Power Engineering

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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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    Long-Term Modeling and Analysis of Optimal Pathways and Scenario Alternatives for The Ethiopian Power Sector
    (Addis Ababa University, 2023-05) Dawit Habtu; Getachew Bekele (PhD); Erik O. Ahlgren (Prof.)
    The United Nations launched a new set of Sustainable Development Goals (SDGs) to guide the world during the next fifteen-year period from 2015 to 2030. With the “Goal 7-Ensure access to affordable, reliable, sustainable and modern energy for all”, the agenda 2030 recognizes the importance of sustainability, security, and affordability of energy supply to all countries but in particular for developing countries. And the greatest increase in demand for energy is envisaged to come from developing countries where, with rapid urbanization, largescale electricity generation with a reliable and optimum supply will be required. To achieve the SDG7 and ensure energy security, countries are required to develop sustainable and appropriate approaches to electricity planning. In this regard, policymakers increasingly rely on techno-economic assessments both to inform policy development and to help set the right national targets. Accordingly, the modeling and investigation of different optimal pathways and possible future scenarios has become a critical planning tool in the power sector. This type of assessment is currently lacking in developing countries, specifically in Ethiopia. Consequently, in line with the global and local needs, this dissertation deals with strategies and practices for sustainable energy system development in Ethiopia. It focuses on long-term electric power security to make timely investments on various energy resources and supply energy matched with the economic developments and environmental needs of the country. In this framework, the goal is pursued by setting the following three specific objectives: (1) To review and evaluate energy development, power sector reforms, policies and resource adequacy in Ethiopia. This objective is pursued to assess and evaluate the effectiveness of existing reforms and policies in Ethiopia in terms of meeting the country’s rising demand for energy by breaking the “business-as-usual” trajectory of the past. An analytical method to calculate resource planning indices such as reserve margin and expected unserved energy is used. The results indicate that the near-future generation reserve is not adequate to supply the increasing demand resulting mainly from expansion of electricity access, development of industrial parks, extensive expansion of railway network, extensive agriculture irrigation schemes, new sugar factories and export plan to East African Power Pool (EAPP) countries. The second specific objective is (2) To assess the fundamental dynamics, variables and policies that characterize the energy development and determine the evolution of electricity demand. The scientific literature reveals a weak understanding of the inherent characteristics and specific features of energy systems in developing countries. As a result, this specific objective is pursued by knowing the trend and capturing the relationship between demand and other independent socio-economic and technological variables. Comparative overview of various existing modeling frameworks is done in terms of several criteria, particularly their applicability to developing countries. Appropriate modelling frameworks are identified for assessing and projecting the long-term energy use in a systematic manner within the context of developing countries. A better system representation and applicable alternative policy scenarios are also developed by considering the unique characteristics of energy systems in developing countries (unsustainable use of traditional energy sources, high population growth, modernization and urbanization, low electricity access, supply shortage, high system losses, informal economy, etc.). Extensive and detailed dataset is used to simulate the alternative policy scenarios. The pathways represented by the scenarios can show the maximum expected rise in demand under different drivers and the best-case energy saving opportunities. The current methodologies employed for long-term energy demand projection are then evaluated, particularly focusing on the electricity demand. The result of the policy scenarios shows that while the application of energy efficiency policies and measures would only have a minor impact on the energy demand, their impact on the electricity demand is large, and that the application of such policies is a very important measure to combat supply-demand mismatch causing power shortages and black-outs. The projection results are compared with previous studies and reasons for the deviations and strength of the followed approaches are discussed. The last objective is (3) To identify the best power generation and capacity mixes to meet future electricity demands subject to various technical, economic, and environmental constraints. This is pursued by developing a soft-linked OSeMOSYS and LEAP model to determine the lowest cost electricity generation and capacity mixes to meet long-term electricity demands subject to certain policy scenarios that may impose technical constraints, economic realities and environmental targets. The model has various data requirement that describe the current and historical installed capacities, efficiencies, costs (capital, operating and maintenance, fuel costs), capacity factors, losses, expansion plans, etc. From the literature survey, it is observed that there is a gap in providing independent assessments of alternative technologies and policy choices that can be essential for developing countries in a way that addresses their particular needs and constraints. Thereby, the model explores the feasibility of including new technologies to the existing system. This includes assessments of centralized and decentralized methods of electricity supply. Novelties are introduced in terms of better system representation on reference energy system diagram, development of appropriate model and identification of relevant scenarios considering the context of the country and applicability to developing nations. Moreover, sensitivity analysis is carried out to study the effect of critical assumptions and varying parameters on the results. Five policy scenarios are employed (reference-ref, grid extension-grx, multiple resource mixmix, renewable and intermittent resource target-vRE, improved efficiency-Eff) to explore different possible futures and balance the long-term electricity needs and resources. The improved efficiency scenario is the most desirable compared to the other scenarios because of lower installed capacity requirements and economic benefits. Attributed to lower investment costs and abundant resource availability, the results show that renewable technologies are more competitive and favorable in the context of Ethiopia. Hydropower will continue to play a key role in the future electricity supply with the addition of alternative resources like wind, natural gas, geothermal, solar PV and CSP.
