Power Engineering

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    Design of Electrical Networks Through Computer-Aidedoptimization Techniques
    (Addis Ababa University, 1993-06) Zewde, Solomon; Mullisa, Girma(PhD)
    The objective of the study reported in this thesis has been to develop a unified algorithm for the computer-aided design of a wide range of electrical network configurations. While the design has been based on well-known techniques established earlier by other researchers, the present work has made significant contributions in simplifying the uses of nodal equation formulation method, graph theoretic concepts and topological formulas, as well as applications of a modified least p-th Taylor method, component damping techniques, sensitivity analyses and related design concepts. The basic computer-aided design approachfor a selected network was realized byfirst generating a voltage gain transfer function from the network connectivity details. Information concerning the gradient vector necessary in the course of an optimization process was then derived through a direct method of sensitivity analysis, without performing the normally needed first orderpartial differentiations. Comparison of a transfer function against desired response was preceded by sampling of the latter at selected frequency points and the whole adjustment was eventually automated via the least p-th Taylor method of optimization. It has been established that this approach avoided the time consuming calculation of a Hessian matrix that is usually required for performing network optimization. Convergence properties of the least p-th Taylor method were improved through a use of Fletcher's modification of the classicalLevenberg-Marquardt method together with component damping techniques. The concept of dynamic memory allocation has also been exploited. The resulting computer-aided network design technique was therefore efficient in terms of both processing time and memory requirements and the entire package has been termed as a Pascal program for optimal network design or P-POND. The algorithm has beenfully tested in its usefor designing both passive and active network types by specifying initial network parameters and input-output relations.
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    (7,3) Maximum - Length Binary Cycle Code Applied to Single Channel Digital Communication System for Error Correction
    (Addis Ababa University, 1996-06) snegash, Yohanne; Alemu, Ketema(phD)
    This paper presents the design and hardware implementation of the (7,3) maximum-length binary cyclic code applied to a single channel communication system. In hardware implementation of the system a PC with a data acquisition board with time <- sharing for interfacing the analog signals. A 12-bit digital output of the PC is divided into blocks of 3-bits for processing by the channel encoder The implementation of the system is carried out using shift registers and logic gates. A sinusoidal input waveform is applied to the system input and a circuit designed with a combination of D-type flip-flops and logic gates is used to introduce the effects of a single-random-error and a double-adjacent-burst error to observe the performance of the system. The code resulted in good performance in correcting a single-random-error and a double-adjacent-burst-error.
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    Neural Network Implementation of Character Recognition
    (Addis Ababa University, 1998-05) Bireda, Tezazu; Adugna, Eneyew(PhD)
    Artificial neural networks, as they are usually called, currently gained much popularity in the design of "intelligent" machines and in programs which are used for automatic pattern recognition as pattern classifiers. In contrast to symbolic-oriented methods in artificial intelligence (Al), artificial neural networks are computing systems that use mathematical algorithms and "imitate" the way the brain, the biological neural network, functions. They are made up of a number of simple, highly connected non linear processing elements and process information by their dynamic state response to external inputs. They are characterized by the ability to learn and generalize, massive parallelism which gives rise to greater speed on computers with parallel processors or on a dedicated analogue VLSI circuit chip, tolerance to significant erroneous data or network fault, and some models exhibit self organization in the learning phase giving optimum network architecture. Their greatest asset compared to other recognition methods, however, is their ability to learn and generalize. In this paper a feed-forward Back Propagation Network (BPN) architecture, which is one of the several network architectures available, is implemented to recognize printed multifont alpha-numeric (English and Amharic or Geez) characters and its performance is investigated. The network model has three layers and is trained in a supervised training mode. In the research, two independent sets of pattern classes of characters were formed each pattern class having four training and two testing sample character patterns. The first set deals with randomly selected pattern classes and the second set deals with very similar pattern classes. And in both sets of training and testing schemes, the relative recognition performance of the network is evaluated. The network recognition rate or performance, only for the test patterns, in percentage for the first set is about 85% and for the second set is about 67%. The overall recognition rate accounting tests with both the training and test patterns is 93% for the first set and 87% for the second. When the test patterns from these two sets were corrupted with noise, the recognition performance of both sets degraded steadily. Test was also made with tilted test patterns on the first set and the performance was unaffected up to a tilt angle of 4.4 degrees from the vertical. A steady improvement in performance was observed as the dimension of the input pattern vectors, the number of training patterns in a pattern class, and network size were increased.
