Electrohydraulic emergency trip system and method for a turbine power

Abstract

An electrohydraulic emergency trip system which automatically shuts off the steam supply to a turbine power plant upon the detection of specific operational contingencies is disclosed. The hydraulic portion of the system includes two pair of combined electrical and hydraulically operated pilot trip valves that are so arranged that the opening of any one valve of each pair decreases the hydraulic trip pressure to close rapidly the steam inlet valves to the turbine; that an open or closed failure of a single trip valve does not prevent a valid trip or cause an unwarranted trip; and finally that an open failure of one pair of the valves does not result in an unwarranted trip. Each pair of valves is electrically operated from an independent voltage source such that the electrical failure of one source does not cause or prevent an unwarranted turbine trip. The pilot portion of the hydraulic system is so arranged that the electrical operation of either pilot valve portion of each pair operates hydraulically the other pilot portion of that pair. The hydraulic portion of the system is also constructed to be responsive to the operation of the conventional mechanical overspeed mechanism. In one embodiment such mechanism operates from the same fluid pressure source to operate the two pair of valves hydraulically. In another embodiment, a second fluid source is used to operate the conventional diaphragm overspeed trip valves of the overspeed mechanism and in turn the diaphragm valve hydraulically operates the two pair of trip valves. In a modification of this embodiment, the diaphragm valves decreases the trip pressure to close the steam inlet valves without the necessity of operating the trip valves.