Masters Degrees (Electrical Engineering)

Permanent URI for this collectionhttps://hdl.handle.net/10413/6856

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A study of rain attenuation on terrestrial paths at millimetric wavelengths in South Africa.
(2006) Olubunmi, Fashuyi Modupe.; Afullo, Thomas Joachim Odhiambo.
Rain affects the design of any communication system that relies on the propagation of electromagnetic waves. Above a certain threshold of frequency, the attenuation due to rain becomes one of the most important limits to the performance of terrestrial line-of-sight (LOS) microwave links. Rain attenuation which is the dominant fading mechanism at these frequencies is based on nature which can vary from location-to-Iocation and from year-to year. In this dissertation, the ITU-R global prediction techniques for predicting the cumulative distribution of rain attenuation on terrestrial links are studied using a five-year rain rate data for twelve different geographical locations in the Republic of South Africa. The specific attenuation rR (dB/km) for both horizontal and vertical polarization is determined. The path attenuation (dB) exceeded for 0.01% of the time is estimated using the available existing models for the twelve different geographical locations on a I-minute integration time rain rate at 0.01% exceedance of the time averaged over a period of 5 years. A comparison study is done on these available rain attenuation mode'ls; The ITU-R model, Crane Global model, and the Moupfouma models at different frequencies and propagation path lengths based on the actual I-minute integration time rain rate exceeded at 0.01% of the time averaged over a period of 5 years for each geographical locations. Finally, from the actual signal attenuation measurements recorded in Durban over a period of 1 year at 19.5 GHz and a propagation path length of 6.73 km, a logarithmic attenuation model and power attenuation model is proposed for Durban, South Africa. Recommendation for future work is given in the concluding chapter for future improvement on this study. Radio communication designers will find the results obtain in the report useful.
Adaptive multiple symbol decision feedback for non-coherent detection.
(2006) Govender, Nishkar Balakrishna.; Xu, Hongjun.; Takawira, Fambirai.
Non-coherent detection is a simple form of signal detection and demodulation for digital communications. The main drawback of this detection method is the performance penalty incurred, since the channel state information is not known at the receiver. Multiple symbol detection (MSD) is a technique employed to close the gap between coherent and non-coherent detection schemes. Differentially encoded JW-ary phase shift keying (DM-PSK) is the classic modulation technique that is favourable for non-coherent detection. The main drawback for standard differential detection (SDD) has been the error floor incurred for frequency flat fading channels. Recently a decision feedback differential detection (DFDD) scheme, which uses the concept of MSD was proposed and offered significant performance gain over the SDD in the mobile flat fading channel, almost eliminating the error floor. This dissertation investigates multiple symbol decision feedback detection schemes, and proposes alternate adaptive strategies for non-coherent detection. An adaptive algorithm utilizing the numerically stable QR decomposition that does not require training symbols is proposed, named QR-DFDD. The QR-DFDD is modified to use a simpler QR decomposition method which incorporates sliding windows: QRSW-DFDD. This structure offers good tracking performance in flat fading conditions, while achieving near optimal DFDD performance. A bit interleaved coded decision feedback differential demodulation (DFDM) scheme, which takes advantage of the decision feedback concept and iterative decoding, was introduced by Lampe in 2001. This low complexity iterative demodulator relied on accurate channel statistics for optimal performance. In this dissertation an alternate adaptive DFDM is introduced using the recursive least squares (RLS) algorithm. The alternate iterative decoding procedure makes use of the convergence properties of the RLS algorithm that is more stable and achieves superior performance compared to the DFDM.
Adaptive sedimentation and patch optimization for multi-viewed stereo reconstruction.
(2015) Khuboni, Ray Leroy.; Naidoo, Bashan.
