Department of Electrical Engineeering

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Generation of electricity by using microbial fuel cell prototype fed by sewage: Cade study University of Dar ea.Salaam
(College of Natural and Applied Sciences, University of Dar es Salaam, 2023-03-31) Said, Mahir M; Saad, Asia A; John, Geoffrey R; Mushi, Aviti T
The access to electricity is still not reliable in Tanzania. Whilst, there are several locations within the country that have waste water cites that are not economically used to produce electricity.
Studying Dielectric Losses of Serially Combined Silicone Rubber and Epoxy Resin
(College of Engineering and Technology, University of Dar es Salaam, 2023-02-28) Mushi, Aviti Thadei; Justo, Jackson John; Kyaruzi, Alexander Lugatona
High voltage outdoor insulation systems are conventionally ceramics and glass with several advantages, such as proven in field, excellent dielectric properties, durability, and long life. However, they are heavy, attract vandals and break easily, and they can lose their dielectric properties easily when subjected to high voltage transients, arcing, and surges. To curb this, polymer insulators are used because they have excellent dielectric properties such as those of ceramics and glass, with the added advantages that they don’t break easily, and they recover their lost dielectric properties after any electrical transients. Therefore, this paper investigates the dielectric properties of polymeric materials – silicone rubber (SR) and epoxy resin (ER). Some of the SR samples were manufactured in the laboratory, and others were obtained from industrial manufacturer. All the ER samples were manufactured in the laboratory. The dielectric measurements were performed with the Insulation Diagnostics System. Within the measured frequency ranges, the dielectric losses of SR manufactured industrially differ with the laboratory manufactured specimens. This is due to presence of filler materials in the industrially manufactured samples. For the case of serially connecting the SR and ER, there was higher influence of dielectric loss of SR than the ER with some remarkable dielectric losses at some frequencies.
Comparison of On-Line Partial Discharge Detection Techniques for High Voltage Power Cable Joints and Terminations
(College of Engineering and Technology, University of Dar es Salaam, 2023-02-28) Chambela, Prisca Paul; Mushi, Aviti Thadei
Cable joints and terminations play a vital role in providing dependable electrical connection, mechanical support and physical safeguard. These provide electrical stress control to shielded power cables. Despite their usefulness, they suffer from partial discharges (PD) because of enhanced voltage stress, moisture ingress and poor workmanship (during installation). Therefore, it is necessary to undertake on-line PD detection to determine their state. Some of these techniques are capacitive coupler (CC); acoustic emission (AE); and high frequency current transducer (HFCT). This article presents a literature review of these techniques based on the cost, availability, and applicability. The comparative analysis is also provided on location of their sensors, quantification and detection ability. The CC technique involves the quantification of the coupler sensor input measured in mV/pC by realizing the time of flight between two sensors for which the results are used to estimate location of the PD. Meanwhile, the AE technique has an advantage of high immunity to electrical noise, with a caveat that acoustic signals are highly attenuated within the cable joints. Additionally, the combination of the acoustic sensors and PD electrical couplers can be used to discriminate PDs from electrical noise. The HFCT has two methods – with denoising (HFCT-WiD) and without denoising (HFCT-WoD). The HFCT-WiD technique can significantly reduce the sensor’s detection sensitivity due to its high value of noise to signal ratio (NSR). Comparatively, the HFCT has the best results of quantification and detection ability for PDs among all three techniques investigated. However, in places where electrical noise is severe, PD activities may be detected effectively with AE technique. Further work is needed to statistically map these methods and establish their correlation with experimental data.
