Hydropower plants are an energy efficient, environmentally friendly, flexible, and reliable facilities for conversation of energy of water into electric energy. Using the energy of water, while at the same time providing flood protection and security of drinking water supply are strategically important benefits of hydropower plants. In addition, through mitigation measures, implementation of the most environmentally acceptable solutions and regular monitoring, the minimal environmental impacts are achieved, making hydropower the cleanest form of energy. Stability, low operating and investment costs per unit of produced energy and a possibility to participate at control of power system parameters, provide them a leading position between renewable sources of energy. They represent the largest rotating mass of all renewable sources, which is the key to ensure stability of the power system and resilience to dynamic transients.
The aim of master thesis is to make mathematical models of hydropower plants on the lower parts of the Sava River, considering actual operational parameters of the hydropower plant. The models allow comparison of the calculated and measured values of flows, powers, net heights of water and efficiencies. The models can be used to determine the optimal engagement of individual units or the distribution of the total power of the hydropower plant between individual production units. This allows us to evaluate the actual on/off algorithms of aggregates from the point of view of minimizing the flow and thus improving the efficiency of potential energy within the flow accumulations.
The first part of the master thesis includes an introduction to hydropotential, hydropower plants, their types, and components. It also describes the energy conversions that generate electric energy from the energy of a water. At the same time, there are losses that define the efficiency of the hydropower plant at each operating point. They are described in Chapter 6, where their calculation is also presented in detail, together with the parameters that can be used to draw conclusions on how to minimise the losses.
The second part of the master thesis presents the modelling of hydroelectric power plants on the lower part of the Sava River, i.e., HPP Boštanj, HPP Arto-Blanca, HPP Krško and HPP Brežice, performed as part of a master thesis. Mathematical models of hydropower plants are made in Python and based on shell diagrams provided by the turbine manufacturer or measured as part of the acceptance and guarantee measurements. By reading any sufficiently large set of points on the shell diagram and the two-dimensional interpolation, the entire operating range of the turbine is written in a numerical form. Due to the constraints of the turbine, we need to constrain the shell diagram, which is achieved by writing the appropriate functions. Models are built based on the physical fundamentals and loss functions from the guarantee measurements, by determining the required flow, turbine power, net heights, and efficiencies of the individual elements and of the whole hydropower plant from the operating power and the level of the upper and lower water. The accuracy of the model calculations is demonstrated by comparisons of calculated and measured values to demonstrate the accuracy of the calculations and adequacy of the models.
In the final part of the master thesis, the results of the optimisation of hydropower plants operation using the developed models are presented. The models allow to determine the optimal load distribution between the individual aggregates to minimise the flow and thus save the energy stored in the flow storage. Based on the operating power and the gross height difference, the software determines all the load distribution options and uses calculations to find the combination that requires the lowest flow rate and thus achieves the highest efficiency. This considers the inlet and outlet losses, the turbine operating point and the generator efficiency. The calculations have been used to verify and validate the actual on/off algorithms of the generators, which also provide an on/off hysteresis. Based on the actual and adjustable timetable, the energy saving of the optimal operation compared to the actual one is finally determined. Hysteresis may result in higher flows, but it is essential to reduce the stresses on the equipment and thus prolong their lifetime.
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