This dissertation presents two main contributions towards the Patch-based Multi-View Stereo (PMVS) algorithm. Firstly, we present an adaptive segmentation method for preprocessing input data to the PMVS algorithm. This method applies a specially developed grayscale transformation to the input to redefine the intensity histogram. The Nelder- Mead (NM) simplex method is used to adaptively locate an optimized segmentation threshold point in the modified histogram. The transformed input image is then segmented using the acquired threshold value into foreground and background data. This segmentation information is thus applied to the patch-based method to exclude the background artefacts. The results acquired indicated a reduction in cumulative error whilst achieving relatively similar results with a beneficial factor of reduced time and space complexity. Secondly, two improvements are made to the patch optimisation stage. Both the optimisation method and the photometric discrepancy function are changed. A classical quasi-newton BFGS method with stochastic objectives is used to incorporate curvature information into stochastic optimisation method. The BFGS method is modified to introduce stochastic gradient differences, whilst regularising the Hessian approximation matrix to ensure a well-conditioned matrix. The proposed method is employed to solve the optimisation of newly generated patches, to refine the 3D geometric orientation and depth information with respect to its visible set of images. We redefine the photometric discrepancy function to incorporate a specially developed feature space in order to address the problem of specular highlights in image datasets. Due to this modification, we are able to incorporate curvature information of those patches which were deemed to be depleted in the refinement process due to their low correlation scores. With those patches contributing towards the refinement algorithm, we are able to accurately represent the surface of the reconstructed object or scene. This new feature space is also used in the image feature detection to realise more features. From the results, we noticed reduction in the cumulative error and obtained results that are denser and more complete than the baseline reconstruction.
The Analysis of computer systems for performance optimisation.
(1987) Meiring, Pierre Andre.; Nattrass, Henry Lee.
The project investigated the problem of performance optimisation of computer systems at the systems level. It was ascertained that no generally accepted technique for approaching this problem exist. A theoretical approach was thus developed which describes the system, the workload and the performance in terms of matrices which are deduced from measured data. An attempt is then made to verify this theory by applying it to a real system in a controlled environment. A dummy workload is used and measurements are made on the computer system for various configurations. The results thus obtained are compared with the expected trends in system performance and conclusions are drawn which appear to verify the validity of the theory proposed.
Analysis of high voltage current transformer under deteriorating and failed insulation.
(2006) Mahlasela, Vusumuzi Samuel.; Chol, A. M.; Jimoh, Abdullahi Adekilekuna.
Data pertaining to the number of failed high voltage current transformers installed in
Analysis of the impact of closed-loop power flow control strategies on power system stability characteristics.
(2005) Ally, As'ad.; Rigby, Bruce S.
The demand for electrical energy in industrialised countries continues to increase steadily. As a result of this growing demand for electrical energy, there is a need for optimisation of the power system in terms of transmission and control. One option could possibly be an increase in transmission facilities to handle the increase in growth; however factors such as environmental issues as well as the possible cost incurred could hamper this particular approach. An alternative resides in loading the existing transmission network beyond its present operating region but below its thermal limit, which would ensure no degradation of the system. For this approach to be realised, improved control of the flow of power in an interconnected network would be advantageous so as to prevent unwanted loop flows and inadvertent overloading of certain lines. This approach can be made possible by the use of Flexible AC Transmission Systems (FACTS) technology. The concept of FACTS incorporates power-electronic compensation devices that can be typically used in an ac power system to enhance the system's power transfer and controllability. There exists a number of FACTS devices, where each device can be utilised differently to achieve the broad objective. One such device is the Thyristor Controlled Series Capacitor (TCSC). The TCSC is a class of FACTS device that makes it possible to alter the net impedance of a particular transmission line in an effort to force the flow of power along a "contract path". This thesis identifies, in the published literature, a set of strategies for the scheduling of power flow by use of variable compensation; such strategies are then considered in more detail in the analysis of the thesis. Firstly, a detailed dynamic model of a TCSC is developed together with its various controls and associated circuitry within the power systems simulation package PSCAD. In addition to this, a power flow controller scheme is then implemented, which exhibits the functionality of the power flow controller strategies reviewed in the literature. In order to test the validity and operation of the TCSC model as well as the analysis of the power flow controller scheme, a single-machine infinite bus (SMIB) study system model is developed and used as part of the investigation. This thesis, firstly, presents a theoretical analysis of two particular modes of power flow control in an interconnected ac transmission system. Secondly it confirms the results of an analytical study in previously published work with the implementation of the two control modes, and further extends the scope of the previous study by examining the impact of the power flow controller's design on the small-signal and transient stability characteristics of the study system. The key findings of this extended investigation are that the power flow controller's mode of operation has an important influence on both small-signal and transient stability characteristics of a power system: in partiCUlar, it is shown that one mode can be detrimental while the other beneficial to both system damping and first swing stability. Finally, the thesis applies the understanding of the power flow controller's operation obtained from the SMIB study system to the problem of inter-area mode oscillations on a well-known, two-area, multi-:generator study system. Real-time simulator results are presented to exhibit the effect of the power flow controller modes and controller design on the oscillatory characteristics of the two-area study system.
Application of bus transfer schemes to stabilise power supply in a coal fired power plant unit auxiliary reticulation.
