294 POWER PLANT ENGINEERING
9.10. Troubleshooting and Remedies
Modern gas turbines are usually equipped with a very sophisticated protection system using
microprocessor and computers, which gives a visual and audio alarm when any pre-established safe
condition is violated. In all types of alarm, it is not necessary to shut the gas turbine down. If an alarm
condition is of sufficient duration and magnitude the unit will trip and shut down automatically.
The following are the principal symptoms of gas turbine malfunctions and the most common
causes of these malfunctions:
(a) Drop in compressor discharge pressure and subsequent drop in load:- Dirty intake screens
- Dirty compressor blades
- Loss of compressor blades
- Damaged labyrinth seals
(b) Smoke or dark stack: - Burner nozzle-dirty or worn
Puffs of smoke indicate that carbon is building up around the fuel nozzle and then passing through
the turbine creating rapid wear of blades, vanes and shrouds. - Uneven distribution of fuel to combustion chambers.
- Combustion chambers damaged or out of position.
(c) Spread in turbine discharge temperatures: - Bad thermocouples
- Uneven fuel to burners or dirty nozzles
- Combustion chambers damaged or out of position
- Unlit burners
- Damaged burner nozzles
(d) High wheel space temperatures: - Cooling airlines plugged
- Cooling air heat exchanger dirty, leaking water or loss of cooling water.
- Bad thermocouples
- Wheel space seals worn due to rubs by axial movement or rotor (worn thrust bearing), bowed
shaft or casing out of round to open seal clearances - Cooling air supply not functioning properly.
(e) High turbine exhaust temperatures: - Loss of turbine blades or damaged inlet vanes
- Bad thermocouples
- Exhaust temperature controller out of adjustment
- Increased blade tip clearances due to radial ribs.
- Dirty air compressor.
(f ) High Turbine Exhaust Pressure:
1.Turning vanes in turbine discharge duct damaged or missing. - Discharge silencer damaged.