GAS TURBINE PERFORMANCE TESTS BASIC INFORMATION AND TUTORIALS

How to conduct gas turbine performance tests.

The performance analysis of the new generation of gas turbines is complex and presents new problems, which have to be addressed. Performance acceptance tests, which are required to be conducted for contractual guarantees, require that the turbine be cleaned before the test.

The average commissioning time for the advanced gas turbine (G Type) units is longer than the F and FA Type units. This is usually due to the increased number of starts and trips during commissioning, due to a lot of fine tuning required for the DLN combustors, cooling systems, and complicated control systems, which increase the number of equivalent engine hours.

It is recommended that contractually the maximum number of equivalent engine hours be limited to about 600-800 hours regardless of the actual equivalent operating hours.

If this is not done then the power output will be corrected to a larger corrected output, reducing the actual power the plant will produce. There have been many cases of 2000 to 6500 equivalent operating hours recorded during commissioning, which in many cases amount to the power and heat rate being corrected by 2 to 5%. This affects the profitability of the plant.

The new units operate at very high turbine firing temperatures. Thus, variation in this firing temperature significantly affects the performance and life of the components in the hot section of the turbine.

The compressor pressure ratio is high which leads to a very narrow operation margin, thus making the turbine very susceptible to compressor fouling. The turbines are also very sensitive to back pressure exerted on them when used in combined cycle or cogeneration duty. The pressure drop through the air filter also results in major deterioration of the performance of the turbine.

If a life cycle analysis were conducted the new costs of a plant are about 7-10% of the life cycle costs. Maintenance costs are approximately 15-20% of the life cycle costs. Operating costs, which essentially consist of energy costs, make up the remainder, between 70-80% of the life cycle costs, of any major power plant.

Thus, performance evaluation of the turbine is one of the most important parameters in the operation of a plant. Total performance monitoring on- or off-line is important for the plant engineers to achieve their goals of:

1. Maintaining high availability of their machinery.
2. Minimizing degradation and maintaining operation near design efficiencies.
3. Diagnosing problems, and avoiding operating in regions, which could lead to serious malfunctions.
4. Extending time between inspections and overhauls.
5. Reducing life cycle costs.

To determine the deterioration in component performance and efficiency, the values must be corrected to a reference plane. These corrected measurements will be referenced to different reference planes depending upon the point, which is being investigated.

Corrected values can further be adjusted to a transposed design value to properly evaluate the deterioration of any given component. Transposed data points are very dependent on the characteristics of the component's performance curves.

To determine the characteristics of these curves, raw data points must be corrected and then plotted against representative nondimensional parameters. It is for this reason that we must evaluate the turbine train while its characteristics have not been altered due to component deterioration. If component data were available from the manufacturer, the task would be greatly reduced.