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    Coding and Transmission of Non Uniform Alphabets
    (Addis Ababa University, 1998-12) Kassahun, Yohannes; Ayele, Hailu (PhD)
    Two algorithms are developed in such a way that the decoding and encoding times for Huffinan encoding scheme are minimized. Algorithm One is tested for compression and decompression of text files, while Algorithm Two is tested for compression and decompression of any form of file, real time text transmission, and compression and decompression of bitmap graphics files. Programs used in the implementation of the developed algorithms in the above mentioned applications are presented. Results of the implementations are also included.
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    Feasibility Study of Renewable Energy Resources for Electrification of Small Islands. A Case Study on Tana Lake Islands
    (Addis Ababa University, 2002) Mekonnen, Abiyot; WoldeMariyam, WoledeGiorigs (PhD)
    The energy problem of islands differs from those in mainland countries because islands need to manage their own energy supplies. The islands are good test beds for the utilization of renewable energy production and storage technologies. The present study relates the main renewable energy resources to the electrical production in the small islands in Lake Tana. The necessity to integrate some renewable energy resources is shown and various storage means are classified. Also, the needs for hydro pumping storage are proposed and investigated as a good solution for promoting to the increase of the penetration rate of renewable energies, particularly in island electrical grid interconnections. In Ethiopia there are two lakes which have Islands (Lake Tana and Lake Zeway). Among them, the island on Lake Tana (Deck Island) is the biggest Island in the country having a total population of about 7000 human residents within five villages. Due to the location of the Island is so far the task of their electrification via grid system very difficult. Kerosene is used for lighting; with diesel power generation isfor milling and pumping, leaving biomass for cooking and dry cells for radio which are being used in this Island. Nothing has been done so far in developing the renewable energy resources, such as small-scale hydro, solar, and wind energy in the Island. In this work, feasibility of renewable energy resources for electric supply system to this small Island is studied using HOMER (Hybrid Optimization Model for Electrical Renewables) software as optimization and sensitivity analysis tool. Meteorological data from National Meteorological Agency of Ethiopia and other sources, such as NASA, have been used for the estimation of solar and wind energy potentials. Electric load for the basic needs of the community, such as, for lighting, radio, television, electric baker, water pumps and flour mills, have been estimated. Primary schools and health posts are also considered as energy users for the community. As a result, based on the storage system, PV/Wind/pumped hydro hybrid system combinations is found as having a cost of energy about $0.151/kWh which is much lower than diesel generators and previously studied PV-battery hybrid systems which is estimated to cost about $0.325/KWh Key words: Wind, Solar, Hybrid, HOMER, Pumped hydro, Load Estimation 8 M.sc Thesis by Abiyot Mekonnen in Electrical power Engineering ECE DeptsAAit Table
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    Internet Self-Similarity, Modelling and Performance Evaluation
    (Addis Ababa University, 2003-01) Abdulkadir, Taye; Devarajan, D (Professer)
    Understanding the nature of traffic and its associated delay process in high traffic systems, such as the Internet, is essential for Engineering, Operations & Performance evaluation of these networks. It has been a common practice to assume packet arrivals as a Poisson Process in modelling high Traffic Networks. However, data communication traffic levels fluctuate over time, and delays through congestion can occur even on lightly utilized links. These fluctuations can occur over very short periods of time giving rise to the concept of a burst of traffic. This high variability or bursty nature can be explained through Self-Similarity and Long-Range Dependence. In this thesis work an attempt is made to verify the Self-Similarity or Long-Range Dependence nature of Internet Traffic and its associated Packet Round Trip Delay process. Also Fractional Auto-Regressive Integrated Moving Average (FARIMA) Model is found to fit the long memory as well as the short memory properties of the collected Internet Traffic Data. An artificial traffic trace synthesis program based on the FARIMA model is also developed. While the research convincingly establishes the presence of LRD over a wide range of time scales in the packet traffic and delay processes, its implication to Queueing performance is a center of argument, in one hand arguments acknowledging LRD in