The power utilities in many countries have come under stress as a result of generation capacity deficits, looming fuel costs and in many developing countries the electricity demand is very quickly outstripping the available electricity supply [1]. Since 2006, Eskom has been utilizing large scale residential efficient lighting roll out programmes as a cost effective short to medium term supply security solution while the longer term capital intensive supply side, “Build Programme” was underway [2]. This mostly involved the use of non-linear compact fluorescent lamps (CFLs) to replace linear incandescent lights (ILs) with very little involvement and influence by the utility QOS (quality of supply) engineers that are responsible for ensuring supply quality on the specifically targeted Distribution networks. This dissertation highlights that while CFLs can provide the desired energy or peak power reduction required, they can also have an impact on QOS within specific sensitive networks if the appropriate CFL standards (i.e. IEC 61000-3-2) minimum requirements are not adhered for both power factor and harmonics. These large scale CFL implementations have cost implications and hence metering and verification methods and models have been developed to simulate and quantify the returns from investing in energy efficient lighting initiatives. CFL manufacturers differ on ballast designs which have a direct impact on lamp efficacy, harmonic distortion and power factor which contribute to network quality of supply. It is for this reason that this dissertation raises an awareness of the importance of appropriate CFL standards i.t.o. the impact on quality of supply from a harmonics and power factor perspective. Due to the lack of more recent available or reliable sources of CFL test data, laboratory investigations were used to confirm the harmonics and PF characteristics of a variety of commercially available CFLs in addition to those utilised in previous large scale rollout programmes. The harmonics and power factor performance measured were compared for compliance against the international limits as prescribed in IEC 61000-3-2. Further investigations on international lighting industry standards for CFL’s has revealed gaps pertaining to harmonics and PF limits. This study is concluded by highlighting the impact of CFLs on power networks. It also provides a brief guide for utility power quality engineers by imparting an understanding of their role for the large scale efficient lighting programmes in order to pro-actively contain any possible impact on quality of supply within the regulatory limits as prescribed in the QOS standards. / M.Sc.Eng. University of KwaZulu-Natal, Durban 2013.

Thesis (PhD)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Multilevel converters were developed as a result of a growing need for higher power converters. This dissertation addresses a specific multilevel topology called the multicell topology. A problem associated with this topology is cell capacitor voltage unbalance. This dissertation addresses the issue of natural balancing of multicell converters. The topology is mathematically analysed and a theory is developed to explain the natural balancing mechanism. The study of the natural balancing property includes a detailed harmonic-, steady-state- and time constant analysis. The theory is verified by a comparison between the theoretical-, simulated- and experimental results. / AFRIKAANSE OPSOMMING: Veelvlakkige omsetters het ontstaan as gevolg van ’n behoefte aan ho¨er drywing omsetters. Hierdie proefskrif handel spesifiek oor die veelsellige omsetter topologie. ’n Probleem wat met hierdie topologie geassosieer word is selkapasitor onbalans. Hierdie proefskrif ondersoek die natuurlike balansering van veelsellige omsetters. Die topologie word wiskundig geanaliseer en ’n teorie word geformuleer om die natuurlike balanseringsmeganisme te verduidelik. Die ondersoek van die natuurlike balanseringseienskap bevat ’n volledige harmoniese-, bestendige toestand- en tydkonstante analise. Die teorie is gekontroleer deur teoretiese-, simulasie- en eksperimentele resultate te vergelyk.

