Patent EA-003111-B1 (EA)
Title: Apparatus for an electrohydraulic control system of a steam turbine
Inventor: SHAPIRO VADIM
IPC: F01D21/18
Filed: 2000-02-15
Abstract: 1. An apparatus for providing a trip response to a pilot valve, the apparatus comprising: the piston valve and a piston connected to an actuator stem and pressing on the pilot valve, wherein a surface area of the piston having an applied pressure; a first surface area of the pilot valve having an applied pressure and providing a force in an opposing direction to that of the pressure applied to the surface area of the piston; and means for relieving the pressure applied to the first surface area of the pilot valve to cause the trip response. 2. The apparatus of claim 1, wherein the actuator to which the piston is connected is an electromechanical actuator. 3. The apparatus of claim 1, wherein the pilot valve has a second surface area having an applied pressure resulting in a force in the same direction as that of the pressure applied to the first surface area of said piston. 4. The apparatus of claim 3, wherein the pressure applied to the second surface area of the plot valve is from a different source than the pressure applied to the first surface area of the pilot valve. 5. The apparatus of claim 3, wherein the resultant of all forces is zero in steady state, due to pressures applied to the surface areas. 6. The apparatus of claim 1, wherein relieving the pressures applied to the surface area of the piston and to the first surface area of the pilot valve results in zero force being applied to the actuator stem. 7. The apparatus of claim 3, wherein relieving the pressures applied to the surface area of the piston and to the first surface area of the pilot valve results in the pilot valve being moved in the direction of the force attributed to pressure on the second surface area of the pilot valve. 8. The apparatus of claim 1, further comprising a trip system, wherein the means for relieving the pressure applied to the first surface area of the pilot valve comprises: not less than three solenoid drain valves, each of said solenoid drain valves is equipped with a two-coil set; and not less than three overspeed trip-device discrete outputs, each connected to two coils and each coil located on a different drain valve. 9. The apparatus as in claim 1, 4, or 8, wherein the pressure applied to the first surface area of the pilot valve is from the same source as the pressure applied to the surface area of said piston. 10. A method for providing a trip response to a pilot-valve assembly comprising the actuator, a pilot valve, wherein a first net force is applied to the pilot valve, the first net force tending to press the pilot valve toward the actuator, thereby assuring simultaneous movement between the actuator and the pilot valve until the trip response is initiated. 11. The method of claim 10, wherein a second net force is applied to the differential-force element, resulting in a negligible net force on the actuator in steady state. 12. The method of claim 11, wherein upon trip, the second net force is significantly reduced. 13. The method of claim 11, wherein upon trip, a direction of the first net force is reversed such that the pilot valve is forced away from the actuator. 14. The method of claim 12, wherein significantly reducing the second net force results in a negligible force applied to the actuator. 15. An apparatus for providing a trip response to a pilot-valve assembly comprising the actuator, a pilot valve, and means to apply a first net force to the pilot valve, the first net force tending to press the pilot valve toward the actuator, thereby assuring simultaneous movement between the actuator and the pilot valve until the trip response is initiated. 16. The apparatus of claim 15 including a means to apply a second net force to the differential-force element, resulting in a negligible net force on the actuator in steady state. 17. The apparatus of claim 16 including means to cause the second net force to be significantly reduced. 18. The apparatus of claim 17 including means to reverse a direction of the first net force such that the pilot valve is forced away from the actuator. 19. The apparatus of claim 17, wherein significantly reducing the second net force results in a negligible force applied to the actuator. 20. The apparatus of claim 15, wherein the actuator is an electromechanical actuator. 21. The apparatus of claim 18, also comprising a trip system, wherein the means for reversing the direction of the first net force comprises: (a) not less than three solenoid drain valves, each equipped with a two-coil set; and (b) not less than three overspeed trip-device discrete outputs, each connected to two coils and each coil located on a different drain valve.