packet traffic affecting Queueing performance, and in the other hand arguments emphasizing LRD has no practical impact and need not be incorporated into performance models. In this research it is tried to do experimentation, which demonstrates the first argument, that LRD in traffic indeed affects Queueing Performance. TCP, the reliable transport protocol of TCP/IP, employs an ACK (acknowledgment)-based window control, that is, a TCP sender updates its congestion window size every time it randomly measures Round Trip Time (RTT) or Packet Round Trip Delay. With the most basic mechanism in the Internet to detect losses, the sender re-transmit a segment if it's ACK has not been received in the expected amount of time. Therefore, TCP throughput performance depends on the RTT. Investigation on the relation between RTT Self-Similarity and TCP throughput performance as measured by the amount of bandwidth wastage due to premature timeouts is also covered. vi Real time traffic must get a fairly regulated number of packets through to the destination in a timely manner. If these packets are late enough to have missed their “play” window, they are useless. Voice over Internet Protocol (VoIP) is one real-time application carried over the Internet. Packet delay variations in Internet tend to create voice degradations, unless proper Quality of Service (QoS) measures are implemented. In this thesis work investigation on Packet Delay and VoIP relations have been done and QoS measures suggested.
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    Design of Pulse Width Modulation (Pwm) and It’s Implementation In Xilinx Field Programmable Gate Array (Fpga
    (Addis Ababa University, 2007-02) Ababu, Teshome; Higelin, Gerald (Professer)
    The following thesis describes the design, the synthesis, and the implementation of pulse width modulation (PWM) in Xilinx Field Programmable Gate Array (FPGA). The contribution of this thesis is the development of PWM in Xilinx Integrated System Environment (ISE) CAD tools and The VHDL modeling is used in the design process of PWM. Pulse width modulation has been widely used in many applications especially in communication and control systems. The paper develops high frequency PWM generator architecture for using FPGA. The resulting FPGA frequency depends on the target FPGA speed grade and the duty cycle resolution requirements. In most industrial application due to the need of design integration in control systems FPGA based PWM controller is advantageous over the other controller systems like microprocessor, microcontroller and so on. As geometries shrink and device counts multiply, opportunities abound to do incredible things with in the confines of a single chip (FPGA). Greater focus on design reuse, where earlier design is utilized and reused in later design. The power, compactness and flexibility of the FPGA based controller could be useful in motor control, particularly in robotics where those qualities are important. The FPGA provides advantages over traditional methods such as microcontroller based designs and PLD/ASIC designs by combining the strengths of both. The FPGA allows for implementation of parallel processing for generating the required waveforms. In addition to this the paper describes the architectural features of Xilinx FPGA to the other programmable logic device and explores the design using Very high speed integrated circuit hardware description language (VHDL). The VHDL model was implemented on the Spartan 3e FPGA and optimized for space. The optimized implementation was found to consume 34 numbers of slices, 18 numbers of slice flip flops, 65 numbers of 4 input LUTs and 11 numbers of bonded IOBs.
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    Wind and Micro Hydro Power Generation for Rural Electrification in the Selected Sites of Ethiopia
    (Addis Ababa University, 2007-07) Tamrat, Bimrew; Alemu, Demiss (PhD)
    Rural electrification has long been top on the development agenda of many developing countries. Nevertheless, the vast majority of the rural population in these countries did not have access to electricity. Electric light is still a luxury enjoyed only by a few in least developed countries like Ethiopia. The population living in uraban and semi urban areas connected to the national grid makes only 15% of the total. The remaining 85% of the population in scattered rural villages and have very remote chance to get electricity from the grid. The only realistic approach to electrify the rural areas seems therefore to be the off grid or self contained system. At present, diesel generation sets are popular and well known in the country. The contribution of renewable sources of energy like micro-hydro power, wind and solar energy to rural electrification are minimal. This thesis focuses on comparative analysis of feasibility of the three of the most well known renewable source of energy micro-hydro, solar photovoltaic and wind power generation for rural electrification.