Thesis (PhD)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: This dissertation considers the wideband modelling of capacitive voltage sensors for open-air transmission line applications. Two novel topologies were introduced, namely a differential parallel plate sensor with a floating faraday cage for the interface instrumentation and a coaxial sensor mounted around the earth conductor with a faraday cage connected to the earth conductor. The modelling and analysis procedures included the derivation of equivalent circuit models in order to simulate the calibration factor, the loading effect of the interface instrumentation and the effect of leakage to ground, both in the time- and frequency domain. In order to obtain a flat frequency response from very low frequencies (less than 5 Hz) to very high frequencies (several MHz) it is important that the interface instrumentation have a high input impedance and galvanic isolation be maintained. This was achieved by developing interface instrumentation with a fibre-optic link operated from battery power. The instrumentation represents a fairly unique approach in that the data is digitised before transmission across the serial fibre-optical link, where-as conventional interfaces use analogue optical technology. Despite the added complexity and high power requirements introduced by the digitising process, the improved versatility is expected to yield a superior interface solution. The instrumentation has a bandwidth of approximately 6 MHz, with an optional anti-aliasing filter at 1 MHz. Special consideration should be given to the support structure as any unbalanced leakage to ground will introduce variations in the frequency response towards the low-frequency end. Leakage of a 100 MQ was found to influence the frequency response of the circuit up to frequencies of 1 kHz. Extensive simulation studies were conducted to obtain qualitative and quantitative insight into the differential sensor topology and the associated electric fields. The improvement of a differential plate sensor over the traditional single element plate sensor was demonstrated using twodimensional simulations. Further simulations with a three-dimensional package showed that the two-dimensional simulations are insufficient, because the boundary conditions and end effects have a great influence on the calibration factor of the sensor. Extensive laboratory tests were also undertaken to evaluate the sensor topology as well as the effects of the interface instrumentation and leakage to ground. Excellent correlation were found between the measured and simulated waveforms, both in the time- and frequency domains regarding the calibration factor as well as the added poles or zeros at low frequencies. It can therefore be deduced that a valid circuit model was suggested for these sensor topologies in the frequency range from 10 Hz to 1 MHz. Keywords: Capacitive sensors, Open-air voltage sensors / AFRIKAANSE OPSOMMING: Hierdie verhandeling beskou die wyeband modellering van kapasitiewe spanningsensors vir opelug transmissie lyn toepassings. Twee oorspronklike topologieë is voorgestel, naamlik 'n differensiële parallel plaat sensor met 'n aparte faraday hok vir die koppelvlak instrumentasie en 'n koaksiale sensor wat rondom die aardgeleier monteer word met die faraday hok ook aan die aardgeleier gekoppel. Die modellerings en analise prosedures het ingesluit die afleiding van ekwivalente stroombaanmodelle vir simulasie van die kalibrasiefaktor asook die belasingseffek van die koppelvlak instrumentasie en lekweerstand na grond in beide die tyd- en frekwensie gebiede. Om 'n plat frekwensieweergawe te verkry vanaf baie lae frekwensies (laer as 5 Hz) tot by baie hoë frekwensies Cn paar MHz), is dit belangrik dat die koppelvlak instrumentasie 'n hoë intreeimpedansie het en galvaniese isolasie verseker word. Dit was bereik deur koppelvlak instrumentasie te ontwikkel met 'n optiese vesel koppeling wat met battery krag aangedryf word. Die instrumentasie verskaf 'n redelik unieke aanslag in die opsig dat die data gemonster word voordat dit oor die seriële optiese vesel skakel gestuur word, terwyl konvensionele koppelvlakke analoog optiese tegnologie gebruik. Ten spyte van die toegevoegde kompleksiteit en hoë drywingsvereistes van die versyferingsproses, het die instrumentasie se veelsydigheid toegeneem tot die mate dat dit as 'n beter koppelvlak oplossing beskou word. Die instrumentasie het 'n bandwydte van ongeveer 6 MHz, met 'n opsionele teen-vou filter by 1 MHz. Die ondersteuningstruktuur is van besondere belang aangesien enige ongebalanseerde lekweerstand na grond afwykings in die frekwensieweergawe sal veroorsaak aan die lae frekwensie kant. Lekweerstand van 100 MQ sal die frekwensieweergawe beïvloed tot by ongeveer 1 kHz. Uitgebreide simulasies is gedoen om kwalitatiewe en kwantitatiewe insig in die differensiële sensor topologie en die geassosieerde elektriese velde te verkry. Die verbetering van 'n differensiële parallel plaat sensor in vergelyking met die tradisionele enkel element plaat sensor is demonstreer met twee-dimensionele simulasies. Verdere simulasies met 'n drie-dimensionele pakket het gewys dat die twee- dimensionele simulasies onvoldoende is aangesien grensvoorwaardes en randeffekte 'n groot invloed het op die kalibrasiefaktor van die sensor. Uitgebreide laboratorium toetse is ook gedoen om die sensor topologie sowel as die effekte van die koppelvlak instrumentasie en lekweerstand na grond te evalueer. Uitstekende korrelasie is gevind tussen gemete en voorspelde golfvorms, in beide die tyd- en frekwensie gebied met betrekking tot die kalibrasie faktor sowel as die toegevoegde pole en zeros by lae frekwensies. Die gevolgtrekking is dus dat 'n geldige stroombaanmodel voorgestel is vir die sensor topologieë vir die frekwensie bereik van 10Hz to 1 MHz. Sleutelwoorde: Kapasitiewe sensors, Ope-lug spanningsensors

