OpenUCT :: Browsing by Author "Pillay, Pragasen"

Browsing by Author "Pillay, Pragasen"

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Open Access
A quantitative analysis of Augmented Reality visual merchandising on online purchase intention: A consumer neuroscience approach
(2022) Abbott, Lara Elizabeth; Pillay, Pragasen; Rosenstein, David; Drummond, Mark
The rapid evolution of e-commerce has led retailers to fixate on how to differentiate themselves and provide an enhanced and engaging experience for their customers. In this dynamic industry, emerging technologies and innovation have become crucial for maintaining a competitive advantage. The purpose of this study is to explore how newer methods of visual merchandising can influence consumer purchase intentions, paying particular attention to Augmented Reality (AR) and how its inclusion in the online shopping industry could mark a pivotal change. The study addresses present difficulties in online retail such as the lack of touch and feel aspect, customer uncertainty and cart abandonment. It is proposed herein that Augmented Reality as a visual merchandising technique will mitigate these difficulties and allow South African online retail to grow in accordance with global standards. Given the recent developments in online retail in South Africa due to the COVID-19 pandemic, it is an opportune moment to investigate consumers and invest in meeting their ever-changing needs, enhancing their experiences, and formulating insight-driven digital marketing strategies. This paper serves to break new ground in nascent AR literature within the field of market research, and particularly in the South African and Neuroscience context. By examining the real-time Emotion and Attention of respondents using Neuroscience technology, this study provides a practical approach for marketing executives to optimize their customers' online experience and thus drive conversion rates. The objectivity of neuroscience methods presented more reliable, evidence-driven insights by accessing unconscious consumer responses that complement traditional measures. The Technology Acceptance Model (TAM), a robust and frequently used model for new technology adoption and the Model of Emotion Regulation were also used, providing the explicit measures for the study. Perceived Ease of Use, Perceived Usefulness and Purchase Intention were all rated favorably, indicating a positive likelihood of AR adoption by the South African market. The positive feedback regarding Purchase Intention is also a significant finding given it has proven previously to be an indicator of actual buying behaviour. Higher levels of arousal in the AR group present a promising indication of the consumers' cognition of the product and ultimately its impact on the consumer decision making process. Therefore, this study suggests the incorporation of AR into marketing strategies to remain successful in a dynamic retail environment.
Open Access
An investigation into the influence of targeted-Facebook advertising through mobile devices on South African consumers' advertisement perceptions
(2021) Wicht, Alina; Pillay, Pragasen; Mbumbwa, Tendai
Digital advertising has become a multi-billion-dollar industry; and it is growing tremendously each year. In times of strong market dynamics, marketers are particularly aware of Facebook advertising as a powerful advertising form. The dynamic market situation also magnifies the need for marketers to monitor and analyse consumers' perceptions. The purpose of this study was, thus, to assist marketers in understanding the influence of targeted Facebook advertising through mobile devices on South African consumers' advertisement perceptions. The form of advertising investigated was in-stream advertisements. The aim of this study was to explore the role of South African consumers' emotions in relation to these consumers' attention to the targeted in-stream advertising on Facebook delivered via mobile phones. South African consumers view videos on their mobile phone through the Facebook platform, which can be interrupted by targeted Facebook advertising. This study investigated the role that the interruption of video watching bears in relation to the interpretation and perception of the advertisement by these consumers. Another objective was to explore the role of South African consumers' attitudes towards brands in relation to what these consumers remember from the advertisements delivered through mobile targeted in-stream Facebook advertising. The sample consisted of 13 South African consumers and was acquired using purposive sampling. This study was based on a perception-formation model, which is a composition formed from the perception models of different authors. The model was investigated using qualitative interviewing and the data gathered was analysed through qualitative content analysis. The results of the study provide support for the theoretical framework and suggest that consumers' perception of in-stream advertising on Facebook is influenced by various factors such as the nature of Facebook usage, emotions, the disruption caused by the advertising, the attitude towards the brand and the Facebook video viewed. Marketers may be able to influence consumers' perception of in-stream advertisements through more precise targeting, a better fit between the in-stream advertisements and the video and by limiting the advertisement occurrence. By shedding light on South African consumers' perceptions of targeted in-stream advertising on Facebook, this thesis could serve as a basis for marketers' decisions, and also lay the foundations for future academic research in this field.