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    Dsp Based Vector Control of Induction Motor
    (Addis Ababa University, 2007-09) Belay, Abraham; Mamo, Mengesha(PhD)
    In this thesis Vector control of Induction Motor using DSP board, type TMS320LF2407 from Wintech digital instruments has been studied and implemented. This new family of DSP controllers enables cost-effective design of intelligent controllers for Induction motors, which can yield enhanced operation, fewer system components, lower system cost and increased efficiency. The vector control Algorithm maintains efficiency in a wide speed range and processes the dynamic model of the Induction Motor. The DSP board is successfully programmed by using C and assembly language in a code composer studio working environment, interfaced with an inverter of type DL2646 from DELORENZO and the Induction motor has been driven by V/f control using SVPWM technique. Experimental and simulation results has been presented and discussed.
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    Online Simulation of Silicon-Germanium Heterojunction Bipolar Transitor Using Nanohub Simulator
    (Addis Ababa University, 2008-02) Tesfaye, Damot; Higelin, Gerald (Professer)
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    The Impact of Employing Security Mechanism on Voip Network Performance.
    (Addis Ababa University, 2008-03) Demissie, Abebe; Abdo, Mohammed (PhD)
    Pe r c e iv e d co nv e r s a t i on a l s pe e c h q ua l i t y i s a n imp o r t a n t me t r i c s in Vo i c e o v e r ip (vo ip) a ppl i c a t i on s . As ip n e two r ks a r e not d e s i gn ed f o r R e a l - t ime a pp l i c a t io ns , t h e n e two rk imp a i rmen t s su c h a s p a ck e t lo s s , J i t t e r a nd d e l a y h a ve a s e ve r e imp a c t on s p e e ch q u a l i t y. Sin c e se cu r i t y h a s b e come a ma j o r c o n c e r n wi t h th e r a p id gr owth o f I nt e r e s t in t h e in t e r n e t , t he th e s i s de a l s wi th t h e s e cur i t y a s p e c t s o f Vo ip s ys t ems an d t h e p e r fo rma n c e ana l ys i s of s e cu r e voip n e two rk s . I t s t r e s s e s o n th e u n de r l yi n g o f vo ip p ro to c ol s l ik e se s s io n in i t i a t i on Pro to c ol (sip) , h.3 2 3 a nd me di a ga t ewa y co nt r ol prot o col (mgcp) . Thi s t h e s i s s t r e s s e s mo r e on i s s u e s r e ga r d in g t h e f i r ewa l l a nd th e P r ob l em f a c ed i n u s i n g i t ’ s f o r vo ip; i t f u r th e r d i s cus s e s t h e r e s ul t s O bt a i n ed wh en s e c ur i t y me c h an i sm a r e a pp l i ed . Thi s th e s i s d e v e lo ps an a l go r i thm o f a n a d ap t iv e me t ho d c od e c S e l e c t io n me ch an i sm whi c h c h an ge s th e v oi c e en co di n g s c h eme in t h e Mid dl e of a n a c t iv e c a l l ba s ed o n t h e n e two rk c on di t io ns . Th e pr op os e d Me c ha ni sm in vo lve s e s t a bl i sh in g a t h r e e -wa y h a n d sh ak e p r o c e s s i n Mid - c a l l t o r e - ne go t i a t e s t a t i on c ap ab i l i t i e s , maki n g the swi t c h a t a D e t e rmin e d s eq u enc e numb e r in a r e a l t ime t r a ns po r t p r ot oc ol (rtp) P a c k e t to sol v e th e p r obl ems an d th en to i n c r e a s e th e pe r f o rman c e of Voip.
