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Some References on variable speed from around the world:
1. Dynamic Behavior of a 2 Variable Speed Pump- Turbine Power Plant Proceedings of the 2008 International Conference on Electrical Machines
2. Adjustable speed operation of a hydropower plant associated to an irrigation reservoir Department of Hydraulic and Energy Engineering, ETS de Ingenieros de Caminos, Canales y Puertos, Technical University of Madrid (UPM),
Adjustable speed operation allows the turbine to operate at higher efficiencies, thus increasing the amount of energy generated and avoiding the appearance of operational problems such as cavitation, draft tube pressure oscillations and shaft torque fluctuations. As a consequence, equipments life can be extended and, in turn, long term maintenance requirements can be significantly reduced.
3. Adjustable Speed Hydro Generation Departamento de Ingeniería Civil: Hidráulica y Energética E.T.S. Ingenieros de Caminos, Canales y Puertos. Universidad Politécnica de Madrid . IEEE TRANSACTIONS ON ENERGY CONVERSION, VOL. 21, NO. 2, JUNE 2006
The application of variable-speed generation schemes to hydroelectric power plants offers a series of advantages, based essentially on the greater flexibility of the turbine operation in situations where the flow or the head deviate substantially from their nominal values. Specifically, the following aspects may be emphasized:
In general, for variations in head and flow, the variable speed option would be more advantageous.
Running the turbine at a variable speed avoids cavitation and draft tube oscillations.
In hydro plants with reservoir, the operating range of head variations can be increased, thus reducing the need for flooded areas.
In the run-of-the-river hydro plants, the continuity of operation may be increased because of the higher range of allowable flows in the turbine.
A simulation performed on a run-of-the-river small hydro plant confirms that significant gains in generated energy may be obtained.
4. Adjustable speed Asynchronous Machine in Hydro Power Plants and its Advantages for the Electric Grid Stability. Daniel Schafer , R&D Manager Electrical Engineering Department ABB Power Generation Ltd. And Prof. Jean-Jacques Simond Swiss Federal Institute of Technology Dept. KWHT DE-LEME 5242 Birr 1015 Lausanne Switzerland
Since a long time, it is known that hydraulic machines can work with an increased efficiency at partial load when the speed can be adapted to this partial load.
5. Maximum Efficiency Point Tracking for Adjustable-Speed Small Hydro Power Plant A. Borghetti, M. Di Silvestro, G. Naldi, M. Paolone, Faculty of Engineering, University of Bologna, Italy and M. Alberti, Seta S.r.l., Faenza, Italy.
Usually, the superior characteristics of synchronous generators force to choose to operate hydraulic turbines at fixed speed. However, the efficiency of these production units can be increased by using variable speed generators.
6. Speed control of run-of-river variable speed hydro plants J. Fraile-Ardanuy, J. R. Wilhelmi, J. Fraile-Mora, J. I. Pérez and I. Sarasúa Departamento de Ingeniería Civil: Hidráulica y Energética E.T.S.I.C.C. y P., Universidad Politécnica de Madrid
The advantages of adjustable speed hydroelectric generation have been highlighted by several authors. The optimum speed for actual working conditions must be continuously implemented by means of an appropriate control system. This process gives rise to dynamic changes in operation variables.