Open Access
An investigation of the components that influence the purchase decision of Congolese millennials in the Democratic Republic of Congo informal clothing market
(2021) Momat, Olga; Pillay, Pragasen; Mbumbwa, T
Informal markets for fashion are a growing phenomenon around the world and more specifically in the Democratic Republic of Congo. In different cities in the Democratic Republic of Congo, there are tents housing vendors who sell second-hand clothes. These markets are becoming the millennials' shopping hubs as millennials are on a quest for uniqueness, fashion trends and value for money. Limited research regarding the shopping patterns and purchase decisions of Congolese millennials and even less regarding the informal clothing market in the Democratic Republic of Congo is available. This research is aimed at investigating factors influencing millennials in the purchase of second-hand clothes in the informal markets in the Democratic Republic of Congo. The theoretical framework was guided by the theory of planned behaviour from which the researcher constructed an adapted model. The purchase of secondhand clothes is the behaviour that is preceded and influenced by the consumer's intention to purchase. In turn, the intention to buy clothing from informal markets is influenced by various factors. Five factors were added to the model, namely quality, clothing interest, peers' opinions, price consciousness and the need for uniqueness. The model was investigated through a qualitative case study analysis. The data was collected through face-to-face interviews and the thematic analysis was conducted and interpreted manually. The target population argued that second-hand clothes are unique, durable and affordable. These clothes allow them to shop the fashion trends they see on social media from around the world. Thus, it is important to have a valuable understanding of the factors influencing Congolese millennials to buy second-hand clothes. Retailers and marketers in the fashion industry of the Democratic Republic of Congo, particularly those in the informal clothing market, can consider the consumer insights acquired in this research and apply them to increase their advantage in the market place.
Open Access
The application of advanced signal processing techniques to the condition monitoring of electrical machine drive systems
(2007) Barendse, Paul Stanley; Pillay, Pragasen
The thesis examines the use of two time-frequency domain signal processing tools in its application to condition monitoring of electrical machine drive systems. The mathematical and signal processing tools which are explored are wavelet analysis and a non-stationary adaptive signal processing algorithm. Four specific applications are identified for the research. These applications were specifically chosen to encapsulate important issues in condition monitoring of variable speed drive systems. The main aim of the project is to highlight the need for fault detection during machine transients and to illustrate the effectiveness of incorporating and adapting these new class of algorithms to detect faults in electrical machine drive systems during non-stationary conditions.
Open Access
Application of advances in automotive technologies to electrification in rural sub-Saharan Africa
(2004) Sebitosi, A B; Pillay, Pragasen
Continued lack of electriﬁcation in rural sub-Saharan Africa poses a major challenge. The consequences are well documented. Major research is required to redress the situation but the meagre ﬁnancial and energy resources are major hurdles. In the meantime elsewhere in the ﬁrst world, investment in research and innovation continue to attract investors. For example a massive automotive energy conservation research drive was initiated in the mid 1990's by a Partnership for a New Generation of Vehicles (PNGV). The PNGV advanced three important public policy objectives: environmental protection, energy security, and U.S. economic competitiveness. To achieve this mammoth challenge they proceeded by re-examining automotive energy conservation right from ﬁrst principles. Their centrepiece was a coordinated portfolio of hundreds of research projects by among others, 19 US Federal National Laboratories, United States Council for Automotive Research (USCAR), automotive parts suppliers, university research facilities and a range of stakeholders. These were subsequently augmented by similar efforts in Europe and Japan. The thrust of this work draws parallels between an automobile and a remote village to consider the adaptation of the new automotive technologies to rural electriﬁcation. The author further augments this by additional contributions in load modelling, mini distribution network loss minimisation and energy economy by appropriate system conﬁguration. The main issues that are shared by an automobile and a remote rural village can be revealed as ﬁnite energy resources without a supporting grid infrastructure, which must cope with, poor energy resource-to-need conversion technologies, adverse human factors, poor load factors, inefﬁcient appliances and poor storage technologies, among others. These must all interact to meet objectives on service quality and the environment. Furthermore, the expected economies of scale in the automotive industry should subsequently make the adoption of these technologies affordable for rural applications.
Open Access
Application of improved core loss formulations to machine design
(2008) Manyage, Marubini J; Pillay, Pragasen
The primary focus of this thesis is in core loss measurement and modeling techniques and their impact in machine design. In practice, steel manufacturers usually supply core loss data either at 50/60Hz, 1.5T or curves (core loss vs. flux density) at 50 and/or 60Hz. There is growing need for lamination characterization at high flux densities (2T) and high frequencies (3.2 kHz) for novel electric machine designs operating at high speeds. The core loss measurement concept is reviewed first. Two core loss measurement formulae are compared using core loss results from different testing frames and materials.