Design of International Airport Hybrid Renewable Energy System
(Tanzania Journal of Engineering and Technology, 2023-02-28) Minja, Monyiachi Nelson; Mushi, Aviti Thadei
This paper presents the design and simulation of a hybrid renewable energy system, utilizing both solar and wind energy sources with a backup generator. The demand for reliable electric energy in support of investments in large social and economic developmental activities such as airport operations has been an agenda worldwide. In Tanzania, Mwanza International Airport (MIA) will expect to consume about 18 MVA annually of electricity power in support of its operations for the next 25 years. About 78-80% of the world commercial energy comes from fossil fuels. Non-renewable fuels apart from other negative effects contribute to global warming through emission of greenhouse gas, carbon dioxide. Additionally, most of centralized conventional methods of power generation require transmission systems, adding complexity of the system and poor power quality. Therefore, the proposal to use a mixed coupled hybrid renewable energy source to power the airport is necessary. The energy mix considered is solar photovoltaic (PV), wind, diesel generator and a battery. There is an average solar irradiation of 5.38 kWh/m2 and wind speed average of 4.20 m/s that could be converted to electricity by installation of a 10 kW wind turbine (this is enough to generate power for MIA) . The intermittency is taken care of by the diesel generator and the battery designed at 140 kVA and 400 Ah respectively. The project will be in operation for a period of 25 years hence its costs are reasonable and the justification is the potentiality of harvesting that estimated energy output of 18 MVA which will meet the load for MIA. The second reason is that for the next 25 years, once the turbine is installed, there will be no further investment on the same. Some mathematical computations were performed and, in the end simulation results displayed different techno-economic Hybrid Renewable Energy Source (HRSE) configurations. The complete design of the selected system would include 78.48 kW PV system comprising 314 pieces of 200 W poly-crystalline modules, 608 batteries of 83.4 Ah, 12 V rating, 140 kVA diesel generator, and 41.64 kVA bidirectional converter. The net present cost of the selected design is US$357,780.8, cost of energy is 0.93US$/kW, and minimum renewable fraction is 40.2%.
Review of On-Site testing and partial discharge diagnosis of power cables
(University of Dar es Salaam, 2022-10-21) Matamwe, Mburuga M; Mushi, Aviti Thadei
Power cables and other high voltage equipment suffer from voltage stress and other environmental factors. As a result, deterioration occur to the equipment. Due to this, power engineers employ On-Site testing (OT) and partial discharge (PD) diagnosis widely to determine the health of these power equipment, especially the cables. Through these tests, it is possible to identify patterns of deterioration and localization of the failures of power cables. Both the OT and PD are nondestructive testing methods and can conveniently be used for cables that are in operation. Therefore, this review paper undertakes to elucidate the OT and PD and how these methods can be used to predict the future condition of the power cables. Both the significances and challenges of these methods are discussed. The review further covers best practice for cable testing by using different methods of testing for such as frequency tuned resonance testing system in the frequency range of 20 – 300 Hz. Some recommendations are made to technical teams of utility companies as to the import of the OT and PD testing in order to avoid shortening of power cable life.
A review on On-Line partial discharge detection techniques for high voltage power cable joints/terminations
(University of Dar es Salaam, 2022-10-21) Chambela, Prisca Paul; Mushi, Aviti Thadei
Cable joints and terminations play a vital role in providing dependable electrical connection, mechanical support and physical safeguard. These provide electrical stress control to shielded power cables. Despite their usefulness, they suffer from partial discharges (PD) because of enhanced voltage stress, moisture ingress and poor workmanship (during installation). Therefore, it is necessary to undertake on-line PD detection to determine their state. Some of these techniques are capacitive coupler (CC); acoustic emission (AE); and high frequency current transducer (HFCT). This article undertakes a literature review of these techniques based on the cost, availability, and applicability. The comparative information is provided on location of their sensors, quantification and detection ability. The CC technique involves the quantification of the coupler sensor input measured in mV/pC by realizing the time of flight between two sensors for which the results are used to estimate location of PD. The AE technique has an advantage of immunity to electrical noise, with a caveat that acoustic signals are highly attenuated within the cable joints. Additionally, the combination of the acoustic sensors and PD electrical couplers can be used to discriminate PDs from electrical noise. The HFCT has two methods – with denoising (HFCT-WiD) and without denoising (HFCT-WoD). The HFCT-WiD technique can significantly reduce the sensor’s detection sensitivity due to its high value of noise to signal ratio (NSR). Comparatively, the HFCT has the best results of quantification and detection ability for PDs among all three techniques investigated. However, in places where electrical noise is severe, PD activities may be detected effectively with AE technique. Further work is needed to systematically establish the advantages of all these methods so that high voltage engineers decide which method to use depending on available resources.
