure and quality

Turbines need fuel gas within a defined pressure range and with stable composition. Pressure drops caused by pipeline events, compressor trips or regulator faults can cause flame-out or trip the unit on low pressure. Liquids or contaminants in the gas damage nozzles and destabilise combustion.

Good fuel gas conditioning, filtration and pressure control, plus coordination with the gas supplier, reduce fuel-related trips. Units with backup liquid fuel can transfer if gas supply fails, provided the transfer system is maintained and tested.

Overspeed and governor problems

Overspeed protection trips the unit if the shaft speed rises too high, for example after a sudden loss of load. Governor and fuel valve problems can cause speed to swing or rise. Overspeed trips must never be bypassed and should be tested as the manufacturer requires.

Load rejection events on island systems are a common cause. Correct governor tuning and load shedding schemes help the unit ride through them.

Instrumentation and controls

Many trips come from instruments and controls rather than the turbine itself: failed sensors, loose wiring, power supply faults or software problems. Ageing control systems with obsolete parts are particularly prone to this kind of trip.

Redundant sensors with voting logic reduce false trips. Our article on controls upgrades and obsolescence discusses when replacing a control system is worthwhile.

Generator and grid events

Generator protection trips the unit for faults such as loss of excitation, reverse power or internal electrical faults. Grid disturbances such as voltage dips and frequency excursions can also trip turbines if protection settings are too tight.

Coordinated protection settings and grid code studies help units stay on line during disturbances while still protecting equipment.

Trips on new units during early operation

New turbines often show a cluster of trips in their first months. Many come from commissioning issues such as loose terminations, sensor calibration, control logic settings or fuel system debris rather than design faults. A structured early-operation review, with the supplier involved, closes these issues quickly. Keep the commissioning team engaged until trip rates settle, and record each fix so the lesson carries to the next unit.

Investigating trips and reducing them

Every trip should be investigated: record the first-out alarm, gather trend data, identify the root cause and take corrective action. A trip log that records causes over time shows patterns and helps target improvements.

Regular inspections at the intervals recommended by the manufacturer catch many problems before they cause trips. Our article on gas turbine inspection intervals explains how those inspections are scheduled.