Combined Measurement Uncertainty on Two Dependent Performance Tests

Abstract

Measurement uncertainty analysis plays an important role in the evaluation process of the net electrical output and the net heat rate during a power plant performance test. Aside from the technical aspect of the test, it bears very significant commercial consequences for the test parties. The ASME Performance Test Codes (PTC19.1) provides elaborative guidelines for test uncertainty analysis. In a combined cycle power plant test, the test uncertainty is heavily influenced by the measuring devices, corrections to reference conditions, and the method by which the test is conducted. A rigorous measurement uncertainty analysis is required to document and minimize the potential gap between the test results and the “actual true” net electrical output and net heat rate of the plant. The purpose of this paper is to estimate the measurement uncertainty of a combined cycle power plant consisting of two power trains. It includes the consideration of correlated uncertainties. Each power train is comprised of a gas turbine, a Heat Recovery Steam Generator (HRSG) and a steam turbine. For the multiple train power plants, some of the measured parameters are not independent and therefore the systematic errors are partially correlated. In this paper, the correlated systematic uncertainties and their contribution to the total uncertainty are evaluated. The uncertainty results are compared with the case when the systematic uncertainties resulting from correlated errors are ignored. Not properly considering the correlated terms may under estimate the uncertainties by over 30%.