Browsing by Author "Manyahi, Mighanda J."

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    Conceptual Synthesis of Multi-Source Renewable Energy Based Microgrid
    (World Academy of Science, Engineering and Technology, 2013-12) Mwinyiwiwa, Bakari M. M.; Manyahi, Mighanda J.; Gregory, Nicodemu; Kyaruzi, Alex L
    Microgrids are increasingly being considered to provide electricity for the expanding energy demand in the grid distribution network and grid isolated areas. However, the technical challenges associated with the operation and controls are immense. Management of dynamic power balances, power flow, and network voltage profiles imposes unique challenges in the context of microgrids. Stability of the microgrid during both grid-connected and islanded mode is considered as the major challenge during its operation. Traditional control methods have been employed are based on the assumption of linear loads. For instance the concept of PQ, voltage and frequency control through decoupled PQ are some of very useful when considering linear loads, but they fall short when considering nonlinear loads. The deficiency of traditional control methods of microgrid suggests that more research in the control of microgrids should be done. This research aims at introducing the dq technique concept into decoupled PQ for dynamic load demand control in inverter interfaced DG system operating as isolated LV microgrid. Decoupled PQ in exact mathematical formulation in dq frame is expected to accommodate all variations of the line parameters (resistance and inductance) and to relinquish forced relationship between the DG variables such as power, voltage and frequency in LV microgrids and allow for individual parameter control (frequency and line voltages). This concept is expected to address and achieve accurate control, improve microgrid stability and power quality at all load conditions.
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    Lightning Strike on Overhead Telephone Line: A Case Study of Tanzanian Telecommunications Company (TTCL)
    (IEEE, 2007) Damas, Jacqueline; Mvungi, Nerey H.; Manyahi, Mighanda J.
    Recently there have been a growing concern over the lightning caused damages, and disturbances on the consumer operated equipments utilizing a telephone line. This concern has been attributed by the fact that most of today’s consumers’ equipments comprise of electronic devices or microprocessor controls that operate at low voltages, which can be superceded by even distant lightning strike. Lightning strike can be either direct or indirect, which causes induced voltage along the telephone lines when it strikes on to the line or at a distance from the line. In this paper the induced voltages on a conductor of 7m height above the ground are calculated as a function of distance from the strike point using Finite Difference Time Domain (FDTD) method, as it could be a necessary data for deciding the possible future protection scheme. It has been shown that finitely conducting ground (lossy case) has pronounced effects for lightning surge propagation and induced amplitude overvoltages along the telephone line above the ground and can not be neglected in the calculations of the induced overvoltages along the line due to lightning strike compared to an infinitely conducting ground (lossless case).
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    On the Viability Analysis of HVDC Light for Electrification of Mafia Island by National Grid
    (International Refereed Journal of Engineering and Science (IRJES), 2015-01) Gabriel, Sospeter; Mwinyiwiwa, Bakari M. M.; Manyahi, Mighanda J.
    HVDC Light systems range from 3MW to about 1000MW transmission technology combining power converters and DC cables. The power converters are based on Voltage Source Converters (VSC) and Pulse Width Modulation (PWM) control. The use of series connection of power semiconductors such as IGBTs is fundamental to the development of the HVDC Light technology. HVDC Light is excellent for underground and under water power transmission. By use of HVDC Light power converters and cables, it is possible to overcome the technical difficulties to connect small loads and small scale generating units to the AC grid and to make the connection economical and environmentally friendly. This paper presents viability analysis of using HVDC Light technology for electrification of Mafia Ireland (Tanzania) from the national grid. In the paper the load demand forecast has been performed to estimate the load for the next 25 years at Mafia Island. HVDC Light model has been developed and simulated using MATLAB/Simulink software. The simulation results show that HVDC Light system performance is capable of delivering reliable and quality power when the Mafia Island is supplied by national grid using HVDC Light system. The benefits include more reliable power supply reduced environmental effects.