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    Performance Assessment of PV mini-grids for effective replacement of diesel based mini-grids at selected sites in Ethiopia
    (Addis Ababa University, 2023-09) Kalkidan Getachew; Getachew Biru
    This study highlights the necessity of transforming diesel generator-only mini-grids into solar mini-grids due to their limited run time, high cost, and environmental impact. To achieve this, it is important to evaluate the operational performance of other nearby solar mini-grids in the same geographical area before designing and replacing the diesel generator-only mini-grid with a solar mini-grid at a specific location. The findings of the evaluation can help determine the operational performance of the newly designed solar mini-grid. Out of the 12-pilot solar mini-grids in Ethiopia, two were selected as benchmarks for designing and replacing the diesel-only mini-grid in Dolo Odo town with a solar, battery, and diesel generator hybrid mini-grid. Omorate town solar mini grid, which exhibited good performance, and Qorile town solar mini grid, which exhibited poor performance, are chosen for evaluation. Homer Pro software is used for optimizing the PV system, while PVsyst software is used for evaluating the performance of the PV system. The results indicate that Omorate system experienced 1027.7 kWh/day unutilized solar potential and had an average yearly PV efficiency of 10.28%, while the Qorile system had unutilized solar potential of 1405.8 kWh/day and average six months PV efficiency of 4.32%. Additionally, total system losses in the Qorile system were found to contribute to 6.84 kWh/kWp/day, which is much higher than the corresponding value of 2.9 kWh/kWp/day in Omorate system. Therefore, the performance analysis of both solar mini-grids showed that they are operating with poor performance, indicating that they are not meeting the expected energy output levels. From the benchmarking, it was found that determining and forecasting the energy requirement and sizing the PV system while considering all derating factors for the system equipment’s is necessary for efficient and optimal performance. The first optimized system for the Dolo Odo hybrid solar mini-grid system consists of a 2 MW PV module, an 8.06 MW battery pack, 2 MW grid inverter, 1.05 MW power conditioning system, and 0.6 MW diesel generator. This system provides 91% of the electricity demand from solar and Battery and the remaining from the diesel generator. The proposed hybrid mini-grid system not only uses less fuel and emits less CO2 than the base system but also has a lower levelized cost of energy of 0.211 USD/kWh and a reasonable net present cost of 16.5 million USD.
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    Studies on Voltage Profile Improvement and Power Flow Control in Ethiopian Transmission Networks using FACTS Devices
    (Addis Ababa University, 2022-07) Dagnachew Solomon; N. P. Singh (Prof.)
    At present Ethiopian transmission network is operating at its full capacity due to increased demand resulting in unbalances in power flows and voltage profile violations. Control of power and voltage through appropriate allocation of active and reactive power suppliers increases system efficiency without the need to expand and build new power generation and transmission facilities. Flexible AC Transmission System (FACTS) controllers employ the latest technology in the design of power electronic switching devices for electric power transmission systems to control voltage and power flow and improve voltage regulation. This study investigated the control ability of employed Thyristor Controlled Series Capacitors (TCSCs) in the alleviation of line congestion, loss minimization, and Static Var compensators (SVCs) in enhancing system voltage profiles in Ethiopian high voltage transmission networks. Modeling and simulation of the transmission network with the incorporation of the FACTS devices have been performed using PSAT/MATLAB toolbox. The sensitivity analysis technique was performed on base case power flow results for optimal placement of the controllers. It is shown how the system behaves and performance is improved with comparative case studies without and with the devices. The final power flow solution result with four FACTS (two TCSC and two SVC) show the improvements and reduction of system maximum line loading, total real power loss, and voltage regulations from 91.16%, 4.46% (115.1 MW), and  15.6% base case to 81.47%, 3.68% (94 MW), and  7.3% respectively by the FACTS.
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    Optimization of Security Constrained Economic Dispatch for Integrated Renewable Energy Systems
    (Addis Ababa University, 2021-06) Shewit Tsegaye; Getachew Bekele (PhD)
    One way of noticing the importance of electricity in our daily lives is when sudden interruption or blackout occurs. Considering a power system with Integrated Renewable Energy Systems (IRES) in which power supply interrupts every time it rains, such power system can cause serious damage to different types of loads connected, service centers and production plants. The main cause is the sudden increase or decrease in power output. According to Ethiopian electric power-network blackout report (2013-2016), 15 major blackouts were reported in three years’ time. Production plants and service centers were down for an average of four months a year. Natural incidents, equipment failure, and supply-demand mismatch collectively called contingencies cause most of these blackouts. The first challenging aspect of power system operation is that electrical energy, unlike other commodities; is difficult to store in significant amounts. Implying that electrical power must be consumed at same time it is generated. For a reliable supply of power, it is therefore essential to maintain the balance between generation and demand. This aspect requires an accurate method of balancing generation and demand considering generation limits, transmission security constraints, contingencies, and uncertainties. The other challenging aspect is the intermittency and variability of renewable energy sources. With increasing emphasis on improving efficiency and utilizing more renewable energy to mitigate climate change effects, power industry is confronted with such generation–demand mismatch challenges. These challenges are related to intermittency and non-dispatch ability of IRES. One of the daily power-system operation tasks that coins these challenges is Security-Constrained Economic Dispatch (SCED). SCED is a process of allocating generation levels to generating units to entirely and economically supply the load while satisfying security constraints. Practical power system economic dispatch is multi objective, constrained, and stochastic, as it has to consider the aforementioned challenges. Practically a solution method that can cope up with the varying generation is needed. This Ph.D. dissertation presents hybrid Genetic Algorithm-Hopfield Neural Network (GA-HNN) based optimization of SCED for IRES that address power mismatch problems of the Ethiopian power grid. Hopfield neural network can learn the stochastic behavior of varying generation and genetic algorithm can improve the convergence of global maxima by both reproducing and mutation the top solutions.This dissertation encompasses four main contributions. First, a review on recent trends and state of the art of SCED applied for renewable energy sources and hybrid systems is articulated. Second, development of global search algorithms that provide approximate solutions for SCED problem, and mathematical modelling of the objective functions of IRES is carried out. Third, study and assessments of security parameters with credible contingencies and uncertainty involving determination of the effect of contingencies and security constraints corresponding to renewable energy sources is made. Finally, optimal generation dispatch of modified IEEE 118 bus system and Ethiopian renewable energy system using hybrid GA-HNN is presented. According to the results obtained, hybrid GA-HNN helps to determine SCED global optimum solution of integrated, intermittent renewable energy systems. The obtained results include saving 0.519 million $/MW within 24 hours of operation at power loss of only 35.23 MW. This makes the proposed approach a strong financial solution in renewable energy markets. Utilizing hybrid GA-HNN resulted in the reduction of power mismatch by 23%. This mismatch enables power system operator deal with the unserved customers and unserved energy produce. Moreover, number of recursive blackouts were reduced by 12.36 % and execution time of the solution method by 56.89 %.