Thesis (MScIng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: The thesis discusses the analysis and design of a three-phase-to-three-phase direct AC-AC matrix converter. A background study of the various matrix converter topologies and their modulation strategies are presented. The associated PWM strategy of each matrix converter topology is investigated. In addition, a detailed explanation of the three safe commutation strategies is presented. The research focuses on the design and analysis of the direct AC-AC matrix converter topology. That includes the design of the main bi-directional power converter circuit, gate drive circuit, current direction detection circuit, voltage measurement circuit and protection circuitry. Moreover, it covers the development of the direct control algorithm based on the four-step safe current commutation- and the two-step voltage commutation strategy. A “PEC33” controller board is used to implement the developed control algorithm. Furthermore, simulation results of the direct and the indirect matrix converter topologies are presented. The results obtained from the experimental test performed on the direct AC-AC matrix converter topology are also presented. The conclusion drawn is discussed at the final stage of the report. / AFRIKAANSE OPSOMMING: Hierdie tesis bevat die analise en ontwerp van ‘n drie-fase na drie-fase direkte WS-WS matriksomsetter. ‘n Agtergrondstudie van verskeie ander matriksomsetter topologieë word aangebied. Die ge-assosieerde PWM beheerstrategie van elke matriksomsetter topologie is ondersoek. Hierby word ‘n gedetaileerde verduideliking van drie veilige kommutasie strategieë ingesluit. Die navorsing fokus op die ontwerp en analise van die direkte WS-WS matriksomsetter topologie. Dit sluit die volgende in: die ontwerp van die hoof bi-direksionele drywingsomsetterbaan; die hek aandryfbaan; die stroomrigting deteksiebaan; die spanningsmeetbaan en die beveiliging stroombane. Dit dek ook die ontwikkeling van die direkte beheeralgoritme wat gebasseer is op die vier-stap veilige stroomkommutasie- en die twee-stap spanningskommutasie strategie. ‘n “PEC33” beheerkaart is gebruik om hierdie beheeralgoritme te implementer. Simulasie resultate van beide die direkte sowel as die indirekte matriksomsetter topologieë word ingesluit. Die eksperimentele resultate wat met die direkte WS-WS matriksomsetter topologie verkry is word aangebied en bespreek. Die gevolgtrekking word in die finale afdeling van die verslag bespreek.

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. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2005

Flexible AC Transmission Systems (FACTS) involves the incorporation of power-electronic controlled devices into ac power transmission systems in order to extend the power-transfer capability of these systems beyond their traditionally accepted boundaries. One particular category of FACTS devices makes use of high-powered voltage source inverters to insert near-sinusoidal ac compensating voltages into the transmission system. This thesis considers this particular category of inverter-based FACTS devices, namely the static synchronous compensator (STATCOM), static synchronous series compensator (SSSC) and unified power flow controller (UPFC). Although the potential for FACTS devices to enhance the operation of power systems is well known, a device such as a UPFC is itself a complicated subsystem of the overall power system. There is therefore also the possibility that the introduction of such devices could cause adverse interactions with other power system equipment or with existing network resonances. This thesis examines the interactions between inverter-based compensators and a particular form of system resonance, that of subsynchronous resonance between a generator turbine shaft and the electrical transmission network. The thesis presents a review of the theory of operation of high-power, multi-pulse inverter topologies actually used in transmission-level FACTS devices. Detailed simulation models are developed of both two-level and three-level multi-pulse inverters. With appropriate controls, simulation models of both the SSSC and STATCOM, and a full UPFC are then developed using these detailed inverter models and the results from these simulation models compared against other results from the literature. These comparisons show favourable agreement between the detailed FACTS models developed in the thesis and those used by other researchers. However, the models presented in this thesis include a more detailed representation of the actual power-electronic circuitry and firing controls of inverter-based FACTS devices than is the case with other models used in the literature. The thesis then examines the issue of whether the introduction of an SSSC to a transmission system could cause subsynchronous resonance (SSR). SSR is a form of dynamic instability that arises when electrical resonances in a series capacitively compensated transmission line interact with the mechanical resonances of a turbo-generator shaft system. The detailed SSSC simulation model developed in the thesis is used to determine the impedance versus frequency characteristics of a transmission line compensated by an SSSC. The results confirm earlier work by others, this time using more detailed and realistic models, in that the introduction of an SSSC is shown to cause subsynchronous resonance. The thesis then considers the addition of supplementary damping controllers to the SSSC to reduce subsynchronous oscillations caused both by the SSSC itself as well as by a combination of conventional series capacitors and an SSSC in a representative benchmark study system. The results show that subsynchronous oscillations in the transmission system compensated solely by an SSSC can successfully be damped out using a single-mode supplementary damping controller for a range of values of SSSC series compensation. However, in the case of the transmission system compensated by both conventional series capacitors and an SSSC, the nature of the subsynchronous oscillations is shown to be complex and strongly multi-modal in character. The thesis then proposes an extension to the single-mode supplementary damping controller structure that is better suited to damping the multi-modal resonances caused when an SSSC and conventional series capacitors are used together to compensate a transmission line. The results obtained from this multi-modal controller indicate that it is able to stabilise SSR for a range of compensation values, but that the controller design needs to be adjusted to suit different values of compensation. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2006.