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    Investigation and Analysis of Ashegoda Wind Farm Integration Impact on Ethiopian Grid
    (Addis Ababa University, 2010-10) Eshetu, Hiwot; Biru, Getachew(PhD)
    Ethiopian electric power corporation is under implementation stage to integrate wind power to exiting grid system which contains mainly hydro generators. Integration of wind power plant with grid system has many challenges that need to be studied thoroughly to identify major problems. The major problems induced by the wind farm depend on level of penetration. In this thesis work operational impacts associated with “Ashegoda Wind Farm (AWF)” integration has been studied, mainly variability, predictability and steady state stability impacts. The variability and predictability impacts have been studied using statistical method on the basis of data supplied from wind project office of “Ethiopian Electric Power Corporations”. Ashegoda wind farm increases the variability of the system load characteristics in case of hourly and thirty minute load. As per the result of the stability study, there is a steady state voltage stability impact under contingency cases. However, in base case, there is no any stability impact. Along with the stability analysis, one of possible solutions, that is, managing the transmission line capacity have been suggested and discussed. In addition to variability impact, predictability impact also studied by developing a wind power forecasting model. Different models have been developed and the one with best forecast accuracy selected on the basis of MAE and compared with persistence model considering as a base model. Key words: integration,Variability, forecasting, stability, modeling, frequency distribution, Variable speed, Ancillary service.
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    Investigation of Vsc-Hvdc System for Dynamic Performance Improvement of Eepco High Voltage Grid
    (Addis Ababa University, 2011-06) Hilawie, Ahadu; Biru, Getachew(PhD)
    The Ethiopian Electric Power Corporation (EEPCO) is, currently, undertaking a huge electric power generation expansion. The generation capacity under construction is about 7757 MW. This huge expansion demands existing AC transmission line upgrading and new transmission line installations. On the other hand, instability problems have occurred frequently within EEPCo system manifesting themselves in the form of system blackouts. Considering these two problems this thesis work proposes integration of Voltage Source Converter Based High Voltage Direct Current (VSC-HVDC) transmission system for improving future system stability and enhancing power transfer capability. The thesis investigates the dynamic performance improvements that can be attained through integrating VSC-HVDC transmission system. The investigation started by developing a monopolar VSC-HVDC transmission model with a complete control system on Digital Simulation and Electrical Network calculation program (DIgSILENT power factory) software. Different controllers are designed including, faster inner current controllers having transient response specifications: rise time 0.0003 s, settling time 0.000842 s; DC voltage controller having transient response specifications: rise time 0.00156 s, settling time 0.0132 s; and outer PQ controllers. Then the performance of the control system is evaluated and found to function satisfactorily at supporting bidirectional power flow and at maintaining stability during disturbances. Finally the designed VSC-HVDC link is integrated to North-Western EEPCo high voltage grid model and time domain simulations are carried out to investigate system dynamic performance improvement. It is obtained that with the proposed option the system pre-disturbance bus voltage values are improved from below 0.95 pu to 1 pu and post disturbance bus voltage values are improved from below 0.9 pu to above 0.95 pu. On the other hand system low load higher voltage values that go beyond upper limit of 1.05 are managed to come within the limit. A better damping of generators’ rotor angle oscillations is also attained showing general system dynamic performance improvement. KEY WORDS: Dynamic performance improvement, VSC-HVDC, Vector Control, North- Western EEPCo, bus voltage profiles.
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    Digital Control for Switched Mode Converters Input Power Factor Correction
    (Addis Ababa University, 2011-07) Anthony Alemayehu; Mengesha Mamo (PhD)
    Input power factor of static power converters is generally low due to angular displacement between input voltage and current plus due to current distortion. On the other hand, static power converters usage is increasing continuously with the increase in use of power supply units to commercial, industrial and residential complex automation and communication systems. This increase in application of power converters has increased the reactive power demand from the utility grid resulting in inefficiency and overloading of the transmission and distribution network. In this thesis, a digitally controlled switched mode PFC (power factor correction) converter has been designed, modeled and simulated. The three major control modes which are used for switched mode converter control are the voltage mode control, current mode control and the PFC mode control. These three control modes have been simulated using the MATLAB Simulink for 100%, 75%, 50%, 25% and 10% power loading. For the 100% load (full load) it has been found that the PFC mode controller achieves a near unity input power factor with power factor of 0.99975. At full load, the voltage mode and current mode controller have a lower power factor of 0.943 and 0.945 respectively. For the other loadings, the PFC mode controller has a near unity power factor which is greater than 0.99, whereas the voltage mode and current mode controller have a lower power factor. The PFC mode controller performs well even if there is variation in input voltage and load. In addition, the lowest total harmonic distortion (THD) and reactive power, and the highest power factor (PF) are obtained using the PFC mode control. From the results obtained, it can be concluded that the PFC mode controller is the best control scheme to be used for such control applications. Digital control for power factor correction is an important field of study since it can be used to reduce the harmonics in the line current, increase the efficiency of power systems, and reduce customers’ utility bills. The results of this study are useful for many applications such as an uninterrupted power supply (UPS), telecom power supply, motor drive inverter, personal computers, battery charging, DC motor drive, welding machine and other power supplies for electronic equipment.