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    Comparative Studies of FACTS Devices for Power Loss Reduction and Voltage Profile Improvement in Radial Distribution Systems (Case Study: Sebbata-I Substation Outgoing Feeder)
    (Addis Ababa University, 2023-07) Tamene Adugna; Singh N.P. (Prof.)
    The power quality of any radial distribution system is determined in terms of voltage profile and power loss level of the system. The FACTS controllers can improve the performance of power transfer capability through controlling of the parameters of the distribution system. This thesis carries out comparative studies and performance analysis of DSTATCOM, SVC and UPQC devices in improving the performance of a radial distribution system. Sabbata-I substation 15 kV outgoing feeder-12 radial distribution network is considered to be a test system to evaluate the effectiveness of these devices. The location for placement of DSTATCOM, SVC and UPQC devices is determined by selecting the buses with higher values of loss sensitivity index which is calculated using MATLAB software. The size of these FACTS devices for each of the candidate buses are decided by using Particle Swarm Optimization (PSO) method. The effectiveness of each of these devices in improving the voltage profile and reducing the power loss under 75%, 100% and 125% of full load condition is evaluated through simulation studies. From the load flow analysis under normal operating conditions bus numbers 83, 36, 33, 81 and 54 are identified as weak buses for the integration of FACTS controllers. The simulation output reveal with installation of DSTATCOM device, the distribution system voltage profile enhanced by 1.86%, 2.97% and 4.18% under the respective loading conditions as compared to those of the system without installation of these devices. It is further observed that installation of SVC device improves the voltage profile by 1.65%, 1.75% and 1.86% while installation of UPQC device results in voltage profile improvement by 2.86%, 4.15% and 5.54% under the same loading conditions. It is also found that with installation of DSTATCOM device, reduction of the real power loss is 48.06%, 49.49% & 50.92% while installation of SVC device results in active power loss reduction by 34.45%, 33.51% and 31.02% under respective loading conditions. It is further observed that with installation of UPQC device, the real line loss is reduced by 64.85%, 65.72% and 66.61% under the same loading conditions. It is also found that with installation of DSTACOM device, the reactive power loss is reduced by 46.22%, 47.70% and 49.19% respective loading conditions. The simulation results further reveal that installation of SVC device results in reduction of reactive power loss by 35.91%, 34.45% and 31.70% while by using UPQC device the corresponding reactive power loss reduction is 64.13%, 65.02% and 65.93% under the respective loading conditions. The cost-benefit analysis reveals that installation of DSTATCOM, SVC and UPQC devices result in saving of 4,349,766.76 ETB, 2,945,561.84 ETB and 5,776,106.31 ETB respectively per annum under full load condition on account of power loss reduction. It is also found that the investment cost on account of installation of DSTATCOM, SVC and UPQC devices requires 8,780,813.64 ETB, 15,074,587.21 ETB and 11,728,658.22 ETB respectively under full load condition. It is concluded that effectiveness of UPQC device is better than those of DSTATCOM and SVC devices in regard to reducing the loss and enhancing the voltage profile of outgoing feeders under reduced, normal as well as overloaded operating conditions. Moreover, UPQC device is cost effective as compared to DSTATCOM and SVC devices. Therefore, use of UPQC device is recommended for power loss reduction and voltage profile improvement of distribution systems rather than using DSTATCOM and SVC devices.
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    Performance Evaluation of Transmission Lines for Power Loss Minimization and Voltage Profile Enhancement Using FACTS Devices (Case Study: 400kV-230kV Transmission Lines in the Ethiopian Power
    (Addis Ababa University, 2022-01) Tokuma, Zeleke; Getachew, Biru
    The transmission system is responsible for transporting the electric power generated at the generation station to the distribution system. When a power transmission system works with severely loaded lines, it suffers from power losses and larger voltage deviations, which can cause the system to malfunction and eventually collapse. Capacitor banks and STATCOM are used in this thesis in order to reduce line loss and enhance the voltage of the considered system. The power flow analysis using the Newton-Raphson algorithm in MATLAB software and particle swarm optimization techniques are utilized to determine the optimal devices sizing and position. The result shows that, with proper placement of the Capacitor banks and STATCOM on the identified candidate buses (68, 65, 27, 20) with their optimal sizes, the active power losses of the system gets improved by 10.78%, 20.57%, 35.84%, 6.602% and 10.76%, 22.29%, 37.79% , 7.76% in the scenarios of base load, 25% overload, 50% overload and 75% underload respectively. In scenarios of base load, 25% overload, 50% overload and 75% underload the voltage magnitudes of weak buses are also improved by 12.5%, 19.41%, 31.15%, 3.23% and 17.5%, 22.8%, 31.4%, 9.84% after the incorporation of Capacitor banks and STATCOM respectively. The improvements made by the placements of Capacitor banks and STATCOM in the 75% underload case are not so much significant as the network is almost in a desirable operating condition under this scenario. Thus, the placement of those FACTS devices for underload (75% of base load) is not recommended. The amount of energy cost saved after installing Capacitor bank is 1,825,856.88726 USD, 2,282,320.79712 USD, 2,518,262.57088 USD with Payback periods of 0.516 years, 0.186 years and 0.0579 years in the scenarios of base load, 25% overload and 50% overload respectively. And after installing STATCOM, the amount of energy cost saved is 15,339,987.264 USD, 31,399,157.216 USD, 33,744,416.832 USD with Payback periods of 4.344 years, 2.369 years and 0.485 years in the scenarios of base load, 25% overload and 50% overload respectively. In general, for power loss minimization and voltage profile enhancements, STATCOM is proposed for the system due to its better performance during overload as observed from the simulation results, manages over voltage at under load case and its dynamic capability to inject reactive power based on the required reactive load.