(2019) Mathebula, Vonani Clive.; Saha, Akshay Kumar.
A multi-function bus transfer system comprising fast, in-phase and residual bus voltage transfer schemes is developed in the thesis. Bus residual voltage magnitude and phase angle are calculated by converting time domain components of a three phase system in an abc reference frame to dq0 components in a rotating reference frame using Park’s transformation equations. Residual bus voltage phase angle is then modelled by a Taylor’s series expansion to calculate the phasor angular position with reference to the alternate power supply ahead of time to enable synchronization of the two supplies. Simulations are performed to verify functionality and performance; and to deduce the characteristics of the respective schemes. The thesis then explores the feasibility of using the bus transfer system to stabilise power supply within a power generating plant auxiliary electrical reticulation when upstream electrical equipment failures occur; in particular focus is placed on the unit boiler furnace draught system which would normally result in reduction of up to half of unit generating capability if one set of the draught system is lost. Simulation results of case studies conducted provided practical understanding on the feasibility of using a bus transfer system, with fast bus transfer scheme being the most preferred method at 70 ms transfer time; which enables the forced draught fan motor to be transferred within 2 s before the unit begins to de-load. The thesis proposes a new reticulation configuration that allows the transfer of both forced and induced draught fan motors simultaneously while maintaining stable draught furnace pressure. The new configuration allows both fan motors to remain connected to the switchboard for up to 3 s before tripping the motors on under-voltage protection when upstream equipment failures occur, even though bus transfer can be executed in 70 ms or 520 ms using fast or in-phase transfer schemes respectively. The speed and minimum impact on the electrical system makes the fast transfer scheme the most preferred transfer method
The application of controllable inverter-based series compensation to power oscillation damping.
(2000) Chonco, Nkosinathi Stanford.; Rigby, Bruce S.; Harley, Ronald G.
Poorly damped oscillations that occur between the generators in large interconnected power systems often limit the amount of power that can be transmitted through a transmission corridor and are a threat to secure system operation. Coordinated insertion and removal of capacitors in series with a transmission line is one of the approaches that has been known for many years to be capable of enhancing the damping of power system oscillations. Unfortunately however, this approach historically relied on the operation of mechanical circuit breakers which were too slow and unreliable for the high-speed and repetitive operation that such an application demands. Recently-emerged, high-speed power-electronic-based switching devices are finding increasing use in modem power systems in the so-called Flexible AC Transmission Systems (F ACTS) concept. One particular FACTS impedance controller, namely the inverter-based series compensator, can rapidly alter the magnitude of capacitive compensating reactance in series with the line to make it practically feasible to enhance the damping of power system oscillations via dynamically-controlled series compensation. This thesis identifies, in the literature, an insightful approach to the design of an idealised controllable series compensator (CSC) damping scheme; such an approach has been considered in the analyses of the thesis. Three mathematical models of a single-machine infinite bus (SMIB) system are developed and are subsequently used in the initial design and analysis of a CSC damping controller carried out in the thesis. The simple SMIB system case study is used to identify and investigate the factors that have a significant impact on the performance of a CSC damping controller before studying the more complex issue of inter-area mode damping using a CSC. This thesis successfully confirms the results of a previous analytical study in which an idealised representation of the CSC was used, and extends the scope of that previous study by also considering a detailed representation of one particular type of CSC: the inverter-based series compensator. The two key findings of this extended investigation are that the inverter-based form of controllable series compensator can successfully be used to damp power oscillations and that, where the damping of oscillations is the particular focus of study, an idealised representation of the inverterbased CSC is suitable for the analyses. In the case of the inter-area mode damping problem, the selection of an appropriate input signal to the CSC damping controller is a key issue, since the oscillations that are to be damped involve a number of participating generators. This thesis examines the suitability of a few candidate input signals that have been proposed in the literature using the conceptually simpler SMIB system analytical models that have been developed. Finally, the thesis applies the understanding of CSC damping controller design gained from the SMIB study to the problem of inter-area mode damping on a four-generator study system. Time-domain simulation results are presented to demonstrate the impact of the controlled inverter-based series compensator on the damping of the inter-area mode of this system.
Application of distance protection for transformers in Eskom transmission.
(2014) Naicker, Kubendran.; Davidson, Innocent Ewean.; Perera, Anura.