Dielectric properties of series joined silicone rubber and epoxy resin formulations
(University of Dar es Salaam, 2022-10-21) Mushi, Aviti Thadei; Kyaruzi, Alexander
Dielectric frequency spectroscopy of polymer materials were done in laboratory. The aim was to investigate the (i) differences in dielectric losses of the industrially manufactured silicone rubbers against laboratory manufactured silicone rubbers, (ii) differences in dielectric losses for the epoxy resin samples manufactured in laboratory, but with different curing time, and (iii) differences of dielectric losses between each single polymer to the losses of the series joined specimens of the two polymers. The measurements were done using the Insulation Diagnostics System in laboratory at ambient room conditions. It has been found out that for different frequency ranges, silicone rubber manufactured industrially differ with the laboratory manufactured specimens. The series joined specimens show higher influence of the silicone rubber in both curve shape, and values of losses at frequencies lower than 1 Hz. At frequencies lower than 1 Hz the joined specimen losses are higher than losses for epoxy resin and lower than those for silicone rubber. At frequencies higher than 1 Hz the losses of the joined samples are close but slightly lower to those of epoxy resin and higher than those of silicone rubbers. Lastly, the curves of the joined specimens have shapes which strongly resembles those of the silicone rubbers.
Design and simulation of hybrid renewable energy sources for Mwanza International Airport
(University of Dar es Salaam, 2022-10-21) Minja, Monyiaichi Nelson; Mushi, Aviti Thadei
This paper presents the design and simulation of hybrid renewable energy sources utilizing both solar energy and wind energy sources with a backup generator. The demand for reliable electric energy in support of investments in large social and economic developmental activities such as airport operations has been an agenda worldwide. In Tanzania, Mwanza International Airport (MIA) consumes about 18 MVA annually of electricity power in support of its operations. About 78–80% of the world commercial energy comes from fossil fuels. Non-renewable fuels apart from other negative effects contribute to the global warming through destruction of ozone layer. Additionally, most of centralized conventional methods of generation require transmission systems, add complexity of the system and poor power quality. Therefore, the proposal to use a mixed coupled hybrid renewable energy source to power the airport is necessary. The considered energy mix are solar photovoltaic, wind, diesel generator and a battery. There is an average solar irradiation of 5.38 kWh/m2 and wind speed average of 4.20 m/s that is able to be converted to electricity by installation of 10 kW wind turbine. The intermittency is taken care of by the diesel generator and the battery designed at 40 kVA and 400 Ah respectively. The project will be in operational for a period of 25 years hence its costs are reasonable and the justification is the potential of the estimated energy. Some mathematical computations were performed and, in the end simulation results displayed different techno-economic HRES configurations. The complete design of the selected system would include 78.48 kW PV system comprising 314 pieces of 200 W poly-crystalline modules, 608 batteries of 83.4 Ah, 12V rating, load following dispatch strategy, 140 kVA diesel generator, and 41.64kVA bidirectional converter. The net present cost of the selected design was $357,780.8, cost of energy $0.93/kW, and minimum renewable fraction of 40.2%.
Viability Analysis of Ubungo II Gas Power Plant Efficiency Improvement Using Co-generation System
(Tanzania Journal of Engineering and Technology, 2022-08-05) Nyanda, Elias E.; Mushi, Aviti T.; Justo, Jackson J.
The power utility, Tanzania Electric Supply Company Limited (TANESCO) is faced with challenges of supplying adequate power to the ever-increasing demand. To this end, this paper explores the installed Ubungo Gas Power Plant (UGP II) located in Dar es Salaam to find means of utilizing it in co-generation method. The study embarked on detailed modelling of the system and run simulations which indicated that the co-generation can result to power generation efficiency increase between 10.42 to 50.92%. It is recommended to change the UGP II to exploit this co-generation method. Further, the study could be improved by including more parameters of the gas and steam plant and verify them experimentally.
