Complete predictive maintenance monitoring of gas turbines requires trends of compressor, gas generator and power turbine performance to optimize run times between maintenance cycles.
The end users of ‘best of the best’ turbines optimize their gas turbine performance monitoring methodology to extend their run times significantly beyond vendor’s recommendations (by as much as 60,000 hours). This requires review of vendor’s performance monitoring capabilities during the bid stage of the project and complete performance monitoring capabilities.
Failure to trend compressor, gas generator and power turbine performance results in the practice of completely following vendor maintenance cycles without the benefit of extending these cycle times by the use of effective predictive maintenance techniques. Vendors now provide diagnostic services that will evaluate turbine condition and recommend when maintenance is to be performed.
This best practice has been used since the 1990s, in which trending of air compressor performance and engine efficiency is highly recommended, when not provided by the vendor. It has to be noted that compressor discharge pressure and temperature must be available for air compressor performance trending.
Calculation of gas turbine efficiency
FAI has developed and used Excel spreadsheets that receive, calculate and trend gas turbine performance (air compressor, gas generator turbine and power turbine) as well as mechanical and support system condition.
Calculation of gas turbine efficiency requires the calculation of the driven equipment power. This calculation can be inaccurate, due to the many variables involved in determining the driven equipment power. Requiring a torquemeter during the project phase will ensure accurate gas turbine efficiency calculations.
Torquemeters can be installed in existing trains but will require:
- Rotor response study
- Torsional study
- Coupling and coupling guard modifications
Gas turbine efficiency calculations will be erroneous and inconclusive in determining maintenance cycles when torquemeters are not installed. Therefore, the installation of torquemeters has been recommended as part of project specifications since 1995. This action has resulted in the accurate determination of critical (un-spared) gas turbine maintenance cycles and significant extension of these cycles.