“Combined Turbine Equipment Performance” represents the combined performance of the Gas Turbine-Generator(s) and the Steam Turbine-Generator(s), while disregarding or holding the performance of the remaining equipment in the Power Plant at its design levels. The lack of established industry standards and methods addressing the manner in which combined turbine equipment performance should be determined has invited confusion and has created opportunities for technical errors to go undetected. This paper presents a method and the supporting theory by which the corrected performance of the turbine-generators within a combined cycle plant can be combined to gauge their combined performance levels for either contractual compliance or for diagnostic purposes. The Combined Turbine Equipment Performance methodology provided in this paper, allows the performance engineer to easily separate the performance contribution of each turbine generator from the overall plant performance. As such, this information becomes a powerful diagnostic tool in circumstances where a reconciliation of overall plant performance is desired. Individual (gas or steam) turbine performance can be determined by conducting a test in accordance with the respective test code (ASME PTC 22 or PTC 6.2). However, each of these test codes corrects the measured equipment performance to fundamentally different reference conditions. Where the gas turbine-generator measured performance is corrected primarily to ambient reference conditions, the steam turbine-generator measured performance is corrected to steam flows and other steam reference conditions. The simple mathematical addition of the corrected performance of each turbine ignores the well-known fact that the steam turbine-generator output in a combined cycle plant is impacted by the gas turbine exhaust conditions, in particular the gas turbine exhaust flow and temperature. The purpose of this paper is to provide a method for the determination of “Combined Turbine Equipment Performance”, review the supporting theory, highlight the assumptions, and develop useful transfer functions for some commonly used combined cycle plant configurations, and bound the uncertainty associated with the methodology.

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