1,721,000 research outputs found
Advanced Optimal Twin‐Setting Protection Coordination Scheme for Maximizing Microgrid Resilience
Get PDFThe increasing penetration of distribution generators (DGs), such as PV systems, has led to a significant power protection concernfor optimal overcurrent coordination. However, existing literature indicates that the traditional phase over current relay (OCR)scheme faces challenges such as instability, insensitivity, and lack of selectivity when handling the integration of DGs andground fault scenarios. To address this issue, this study proposes a new optimal twin-setting OCR coordination scheme forphase and ground events using standard and nonstandard tripping characteristics. The water cycle optimization algorithm(WCOA) is utilized to develop a coordinated optimum strategy that mitigates the effects of DGs on the currents and locationsof faults across the power grid. To demonstrate the efficacy of the proposed approach, different case studies of an IEEE powernetwork (9 buses) equipped with two 5 MW PV systems are conducted using industrial software (ETAP). Under various faultconditions (phase and ground faults) and power network operation modes (with and without PVs and islanding modes), theoutcomes of the newly developed optimal coordination scheme are compared to the results of conventional schemes. Theproposed twin OCR coordinating scheme is found to reduce the total tripping time of OCRs up to 62.3% and increase theselectivity of the relays without miscoordination events
Induction motor steady-state performance under varying quality of supply and stator winding short circuit location using negative sequence current.
Get PDFMasters Degree. University of KwaZulu-Natal, Durban.Abstract available in the PDF.Abrreviations on page v
Reliability of multi-channel IEC 61850 mission-critical substation communication networks based on Markov process incorporating linear dynamical systems and calculus inferences.
Get PDFDoctoral Degree. University of KwaZulu-Natal, Durban.IEC 61850 based Substation Communication Networks (SCN) enable substation processes to be digitalised to fulfil the most sought substation monitoring, protection and control of electrical systems. The standard enables peer-to-peer communication of mission critical messages, aided by onboard diagnostic capabilities to ease the identification of system faults. The implementation of Safety-Related Systems in industrial facilities comprising sensors, logic solvers and final elements in power distribution centres necessitate compliance to IEC 61508 standard, where circuit breakers act as final elements to isolate electrical machines. In recent times, combinatorial methods such as the Reliability Block Diagram have been used to evaluate the architecture of IEC 61850 based SCN reliability and availability due to the simplicity of the approach. These methods, however, assume that all system faults are identified and fully repaired, which is not the case in practice. In this thesis, the reliability of a repairable multi-channel IEC 61850 based SCN architecture is modelled using a structure function and the Markov process while Systems Thinking integrates imperfect repair factors into the model. Thereafter, a novel eigenvalue analysis method based on Markov partitions
and symbolic dynamics in the context of linear dynamical systems is used to investigate the impact of imperfect repairs on the system's reliability based on the number of mean state transitions and dynamical behaviour. The eigenvalue method is then advanced by a complimentary analysis technique based on the absorbing Markov Chain process and matrix calculus methods to determine the system's responsiveness to repair factors. The case studies results demonstrate that imperfect repairs cannot be ignored for mission-critical applications because the simplifying assumptions of combinatorial analysis methods greatly over-state the system's reliability performance. The results also indicate that common causes of failure coupled with imperfect repairs significantly negatively impact the system's performance.
Moreover, system performance is highly dependent on the diagnostic coverage of the individual subsystems than their repair efficiencies for high diagnostic coverages at 90% and 99% based on ISO 13849-1. Hence, the results demonstrate that emphasis should be more on the system diagnostic coverage for the fact that it is embedded in the system design itself that cannot easily be changed once the system is commissioned and operational
Maximum power point tracking algorithm for photovoltaic home power supply.
Get PDFThesis (M.Sc.Eng)-University of KwaZulu-Natal, Durban, 2011.Solar photovoltaic (PV) systems are distributed energy sources that are an environmentally friendly
and renewable source of energy. However, solar PV power fluctuates due to variations in radiation
and temperature levels. Furthermore, when the solar panel is directly connected to the load, the power
that is delivered is not optimal. A maximum peak power point tracker is therefore necessary for
maximum efficiency.