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    Design of Fuzzy Sliding Mode Controller for the Ball and Plate System
    (Addis Ababa University, 2011-07) Negash, Andinet; Singh, N.P (Professor)
    The Ball and Plate system is a non-linear, multivariable and under-actuated system which provides a suitable experimental platform for control algorithm development and investigation of both stabilization and trajectory tracking control of unstable systems. Sliding mode control, as one of the tools available to design robust controllers, is introduced in the outer loop of a double-loop feedback configuration. Since the robustness of sliding mode control is obtained at the cost of infinite switching of the control input, undesirable phenomenon known as chattering will be a concern in practical implementations. To this end, Fuzzy Logic is used to tune the gain of the switching control component based on the distance of the system trajectory from the sliding surface. Genetic algorithm is implemented to determine the parameters of the fuzzy system in an optimal manner. Linear algebraic method is used to design an inner loop angle controller from a set of Diophantine equations. An implementable zero-position error transfer function is selected from tabulated results of analog computer simulations of Integral of Time Multiplied Absolute Error (ITAE) optimal systems. Specifications for the desired settling time and limitation in the actuator voltage are used as constraints to obtain the coefficients of the overall transfer function. The mathematical model of the Ball and Plate system, solved from Euler-Lagrange Equations of Motion, is investigated by realizing the designed controllers using Simulink ® and Real-Time Windows Target™ rapid prototyping software. The 3-D model of the system designed using V•Realm™ Builder based on the standards of Virtual Reality Modeling Language (VRML) is interfaced with the Simulink ® model via Simulink® 3D Animation™ product. Simulation results show that the ball could be stabilized anywhere on the plate in 3.5 seconds and it could also track a circular trajectory of 0.4m radius at 0.8 rad/s in 10 seconds without significant chattering. Key Words: Fuzzy Sliding Mode Control, Variable Structure Control, Linear Algebraic Method, Ball and Plate control, VRML, Simulink® 3D Animation™/MATLAB®
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    Design of Self-Tuning Fuzzy Controller for Micro Hydropower Plansts on Irrigation Dams
    (Addis Ababa University, 2011-07) Hayato, Jemal; Singh, N.P(PhD)
    Micro hydro power plants are stand alone renewable energy sources and free from emission of green house gases. It is an appropriate choice for rural electrification where supplying grid electricity is not economical. In Ethiopia, we have several irrigation dams, streams and running rivers which have considerable hydropower potential. Micro hydropower plants can be installed on the existing irrigation dam with less investment and time. Nowadays, electronic load controller is used to control the frequency of micro hydropower plants. However, electronic load controller wastes big amount of water during low power demand which can be diverted at high head for irrigation purposes. In addition, micro hydropower plants are characterized by parameter variations like damping constants where fixed control does not provide the desired performance under different operating conditions. Thus, development of an appropriate control scheme for micro hydropower seems inevitable to obtain the desired performance under different operating conditions. This thesis proposes fuzzy logic controller to tune the parameters of PI controller for frequency control of a micro hydropower plant and to supervise the energy dissipated on the ballast load. A detail dynamic model of micro hydropower plant is developed to design the proposed controller. Genetic algorithm is used to optimize the membership functions of the fuzzy logic controller. To meet a sudden consumer demand of power, 0.25p.u. power is dissipated on the ballast loads under steady state condition. It is observed from the simulation results that the average overshoot for 30% load change is 4.6% and the settling time is 7.5 seconds with the proposed fuzzy logic controller while overshoot is 8.9% and 13.5% and settling time is 11 seconds and 29 seconds with PI load control and PI flow control, respectively. Moreover, even for 70% load rejection, overshoot is only 11.6% and the settling time is 11 seconds. It is further observed that the change in energy wasted on ballast load from the desired value is always around zero at steady state conditions. Key Words: Micro Hydropower, Irrigation Dams, PI Controller, Fuzzy Logic Controller, Genetic Algorithm Chapter One
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    Energy Distribution and Utilization Assessment in Industries (Case Study at Mughar cement factory
    (Addis Ababa University, 2011-07) Tilahun, Alebachew; Bekele, Getachew(PhD)