Eskom is South Africa’s state owned utility who is responsible for the generation, transmission and distribution of electricity. The transmission network in Eskom consists of thousands of kilometres of lines operating at voltages from 220kV to 765kV. Three winding transformers, two winding transformers and autotransformers are employed in Eskom’s transmission network. High Voltage (HV) Inverse Definite Minimum Time (IDMT) overcurrent protection and Medium Voltage (MV) IDMT overcurrent protection are employed to provide backup for these transformer’s differential protection and for uncleared through faults. Eskom’s Transmission setting philosophy states “that the HV and MV IDMT overcurrent elements must be stable at 2 x full load current of the transformer”. This has resulted in MV and HV over-current protection not detecting MV multiphase busbar faults in substations with low MV fault levels which are located far away from generating stations. In such cases a possible solution is to use distance protection for transformers. This research study investigates how the different vector groups of the power transformer affect the impedance measured by the protection relay, and how standard distance algorithms in protection relays respond to faults located on the MV side of the power transformer. The study consists of a literature review of current practices of transformer distance protection. Autotransformers and distance relays are discussed with manual fault calculation examples. The effects of tap-changers and transformer inrush current on transformer distance protection are also discussed. DigSilent Power Factory software version 15.0.2 was used in the modelling and simulation of faults. The response of distance elements for various faults located on the MV side of transformers are analysed and summarised in two tables which indicate which loops will measure the precise distance to fault through the various transformers and which loops will measure the distance to fault with a slight error. Multifunction Intelligent Electronic Devices (IEDs) with both distance and differential functions are now being commissioned in the Eskom transmission network for the protection of transformers. The distance elements employed in transformer IEDs are similar to distance elements found in a line distance relay. These distance functions can be set to provide local backup protection for uncleared HV and MV busbar faults in the Eskom Transmission network.
The application of electrical resistance tomography within a vacuum sugar pan in order to better understand its boiling dynamics.
(2010) Sanderson, Daniel.; Jarvis, Alan Lawrence Leigh.
This dissertation is concerned with the application of tomography within the sugar industry; in particular non-accessible locations found in a sugar mill. In this study, the focus of research is that of a vacuum pan, and if better understood through tomographical techniques could significantly improve mill efficiency and throughput. The tomography system comprises unique mechanical interfaces, data acquisition modules and software algorithms in order to generate images which reflect the dynamics in the tomographical sensor zone. The distribution of gas (low conductivity) and liquid (high conductivity) within a tube is of main interest in order to understand the boiling dynamics and ultimately pan design. This is attained by determining the internal cross-sectional spatial distribution of conductivity of a number of tubes within the pan simultaneously. Thermal properties of the contents of the sugar pan (a syrup-like substance known as massecuite) at different boiling stages can be estimated based on the tomographical data. Data acquisition is achieved via an in-house designed electronic state machine. A neighbourhood back-projection reconstruction technique was developed in MATLAB in order to generate tomographical images. Results from the system have identified different boiling dynamics which improve the understanding and design of vacuum sugar pans.
Application of HVDC technology in medium voltage distribution systems.
(2005) Chetty, Somasundran.; Ijumba, Nelson Mutatina.; Venter, Frik.
Approximately 60% of all South Africans do not have access to electricity from the national grid and 80% of the dwellings in the rural areas are not electrified. This is due to the fact that many rural South Africans, similar to other rural markets in the developing world, live in sparsely populated, widely dispersed villages, which cannot be reached within the grid electrification program. HVDC technology provides a viable option to transmit electricity to small distant loads. The objective of the present study is to demonstrate the application of HVDC technology in a medium voltage distribution system, to provide electrical power to Kwa·Ximba, which is a small distant rural area, located in KwaZulu-Natal, South Africa. The proposed system generates electricity from a hydroelectric generation scheme namely Nagle Dam and transmits the excess power to Eskom's Caltoridge-Georgedale sub-transmission network for system enhancement purposes. Extensive