Open Access
An automotive interior lighting application using white light-emitting diodes
(2008) Solomon, Ramzi; Pillay, Pragasen; Sebitosi, A B
In this thesis the commercially available white light-emitting diode (LED) with its inherent efficiency, longevity and mechanical strength, is used to show, that success in energy efficiency can be obtained. Two cases are used to illustrate the need for efficient demand-side technology: the electricity shortages of the Western Cape Province in South Africa and a white LED pilot project in Namulonge, Uganda.
Open Access
Condition monitoring of polymer electrolyte membrane fuel cells
(2014) De Beer, Chris; Barendse, Paul Stanley; Pillay, Pragasen
As the global demand for energy continues to grow new technologies and systems must be developed to supply the market. This includes renewable energy generation, storage and conversion systems. The primary storage technology in use today in the portable electronics, the automotive sector and to a lesser extent power networks is battery based systems. To overcome some of the limitations inherent in batteries, fuel cell based power generators and converters have been developed. Fuel cells act as electrochemical energy converters that convert a fuel source such as natural gas directly into electrical power without any secondary phases. For systems running on Hydrogen generated via renewable or natural sources, the input/output cycle becomes completely sustainable. Out of the different fuel cell types available and under development, the Proton Exchange Membrane or Polymer Electrolyte Membrane (PEM) fuel cell has emerged as the technology of choice, and currently owns more than 80% of the commercial fuel cell market. This has spurred further research in the field to increase performance and life expectancy of the cell materials. A promising development in the form of High Temperature PEM (HT-PEM) fuel cells has recently emerged and addresses some of the shortcomings of the low temperature counterparts. A critical field of research is the condition monitoring strategies and technologies for the electrochemical device that ties in with the power conditioning sub-systems. This thesis presents the development of condition monitoring systems by conducting detailed studies on the fault/degradation mechanisms prevalent in the cell materials for the purpose of detection, classification and implementation of possible mitigation strategies. Specific consideration is given to the detailed analysis of the fault mechanisms in HT-PEM fuel cells that are not yet fully understood and commercialized. In particular, electrochemical equivalent circuit models and reduced order semi- empirical models are developed to facilitate fault detection. Based on these models, mitigation strategies for specific faults are proposed and experimentally verified. New systems and methods are developed for rapid online impedance signature mapping that provide a basis for early fault prediction that can increase system performance and life expectancy. The findings in this research provide valuable insight into the effect that most prevalent faults have on the internal electrochemistry and the impact on electrical performance. From the experimental results, a semi-empirical electrochemical model is developed to assist with life time estimation and system optimization. The model is integrated with a real time emulator platform that can reproduce single cell voltage levels at the high output currents and transient characteristics. A detailed analysis is conducted on CO poisoning and the resulting effects on key equivalent circuit parameters that enable quantification of the fault condition. It is shown that the catalyst at the higher operating temperature is still susceptible to a certain degree of semi-permanent degradation. To mitigate these effects, a new active current control strategy is proposed to enforce electro-oxidation of the CO to recover the lost active area that delivered superior results compared to current pulsing strategies. New rapid online detection strategies are proposed by using small voltage transients in an operational HT-PEM fuel cell. The method makes use of the discrete S-transform that overcomes some of the limits in other signal processing methods used in fuel cell diagnostics. To enable detailed parameter calculation, a population based incremental learning algorithm is implemented in the developed method. A new condition monitoring system is developed that makes use of Optimized Broadband Impedance Spectroscopy. The hardware is designed to accommodate both single cell and stack level implementation. It is shown that the proposed system is able to deliver measurements under extreme non-linear conditions that can occur in PEM fuel cells in a fraction of the time associated with normal EIS based systems.
Open Access
Contributions to permanent magnet wind generator design including the application of soft magnetic composites
(2006) Khan, Mohamed Azeem; Pillay, Pragasen
The main objective of this dissertation is to contribute knowledge toward the design of small PM wind generators, which includes the application of soft magnetic composite (SMC) materials to the desing of these machines. A problem is first addressed of adapting a PM wind generator, intended for high-speed operation with a small 3-bladed wind turbine, for low speed operation with a new multi-blade, high solidity turbine. An analytical model is formulated and then used to examine the effect of several changes to the design of the wind generator. A new specification of the redesigned machine is then set. The overall performance of the redesigned machine coupled to the new turbine is shown to be satisfactory.