A complete PV system equipped maximum power point tracking (MPPT) system includes a solar
panel, MPPT algorithm, and a DC-DC converter topology. Each subsystem is modeled and simulated
in a Matlab/Simulink environment; then the whole PV system is combined with the battery load to
assess the overall performance when subjected to varying weather conditions.
A PV panel model of moderate complexity based on the Shockley diode equation is used to predict
the electrical characteristics of the cell with regard to changes in the atmospheric parameter of
irradiance and temperature.
In this dissertation, five MPPT algorithms are written in Matlab m-files and investigated via
simulations. The standard Perturb and Observe (PO) algorithm along with its two improved versions
and the conventional Incremental Conductance (IC) algorithm, also with its two-stage improved
version, are assessed under different atmospheric operating conditions. An efficient two-mode MPPT
algorithm combining the incremental conductance and the modified constant voltage methods is
selected from the five ones as the best model, because it provides the highest tracking efficiencies in
both sunny and cloudy weather conditions when compared to other MPPT algorithms.
A DC-DC converter topology and interface study between the panel and the battery load is performed.
This includes the steady state and dynamic analysis of buck and boost converters and allows the
researcher to choose the appropriate chopper for the current PV system. Frequency responses using
the state space averaged model are obtained for both converters. They are displayed with the help of
Bode and root locus methods based on their respective transfer functions. Following the simulated
results displayed in Matlab environment for both choppers, an appropriate converter is selected and
implemented in the present PV system. The chosen chopper is then modeled using the Simulink
Power Systems toolbox and validates the design specifications.
The simulated results of the complete PV system show that the performances of the PV panel using
the improved two-stage MPPT algorithm provides better steady state and fast transient characteristics
when compared with the conventional incremental conductance method. It yields not only a reduction
in convergence time to track the maximum power point MPP, but also a significant reduction in
power fluctuations around the MPP when subjected to slow and rapid solar irradiance changes
Interconnection of solar power to the grid through the power plant auxiliary system.
Get PDFM. Sc. Eng. University of KwaZulu-Natal, Pietermaritzburg 2015.In this thesis, an improved mathematical model based on classical equations and control
approach for the photovoltaic system is developed and implemented using a pulse width
modulation as the interfacing. The functionality of the developed model with the inclusion of a
maximum power point tracking is verified against the generic model in Power Factory library
which is constrained by assumptions, such as: no maximum power point tracking and uses static
generator as the interfacing converter but gives an acceptable basic understanding of
photovoltaic operation. The new improved mathematical model characterizes the solar cell with
sufficient degree of precision with a percentage error of 0.03% measured in comparison with
experimental data. The developed photovoltaic system under established control fulfils the
operational requirements for a grid-connected photovoltaic system according to the South
African Grid Code. Based on the developed mathematical model, various studies are performed,
such as: steady-state and transient analysis to ascertain the impact of photovoltaic system
integration with the power station reticulation system. The effects are analyzed with the
photovoltaic system connected on the 11 kV bus bar which is the closest point to the generator
to simulate an extreme circumstance. Case studies to demonstrate the photovoltaic effect on the
reticulation system are evaluated for voltage stability and local generator behavior. Apparent
features of the photovoltaic system such as the rapid power variation due to atmospheric
changes (irradiance and temperature), tripping the photovoltaic system and simulating an
electrical fault are implemented with various photovoltaic penetration levels. The results
provided practical insight on the feasibility of interconnecting photovoltaic system to power
station auxiliary network. Results illustrated at steady state the benefits of the generation
capacity to be reduced relatively to photovoltaic penetration level and reactive power control
which assist in supporting voltage during voltage dips at the point of connection and lastly the
photovoltaic inverter presented the ability to limits/control fault current to about 1.5 p.u. which
is lower than the 4 - 10 p.u. fault current typically caused by rotating machines. Transient
studies discovered that the changes in atmospheric conditions do not impose stability threats but
increased photovoltaic penetration level will increases the risk of generator becoming unstable
during abnormal situations
Impact of different pulse width modulation (PWM) techniques on the performance of a three phase Z-Source inverter (ZSI).
Get PDFMasters Degree. University of KwaZulu-Natal, Durban.Abstract available in PDF.Acknowledgements on page iii
Effect of neutral earthing in LV distribution system.
