In the process of load rejection test for one 600 MW steam turbine unit

a repeated fluctuation phenomenon of open degree for reheated steam control valve and appeared in the fast closing process

leading to actuation of the overspeed protection for the steam turbine.Through analysis of the test results and of the fast closing process for reheated steam control valve

and combining with the fast closing test of said valve under dynamic state

it is believed that the fundamental cause resulting in abnormal fast closing process of the reheated steam control valve is the sudden drop of pressure in the pressure-equializing chamber.The disposal measure of drilling holes on the sleeve of said control valve has been adopted

test result after retrofitting shows that the said measure is simple and convenient

boasting good effectiveness.