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Application of variable speed operation on Francis turbines
Aplicación de la tecnología de velocidad variable a turbinas Francis
Keywords:
Hydropower, Francis turbine, turbomachinery, variable speed, double-fed asynchronous machine, water head, unitary speed, unitary flow (en)Energía hidroeléctrica, turbina Francis, turbomáquina, velocidad variable, generador doblemente alimentado, salto, velocidad unitaria, caudal unitario (es)
Francis turbines that are directly coupled to a synchronous generator operate at constant rotational speed around a design point characterized by a given water head, flow and guide vane aperture. When important changes occur in headwater level in power stations with large reservoirs, the turbines suffer a significant loss of efficiency. By applying variable speed technology it may be possible to adapt the runner speed and to operate with a higher efficiency over a wide range of water heads. This investigation is intended to reveal the possible benefits of using variable speed operation in regard to gains in efficiency and power output.
Based on model test data it is possible to determine the characteristic curves of unitary speed and unitary flow of the respective prototype turbine for varying guide vane apertures. By varying rotor speed it is possible to maintain values that correspond to maximum efficiency. An analysis is made keeping guide vane aperture constant and introducing a proportionality factor of water flow to corresponding power output. The results show that for guide vane apertures and heads different from the design point, best efficiencies can be kept by adjusting rotor speed. At heads lower than the design head, significant efficiency gains can be achieved. Consequently, a significant proportion of the flow can be saved while generating the same amount of power.
Las turbinas Francis están acopladas directamente con sus generadores síncronos. Debido a esto la geometría de sus turbinas está diseñada para operar con velocidad sincrónica en un punto característico que corresponde al salto y el caudal de diseño con una respectiva apertura de los álabes. Para otros saltos mayores o menores al de diseño y sus correspondientes caudales la eficiencia será menor que la máxima esperada en el punto de diseño.
En este trabajo se investiga la posibilidad de mantener la turbina operando en el punto de mejor eficiencia mediante la variación de la velocidad. La investigación demuestra la posibilidad de obtener beneficios aprovechando la velocidad variable en cuanto a la eficiencia y la potencia útil. Se obtienen de las pruebas de modelo las curvas características de velocidad unitaria y caudal unitario, tanto del modelo como del prototipo para diferentes aperturas de los álabes. Gracias a la velocidad variable es posible mantener los valores correspondientes a la mayor eficiencia. Se analizan para aperturas fijas de los álabes los aumentos de eficiencia para el rango de saltos y se introduce un factor de correlación entre caudal y potencia. Para saltos inferiores al de diseño, se pueden obtener aumentos de eficiencia y ahorros de caudal significativos generando la misma potencia.
References
Avellan, F. (2004). Introduction to cavitation n hydraulic machinery. Lausanne, Switzerlan: EPFL Swiss Federal Institute of Technology.
Campos-Barros, J. G., Saidel, M. A., Ingram, I., & Westphalen, M. (1996). Adjustable speed operation of hydroelectric turbine generators. ELECTRA, 167(August), 17-37.
Farell, C., & Gulliver, J. (1987). Hydromechanics of variable speed turbines. Energy Engineering, (133), 1-13.
Fraile-Ardanuy, J., Wilhelmi, J. R., Fraile-Mora, J. J., & Pérez, J. I. (2006). Variable-speed hydro generation: operational aspects and control. IEEE Transactions on energy conversion, 21(2), 569-574.
International Electrotecnical Commission IEC (1999). Standard 60193, second edition 1999-11. Hydraulic turbines, storage pumps and pump-turbines - Model acceptance tests. Geneva, Switzerland.
Simond, J.-J., & Schafer, D. (1998). Adjustable speed asynchronous machine in hydro power plants and its advantages for the electric grid stability. Lausanne, Switzerland.
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Copyright (c) 2015 Gregor Paul Heckelsmueller
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