Renewable Energy Microgrids to Improve Electrification Rate in Democratic Republic of Congo: Case of Hydro, Municipal Waste and Solar
(Tanzania Journal of Engineering and Technology, 2022-08-05) Josue, Ngondo Otshwe; Mushi, Aviti Thadei
Worldwide, it is imperative for citizens to have access to electrici-ty. This applies to Congolese--rural and urban dwellers, and if possible, it should be guaranteed by government’s laws and poli-cies. However, the rural and urban areas of Democratic Republic of Congo (DRC) suffer majorly from lack of access to electricity. The major reasons are the high costs associated with connection to the national central grid and production insufficiency. There-fore, one feasible approach to electrify these areas is to use mi-crogrids. This technology is decent and viable option for energy revolution since it incorporates energy storage systems, distribut-ed generators, and localized loads. This paper has taken to im-plement this solution by firstly analysing some cities located at the borders of large rivers or watercourses (with known depth and width), such as the Congo River considered for hydrokinetic pow-er (HKP). However, where the Congo River does not pass through, the paper will consider largest rivers passing in the area. For the case of photovoltaic electricity production, large cities are considered those with good sunshine and large population who have purchasing power for the photovoltaic electricity. The waste to energy power plans will consider the top ten densely populated cities in DRC. The proposed microgrids will operate in isolation (islanded) mode. This paper proposed 44 projects to generate 795 690 kW total energy from the microgrids. These energies are divided as 661 000 kW from solar photovoltaic, 83 790 kW from waste to energy, and 50 900 kW from hydrokinetic generation. The urban share will be 94.9% and rural area share will be 5.1% of this generation. Further work needs to include biomass as a possible renewable energy to add in the mix.
Feasibility analysis of using SWER for Homboza village electrification
(University of Dar es Salaam, 2020-09-25) Irechukwu, Michael Enyinaya; Mushi, Aviti Thadei
The electrification level in Homboza village, one of the many rural areas in Tanzania, is very low. Out of the 5,565 Homboza dwellers, less than 10 percent access electrical energy. The major barriers to improved electrification rates in rural communities are high investment costs of extending the grid to rural areas, and the small, dispersed nature of electricity demand, arising from a population of low density and low-income levels. To overcome these, this paper proposes Single Wire Earth Return (SWER) electrification scheme. This is because SWER's installation costs are about one third of a three-phase system and a half of the single phase system. This paper presents a Carson line model of SWER for Homboza village and is simulated in MATLAB/Simulink, and for comparison, a single-phase system is simulated too. The simulation results show that the earth potential between the ground electrodes is 18.15 V for the SWER. Further, SWER shows 10.07% voltage drop and 10.34% power loss over 20 km of distribution line, while single phase system shows 18.89% voltage drop and 19.58% power loss over the 20 km of distribution line. There is a possibility of supplying Homboza using SWER technology.
Performance Evaluation of DSTATCOM for 180 km 33 kV Feeder from Shinyanga to Bariadi in Tanzania
(Jordan Journal of Electrical Engineering (JJEE), 2021-12-01) Mhagama, Godfrey; Mushi, Aviti Thadei; Kundy, Beda Jerome
Tanzanian medium voltage of 33 kV and 11 kV is used as the system voltage for primary distribution feeders. The design of these feeders is mainly radial topology. Due to the nature of dispersed and scattered load centers (towns) in Tanzania [1], the feeders have to run over long routes, such as the 180 km 33 kV Shinyanga–Bariadi line [2]. The feeder runs all this distance without any voltage control compensators; thus at the receiving end, it suffers a voltage drop of more than 7%. The result of this voltage drop is failing to start the large water pumping motors connected close to the end of the feeder, especially during peak load. Voltage improvement can be achieved using the volt-ampere reactive (VAR) compensation, series compensation and flexible alternating current transmission system (FACTS). However, these methods cannot handle dynamic voltage changes effectively. Therefore, fast reactive power compensation is necessary [3]. Distribution static synchronous compensator (DSTATCOM) can provide fast and continuous reactive power (𝑄) compensation to control the voltage of the feeder. However, off-the-shelf DSTATCOM cannot be used without the knowledge of the line parameters, control, power and other data of the feeder. Therefore, this paper proposes the use of the DSTATCOM for the 180 km 33 kV feeder for the Shinyanga– Bariadi line.
