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- современной системе мониторинга работы электростанции;

- возможных дополнительных функциях приводных механизмов;

- том, как приводной механизм приводится в движение.

Valves & Actuators: The Path to Greater Efficiency & Performance

14 April, 2014 by Russell Ray

http://www.power-eng.com/

Valves and actuators are critical in almost every aspect of power plant operations. They are used in a wide range of applications, including pollution control, feed water, cooling water, chemical treatment, bottom ash and steam turbine control systems. They are exposed to a variety of chemicals, abrasive materials and very high temperatures. They are critical in optimizing efficiency, and they are often the final control element in the operation of a power plant.

Although the basic technology for most valves and actuators has remained unchanged, innovative applications and design modifications for problem solving have led to notable improvements in actuator technology. These improvements can reduce costs by supporting the control valve's ability to throttle accurately, thereby providing better performance for high-pressure steam bypass, turbine bypass and other critical power plant operations.

Actuators regulate mass and energy flows by adjusting valves, flaps and cocks.

The actuator and valve create a single unit — the control valve. Actuators perform different motion sequences, including linear, pivoting and rotating motions, and they are powered by pneumatic, hydraulic or electrical energy.

Actuators receive a control signal from automation systems. The signal is converted into a motion so that the control element of the actuating element assumes a corresponding position. With control valves, this is a stroke motion. With flaps, ball cocks or rotary plug valves, this is a pivoting motion.

Though the general technology of a power plant has basically remained the same during the past decades certain practices are being adopted to allow for reliability and maintenance.

Motor operated valves in particular are key to high plant performance. Until 20 years ago motor operated valves tended to have motor control centers remote from the valve. This did not allow for the benefit of technology advances in electric actuators.

The early 1990s saw a trend towards smart actuators with integral data logging capabilities. These actuators could also be networked to the control system. Today, there has been a major change in the availability of better information from the motor operated valves. Instead of being alerted after the fact, the electric actuators are now monitoring the systems and providing data ahead of potential failures in the equipment.

As an example, early actuators had torque switches which tripped after the valve had an internal failure which caused it to require more force than originally designed for. The more recent smart actuators have an internal data logger inside which has had the ability to monitor torque output.

The most recent electric actuator also has a monitoring set point above the baseline torque to alert the plant operator that there is a problem that needs to be addressed.

Miscellaneous trip alarms are also included to monitor things like starts per hour to insure the internal contactors are not being overused. There are also maintenance interval settings that can be adjusted by the plant operator. Another advance in electrical engineering technology is the development of Cycle Isolation testing which utilizes acoustic monitoring instruments to help customers monitor valve performance and detect leaking valves.

Steam plants are powered by energy differences and the greater this difference, the greater the fuel efficiency. Valves maintain the separation by isolating the high energy processes from the low energy processes. When valves leak, they are acting in direct opposition to the forces that drive the plant by allowing energy to leave the high energy processes and enter the low.

The cornerstone to solving this problem is diagnostics. A systematic approach to accurately measuring valve leakage eliminates uncertainties that manifest as unnecessary added costs. Improvements to valve leakage diagnostic programs quickly result in plant performance improvements as well as sustained reductions to valve costs.