Browsing by Author "Desta, Melaku"

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    Design and Evaluation of High Voltage Transmission System for the Grand Renaissance Hydro Electric Power Plant in Ethiopia
    (Addis Ababa University, 2012-12) Desta, Melaku; Biru, Getachew(PhD)
    The Ethiopian Electric Power Corporation (EEPCo) is, currently, undertaking a huge electric power generation expansion plan. The generation capacity under construction is about 7757 MW. This huge expansion demands new transmission line installations. Among the Electric power Generations that are under construction is the Grand Renaissance Hydro Electric Power Plant. This project takes the lion share which accounts about 5250 MW. To transmit this huge power EEPCo planning department designed two dual circuit 500 kV HVAC transmission lines. The length of these transmission lines from GRHEPP to Menagesha substation (Main Grid) is about 574 km. Estimates showed that the break even distance is around to 500 km. the range of this value vary depending on the range of power transmitted and cost of equipments incurred. The intention of this thesis work is to develop two 500 kV bipolar HVDC transmission system and compared with the HVAC transmission system in terms technical performance and costs incurred for each transmission systems. In technical performance: transmission line efficiency, voltage regulation, corona losses are considered and in cost analysis: investment cost and power loss cost over the entire life cycle (i.e. 35 years) of the transmission lines are considered. From the technical performance it can be saved 133 MW power, if two bipolar HVDC transmission line is implemented, the HVDC line is more regulated than HVAC line and the HVAC line is less friendly to the environment than the HVDC line. From the cost analysis the break even distance obtained is around 400 km i.e. below 574 km. So the bipolar HVDC transmission system is less costly than HVAC transmission system for distances above the break even distance. And the dynamic performance of the HVDC transmission system during transient states is analyzed and observed obtained that during three phase short circuit faults applied on ac side of both transmission lines, the HVDC line reached its steady state condition after 4 cycles (EEPCo standard). The designed HVDC transmission system has better technical performance and also cheaper in investment cost when compared with the HVAC transmission system. KEY WORDS: HVDC, HVAC, Break even distance, Transmission line efficiency, corona loss, Loss cost, Current controller, Gamma angle controller.
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    Thermodynamic Modelling of Biomass Integrated Gasification Combined Cycle (Bigcc) Power Generation System
    (Addis Ababa University, 2011-11) Desta, Melaku; Dama, Tesfaye
    An attractive and practicable possibility of biomass utilization for energy production is gasification integrated with a combined cycle. This technology seems to have the possibility to reach high efficiencies based on a fundamentally clean and renewable fuel. Biomass Integrated Gasification Combined Cycle (BIGCC) systems replace the traditional combustor with a gasifier and gas turbine. Exhaust heat from the gas turbine is used to produce steam for a conventional steam turbine. The gas and steam turbines operate together as a combined cycle. This paper investigates the ultimate potential for application of Biomass Integrated Gasification Combined Cycle (BIGCC) to biomass based power systems. It describes the elements of the gasification system and the methods to model the components of BIGCC system thermodynamically. A computer program using MATLAB is used to estimate the syngas composition of the gasification system using a down draft gasifier and wood as input. It predicts the effects of moisture content, temperature, pressure, and air to fuel ratio on syngas composition. This study also includes the economic importance of Biomass Integrated Gasification Combined Cycle (BIGCC) system over conventional bio-fuelled power plants