Abstract
Climate change and environmental degradation has resulted in a reduction in water inflow at hydropower plants, as well as a decrease in reservoir levels. Existing hydropower plants suffer from water head reduction, mainly with decrease in efficiency of energy conversion in hydro turbines. This paper showcases the benefits of operations with variable speed in existing hydropower plants, when working at a lower water head than the rated one. Theoretical analyses and tests were performed in a special constructed laboratorial setup aiming at evaluating the amount of efficiency recovery with variable speed operation. Connection alternatives for a constant frequency grid and applications of the learned concepts in an existent hydropower plant are presented. The investigations were applied to the Furnas hydropower plant. The results point out that economic feasibility of the application can be achieved.
Highlights
Variable speed operation in a hydropower plant has been the subject of many studies for a while and has been examined by researchers [1,2,3]
Other economic benefits of the application of variable speed are the reduction of machine stopped time and reduction of expenses with maintenance of turbine and bearings, which are proportional to the diminution of cavitation and associated vibration
As a consequence of climate change, hydro cascade operation, and inflow reduction, the upstream level of the reservoirs of some hydropower plants has decreased. This has further caused a reduction in the resulting water head and energy conversion of hydro turbines
Summary
Variable speed operation in a hydropower plant has been the subject of many studies for a while and has been examined by researchers [1,2,3]. On the other hand, uprating implies changing the side equipment and the alternatives of the retrofit, and amendment of the main equipment as well This can include the turbine or the generator, increasing the height of a dam, as well as other entities that aim to improve the overall power plant capacity. When considering retrofit, some of the alternatives to change from a constant speed to a variable speed hydropower plant are presented in this paper It will be theoretically and experimentally shown how the reduction of speed can increase the efficiency of the turbine, making it work much closer to its specific speed. An increase of using variable speeds in existing hydropower plants will be evaluated, for both flow and height reduction
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