technical and economical analyses of the proposed system has been conducted. An HVAC system was also considered for the same purposes in order to make technical and economical comparisons between the use of a HYDC and a HYAC system. In addition, grid extension from Eskom's Catoridge-Georgedale sub-transmission was considered to provide power to Kwa-Ximba without the use of a hydroelectric generation scheme. The proposed networks were therfeore (i) Network A:- Power supply to Kwa-Ximba. and the Catoridge-Georgedale sub-transmission network, from a hydroelectric generation scheme, using HYDC technology, (ii) Network B:- Power supply to Kwa-Ximba, and the Catoridge-Georgedale sub-transmission network, from a hydroelectric generation scheme, using HYAC technology and (iii) Network C:Power supply to Kwa-Ximba by extending Eskom's existing AC CatoridgeGeorgedale sub-transmission network with the hydroelectric generation scheme switched off. It is proposed that Nagle Dam, which is situated adjacent to Kwa-Ximba be used as a hydroelectric generation plant. In order to detennine the most efficient and cost effective use of generator sets, the flow rate, available hydraulic power and available electrical power from the year 2005 to the year 2032 were calculated. The increase in flow rate was based on an annual growth rate of l.5% in water demand. The increase in electrical power demand for Kwa-Ximba was calculated for the next 29 years based on an annual growth rate of 1.8 %. Load flow analyses was conducted on the various power line and busbars that constitute each of the networks, in order to determine the effectiveness of each network. In order to maintain flexibility in power generation, five sets of hydro electrical generators were chosen to give a combined power delivery of 20MW. The first three hydro electrical generators are rated at 5MW each, the fourth set rated at 3MW and the fifth set rated to deliver 2MW, (G I to GS operate 11 KV, 3 phase). The combination of generator sets in use (01 to 05) will vary depending on the electrical power demand in any given year. Analyses of the predicted load flow pattern revealed that in the year 2005, Kwa-Ximba will receive 10.5 MW of power while 8.64 MW of power will be used to enhance the Eskom's Catoridge-Georgedale sub-transmission network, with a 4% spinning reserve. By the year 2014 power supply to the subtransmission network will cease since Kwa-Ximba will be absorbing 12.2 MW of power with a 17.5% spinning reserve. By the year 2032, Kwa-Ximba will absorb 17MW of power with a spinning reserve of 14.63%. The converter stations required for the HYDC transmission network (Network A) will be equipped with YSC and PWM technology and have a true power rating of a 20MW. This wi ll be adequate to supply Kwa-Ximba's power demand right up until the year 2032 when the demand will be 17 MW. Converters will include 10BTs. Two 45 km long, 30 MW, 80 kV triple extruded polymetric HYDe cable will be buried 700mm below natural ground level. The Rectic Master software was used to select an appropriate overhead line for HVAC transmiss ion (Networks B and C). An aluminium, wolf conductor was selected to transmit 20MW of active power. Load flow analyses revealed that the HYDC link contributes positively to network stabil ity by absorbing more reactive power than the HYAC link. The HVDC system absorbed a combined (Kwa-Ximba, Catoridge-Georgdale sub-transmission network) reactive power of 22.04 MY AT, as opposed to the HVAC transmission system where a combined reactive power 1.89 MVAT was absorbed from the connected network. This demonstrated that the HVDC link had the ability to absorb more reactive power from the Catoridge-Georgedale sub-transmission network, therefore contributing positively to the enhancement and stabi lity of the sub-transmission network. Network A contributes more to system stability than Network B. It has also been shown that if Eskom's Catoridge-Georgedale sub-transmission network (Network C) is extended to supply electricity to Kwa-Ximba, this would result in system instability, in the long term. It is evident that Eskom would attain direct benefit from the installation of Newtork A, rather than Networks Band C. The technical and environmental differences noted in the present study, between the HVDC and HVAC systems does not, however, justify the economics to install a HVDe system in order to supply power to Kwa-Ximba. Economical analyses revealed that the implementation of Network A would cost 64% more to install and result in a 75% less annual net profit than Network B. Network B would yield the highest annual net profit for the developer. From the developer's perspective, Network B will be the most feasible network to implement. However, from Eskom's perspective, Network A will be the most bene ficial. Various recommendations have been made by the researcher that would benefit the community of Kwa-Ximba, Eskom and the developer in the long term.
Application of optimization techniques to solve overcurrent relay coordination.
(2021) Langazane, Sethembiso Nonjabulo.; Saha, Akshay Kumar.