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    GIS Based Modeling and Performance Improvement of Distribution Network (Case Study: Adama Town 15 kV Distribution Network)
    (Addis Ababa University, 2021-12) Tefera, Derbe; Kiros, Tesfaye (PhD)
    Different Studies show that power distribution systems in Ethiopia is the weakest area compared to generation and transmission. In this thesis work, Geographic Information Systems (GIS) based modeling and performance improvement of Adama town 15kV distribution network was done that can enable operation and planning offices to take measurements based on the proposed methods. The attribute and electrical data are obtained from the already available data base and also additional data was collected on field visit. Then database was created and the network was mapped using Geographic Information Systems (GIS). By integrating the GIS database with the Electrical Transient Analyzer Program (ETAP), modeling and power flow analysis were done by ETAP Software for all ten (10) 15kV feeders under the study. Line 1 was selected as it is experienced significance power loss and voltage drop compare to the others. This thesis was mainly concerned with the power losses and voltage drop of the distribution network. Optimal Capacitor Placement (OCP), Conductor Upgrading (CU), and the combined solution of OCP and CU techniques were used to reduce power loss and improve voltage profile for both the normal and design scenarios for distribution network. The result shows that the combined solution of OCP and CU gives the maximum active power loss reduction (57.6%), followed by CU (42.9%) and OCP (32. 9%). It also shows the highest bus voltage prof ile (≥ 0.971pu), f ollowed by OCP (≥ 0.942pu) and CU (≥ 0.91pu). However, the combined solution of OCP and CU needs higher initial capital investment cost of Birr 8,652,573.61 with return of investment of 1.40 years, whereas CU and OCP needs initial capital investment cost of Birr 5,607,309.85 and Birr 3,045,263.76 with return of investment of 1.21 year and 0.86 year, respectively. Thus, among the three cases, OCP is selected f or the current scenario due to its best active power loss minimization and minimum voltage drop with best return of investment. On the other hand, the result for the design scenario (10 years forecast) shows that the combined solution of OCP and CU gives the highest active power loss reduction (57.7%), followed by CU (46.3%) and OCP (22.3%). It also shows the highest bus voltage profile (≥ 0.894pu), while the maximum bus voltage for CU and OCP were 0.840pu and 0.835pu, respectively. Hence, among the three cases, the combined solution of OCP and CU is selected for the design scenario (10 years load forecast) due to its best power loss minimization and minimum voltage drop. In general, the results of this study revealed that for short term solution, optimal capacitor placement (OCP) method is proposed, whereas for long term solution, the combined solution of optimal capacitor placement and replacement of overloaded conductor with optimal conductor size is proposed, to be implemented to improve the performance of distribution network on the bases of loss reduction and voltage profile improvement.
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    Study On the Power Loss Reduction and Voltage Profile Improvement of Kotebe Distribution System By Optimal Placement of D-Statcom Using a Hybrid Of Genetic Algorithm and Particle Swarm Optimization Method
    (Addis Ababa University, 2022-04) Biniyam, Abayneh; Fekadu, Shewarega (PhD)
    This research presents the way of improving the performance of the distribution network by improving the voltage profile and reduces the power loss by integrating D-STATCOM to Kotebe K3 distribution feeder. Kotebe distribution substation is one of the distribution substations found in Addis Ababa, Ethiopia feeding areas around Kotebe, Wesen, CMC, Figa and Gurdshola. Among those feeders, Kotebe K3 has been selected as test system due to its longest rout length, large loads and high permanent power interruption rate. The selected feeder has been modeled in MATLAB computational tool and load flow analysis has been simulated using Newton-Raphson method. It has been observed that the Newton-Raphson load flow simulation of Kotebe K3 gives a power loss of 1.7351 MW and 0.7080 MVAR respectively and 41 buses below the expected voltage range. This research uses a hybrid of Genetic Algorithm (GA) and Particle Swarm Optimization (PSO) for optimal placement and sizing of D-STATCOM for power loss reduction and improvement of voltage profile. The GA-PSO optimization technique considers both real and reactive power losses. The combined sensitivity factor uses both real and reactive sensitivity factors to identifying the candidate buses for D-STATCOM allocation. The combined sensitivity factor identifies bus 22,23,24,25 and 26 as the most five sensitive buses, which are used for placement of D-STATCOM. The GA-PSO optimized result shows that bus 22 is the most effective bus for placing D-STATCOM in terms of reducing the power loss at relatively small size and keeps the bus voltage under the acceptable range. The simulation result of the integrated D-STATCOM on bus 22 reduces the real power loss from 1.7351 MW to 1.0948 MW, which is by 36.90%, and the reactive power loss from 0.7080 MVAR to 0.4453 MVAR, which is by 37.11%, while maintaining all bus voltages in the range between 0.95 and 1.05pu. Furthermore, a comparison analysis shows that GA-PSO method gives the greatest reduction in both real and reactive power loss compared to GA and PSO methodologies.
