Inspection and Maintenance Instructions for 7FA.05 Gas Onl
and Dual Fuel Gas Turbine
GEK 116862
XX. HAZARDOUS GAS DETECTION
A. Infrared (IR) Detectors
The IR detectors have a manual self-test feature to verify proper operation.
For additional information on the IR detectors, refer to the Operation and Maintenance Manual under
the Hazardous Gas Detection System.
XXI. TEMPERATURE CONTROL
A. Exhaust Thermocouples (Control and Over temperature)
Daily reading of the exhaust thermocouples will aid in monitoring the combustion system and in
detecting faulty thermocouples. Changes in the combustion system will be detected easily after a
normal pattern of temperature has been established. Diverging temperatures in the exhaust system
usually indicate deterioration of the combustion chamber, or poor fuel distribution (dirty fuel
nozzles). Below normal thermocouple readings indicate thermocouple deterioration. It is important to
define a “baseline value” of exhaust temperature spread with which to compare future data. This
baseline data is established during steady state operation after each of the following conditions:
1. Initial startup of unit
2. Before and after a planned shutdown
3. Before and after planned maintenance
It is important when reviewing exhaust temperature readings to observe any trend which may indicate
deterioration of the combustion system. Gradual and/or sudden temperature excursions should be
investigated as soon as possible to determine validity of readings. Faulty thermocouples should be
replaced as soon as feasible. Refer to the Control Specification drawings for actual exhaust
temperature control settings and allowable spreads.
B. Wheelspace Thermocouple Temperature Limits
The wheelspace thermocouples, identified together with their nomenclature, are on the Device
Summary. A bad thermocouple may cause a “High Wheelspace Differential Temperature” alarm. The
faulty thermocouple should be replaced at the earliest convenience.
When the average temperature in any wheelspace is higher than the temperature limit, it is an
indication of trouble. High wheelspace temperature may be caused by any of the following faults:
1. Restriction in cooling air lines
2. Wear of turbine seals
3. Excessive distortion of the turbine stator
4. Improper positioning of thermocouple
5. Malfunctioning combustion system
6. Leakage in external piping
© General Electric Company, 2011. GE Proprietary Information. All Rights Reserved.
35
To Next Page