Compressor Controls Corporation

Dmitry Drob

Mykhailo Volynskyi

Naum Staroselsky

Vadim Shapiro

Boris Zilberman

A method and apparatus for turbine overspeed protection, useful for steam and gas turbines, is disclosed. The apparatus comprises a spring-loaded rod held by a plurality of energized solenoids in an operating position any time the turbine's shaft rotational speed is less than a trip rotational speed set-point. When the rotational speed reaches the trip rotational speed set-point, both solenoids are de-energized and the spring-loaded rod moves to provide turbine trip. Increased reliability of the solenoids is provided by compressing the spring during the resetting of the rod with an additional electromechanical actuator and by using a plurality of solenoids, each of which is able to provide the force required to hold the spring in its compressed state.

Turbine overspeed protection

Steam turbine speed-control systems often incorporate pilot valves for the purpose of controlling the position of hydraulic actuators for steam valves. However, the operational efficiency of these pilot valves can suffer from imperfections due to manufacturing defects, wear, and the like, thereby impairing the control system's overall performance. For these reasons, this disclosure relates to a method for overcoming a faulty pilot valve by incorporating a control system (including additional controllers) dedicated to the pilot valve. In this type setup, not only can the position of the pilot valve be a control variable, but the velocity of actuation of this valve can also be used as another control variable. Therefore, the results of separate controllers, using these two control variables, can be combined to improve the dynamic response of the steam turbine speed-control system.

Method and apparatus for steam turbine speed control

Pilot valves used in electrohydraulic control systems are driven by either an electromagnetic electromechanical actuator or an electromotor electromechanical actuator. A drawback of electromagnetic actuation is that on brief interruptions of electrical power the actuator causes a trip response to the pilot valve, whereas a drawback of electromotor actuation is that on complete interruptions of electrical power the actuator cannot independently cause a trip response of the pilot valve on demand. The proposed modification, involving the pilot valve, provides a means to effect a trip response regardless of the electromechanical actuator type used, together with overcoming the drawback of electromotor actuation. To realize the trip response, an additional piston (connected to the electromotor actuator's stem) is positioned between the actuator stem and the pilot valve. A surface area of the additional piston and one surface area of the pilot valve are loaded by pressure from an oil trip line in the hydraulic system. The loaded surface area of the pilot valve causes a force in the direction opposite to that of a trip, while the force on the additional piston is in the direction required for a trip. When a trip is required, hydraulic pressure in the trip line is reduced causing (1) the force on the actuator stem to go to zero; and (2) the other force, intrinsically found on the pilot valve, to actuate the pilot valve into a trip condition. The decrease of trip line pressure is carried out by three solenoid drain valves (each equipped with two solenoid coils) manipulated by three electronic overspeed trip devices operated by a two-out-of-three voting scheme. Consequently, this invention not only negates the disadvantage of using electromotor actuators, but it also provides overspeed protection and an under-load test of various control system elements.

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West Des Moines, IA, United States of America

Dmitry Drob