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    Power Distribution System Failure and Vulnerability Analysis in Ethiopia Case Study : Kotebe Distribution System
    (Addis Ababa University, 2021-11) Ayalsew, Tariku; Getachew, Bekele (PhD)
    Distribution systems are usually the main areas where power outages occur. Electric power interruptions in the capital city of Ethiopia,i.e. Addis Ababa, are usual problems. Even there are situations that electric power interruption occurs several times a day. This thesis tries to identify the causes of power interruptions for the Kotebe distribution system and the vulnerability of the existing components. It is a componentbased failure analysis on a selected feeder of the distribution system. It is selected considering the total annual frequency of interruptions for each feeder of the distribution system. Feeder 6 of the Kotebe substation is the most frequently interrupted line. The existing conditions of the components on the feeder are inspected. Distribution poles, conductors, insulators, transformers, protection and other auxiliary devices are the inspected components. The probable effect of the most frequent causes of interruptions identified in the distribution on the poor distribution components is studied. Interruption during operation and maintenance is the common cause identified in the distribution. But this is through the order of the maintenance workers of the utility. Sudden faults are usually due to weather influences. It accounts for 48.66% of the total known faults excluding interruption due to operation. The vulnerability to failure of the existing distribution poles is identified through modelling the distribution poles, gravitational force of tilted poles and weather influence by COMSOL software. Decay depth of wooden poles considering the selected area weather condition is studied using TimberLife software, and its effect for failure is simulated using COMSOL. Poles will deflect upto 3.050 and 1.7490 with and without considering decay depth at the worst condition of a certain weather influence, respectively. Poles resilience condition is also identified by analyzing deflection and stress on their surface. Many of the existing distribution transformers are working overloaded. The loss of life of distribution transformers and their vulnerability is studied using the IEEE standard (C57.19-1995) guidelines. The hot spot temperature, ageing acceleration factor, and percent loss of life of each transformer are calculated. 83 of 157 transformers are expected to sustain below the IEEE standard expected life (i.e., 20.55 years). The effect of lightning considering soil resistivity of the area is also studied by modelling the feeder 6 of Kotebe distribution system using Matlab/Simulink. Metal Oxide Varistor(MOV) Surge arresters with grounding resistance above 25Ω would have higher surge magnitude that could damage the transformers and surge arresters.
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    Study and Analysis of Geomagnetic Induced Current in Ethiopian Electric Power System
    (Addis Ababa University, 2021-07) Habib, Abdurahman; Mengesha, Mamo (PhD)
    In this master thesis the effect of GIC on Ethiopian electric power system is investigated using the power world simulator software and python coding. GIC flowing in the transformers core lead to a higher magnetizing peak current, which produce a higher flux, that also contains a lot of harmonics. This leads to a large increase of eddy and circulating current in both windings and structural parts of the transformers, causing unnecessary heat generation. Such unnecessary heat generation causes tripping of transformers components like relays, SVC, capacitor bank controllers and burning of transformer sheet cores. GIC not only affect transformers but also affect transmission lines. The effect of GIC on power transmission lines is a high voltage drops at the receiving end due to the varied geo-magnetic and geo-electric field value. The equatorial electro-jet magnetic field ( GIC Max-H and GIC Max-L) undergoes variability in the high latitude region of Ethiopia and low latitude region of Ethiopia. The equatorial electro-jet magnetic field value for high latitude region of Ethiopia is 192 nT and the equatorial electro-jet magnetic field value for low latitude region of Ethiopia is 100 nT. The GIC is propagated from 45 degree to 315 degree eastward in the high latitude region of Ethiopia and from 135 degree to 225 degree westward in the low latitude region of Ethiopia. It is also found that the percentage of GIC flowing in the transformers core is approximately 1000 percent greater than the rated peak magnetizing current of the transformers. And finally, a GIC value of 34kA is measured in the high latitude region of ethiopia. For this GIC value of 34kA, an 80 MVAR of reactive power is absorbed by a transformers located in high latitude region of Ethiopia. The result showed that the Impact of GIC on transformers and transmission lines is severe in High latitude region of Ethiopia compared to the low latitude region of Ethiopia. The reactive power consumptions of transformers located in high latitude region of Ethiopia is high compared to low latitude region of Ethiopia. One of the primary reasons for such difference in reactive power consumption is that, the differences in the geomagnetic fields of the two region which is 360 T in high latitude region compared to 150 T for low latitude region. Therefore, it is recommended that EEP should re-arrange the position of the transmission lines and transformers with respect to GIC propagation to minimize the effect caused by GIC.
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    Assessment and Improvement of Reliability of Electrical Power Distribution System Case Study: - Sheno 15 Kv Distribution Feeder, Debre Berhan
    (Addis Ababa University, 2019-10) Meron, Alebachew; Singh, N.P. (Prof.)
    Distribution feeders are to deliver energy consistently to customers as electric power distribution systems reliability is a foremost concern to any electric power utility company. Power utility companies are working to provide reliable power through many systems. This thesis assesses the reliability of an electric power distribution feeder named Sheno 15 kV distribution feeder among the feeders that supplies an electric power to Debre Berhan city, an old city in Ethiopia. Power interruption data on daily basis for a period of two years on the feeder was collected and analyzed for the main causes of interruptions along with other two feeders namely Enewary and Aliyu Amba. Based on the data collected, system reliability indices (SAIFI, SAIDI, CAIDI, ASAI, EENS and ECOST) of the feeder were calculated using both mathematical and simulation methods andthe obtained results are 103.1271 f/customer.yr, 289.7872 hr/ customer.yr, 2.81 hr/customer interruption, 0.9669 Pu, 1361.01 MWhr/yr and 5,820,054 $/yr respectively. These values indicate poor reliability of the feeder when the results obtained are compared with averages of some countries. Currently, power utilities are trying to provide reliable electric power to their customers through many possible ways. Studying these methods; the method of adding a distributed wind power seems better option for our case study. Predictive reliability assessment of the feeder under study with the added distributed wind power along with possible locations of connection is performed and the results showed much improvement in system reliability indices of the feeder at bas bar 34(B34). These are 36.9719 f/customer.yr, 107.6154 hr/ customer.yr, 2.911 hr/ customer interruption ,0.9877 Pu , 579.565 MWhr/yr and 2,758,927 $/yr. Afterwards, the cost of realizing this method of reliability improvement for the distribution feeder has been performed. The cost analysis showed that reliability improvement with the help of distributed wind power can be realized economically.
