Patent ID: 6901348

Claim:
A method for measuring expansion efficiency of a turbine within a combined cycle power plant, said method comprising: operating the power plant at a first load, wherein a gas turbine is operated with a first fuel flow and a first gas turbine inlet air flow, and wherein a steam turbine within the combined cycle power plant includes at least a first turbine exhausting superheated steam and a second turbine exhausting two phase steam; determining a first shaft output at the first load with steam supplied from a heat recovery steam generator (HRSG) to both the first steam turbine inlet and the second steam turbine inlet; maintaining the first gas turbine fuel flow, the first gas turbine inlet air flow, and the first steam turbine inlet steam flow while isolating the steam supplied to the second steam turbine; determining a second shaft output while the second steam turbine is isolated from the steam admission flow; and determining an expansion efficiency of the second steam turbine based on the first shaft output and the second shaft output and a measured change in the second steam turbine admission steam flow.