A New Electro-Mechanical Approach to Failsafe Actuators in Gas Turbines

Moog has been involved in providing motion control for the Power Generation Industry for over a decade and has been a trusted partner of the leading builders of gas and steam turbines. Over our history Moog has provided over 10,000 servovalves to over 1,000 plants worldwide. Today we design complete control assemblies and unique products in both hydraulic and electric technologies for a variety of turbine control applications. In addition to understanding the design needs of the turbine manufacturers for enhanced safety, up-time, and space saving, we also have vast experience in helping power plants run effectively by facilitating commissioning, operations, maintenance, and troubleshooting motion control systems.


Traditionally most of the process valves on a turbine are hydraulically operated. In this industry, performance measures are closely related to production availability including maintenance hours and startup time. The concept of using an Electro-Mechanically (EM) operated valve is very appealing to the industry for following reasons:

  • Elimination of potential fire hazard of high pressure oil leaks
  • Removal of plumbing and the decentralized power unit
  • Provision of extensive diagnostic capabilities and easy setup due to decentralized intelligence independent from the turbine controller
  • Forward -looking system allowing for preventive maintenance concepts
  • Overall cost saving, when comparing the total cost of ownership of EM to hydraulic solutions


Main parameters of a gas turbine are controlled through the opening and closing of a valve outlet. In case of an emergency shut-down the valve needs to dynamically close against the gas pressure, otherwise there will be severe damage to the turbine. The safety-relevant closure of the valve is accomplished in this industry through a spring arrangement. In hydraulicly-operated valves the spring is constantly engaged during the operation of the valves. Earlier EM designs mimic this operation and failed due to safety consideration such as a possible jamming of the mechanism or the maximum time allowed to close the valve. Additional problems with the traditional drive train approach were due to the additional spring in the load path being oversized, resulting in larger drives, motors and actuators that were less cost competitive when compared to the existing solutions.

Patented, Innovative Solution

Through collaboration with an industry leader, Moog developed an understanding of the needs and challenges in this application. We received constructive feedback on our designs and perfected our concept through several iterations based on our customer input to arrive at the ultimate design.

Early on in the process, Moog decided to separate the actuation system in two functional parts. The first part was the normal operation of precise position control of the opening and closing of the valve dependent on the target position provided by the turbine controller. The second part was the safety mechanism represented by a spring arrangement that is being compressed during a reference movement and locked in place by the use of a magnetic clutch arrangement.

The traditional disadvantage of EM designs were overcome by the following design innovations:

  • Servodrive, servomotor and actuator are only sized for the process forces
  • The failsafe is executed by the loss of power to the magnetic clutch. It fulfills the required closure time due to low acceleration mass and does not require back-driving capabilities of the actuation systems.
  • Further innovation of the use of a toggle device has minimized the size of the magnetic clutch

Sketches showing the two functional parts


The innovative approach that Moog used in this application resulted in a world-wide patent granted to Moog. This unique failsafe device is currently designed and under testing for small frame gas turbines. The modular design approach will further allow the use in large frame gas turbines and steam turbines. Most importantly, Moog’s solution has enabled the industry to overcome a major impediment to the quest for the all electric turbine, thereby continuing our history of helping the industry to overcome its challenges and continually increase performance.


Thomas H. Czeppel is the manager responsible for the development and application of solutions using electro-mechanical technology in Europe. He has worked for Moog for 11 years in engineering and application functions in Germany and the US. He studied Precision Engineering in the University of Esslingen and holds an MBA at the SIMT in Stuttgart.