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    Studies on Ethiopian High Voltage Grid Security Enhancement Using UPFC
    (Addis Ababa University, 2021-07) Gezahegn, Shituneh; Getachew, Biru (PhD)
    Nowadays, more attention is given for electrical energy transportation system security. Securing electrical energy transportation system in such a way that it can deliver the demanded energy both under normal steady state operation (NSSO) and contingency conditions is very important in a power system. Ethiopian Electric Power (EEP) manages and operates national power system centrally which consists of geographically dispersed generation stations and long-interconnected transportation system. In this study, existing national grid is modeled and the model under study has network elements of 106 buses, 146 transmission or sub-transmission lines, 51 transformers, 17 power plants, 23 lumped shunts and 69 merged loads. The grid is simulated using Power System Analysis Toolbox (PSAT) in MATLAB so that 30 top ranked MVA line flows of transmission lines (TLs) and 11 top ranked installed capacity of power plants (PPs) are selected for further outage case studies. The criticality of the selected contingent elements are ranked by using Overall Composite Severity Index (OCSI). Moreover, feasible locations for the UPFC deployment are identified using OCSI and Individual Severity Indice (ISI). Then, grid model with unified power flow controller (UPFC) is simulated both under normal steady state operation (NSSO) and contingency conditions. After all, the results obtained without and with UPFC deployment is compared in terms of TL loading and bus voltage of NSSO condition and in terms of Line Stability Index (LSI), Real Power Performance Index (PPI), Individual Composite Severity Index (ICSI) and OCSI for all outage case studies. At NSSO condition, 37 bus voltage limit violations (far below acceptable minimum voltage) without UPFC but 27 bus voltage limit violations with UPFC deployment yet appreciably improved. In addition, 400 kV TL from Gilgel Gibe II to Wolyta Sodo , 11_GG-II PP to 7_Wolyta, is overloaded without UPFC deployment hence, its line flow determined is 12.217675 pu apparently where its thermal limit is 12.17 pu but solved after UPFC is deployed i.e., the line flow changed from 12.217675 pu to 3.796130 pu. It is investigated from the simulations of the grid before UPFC deployment that 140 statically instable TLs when evaluated in terms of LSI, 5 overloaded TLs when evaluated in terms of PPI and 27 TLs’ limit violated when evaluated in terms of ICSI. Following the same procedures but with UPFC devices deployed on the grid: 90 TLs are statically stabilized, 41 TLs improved, and 9 TLs negatively impacted when evaluated in terms of LSI; overloading status of 2 TLs solved, and 3 TLs are a little bit negatively impacted when evaluated in terms of PPI and 17 limit violated TLs solved, 1 TL improved, and 9 TLs are negatively impacted when evaluated in terms of ICSI. Finally, the security of grid with UPFC deployed is enhanced for 38 contingency case simulations whereas for 2 contingency cases, it is negatively impacted as evaluated in terms of OCSI. As per the grid security enhancement evaluation carried out by using UPFC, the existing grid security is weak, and implementation of this study is highly recommended.
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    Energy Auditing and Conservation in Cement Plant (Case Study: Diredawa National Cement Plc)
    (Addis Ababa University, 2021-03) Gebregziabher, Gebremeskel; Getachew, Bekele (PhD)
    The cement production method has been extremely energy and price-intensive. To attain an actual and well-organized energy handling system, electrical and thermal energy review investigation was active on the cement plant. The cement plant requires 4,473.06 hours per year of the total operating hours to produce 587,375.67 tons of clinker. The factories have the problem of proper utilization of energy, due to lack of proper replacement, regular maintenance, and control efficiency of most industrial equipment and processing is lower than the expected. This study focuses on energy audit and conservations in an exceedingly national cement plant that has been victimization knowledge collected from the cement plant, an in-depth assessment has been taken on energy using and loss. Due to these losses, Energy efficacy evaluations of the most energy-intensive equipment such as electrical motors and drives, lamps have been done. Additionally establish technological opportunities to decrease the energy consumption of the plant, increase productivity, and improve the assembly method. Specializing in energy consumption reduction efforts through method improvement, production management, and introducing new technologies achieved vital results. By replacing the more efficient lamps (from T-12 to T-8 lamps) 92.52 MWh/year energy is conserved and saves 1713.33 Dollars/year. Motor Master international is used to choice good electric motor in form of efficacy, price-efficacy & energy conserving possible. Consequently, Motor Master + international software, 240.222 MWh/year energy is conserved and saves 13,223 Dollars/year. The Energy-efficient cement factory were nominated as a standard to compare their difference in electrical and fuel energy intensity (19.5 kWh/t and 779.4 KJ/Kg) and pays additional payments of 1, 1042,314.0974 Dollars per year.
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    Hybrid Active Power Filter Technique to Enhance Power Quality of Electric Railway Traction Substation (Case Study: Minilik Square Traction Substation NS27)
    (Addis Ababa University, 2020-11) Kibru, Zewdie; Mengesha, Mamo (PhD)
    Addis Ababa Light Rail Transit (AALRT) is an electrified railway traction system with large amount of harmonic currents being generated due to the nonlinear characteristics of rectifiers and inverters devices and inject the harmonics back into the grid. This has caused serious impact on the power supply network and resulted in power quality problems within the traction substation that has led to multifunction of some system components. For the overall quality of railway service, there should be reliable, efficient and safe power distribution systems by improving the power quality. The power quality enhancement has been proposed by using hybrid active power filter harmonic current compensation technique. This study presents theoretical and practical aspects in improving the power quality of Minilik Square NS27 railway traction substation network by reducing 11th and 13th harmonic currents using hybrid active power filter (HAPF). Simulation studies of the Minilik Square NS27 railway traction substation network is carried out using MATLAB Simulink in a discrete mode, variable step size with ode45 (Dormand-Prince) solver. The simulation results show that 11th order current harmonics is reduced from 26.99% to 3.75% while 13th order current harmonics is reduced from 11.05% to 4.38% at the point of common coupling (PCC). Consequently, the total harmonic distortion (THD) of currents at PCC is reduced from 88.19% to 80.55%. It is further noted that at primary side of the transformer 11th order current harmonics is reduced from 17.99% to 1.55% while 13th order current harmonics is reduced from 13.43% to 0.89%. Thus, the overall total harmonic distortion (THD) of currents is reduced from 26.46% to 6.88% on the primary side of the transformer. Furthermore, it is observed that the distortion power factor is also improved from 0.955 to 0.995 due to the reduction of 11th and 13th order harmonic currents. Therefore, the effective value of fundamental current has been improved due to the reduction of 11th and 13th order harmonic currents and consequently the corresponding active power in the traction network is also improved. Thus, the simulation results demonstrate the effectiveness of the proposed HAPF technique for selective harmonic currents reduction and thereby power quality enhancement of Minilik Square NS27 railway traction substation network of AALRT.