Distribution systems continues to grow and becoming more complex with increasing operational challenges such as protection miscoordination. Initially, conventional methods were favoured to optimize protection coordination; however, the implementation process is laborious and time-consuming. “Therefore, recent studies have adopted the utilisation of particle swarm optimization and genetic algorithms to solve overcurrent relay coordination problems and maximise system selectivity and operational speed. Particle swarm optimization and genetic algorithms are evolutionary algorithms that at times suffer from premature convergence due to poor selection of control parameters. Consequently, this thesis aims to present a comprehensive sensitivity analysis to evaluate the effect of the discrete control parameters on the performance of particle swarm optimizer and genetic algorithms, alternatively on the behaviour of overcurrent relays. The main objectives of this research work also include modelling and simulation of distribution system protection scheme, employment of evolutionary algorithms with control parameters that perform efficiently and effectively to maximise protection coordination between relays, optimize relay operating time and maintain the stipulate coordination time interval, and lastly, to outline future recommendations. The distribution network understudy was modelled and simulated on a real-time digital simulator to validate protection settings, and the verification of evolutionary algorithms performance was displayed on Matlab/Simulink. An extensive parametric sensitivity analysis was conducted to understand the impact of the individual control parameters and their respective influence on the performance of evolutionary algorithms. The findings indicate that particle swarm optimization is more sensitive to inertia weight and swarm size while the number of iterations has minimal effect. The results also depict that genetic algorithms’ performance is mostly influenced by crossover probability, mutation probability, and population size. Sensitivity analysis results were verified by comparing the performance of particle swarm optimizer with genetic algorithms, which demonstrated that particle swarm optimization performs efficiently and robustly in solving the considered problem, especially in terms of convergence speed. Furthermore, overcurrent relays were more sensitive, selective, and the operational speed was reduced for particle swarm optimizer compared to other algorithms. The optimal protection coordination achieved using particle swarm optimization showed superiority of the algorithm, its ability to circumvent premature convergence, consistency, and” efficiency.
Application of quantitative feedback theory to robust power system stabiliser design.
(2003) Chetty, Paramasivan.; Boje, Edward Sidney.
This thesis aims to verify the use of quantitative feedback theory (QFT) as a viable tool for designing power system stabilisers (PSS) for a single machine infinite bus system. The result of the QFT design is verified by simulation of the linear and nonlinear models representing the power system, and also by experimental procedures carried out in a laboratory. QFT falls into the classical control category, and is a frequency domain design method. It is an alternative to other design methods such as root locus and Hoo . The QFT design procedure can be extended to a multimachine system and QFT designs of MIMO systems has gained impetus. From theory, through simulation, and to the final laboratory testing on a single machine, infinite bus system, it will be shown that the application of QFT to robust PSS design does indeed work. QFT is a design method that allows the designer to choose a set of realistic operating points and to produce a design that include those points. Other methods allow the designer to produce a design for single operating point, and one has no idea how the design performs at the other operating points.
The application of volt/var optimisation on South African distribution power networks.
(2016) Chetty, Dayahalan Thangavelloo.; Davidson, Innocent Ewean.; Bello, Mashood Mobolaji.
Electric power utilities can achieve cost savings by maximizing energy delivery efficiency and optimizing peak demand. Technical losses are influenced by both network impedances and currents. Power flow through distribution components are composed of active and reactive components. The reactive power does no real work, but contributes to the overall technical losses. By the appropriate placement and operation of reactive power compensation devices, reactive power flows could either be eliminated or significantly minimized, thus, inherently reducing technical losses. This research investigation presents a method for reactive power compensation of medium voltage radial networks as a cost-effective approach to achieve loss minimization and voltage regulation improvement. The study addresses the optimal placement of distributed shunt capacitors along distribution feeders. A mathematical formulation is developed to show that there is a specific location for a given size of capacitor bank that produces the maximum power loss reduction for a given load distribution on a network. In the Eskom distribution system, for those networks that are voltage constrained, the application of capacitors will also consider raising voltages to statutory requirements, however at the expense of the power loss reduction capability. The method developed maximizes both voltage and power loss reduction. Switching and control strategies are developed to meet these objectives throughout a day cycle. The methodology was tested on an Eskom distribution medium voltage network by power system simulation. Results obtained of improvements in voltage regulation and feeder losses are presented and discussed. The application of shunt compensation and the associated feeder voltage regulation improvement is an enabler for Conservation Voltage Reduction (CVR) that can be applied for demand reduction during peak times. Control strategies for CVR are presented, to cater for an integrated Volt/VAr solution for distribution networks. Furthermore, an assessment of CVR potential within Eskom Distribution networks is presented. This research forms the inception for a series of studies aimed at incorporating Volt/VAr optimization within Eskom Distribution networks.
An application specific low bit-rate video compression system geared towards vehicle tracking.
(2003) Spicer, Ryan David.; Peplow, Roger Charles Samuel.
