Browsing by Author "Yabebal, Adeyabeba"

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    Non-Linear Adaptive Control of Hydropower Generator Cooling System
    (Addis Ababa University, 2018-11) Yabebal, Adeyabeba; Dereje, Shiferaw (PhD)
    This thesis describes the use of nonlinear adaptive control to design the cooling system of hydropower generators. The increasing load demands are posing serious threats to reliable operation of power systems. These days, in the light of the attention given to reduction of carbon dioxide emissions and efficient usage of raw materials, high-efficiency electric generators are in the lime light over the world. As all losses generate heat it is important to have a cooling system that can maintain a sufficiently low operating temperature within all parts of the generator. The objective of this research was to model, design and simulate a reliable and efficient cooling system for hydropower generators using nonlinear adaptive control. As the load on a generator varies with time, the generators heat dissipation also varies. This variation in the heat causes the temperature of the air surrounding the generator in the closed generator room to vary. In this thesis this variation of temperature is studied and heat transfer analysis method is used to determine the heat loss of the generators. Following that appropriate size of butterfly valve is chosen which is driven by a DC servomotor and a tubular heat exchanger is designed using dimensionless number analysis method which includes determining the Reynolds number, Prandtl number, and Nusselt number. Then the required amount of cooling water is supplied through the tubular heat exchanger according to the load on the generator. In this research the cooling system is designed to keep the generator temperature below 50 C in other words keeping the temperature of the surrounding air inside the generator room below 27 0 0 C. Matlab Simulink software is applied for performance analysis of the designed cooling system. The simulation results show that the designed cooling system keeps the surrounding air at a temperature of 27 C with a settling time of 0.6 seconds and without any overshoot when it exceeds this set point (27 0 C). For this study we choose the Koka Hydropower Plant and the required data for the design is collected from there. The butterfly valve opening angle for adjusting the valve at the desired position in order to allow the required flow rate is related with the temperature of the generator room in a non-linear way specifically having an exponential relation. Thus an ANN controller is used which accounts for this process nonlinearity so that increasing model robustness and reducing the generator stoppage time due to cooling system failure. This results in increasing the efficiency of the hydropower plant as a whole.