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    Active Power Flow Control in Ethiopian High Voltage Transmission Networks Using Phase Shifting Transformer to Enhance Utilization of Transmission Lines
    (Addis Ababa University, 2018-06) Yemane, Esayas; Fekadu, Shewarega (PhD)
    The electricity supply industry of Ethiopia is undergoing a major transformation that requires a redefined approach to increase the utilization of existing transmission line assets. Overloading of transmission lines in a power system sometimes result stability issues, which may lead to unwanted tripping or failure of equipments. The cause could be uneven loading of interconnectors or parallel transmission lines in meshed networks due to different impedances caused by the tower geometry, conductor sizing, number of sub-conductors and line length. Under these conditions, to ensure economical and reliable operation of the grid, active power flow through the lines should be controlled within their capability limits. In view of above, the power flow needs to be controlled in order to enhance utilization of high voltage transmission lines and secure the power system. Thus Control of power in AC network requires special technology to be implemented on case to case basis. Operating efficiency of electric transmission system can be improved by using appropriate Flexible Alternating Current Transmission System (FACTS) devices. Phase shifting transformer is one of the FACTS families, which can be used for power control in ac network. This thesis presents a study on active power flow control within Ethiopian network for optimum utilization of transmission lines using phase shifting transformer (PST). The study is performed first by reviewing literatures on the use of phase shifting transformers how to redirect active power flow in transmission networks throughout the world. To demonstrate the active power flow control in the network, a 400/400 kV phase shifting transformer having a size of 685 MVA with a phase shifting angle range of -200 to+200 and the high voltage transmission networks was modeled using PSSE software(Power System Simulation for Engineers) for the peak load of 2040 MW in the year 2017. From the power flow studies/solution, various overloaded and under loaded transmission lines are identified. By varying the phase angle of the phase shifting transformer, several simulations are conducted to investigate the impact of PST on the active power flow distribution. In this study, it has been demonstrated that the active power flow patterns which originally flow via the low impedance and lower voltage system is fully controlled and restructured using phase shifting transformer. By varying the phase shifting transformer angle, the active power flow in the transmission lines can be redirected towards the alternate high voltage path. As the Phase shifting transformer angle increased from -20° to +20°, the loading of Wolayta - Gibe II and Sebeta IIGibe II 400kV transmission lines vary from 4% to 35% and 11% to 42% respectively. Similarly, Gelan - Wolayta400kV transmission line load increases from 15% to 43% as the Phase shifting transformer angle decreases from +20° to -20° Conventional ways of solving the network bottlenecks based on reinforcement and building new transmission lines cannot be taken as sufficient and fast due to the problems of acquiring new corridors and environmental limitations. Installation of Phase Shifting Transformer in the transmission network is a better solution for controlling the active power flow and effective utilization of existing high voltage transmission network assets.
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    Fault Location Estimator Design for Power Distribution System Using Artificial Neural Networks
    (Addis Ababa University, 2018-07) Samuel, Shawul; Dereje, Shiferaw (PhD)
    Fault location in distribution system is critical issue to increase the availability of power supply by reducing the time of interruption for maintenance in electric utility companies. In this thesis fault location estimator for power distribution system using artificial neural network is developed for line to ground, line to line, line to line to ground and three phase to ground faults in distribution system. To develop this estimator one of rural radial power distribution feeder in Ethiopia, Oromia, Assela substation Gumguma line feeder is used as a test feeder. This feeder is simulated using ETAP software to generate data for different fault condition, with different fault resistance and loading conditions, which is the fault phase voltage and current. The generated data is preprocessed and put as an input for neural network to be trained. MATLAB R2016a neural network toolbox to train ANN and programming toolbox is used to develop graphic user interface for fault estimator. The feed forward multi layer network topologies of neural network with improved back propagation, Levenberg Marquardt learning algorithm is used to train the network. After the network (6-15-8-4) is trained the mean square error performance, regression plot and error histogram analysis was made and found to have an excellent performance with regression coefficient 0.99929 , validation performance of 0.000102 and error histogram range -0.015 to 0.019. In this thesis for practical implementation the fault records at the test feeder is handled by intelligent electronic device (IED) installed at the substation feeders. The fault record of IED can be read by PCM600 tool using laptop or manually using IEDs human machine interface, this fault recorded data feed to the graphic user interface to estimate the fault location as well as the fault type. Finally it is found that artificial neural networks are one of the alternate options in fault estimator design for distribution system where sufficient distribution network data are available with narrow fault location distance range from the substation. This has benefits in assisting for maintenance plan, saving efforts in fault location finding and economical benefits by reducing interruption time.
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    A Study on Blackout Problems of Ethiopian National Grid and Its Mitigation Techniques Using Adaptive Under Frequency Load Shedding Scheme
    (Addis Ababa University, 2019-06) Dagim, Dessalegn; Sing, P.N. (Prof.)