Open Access
Design and implementation of variable speed wind energy induction generator systems for fault studies
(2004) Barendse, Paul Stanley; Pillay, Pragasen
Due to the economical and environmental benefits, Wind Energy Conversion Systems (WECS) have received tremendous growth in the past decade. The increased interest in wind energy has made it necessary to model and experimentally evaluate entire WECS, so as to attain a better understanding and to assess the performance of various systems. As a direct consequence of the increase in wind generation systems, comes the need for the reduction of operational and maintenance costs of these wind generators. The most efficient way of reducing these costs is by the early detection of the degeneration of these generators health, thus facilitating a proactive response, minimizing downtime, and maximizing productivity. The more common induction machine failures are caused by the deterioration of the stator insulation and by the breaking of rotor bars. The thesis describes the design, modeling and implementation of two different variable speed induction generator systems for studying faults in wind energy applications. This project served as a platform for further research into the development and evaluation of a non-stationary fault detection technique suitable for wind energy induction generator purposes. Some common faults are implemented on the wind generators in an attempt to identify them from measurements and by using a steady state fault analysis technique (Motor Current Signature Analysis). For variable speed wind generation, there are two systems using induction generators. The first consist of a squirrel cage induction generator, which uses back-to-back converters in the stator circuit, as shown in Fig. 0.1. The second consists of a wound rotor induction generator, whereby the stator is directly connected to the grid and the rotor circuit consists of back-to-back converters, as shown in Fig. 0.2. When both the rotor and stator are capable of delivering power as with the wound rotor induction generator, they are known as doubly-fed induction generators (DFIG).
Open Access
Design considerations and implementation of an electromechanical battery system
(2007) Johnson, David; Pillay, Pragasen
This thesis covers the design and implementation of a low cost electromechanical battery using an outside rotor permanent magent Halbach array with hybrid magnetic bearings and heat pipe cooling. The theoretical calculations include finite element analysis. A dipole Halback array produces a uniform flux distribution inside the cylindrical statoe, where straight windings on an iron-less stator are placed near the inner boundary.
Open Access
Design considerations for low pressure solar water heating in South Africa
(2012) De Meyer, Oelof; Pillay, Pragasen; Sebitosi, A B; Okou, Richard
This thesis investigates the application of solar water heating in South Africa. The solar water heating system investigated work on the thermosiphoning effect or natural convection. An extensive literature study has been undertaken to investigate this phenomena. The three partial differential equations (governing equations) are non-dimensionalized and a similarity solution is applied to obtain two coupled non-linear ordinary differential equations. These equations are then solved in MATLAB to obtain the velocity and temperature profiles. Two scenarios were considered, a vertical wall with a constant wall temperature and a vertical wall with a constant heat flux. LP SWH systems use vacuum tubes to absorb solar radiation and transfer it to the water, which is similar to the vertical wall with a constant heat flux. A simulation model has been developed for a LP SWH system which is able to simulate the system performance for a given geographical location, where the user can specify the system component attributes. Experiments on the system were conducted to validate the simulation model. The simulation model accompanies a 6-Step Design Guide developed to assist the user to design a system able to satisfy the consumer's hot water demand. The 6-Step Design Guide developed can be used in future design considerations for LP SWH systems in South Africa.