Optimal Design of Hybrid Renewable Energy for Tanzania Rural Communities
(Tanzania Journal of Science (TJS), 2021-12-01) Marcel, Ester Thomas; Mutale, Joseph; Mushi, Aviti Thadei
Rural communities in developing countries lack access to electricity due to high costs of grid extension. This paper proposes a hybrid system of renewable energy (HRES) as solution. The HRES consists of solar, wind, and battery energy storage (BES). The village called Ngw’amkanga in Shinyanga region of Tanzania, East Africa is selected as a case study. An iterative method to determine the size of wind and solar photovoltaic (PV) generation required assuming a project life of 25 years at minimum annualised cost of the system ( ) is proposed. The project life time is fixed on the life span of the main component, solar PV at 25 years. The iteration is undertaken to meet the energy demand ensuring the BES is charged throughout the year. The required BES has three days of autonomy, and a maximum battery depth of discharge 50%. At minimum ACS, the HRES comprises only solar PV and BES, due to insufficient wind at this site. The levelised cost of energy ( ) of the HRES is 27.18 p/kWh, paid by the users. This is cheaper than the grid connected small power producers of Tanzania as discussed in the paper.
NON-CERAMIC INSULATORS IN COASTAL TROPICAL CLIMATES-The Case Study of Tanzania Field Performance of Polymeric Insulators and Dielectric Characteristics of Silicone Rubber and Epoxy Resin Formulations
(The University of Dar es Salaam, 2010-08) Thadei, Aviti
Since use of non-ceramic insulators (NCIs) began worldwide in 1970s, researchers have been busy perfecting these products, monitoring them in service and analysing their failure modes. In Tanzania, there is need to monitor and evaluate NCIs for use in its tropical climates. This tropical climate is characterised by heavy rains, high insolation resulting to high temperatures and high humidity. One aim is to investigate and evaluate aging and performance of NCIs in these climates regarding their hydrophobicity (HC), layer conductivity, quantifying oxidation and chalking indices. Another aim is investigation in order to characterise the dielectric properties of polymeric formulations. Achieving those objectives necessitated adopting methods such as field visits, Swedish Transmission Research Institute (STRI) guide for HC measurements, guide for visual observations of damage and deterioration (STRI, 2005) and Fourier Transform Infrared Spectroscopy (FTIR) spectra. In addition, characterising the polymeric formulations used surface and volume resistivity methods and dielectric frequency spectroscopy. Fit of the resistivity data to curves used robust regression methods, which are resistant to outliers. Results indicated excellent performance of NCIs in Tanzania regardless of poor HC, higher layer conductivity caused by high contamination, deterioration and damage. Contamination caused failure of one insulator from Masaki substation with its surfaces showing presence of oxidation and chalking products. In addition, High Voltage yard insulators showed varying degrees of material deterioration and layer conductivity with varying degrees of HC. Dielectric characterisation of polymeric formulations showed higher surface and volume resistivities. Furthermore, there were higher dielectric losses in silicone rubber (SIR) than in epoxy resin. SIR displayed both low and higher frequency relaxations whereas epoxy resin displayed higher frequency relaxations. There was low and higher frequency relaxation exacerbated by electrode polarisation in series combined SIR and epoxy resin. The dielectric losses contained dc conductivity, hopping conductivity and electrode polarisations. With these findings, the Tanzania utility is urged to speed up upgrading insulation for distribution and transmission lines. In addition, it could set up a R&D department to deal with NCIs.
The 3rd International Training Course in Information Technology-based for Electric Engineering Education
(2009-11) Mushi, Aviti Thadei; Justo, Jackson John
This is a report from the representatives of Tanzania to the Third International Training Course in Information Technology-based for Electric Engineering Education. It was held at Electronic Engineering Polytechnic Institute of Surabaya (EEPIS).