    Energy conservation and efficient usage are vital to the country’s development. Demand for energy is ever increasing worldwide due to the depletion of fossil fuel sources and other related issues. Focusing on energy utilization assessment and consumption reduction efforts through improvement, better production management and also introduction of new technologies significant results can be achieved; saving money on energy bills, improving energy efficiency and maintaining sustainable environment. The cost of energy as part of the total production cost is significant in the mughar cement industry in Ethiopia. They spend millions of dollars annually on electric power and fuel oil for their energy requirement. Hence, considerable work of efficiency improvement on energy utilization efficiency at the selected cement factory is important. The aim of this thesis is to assess the energy sources and utilization in the selected factory. And also, it is to study and identify energy utilization efficiencies of the different utilities of the factory. Finally, to suggest alternatives based on measurements collected data and benchmarked cement factories experiences. In this thesis work energy losses at the selected factory have been assessed. Based on the losses, energy efficiency performance assessments on the major energy intensive equipments like electric motors and drives, lightings and the kiln have been done. At last energy efficiency improvement opportunities both for electrical energy as well as fuel energy are recommended. Key words: Energy efficiency, energy intensity Mughar cement factory, electric motors, industrial energy.
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    Study and Evaluation of The Reliability and Design of Power Distribution System : Case Study Addis Ababa Power Distribution
    (Addis Ababa University, 2014-06) Tesfay, Kiros; Biru, Getachew(PhD)
    Electricity is produced and delivered to customers through generation, transmission and distribution systems. A stable and reliable electric power supply system serve customer loads without interruptions. Distribution systems deliver power from bulk power systems to customers. Distribution reliability primarily relates to equipment outages and customer interruptions. Electric power interruption in Addis Ababa region distribution is becoming a day to day phenomenon. Even there are times that electric power interruption occurs several times a day, not only at the low voltage but also at the medium voltage distribution systems. This thesis work attempts to thoroughly identify causes for power interruptions and customer dissatisfaction and discusses the design, reliability and operation and maintenance of Addis Ababa distribution system. Furthermore, based on load forecast for 25 years, a model distribution substation design have been carried out to help EEPCO use the model in its design practice, as many of the substations have been designed without considerations of future power load growth and are suffering from overload operation. The model design is carried out for the 250MVA, 132/33kV distribution substation for Addis Center distribution system to upgrade the existing 63MVA, 132/15kV distribution substation. Distribution reliability indices such as SAIFI, SAIDI, CAIDI, and ASAI have been analyzed thoroughly on the Addis Ababa distribution substations (Addis Center) using on data collected from EEPCO. The analyzed and calculated distribution reliability indices values have been compared with standard benchmark values and comparison clearly indicates that Addis Ababa distribution system is extremely unreliable. The values for SAIDI, SAIFI, CAIDI and ASAI are 23 minutes/year, 0.5 interruptions/customer, 112 minutes/year and 99.97% respectively in a Germany standard, whereas the corresponding values for the existing distribution system of Addis Center are 252 minutes/month, 3.65 interruptions/customer, 2280 minutes/month and 99.425% respectively. In addition to the model design, the study discusses the measures to be taken in terms of operational and maintenance tasks to improve the serious reliability problem of Addis Ababa distribution system. Key words: Power Distribution System, Voltage Drop, Distribution Substation Design, Feeders, Reliability Indices, Reliability Indices Analysis, Operation & Maintenance
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    Assessment of Resource Potential And Modeling of Standalone Pv/Wind Hybrid System for Rural Electrfication, Case Study Axum District
    (Addis Ababa University, 2014-07) Kiros, Solomon; Bekele, Getachew(PhD)
