ES230206 test WHG

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Wind, Hydro and Geothermal Power Generation (AY 2022-23) 6th February 2023 Prof. Paolo Silva Time: 90 minutes Instructions for the examination: 1) Clearly indicate your name on all the sheets you will deliver. 2) Give a synthetic and clear answer to as many questions as possible. The final score will be normalized according to the average results. 3) Talk with colleagues and / or cheating will cause the cancellation of the exam. 1. Consider a three-bladed, large-scale horizontal axis wind turbine whose control strategy is designed to operate at sea level based on undisturbed wind speed measurement. How would the power curve change if the same turbine were installed in the mountains, respectively (i) with no adjustment of the regulation strategy and (ii) with adjustments? (5 points) 2. With reference to geothermal power plants, what are hybrid cycles and in which cases are they applied? What are the potential advantages over both direct and indirect cycles? (5 points) 3. What are the effects of a gust on a modern large-scale wind turbine? What are the methods and technol- ogies to mitigate its negative effects? (5 points) 4. How does the ecological flow affect the annual energy production of a hydroelectric plant? What kind of plants are affected by this limitation? Explain how to calculate the reduction in energy production and plot the effect on the flow duration diagram. (5 points) Exercise (11 points) A three-bladed horizontal axis wind turbine is equipped with a variable speed and variable pitch regulation system. The turbine has a rotor diameter of 123 m, a rated wind speed of 11.5 m/s, a nominal electrical power output of 5 MW and is designed for an optimal λtip equal to 7.8 (air density 1.225 kg/m3). Knowing that the efficiency of the gearbox is equal to 97% and…