Research Training Fellowship for Developing Country Scientist (RTFDCS) Report
(2011-03) Mushi, Aviti Thadei
Natural phenomena and advances in technology have worsened electromagnetic energy emission to the environment. This electromagnetic energy emanate from both intentional and non-intentional sources. This energy when it attains enough strength affects and interferes with the operations of most electrical and electronic equipment. Generally these effects are called electromagnetic interference (EMI) noise. Power electronic converters are mostly either sources or victims, or both, at the same time, of the EMI noise. Stricter EMI regulations, circuit miniaturisation along with advances in semiconductor switching speeds have created difficult engineering tradeoffs for designers of power electronic equipment. Faster switching requirements on power devices in order to reduce losses and device size inherently result in increased high frequency EMI noise. This noise brings about the problem of nonconformity to electromagnetic compatibility (EMC) standards. Also, the miniaturisation happening nowadays causes power electronic converters to become susceptible to the noise they generate.
Proposing Mixed Coupled Hybrid Renewable Energy Sources for Mwanza International Airport
(University of Dar es Salaam, 2021-11-12) Minja, Monyiaichi Nelson; Mushi, Aviti Thadei
Mwanza International Airport (MIA) consumes about 18 MVA annually. It is expensive to depend totally on the grid and the backup diesel generator (DG) alone. Therefore, this paper proposes a mixed coupled hybrid renewable energy sources (MCHRES) to power the airport. The considered energy mix are solar photovoltaic (PV), wind, DG and a battery. The energies are estimated based on the site data, and the power system components are designed and their prices are presented. The project costs are reasonable and the justification is the potential of the estimated energy.
Grid Connected PV-Wind Energy System for Luxmanda Village in Tanzania
(University of Dar es Salaam, 2021-11-12) Fungo, Lucy Joseph; Mushi, Aviti Thadei; Msigwa, Consalva Joseph
There are rural areas in Tanzania which still lack access to the national grid. One of such locations is Luxmanda village in Manyara region. This village gets its power from islanded renewable energies microgrid (MG) which is able to supply about 25.4 kW. However, this is way below the projected consumption. Therefore, this paper proposes connecting the islanded MG to the grid to supply enough power to the village for prosperity. The paper discusses the solar photovoltaic generation, wind generation and the DC grid. Steady state operating of the MG is established at 750 V DC.
DC Voltage Regulation of Solar PV/Wind and Biofuel System Incorporating Battery Storage
(University of Dar es Salaam, 2021-11-12) Juma, Mwaka Ismail; Mwinyiwiwa, Bakari Mohammedi Mfaume; Msigwa, Consalva Joseph; Mushi, Aviti Thadei
Tanzania has several places which lack the access to grid. These areas can be powered by utilizing hybrid energy systems (HES) such as solar photovoltaic, wind, and biodiesel. However, such a system produces voltage control challenges at the DC bus due to stochastic nature of those sources, if battery is not coupled. Therefore, this paper first proposes a HES that is coupled to a battery. Secondly, it proposes a control that can regulate the three sources of energy such that the DC bus is maintained at 750 V. Simulation results have shown that a conventional proportional and integral controller can achieve DC bus voltage regulation for the system proposed in this paper regardless of irradiance variation, wind speed variation, or the load variation. This type of energy sources is feasible for use in rural arrears of Tanzania.
Design of a Hybrid Energy System with Energy Storage for Standalone DC Microgrid Application
(Multidisciplinary Digital Publishing Institute, 2021-09-21) Juma, Mwaka Ismail; Mwinyiwiwa, Bakari Mohammedi Mfaume; Msigwa, Consalva Joseph; Mushi, Aviti Thadei
This paper presents microgrid-distributed energy resources (DERs) for a rural standalone system. It is made up of a solar photovoltaic (solar PV) system, battery energy storage system (BESS), and a wind turbine coupled to a permanent magnet synchronous generator (WT-PMSG). The DERs are controlled by maximum power point tracking (MPPT)-based proportional integral (PI) controllers for both maximum power tracking and error feedback compensation. The MPPT uses the perturb and observe (P&O) algorithm for tracking the maximum power point of the DERs. The PI gains are tuned using the Ziegler–Nichols method. The developed system was built and simulated in MATLAB/Simulink under two conditions—constant load, and step-load changes. The controllers enabled the BESS to charge even during conditions of varying load and other environmental factors such as change of irradiance and wind speed. The reference was tracked extremely well by the output voltage of the DC microgrid. This is useful research for electrifying the rural islanded areas which are too far from the grid.

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