<p>A self-contained electrohydraulic actuator, originally developed for use in gas and steam turbines by Voith Turbo, transmits 56 tons of force from a package that combines the advantages of hydraulics with the convenience and energy efficiency of electromechanical drives. Photo by Christian Kuhna, courtesy Siemens AG.</p>

Self-Contained Electrohydraulic Actuator Offers Failsafe Operation

Gas and steam turbines often integrate hydraulic cylinders for valve-actuation purposes. Hydraulic cylinders usually can transmit extremely high force and precise position and force control within a much smaller package than electromechanical actuators. However, it is sometimes impractical to route hydraulic lines and install valves and other support components near the hydraulic cylinder.

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An alternative solution was developed by Voith Turbo GmbH & Co., Heidenheim, Germany. Called the Voith SelCon, it was designed primarily as a linear actuator with safety function for valve control in turbines. The SelCon is a hydraulic cylinder with a self-contained drive motor, pump, reservoir, filtration system, and control valves. The main benefit of the actuator is that it combines the high thrust of hydraulics in a small package with the simple, cost-effective system integration of an electromechanical actuator. The SelCon can generate forces up to 500 kN (56.2 tons), and ATEX certification allows it to be used on turbines under virtually all conceivable ambient conditions.

Advantages over Alternatives

The configuration reduces initial costs as much as 35% compared to a conventional hydraulic or electromechanical actuator. In addition, the system has a considerably higher operational reliability because it eliminates external hydraulic disturbances, such as pressure fluctuations, mismatched pipe diameters, and vacuum in the pump suction line.

A variable-displacement servopump controls actuator stroke. As a result, the actuator offers high-energy efficiency and generates low heat. Energy costs to operate the SelCon actuator are up to 50% lower than for conventional hydraulic cylinders using valves and an external power unit. The control through the servopump provides the same or better dynamics and control response as comparable electromechanical actuators.

The modular SelCon design is typically compatible with existing hydraulic, electromechanical, and pneumatic actuators. Integration into new systems and the modernization of existing systems can be accomplished cost-effectively with minor planning effort.

Built-in Features

The SelCon also provides fail-safe operation using a simple internal return spring. This reduces the danger of direct and consequential damage because the trip time for the valve controls typically runs less than 300 ms.

Various standardized communication interfaces and the use of real-time Ethernet protocols make the SelCon ready for Industry 4.0 (Internet of things) concepts. For example, intelligent process optimization, remote diagnostics, and condition monitoring come to mind.

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