No full textMasters Degree. University of KwaZulu-Natal, Durban.In any power system, a neutral point is a common point between the three single phase voltages used to close the circuit and it is a current return path to the transformer point. This neutral point may or may not be accessible, distributed and earthed. During the investigation, it was learnt that an unearthed system leads to dangerous touch and step voltages and unstable voltages in the interconnected installation. However, the values of the fault current touch voltage and overvoltage and the extent of damage is associated to the kind of neutral earthing employed in that particular network. The earthing system in low voltage is more concerned about the combination of earthing at the source side and also at the installation (consumer/customer’ premises). This research focuses on the detailed comparative study of the following neutral earthing in low voltage power systems namely: earthing where the source and load are earthed independently, earthing where the supply is not earthed or is earthed through the impedance and the load is independently earthed), earthing that is further broken down into earthing where the source is earthed and the neutral is combined with earth to form protective earth neutral conductor and earthing that starts from the source (such as a utility company) with a combined protective earth neutral conductor until the customer installation service entry point, e.g. a residential unit, is reached, where the neutral and earth conductors are split throughout. The research was conducted by a simulation method of single phase and three phases to ground fault whereupon the behavior of various earthing methods was studied. The focus was on following aspects including but not limited to the detailed study of the various types of neutral earthing, the study of the unearthed system comparative to study between the neutral earthing systems. The study went about simulating the behavior of the unearthed system as a base case and the other other neutral earthing system in order to determine the effect of earthing the neutral. It was learnt that the selection criteria for the best neutral earthing method depends on the governing requirements, the supply continuity, operating condition and the typical system loading. The main hazard that was identified in the study was that of the challenges associated with the loss or detection of the neutral, protective earth (PE) and protective earth neutral (PEN) and these pose a serious risk on all these low voltage networks in a form of damage to equipment and endangering the lives of the people
Impact of three-dimensional photovoltaic structure on solar power generation.
Get PDFDoctoral Degree in Electrical Engineering. University of KwaZulu-Natal, Durban 2016.Abstract available in PDF file
Power quality improvement in low voltage distribution network utilizing improved unified power quality conditioner.
Get PDFDoctoral Degree. University of KwaZulu-Natal, Durban.The upgrade of the power system, network, and as it attained some complexity level, the voltage related problems and power loss has become frequently pronounced. The power quality challenges load at extreme end of the feeder like voltage sag and swell, and power loss at load centre due to peak load as not received adequate attention. Therefore, this research proposes a Power Angle Control PAC approach for enhancing voltage profile and mitigating voltage sag, voltage swell, and reduced power loss in low voltage radial distribution system (RDS).
The amelioration of voltage sag, voltage swell, weak voltage profile, and power loss with a capable power electronics-based power controller device known as Improve Unified Power Quality Conditioner I-UPQC was conceived. Also, the same controller was optimally implemented using hybrid of genetic algorithm and improved particle swarm optimization GA-IPSO in RDS to mitigate the voltage issues, and power loss experienced at peak loading. A new control design-model of Power Angle Control (PAC) of the UPQC has been designed and established using direct, quadrature, and zero components dq0 and proportional integral (PI) controller method. The simulation was implemented in MATLAB/Simulink environment.
The results obtained at steady-state condition and when the new I-UPQC was connected show that series inverter can participate actively in ameliorating in the process of mitigating sag and swell by maintaining a PAC of 25% improvement. It was observed that power loss reduced from 1.7% to 1.5% and the feeder is within the standard limit of ±5%. Furthermore, the interconnection of I-UPQC with photovoltaic solar power through the DC link shows a better voltage profile while the load voltage within the allowable range of ±5% all through the disturbance and power loss reduction is 1.3%.
Lastly, results obtained by optimal allocation of I-UPQC in RDS using analytical and GA-IPSO show that reactive power injection improved the voltage related issues from 0.952 to 0.9989 p.u., and power loss was further reduced to 1.2% from 3.4%. Also, the minimum bus voltage profile, voltage sag, and power loss are within statutory limits of ±5 % and less than 2 %, respectively. The major contributions of this research are the reduction of sag impact and power loss on the sensitive load in RDS feeder.Publications on page iii
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