The ability to communicate over a low bit-rate transmission channel has become the order of the day. In the past, transmitted data over a low bit-rate transmission channel, such as a wireless link, has typically been reserved for speech and data. However, there is currently a great deal of interest being shown in the ability to transmit streaming video over such a link. These transmission channels are generally bandwidth limited hence bit-rates need to be low. Video on the other hand requires large amounts of bandwidth for real-time streaming applications. Existing Video Compression standards such as MPEG-l/2 have succeeded in reducing the bandwidth required for transmission by exploiting redundant video information in both the spatial and temporal domains. However such compression systems are geared towards general applications hence they tend not to be suitable for low bit-rate applications. The objective of this work is to implement such a system. Following an investigation in the field of video compression, existing techniques have been adapted and integrated into an application specific low bit-rate video compression system. The implemented system is application specific as it has been designed to track vehicles of reasonable size within an otherwise static scene. Low bit-rate video is achieved by separating a video scene into two areas of interest, namely the background scene and objects that move with reference to this background. Once the background has been compressed and transmitted to the decoder, the only data that is subsequently transmitted is that that has resulted from the segmentation and tracking of vehicles within the scene. This data is normally small in comparison with that of the background scene and therefore by only updating the background periodically, the resulting average output bit-rate is low. The implemented system is divided into two parts, namely a still image encoder and decoder based on a Variable Block-Size Discrete Cosine Transform, and a context-specific encoder and decoder that tracks vehicles in motion within a video scene. The encoder system has been implemented on the Philips TriMedia TM-1300 digital signal processor (DSP). The encoder is able to capture streaming video, compress individual video frames as well as track objects in motion within a video scene. The decoder on the other hand has been implemented on the host PC in which the TriMedia DSP is plugged. A graphic user interface allows a system operator to control the compression system by configuring various compression variables. For demonstration purposes, the host PC displays the decoded video stream as well as calculated rate metrics such as peak signal to noise ratio and resultant bit-rate. The implementation of the compression system is described whilst incorporating application examples and results. Conclusions are drawn and suggestions for further improvement are offered.
An assessment of high distributed PV generation on eThekwini electricity distribution network.
(2019) Goqo, Zama.; Dorrell, David George.; Davidson, Innocent Ewean.; Sewchurran, Sanjeeth.
Small-scale Distributed Photovoltaic Generation (DPVG) continues to grow with increasing operational challenges for electricity utilities and Distribution Network (DN) operators. In Low Voltage (LV) DNs, there are well researched potential issues that arise with high Photovoltaic (PV) penetration. These include: feeder voltage rise, voltage fluctuations and reverse power flow. Among these, the most important issue is voltage rise at the LV distribution feeder. In a broader perspective, to this point in time, there has not been more detailed research on small-scale DPVG interconnections in the LV networks in South Africa (SA) and in the KwaZulu-Natal (KZN) region. There is a great need for research in this field for ensuring network efficiency, reliability and future regulatory standards. Other network systems have been studied around the world were conditions, environment, network characteristics and electricity customer loads will be different; e.g in the North-West of England, Germany, and Queensland, Australia. Hence, the main objective of this research study is to analyze the mentioned problems, identify and test the appropriate mitigation solutions, in the event of high DPVG. This study was carried out on a typical SAn LV DN model, which represents an existing housing development estate at eThekwini Municipality. Consequently the aim is to identify solutions suitable for networks in SAn or of similar architect and characteristics. As a result, a specific application is undertaken at the KZN region, which is also representative of network characteristics of SAn networks. A voltage rise, voltage fluctuation and network power loss issues were analyzed at different PV penetration levels and varying customer loads. An innovative approach of utilization of a standard central On-Load-Tap-Change (Off-LTC) transformer for voltage regulation with high DPVG was tested. Usage of this technique has not been reported in the literature to date. National standards in SA were used as a basic guide in this study and stated the possibility of grid voltage control of distributed PV inverters. Assessment of the typical LV network showed that there is indeed voltage rise and hence possible voltage fluctuation, when PV system output power varies. The Off-LTC transformer was able to maintain network voltages within the allowed operational range and reduced the magnitude of voltage rise. This implies that there is a possibility of avoiding expensive upgrades of the existing and widespread Off-LTC transformers technology.
Assessment of the electrical performance of the Cahora Bassa HVDC scheme.
(2005) Sithole, Vusi.; Ijumba, Nelson Mutatina.; Britten, Anthony C.