This study intends to recover and expand the analytical work of Vadasz (1998) for linear and weak non-linear stability of a rotating porous media heated form below and subject to gravity and Conolis forces. It is shown that the viscosity has a destabilising effect at high rotation rate. It has been established that the critical wave number in a plane containing the streamlines is dependent on rotation. Finite amplitude calculations provide a set of differential equations for the amplitude and phase, corresponding to the stationary and over-stable convection, identifying the post-transient conditions that a fluid is subject to, i.e. a pitchfork bifurcation for the stationary case, or a Hopf bifurcation in the case of over-stable convection. The previous model (Vadasz [1998]) was extended with an additional time scale in order to represent amplitude fluctuations and a short space scale to include horizontal modes of oscillations. When the complete solution for the stream function or temperature is analysed, where left and right travelling waves are considered, we obtain a set of differential equations for the amplitude and phase. The solutions are discussed in this context. / Thesis (Ph.D.)-University of Durban-Westville, 2000.

Electric power utilities are faced with the challenge of meeting increasing demand for electric power whilst many factors prevent traditional remedies such as the expansion of transmission networks and the construction of new generating facilities. Due to issues of environment, health and rights-of-way, the construction of new generating plants and transmission lines were either excessively delayed or prevented in many parts of the world in past years. 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. This alternative approach has been possible with the emergence of Flexible AC Transmission Systems (FACTS) technology. The FACTS concept involves the incorporation of power-electronic controlled devices into AC power transmission systems in order to safely extend the power-transfer capability closer of these systems to their stability limits. One member of the family of FACTS series compensators is the Static Synchronous Series Compensator (SSSC), and this thesis considers the use of the SSSC to carry out closed-loop control of AC power flow in a transmission system. Although the SSSC has the potential to enhance the operation of power systems, the introduction of such a device can cause adverse interactions with other power system equipment or existing network resonances. This thesis examines the interaction between high-level power flow controllers implemented around the SSSC and a particular form of system resonance, namely subsynchronous resonance (SSR) between a generator turbine shaft and the electrical transmission network. The thesis initially presents a review of the background theory on SSR and then presents a review of the theory and operation of two categories of SSSC, namely the reactance-controlled SSSC and the quadrature voltage-controlled SSSC. The two categories of SSSC are known to have different SSR characteristics, and hence this thesis considers the impact on the damping of subsynchronous torsional modes of additional controllers introduced around both categories of SSSC to implement AC power flow control. The thesis presents the development of the mathematical models of a representative study system, which is an adaptation of the IEEE First Benchmark system for the study of SSR to allow it to be used to analyse the effect of closed-loop power flow control on SSR stability. The mathematical models of the study system are benchmarked against proven and accepted dynamic models of the study system. The investigations begin by examining the effect of a reactance-controlled SSSC-based power flow controller on the damping of torsional modes with an initial approach to the design of the control gains of the power flow controller which had been proposed by others. The results show how the nature and extent of the effects on the damping of the electromechanical modes depend on both the mode in which the power flow controller is operated and its controller response times, even for the relatively-slow responding controllers that are obtained using the initial controller design approach. The thesis then examines the impact of a reactance-controlled SSSC-based power flow controller on the damping of torsional modes when an improved approach is used to design the gains of the power flow controller, an approach which allows much faster controller bandwidths to be realised (comparable to those considered by others). The results demonstrate that for both of the modes in which the power flow controller can be operated, there is a change in the nature and extent of the power flow controller’s impact on the damping of some the torsional modes when very fast controller response times are used. Finally, the thesis investigates the impact of a quadrature voltage-controlled SSSC-based power flow controller on the damping of torsional modes in order to compare the influence of the design of both Vsssc-controlled and Xsssc-controlled SSSC-based power flow controllers on torsional mode damping for different power flow controller response times. The results obtained indicate that a Vsssc-controlled SSSC-based power flow controller allows a larger range of SSR stable operating points as compared to a Xsssc-controlled SSSC-based power flow controller. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2012.