    An interconnected electric power system must balance load and generation in order to maintain frequency within acceptable range. The balance between generation and load within an interconnected electric power grid is expressed in the frequency of the system. Under frequency protection schemes are drastic measures employed if the system frequency falls below a specified value. Power system blackout is one of the worst events that power supply is totally interrupted so that industrial, commercial and domestic customers will be forced to use an alternate energy sources mainly diesel generators which are inefficient, expensive and environmentally not friendly. Under Frequency Load Shedding (UFLS) is a common technique to maintain power system stability by removing overload that might be created following system disturbance mainly during outage of power generating units. In this regard, the Ethiopian national grid under frequency load shedding scheme has been implemented many years before and it has not been revised despite the fact that a lot of big generating plants are connected in the grid. Due to this fact the system is unable to withstand major outages and system blackout is becoming frequent in our grid. The methodology used for the proposed load shedding algorithm is Adaptive Under Frequency Load Shedding (AUFLS) which considers both frequency and voltage as inputs for the design of AUFLS scheme. The disturbance magnitude is estimated using the rate of change of frequency and the location and the amount of load to be shed from each bus is decided using the voltage sensitivities. The national grid is properly modeled, and load flow and dynamic simulations are conducted using PSSE power system analyzing software for different disturbance cases that can affect the system frequency. The frequency and the voltage response for the simulated disturbance cases are analyzed and based on the results of the analysis new AUFLS scheme is proposed to improve performance of the existing UFLS scheme. The proposed AUFLS schemes are implemented on the modeled system and simulated again to see the performance of the new scheme. The study found out that the current under frequency load shedding protection is not supporting the grid for g
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    Long Term Distribution Expansion Planning with the Consideration of Distributed Generation (Case Study; Bishoftu Substation II)
    (Addis Ababa University, 2020-01) Wulta, Beletew; Getachew, Bekele (PhD)
    Nowadays, due to economic development of the country the electrical energy demand of Ethiopia increases by 30% yearly. But in order to satisfy customers’ power demand the planning and expansion of power must be done using a proper load forecasting method. This thesis is focused on demand forecasting of Bishoftu town and distribution expansion planning of Bishoftu substation II with the help of distributed generation. Historical energy demand data, historical energy growth rate, economic growth rate and distribution system’s reliability related data were assessed from Ethiopian electric power corporation and Bishoftu city administration. To forecast the load from 2019 to 2029 extrapolation simulation approach is applied. From the results of demand forecasting, it is found that the energy demand and peak demand in 2028 will be 2,005,457.41 MWH and 401.64 MW respectively. But the existing peak demand of the town is 54.7MW and the current total capacity of the distribution system is 43.8 MW. The existing distribution network cannot meet not only the future demand but also the existing demand. So, improving the reliability of the existing system with the help of distributed generation is required to expand the system and to meet the future demand. The Substation has encountered frequent power interruptions. The interruptions are caused mainly by short circuit (SC), earth fault (EF) and planned outages for operation and maintenance purpose. The substation’s System Average Interruption Frequency Index (SAIFI) and System Average Interruption Duration Index (SAIDI) are 199.92ints/yr and 264.22hrs/yr respectively. The reliability of the substation does not meet the requirements set by Ethiopian Electric Agency (EEA) which set (SAIFI =20 int/yr and SAIDI= 25hrs/yr). Then three feeders of Bishoftu substation-II are selected for connecting DG due to high frequency and long duration of interruptions. Distributed generation is a generation of an electric power close to the load which has resources like mini hydro, photovoltaic Array (PV), fuel cells, wind generators and micro turbines. In this thesis, microturbine is selected based on availability of the resource, cost factors, and utilization area. The size of single DG is 3.71MW but the total capacity of DG 11.13MW is fed to the grid as backup when there is an interruption. A simulation study for reliability analysis is carried out using DigSilent software. With the presence of DG, the simulation result shows that the reliability indices improved SAIFI by 65.16% and SAIDI by 75.62%.
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    Energy Auditing And Conservation In Textile Factories (Case study: Quiha Maa- Garment and Textile Factory)
    (Addis Ababa University, 2020-01) Goitom, Gebru; Getachew, Bekele (PhD)
    Sufficient and reliable supply of energy is needed to develop any country in the world. But there is a problem in conversion and usage of these energy sources that is they causes high energy wastage, high cost of energy to convert and use and high carbon emission to the environment. This is most of the time occur in developing countries like Ethiopia which has low knowledge on energy conservations and usage, this make to these developing counties to generate higher energy instead of using the existing energy effectively [1]. Industries like textile, sugar and cement factories consume a large amount of energy but do not use effectively which results in paying of extra money that affects to the factory and to the country in general. In this study we have used, software like Micro soft Visio and Microsoft excel to design diagrams and Motor Master Software which is used to select/choose the best and efficient motors based on their efficiency, cost effectiveness and energy savings. We have also used measuring devices such as portable flue gas analyzer, energy meter, thermograph, temperature probe, different reading gauges to get appropriate data of the equipment’s. Therefore, this thesis focuses on energy auditing and conservation in Quiha Maa-Garment and Textile Factory and its goal is to improve the energy efficiency of the industry by proposing energy efficiency increasing techniques. These techniques include replacing high energy consuming materials like changing of T12 lighting tubes by T8 lighting tubes, boiler air ratio control, implementing boiler flue gas waste heat recovery system, thermo boiler air ratio control, implementing thermo boiler waste heat recovery system, heat transport facility reinsulating, dyeing machine waste water heat recovery system, dyeing machine adiabatic paint coating, air compressor intake temperature improvement, using of energy efficient electric motors, changing damaged materials and by best rewinding of motors. It is found that by adopting the suggested energy conservation techniques, the total electrical energy saving is 90.3Mwh/yr and the thermal energy saving is 129.304 kl/yr. Thus, the total energy saving converted into the same unit (i.e., toe/yr) is 137.13toe/yr. Further, it is observed that carbon emission reduction due to electrical energy saving is 11.151 tc/yr and the reduction on account of thermal energy saving is 98.525tc/yr. Thus, the total carbon emission reduces to 109.676tc/yr. Furthermore, it is found that the saving in cost on account of electrical energy is 52,061.5 birr/yr (or $ 1735.4), due to saving in thermal energy is 2,197,699.15birr/yr($73256.64) and total cost is 2249760birr/yr Key Words: Maa-Garment and Textile Factory, energy efficiency improvement techniques, Microsoft Visio, portable flue gas analyzer, thermograph, Motor Master + international software.