    So far the Ethiopian Electric Power Corporation (EEPCo) has been electrifying the remote rural areas of the country by extending the national grid. Despite the tremendous efforts exhibited during the past few years, there are still exceedingly many people without access to electricity services. Some among them is rural populations living in the historically important district of Axum. However, the district has renewable energy resources, such as Wind and solar, with the capability of providing the needed service without requiring the extension of the national grid. But little studies investigating the value of such alternatives exist. This thesis work focuses on comparing the economic performance of using various scenarios of stand-alone PV-Wind hybrid system,- with battery storage and diesel as a backup,- for electrifying Kutur village of Awlio kebele of the Axum district (which is 30 kms away from the closest national grid) to - the possibility of extending the grid. Axum district which is located at latitude of 14° 07' N and longitude of 38° 43' E is found to have 4.28 m/s wind speed at a height of 10m, and 6.19KWh/m2/day solar radiation. Two electric load scenarios are estimated by considering set of incandescent and efficient lamps for lighting for the existing 120 households. The over mentioned solar radiation and wind speed are then used as an input to simulate the hybrid setup for the high and low load estimation using HOMER. Simulation result shows that the NPC corresponding to high and low load scenarios were $278,856and $194,174, respectively. In addition, a simple load forecasting is done by considering 2013 G.C as a reference year to see the effect of the increase in electric demand of the community on the required investment to install stand alone hybrid setup. The NPC after load forecasting is found to be more than three folds of the NPC required for the reference simulation result. In both cases the results of the simulation indicates that using standalone PV/wind hybrid system with battery storage and diesel generator as a backup for electrifying Kutur village is cost effective and comparable against the cost required for electrifying the village by extending the grid. Key words: national grid, hybrid PV-Wind, battery storage, diesel and HOMER.
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    Feasibility Study of Standalone PV/Wind/Biogas Hybrid System for Rural Electrification: (A Case Study of Midrwa Community in Adigrat District)
    (Addis Ababa University, 2014-08) Fitwi, Sisay; Bekele, Getachew(PhD)
    So far, Ethiopian Electric Power Corporation utility company uses extension of grids and installation of diesel generators as an option for the electrification of rural villages. Grid expansion to such areas is either financially not viable or practically not feasible as these locations are geographically isolated, sparsely populated and have a very low power demand. The use of diesel generators has also harmful effect on the environment in addition to their higher cost of fuel, maintenance and operation. Consequently, rural areas are dependent on local solutions for electricity supply. These areas have been using Kerosene for lighting, diesel for milling and pumping, traditional biomass as source of energy for cooking and dry cells for radio and tape recorders. However, the current increase in oil price and the negative effects of fossil fuels on the environment motivates to search for other alternative (preferably renewable) sources of energy. In this work, feasibility of PV-Wind-Biogas hybrid system with battery storage as a backup is studied to electrify the village in Adigrat district. It also compares the cost of the hybrid system against the cost required to electrify the village by extending the grid. The feasibility of this paper is analyzed using HOMER (Hybrid Optimization Model for Electrical Renewable) software. The data for biogas energy potential estimation is obtained from the Ministry of Mines and Energy (MME) of Ethiopia. The paper utilized meteorological data obtained from National Meteorological Agency of Ethiopia, NASA and SWERA to estimate the solar and wind energy potentials. The data needed for calculating the cost of extending the grid is taken from Ethiopian Electric Power Corporation, and is analyzed using interlinked Microsoft office excel spread sheet prepared by Universal Electric Access Program. Electric load estimation and forecasting for the basic needs of the community, such as, for lighting, radio, television, water pumps and flour mills, is done. Primary school and health clinic are also considered for the community. The simulation results show many feasible hybrid system combinations having a cost of energy less than $0.295/kWh which is much lower than diesel generators and previously studied PV/Wind hybrid systems. The hybrid energy system optimized by HOMER for this village is cost effective as compared to the cost required to electrifying the village. The breakeven grid extension distance is found to be 14.9kms, which implies that this hybrid energy system is cost-effective for areas greater than the breakeven distance Keywords: national grid, wind energy, photovoltaic, biogas energy, HOMER, PV-wind-biogas hybrid, standalone system, breakeven grid extension distance