Overspeed protection controller employing interceptor valve speed control

Abstract

An overspeed protection controller (OPC) which is incorporated as part of a turbine speed/load control system for the purposes of controlling the monitored speed of a steam turbine at a first predetermined speed valve subsequent to an OPC activation is disclosed. The governor and interceptor valves of the steam turbine are positioned controlled by a set of electrohydraulically operated valve position servo systems. The OPC provides for rapid hydraulic closure of each valve when activated by either a detection of an interruption of generated electrical power flow to a power system load when the generated electrical power is greater than a predetermined value or the detection of the monitored turbine speed being greater than a second predetermined speed value. The rapid closure of the valves results in an interruption of steam flow to the high and lower pressure turbine sections of the turbine system which causes steam energy to be trapped in the reheater which is disposed between the turbine sections. The OPC is deactivated subsequent a predetermined time interval after the detection of generated power interruption when the monitored turbine speed is no longer greater than the second predetermined speed value. In response to the deactivation, the OPC controls the rotating speed of the turbine by positioning the interceptor valves to admit steam from the reheater to the lower pressure turbine sections in accordance with a continuous function based on the difference between the monitored turbine speed and the first predetermined speed value. Thus, the trapped steam energy in the reheater is utilized for keeping the turbine at the first predetermined speed value to permit rapid resynchronization of the turbine system with the power system load.