The aim of this study was to assess the electrical performance of the Cahora Bassa HVDC scheme. For practical reasons a database was developed to hold and analyse the performance data. Microsoft® Access 2002 relational database management system was chosen for this work. The principle of simplicity and flexibility were used in the design of the database. The Apollo year 2002 faults data was populated into the database. The database stored the information in a format that enables the user to extract results and the information required by Ciqre, The Ciqre Working Group 14 collects performance information from all the participating HVDC schemes around the world annually. The Apollo converter station's 2002 performance data was compared to other similar HVDC schemes that submitted to Cigre in the year 2002. In addition performance trends were drawn from similar schemes that submitted to Cigre over the past years. The Apollo performance data is quite comparable to other similar schemes in 2002 and over the past years.
Asset health appraisal of transformers in Eskom's distribution network.
(2017) Singh, Adesh.; Swanson, Andrew Graham.
Master of Science in Electrical Engineering. University of KwaZulu-Natal, Durban 2017.
Automated hybrid solar and mains system for peak time power demand.
(2015) Habyarimana, Mathew.; Venugopal, Chitra.
The power demand during peak period causes large power fluctuations in the commercial grid. The reduction in using grid supply during peak time benefits the supplier and consumer. There are many methods such as monitoring the usage of grid supply, load shedding, using local generators and disconnecting unwanted loads during peak time used to reduce grid dependency during peak time. These methods reduce power demand from grid by either supplying interrupted power to the load or by establishing additional power source. In South Africa, solar energy is abundantly available and it can be utilized to solve the power demand during peak time. In this research, solar and grid power are chosen as two power sources and automatic switching system to select the power source to supply uninterrupted power to the load is designed. The important aspect of using solar system is estimating the system output. The maximum power point tracking system using perturb and observe algorithm is designed. The boost converter and inverter circuits are designed to supply power to the coffee shop loads at Howard College Campus. Battery charger circuit is designed to charge the battery from solar or grid and supply power to the load whenever required. The switching algorithm connects the load to solar or battery during peak time and connects it to grid during off peak time. The switching algorithm is designed to supply uninterrupted power to the load by connecting it to available source when any one of the source failure occurs. The power output from the panel is maximized by automatic panel cleaning system. The panel cleaning starts at the pre-programmed schedule and provision for manual override option to reschedule panel cleaning operation is also provided. The designed system is tested in MATLAB and Proteus simulation software. The results of each section are discussed. It can be seen that designed automatic selection of power sources for supplying 1kW of power during peak time to the selected coffee shop considerably reduces the cost and power demand from the grid during peak time. The designed system is economically feasible and efficient in supplying uninterrupted power to the load.
Beach water quality: a comprehensive analysis of the pathogenic pollution of the Durban coastline.
Johnson, Katelyn Ann.; Stretch, Derek Dewey.
South Africa's beaches have many local and international visitors. Various recreational activities occur along the Durban coastline, especially during the holiday seasons. Beach water quality is negatively affected by pathogenic pollution which enters coastal water via stormwater and river discharges. Poor water quality jeopardises public health and has an adverse effect on tourism and the economy. The focus of this research is pathogenic pollution of Durban‟s coastal waters. In an attempt to understand the changes and establish any trends in pathogenic water quality conditions over the past decade, a critical assessment and statistical review of the historical water quality conditions of the Durban beaches has been done. This involves a general statistical analysis and water quality classification according to the new South African Water Quality Guidelines. Statistical parameters considered include arithmetic mean, standard deviation, geometric mean, and percentiles. A total of 42 beaches were analysed. Beaches were grouped into 4 sections: Northern, City, Bluff, and Southern. Water quality data for E.coli and Enterococcus were analysed from 2003 to 2013. The highest concentrations of both bacteria occurred in summer and autumn most often. Generally the average levels of both bacteria have either remained consistent or increased. Large standard deviations noted indicate variability in pollution as they represent a large spread of data from the average pollution values. Geometric mean comparisons show that Enterococcus levels were generally higher than E.coli, but both bacteria follow same patterns. Classification of water quality conditions shows that water quality has deteriorated as the frequency of poor water quality has increased. Water quality is classified as poor more frequently based on Enterococcus when compared to E.coli. However, higher levels of E.coli are allowed than Enterococcus as per the guidelines. Beaches located near rivers and stormwater outfalls are adversely affected and are shown to exhibit poorer water quality conditions. A case study was completed involving the analysis of the beach water quality data for 2009 to 2013 to determine the possible eligibility of Durban‟s beaches to receive the Blue Flag Award. Based on the microbiological water quality, it is unlikely that Durban will be a “Blue Flag coastline” in the immediate future. Most beaches have not managed to consistently meet the criteria for both E.coli and Enterococcus. As of October 2014, 7 beaches had pilot status.

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