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.

Abstract: An electrohydraulic system for rapidly reducing the steam flow through the high pressure and lower pressure stages of a turbine power plant in response to a partial loss of electrical load, is disclosed. In response to the detection of a partial loss of load, the system provides for controlling a portion of the governor valves and all of the interceptor valves to close rapidly and independently of the turbine control system; also to operate the turbine control system to cause the remaining governor valves to operate to a predetermined partially closed condition independent of the normal governor valve reference demand signal by applying a signal for changing the open limit position of the governor valves; and to eliminate the affect of the impulse pressure loop from the turbine control system. The upper valve position limit signal and the slower rate of change reference demand signal is matched to the applied signal.