A method of testing an overspeed protection system of a powerplant comprising a gas turbine and a steam turbine, the method comprising: providing a powerplant comprising multiple powerplant machines operationally integrated by a shaft that rotates during operation of the multiple powerplant machines; providing an overspeed protection system configured for detecting an overspeed event associated with the shaft; a control system selecting a methodology (300, 500) for testing the overspeed protection system; wherein the control system performing the methodology (300, 500) determines whether the multiple powerplant machines are operating in a shutdown mode or an operating mode, wherein the methodology comprises a shutdown mode procedure configured for the shutdown mode, and an operating mode procedure configured for the operating mode, and wherein a) the shutdown mode procedure will be selected if the power plant is about to commence and initiate a shutdown process and b) the operating mode procedure will be selected if the gas turbine and the steam turbine are operating at full speed with no load; determining whether the speed of the shaft exceeds a shutdown value representative of the overspeed event, if the multiple powerplant machines are in the shutdown mode; determining whether the speed of the shaft exceeds an overspeed trip value representative of the overspeed event, if the multiple powerplant machines are in the operating mode; changing the overspeed trip value; and determining whether the overspeed protection system would operate to trip the multiple powerplant machines; wherein the method reduces the possibility of a trip occurring during testing of the overspeed protection system. providing a powerplant comprising multiple powerplant machines operationally integrated by a shaft that rotates during operation of the multiple powerplant machines; providing an overspeed protection system configured for detecting an overspeed event associated with the shaft; a control system selecting a methodology (300, 500) for testing the overspeed protection system; wherein the control system performing the methodology (300, 500) determines whether the multiple powerplant machines are operating in a shutdown mode or an operating mode, wherein the methodology comprises a shutdown mode procedure configured for the shutdown mode, and an operating mode procedure configured for the operating mode, and wherein a) the shutdown mode procedure will be selected if the power plant is about to commence and initiate a shutdown process and b) the operating mode procedure will be selected if the gas turbine and the steam turbine are operating at full speed with no load; a) the shutdown mode procedure will be selected if the power plant is about to commence and initiate a shutdown process and b) the operating mode procedure will be selected if the gas turbine and the steam turbine are operating at full speed with no load; determining whether the speed of the shaft exceeds a shutdown value representative of the overspeed event, if the multiple powerplant machines are in the shutdown mode; determining whether the speed of the shaft exceeds an overspeed trip value representative of the overspeed event, if the multiple powerplant machines are in the operating mode; changing the overspeed trip value; and determining whether the overspeed protection system would operate to trip the multiple powerplant machines; wherein the method reduces the possibility of a trip occurring during testing of the overspeed protection system.