Evaluation of gas path analysis methods for gas turbine diagnosis

In the present paper, limitations concerning three implementations of gas path analysis (GPA) methods are investigated and their diagnostic effectiveness is evaluated. The methods were tested for different sets of faults on a twin shaft gas turbine with an instrumentation set typical of today's engines. Test results revealed that classical GPA is not sufficient. Correct diagnosis is provided only when one already knows a subset of components containing the fault; otherwise, the fault may be attributed to other component (s). The effectiveness of a second method that implements Multi Operating Point Analysis (MOPA) is related with the assumption of non varying health parameters with deviations along with the operating point. Cases of wrong diagnosis were detected when the above assumption was violated. Improvement on the diagnostic effectiveness of the MOPA method has been verified through careful selection of the parameters defining the operating point. Further improvement on diagnostic ability was achieved when a third, recently proposed method was applied. The method uses information produced from existing sensors when artificial operating points are defined close to the initial operating point. It was found that the third method can detect and correctly identify faults even in cases where the multipoint method fails.