Pneutronic speed governor for small hydropower plants: a new application for pneumatics

This paper describes the development of a new approach for speed governors of small hydropower plants (SHPs) employing servo-pneumatic positioning system (pneutronic system). Aiming at cost reduction, easy maintenance, and obtaining an environmentally friendly product, a pneumatic system is designed for the control of wicked gates in Francis turbines to replace the conventional approach using a hydraulic system. The positioning system development is based on the non-linear modeling of the pneumatic valve and cylinder and includes a PID controller with dead zone compensation. Using a test bench corresponding to a 400 kW power plant, the model is validated and the performance requirements, according to international standards, are fully satisfied. Results are presented for a speed governor prototype installed on-site in a 35 kW Francis turbine where load rejection and step response tests were carried out. The theoretical and experimental results show that a servo-pneumatic speed governor can be used successfully for SHPs, being restricted to turbines of up to 1 MW considering only the pneumatic component costs.