ESKOM has relied primarily on impedance-based measurement protection relays for the protection of transmission lines. One of the main disadvantages of distance relays is the limited fault resistance measurement capability. High-resistance faults are characterised by low fault currents, therefore the impedance calculated would be much bigger and so the fault will appear to be beyond the protected line. The main aim of the study is to gain clear understanding of the capability of the existing relays used in Eskom Transmission network, to be able to give recommendations on the refinements to the transmission line protection philosophy required to improve future protection performance. Omicron relay tests, showed that the dynamic characteristics of the three selected relays which were tested covers more fault resistance than that of the normal static impedance and also that the effect of DC offset is negligible with regards to fault resistance measurement capability. Normally the relays have built in algorithms which are able to filter nuisance signals. Theoretical case study that compared the most used relays in Eskom Transmission was done and the results are documented. Settings recommendations to improve fault resistance coverage were deduced from the above study. Fault investigation by using digital simulations (Matlab simulations) has proven the lack of capability to operate for some impedance relays in some fault conditions, as the fault resistance sometimes moves fault impedance beyond relay characteristic even when actual . polarization of the relay is considered. Analysis of the protection performance in transmission proved that high resistance faults accounts for at least half of protection equipment performance index (PEPI) incidents. Finally the author made recommendations to improve the protection performance concerning high resistance faults. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2006.

Emanating from the proceedings of CIGRE 2004, a new idea for higher power transmission by recycling and up rating high voltage alternating current transmission lines for high voltage direct current application was presented at the HYDC working group session. To date, there is no known application of the idea. Globally, transmission congestion, power transfer bottlenecks with restricted and limited power transfers and unobtainable servitudes challenge electric power utilities. The literature review shows that since the early sixties, several authors have studied this proposal. However, no applications were done. Admittedly, early HYDC technology was troubled by problems with multi-terminal designs, external insulation breakdown in the presence of DC stress and mercury valve rectifiers struggled with arc backs. To date, power electronic and external insulation technology has grown and matured for confident application both in point to point and multi-terminal application. The economic costs of introducing the DC technology are also more affordable given reducing prices due to higher volume of purchases. With promising developments in insulation and power electronic technology and driven by South Africa's surging growth in the consumption of electrical energy; the subject of upgrading HYAC transmission for HYDC application is revisited. For the research, the emphasis is beyond FACTS and towards a solution that could develop into a new supergrid that could overlay the existing national grid. Thus, the solution is prepared specifically for the case of recycling existing assets for higher power transfers. The working environment is defined by the difficulty in acquiring new powerline servitudes, transmission congestion in complex networks, the need for electrical islands within complex interconnections, and the need for enhanced power system stability and to promote new ancillary services energy management. The focus of this research study was to determine the technical feasibility of upgrading of existing HYAC circuits for HYDC application. It is assumed that the transmission line will remain as is in structure, layout and mechanical design. The changing of external line insulators using live line technology is an accepted modification to the original HYAC line, if required. From the study, we conclude that not all HYAC lines are recommended for upgrade to HYDe. We introduce boundary conditions as a first step towards checking on the suitability of the proposed upgrade from HVAC to HYDC mode. Emanating from this study, the first paper published introduced the initial boundary conditions as being only those lines where the "unused gap" between surge impedance loading and conductor current carrying capability is appreciable and large; generally three to four times surge impedance loading. In the case where the unused gap is the smallest or negligible, then we do nothing. In between, where the unused gap is about two to three times the surge impedance loading, then we can consider active or passive compensation using the HVAC FACTS technology options as proposed by EPRl. Having determined the candidate transmission line configuration for the proposed upgrade to HYDC application, we select the DC operating voltage as based on the voltage withstand capability of external insulation for varying environmental conditions. In addition, the DC voltage will generate allowable electrical fields and corona effects within and outside the transmission servitude. The optimum DC operating voltage would satisfy the conditions of minimum transmission power losses and volt drop for the case of maximum power transfers; within the limits of electrical fields and corona effects. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2007.