Open Access
Examining the factors structures of brand loyalty of men’s deodorants among generation X and generation Y consumers in Cape Town
(2019) Lokosang, Lobojo; Pillay, Pragasen
This study examines the structures and reliability of brand loyalty in men’s deodorant consumption, as suggested by Moolla’s (2010) framework. This is due to the fickle or disloyal nature of male Generation X and Generation Y deodorant consumers. Although, the subject of brand loyalty is popular, there is a lack of research in the investigation of Generation X and Generation Y consumers specifically in the men’s deodorant industry in Cape Town. This study attempted to close the gap by examining brand loyalty of Generation X and Generation Y consumers in Cape Town through the brand loyalty framework. Based on Chronbach Alphas, the study assessed the degree to which each factor of deodorant brand loyalty loads unto a construct or internal consistency. This study’s motivation is to attempt to assist management develop appropriate strategies, and to expand the body of knowledge for academics, due to limited information and to pave the way for researchers to explore various product categories specifically utilised by men as well as assist them with a tested brand loyalty framework. A positivist research paradigm provided the belief system in which data for the current study was gathered, analysed and used to provide solutions. A descriptive research design chosen for the study resulted in the application of a quantitative research methodology. With reference to Moolla’s research questionnaire, data for the current study was collected from men between the ages of 36 and 52 (Generation X) and Generation Y (men between the ages of 18 and 35). A total of 245 responses were received from Generation X and Generation Y men who are brand loyal to men’s deodorants and the data were collected by statistically analysing this sample. This research established that there were leading brands that consumers were brand loyal to and that there were dominant brand loyalty influences for both Generation X and Generation Y consumers in the men’s deodorant industry. In addition, it was revealed in the study that the suggested recommendations were that there needs to be further research in the men’s deodorant industry, a comparative study should be conducted, brand loyalty of other product categories should be investigated and marketers should focus on culture as a significant influence of brand loyalty. For future research, it was recommended that this study be continued on a larger scale in the men’s deodorant industry to endorse or rectify the results of this study
Open Access
Exploring the Factors that Impact on the Attitude to Purchase: A spotlight on counterfeit luxury handbags among Durban's emergent Black Middle-class Females
(2020) Jugnundan, Mishka; Pillay, Pragasen
Increased sales of counterfeit luxury branded handbags are a significant transnational concern. Research effort concerning understanding this purchase behaviour has largely been contextualised outside of Africa, with varying results relating to the impact of attitude on the purchase decision-making process having emerged. With South Africa serving as one of the most profitable counterfeit luxury handbag markets on the continent, this study sought to fundamentally determine whether consumers' attitude effected their buying rationale. The study was conducted in Durban, home to a large female middle-class population, deemed to satisfy many of the characteristics attributed to the typical counterfeit handbag consumer. The study adopted a post-positivist research paradigm and employed a causal research design. In terms of research strategy, the study made use of a quantitative approach. The target population regarding the investigation pertained to Durban's emergent Black middle-class females. In order to segment this population, nonprobability sampling was utilised, with convenience and snowball sampling having been selected. The total sample size amounted to 350 individuals, who provided data by means of a self-administered questionnaire. Once collected, this data was interpreted through factor and regression analyses. The findings of the study confirmed that individual, product and service factors impacted upon the attitude to purchase of counterfeit luxury handbags among Durban's emergent Black Middle-class females. Furthermore, it was discovered that the attitudinal antecedent's of knowledge, perceived risk, ethical obligation, product price and service quality significantly influenced attitude formation, and in turn, attitude to purchase. As such, the information collated allows for those combating counterfeit sales activity to focus their efforts and resources in a more predetermined manner. It is therefore primarily recommended that anti-counterfeiting agents place greater emphasis upon defending intellectual property rights through demand, or ‘consumer focused' initiatives which target specific purchase-prompting variables. This investigation also provides interesting opportunities for future research, including determining whether attitude continues to play an important role across different South African provinces, as well as within international settings.
Open Access
Impact of solar water heating on Eskom's peak demand
(2008) Ijumba, Ketrine Pamela; Pillay, Pragasen; Sebitosi, AB; Folly, K
Includes abstract. Includes bibliographical references (p. 98-102).
Open Access
Induction motor variable speed drive performance and impact on energy savings
(2001) Khumalo, Siboniso T; Pillay, Pragasen
ESKOM, together with Municipalities distribute power at a line-to-line voltage of 400+/-10%. Hence in theory, the user ends up with a voltage of 340 to 440. In urban areas 2% voltage unbalance is considered acceptable, while 3% voltage unbalance is considered acceptable for rural areas. The combined effects of under or overvoltages coupled with "acceptable maximum" voltage unbalance is not understood or documented. This project is a comprehensive study of the effects of voltage unbalance in combination with under or overvoltages on induction machines (1M) variable speed drives. In addition the performance with PWM inverters connected to 1M via long cables is also studied. The project starts by an evaluation of previous work on the subject and related topics. Relevant conclusions are made based on the literature review in Chapter One. The second step of the project was to develop two test beds in the UCT Machine's Laboratory. The test beds are for performance testing of low (up to 15kW) and medium (up to 75kW) power 1M and their VSDs. The test bed losses are determined at 4 different operating points and documented. Several tests such as the blocked rotor and no load tests were undertaken to determine the machine parameters. A PSpice simulation model was developed and tested for the low voltage test bed. The test results compared well to simulation predictions. Furthermore, tests under unbalanced and overvoltage conditions were performed and the results verified with simulations. This proves that the developed PSpice model can reliably simulate the actual test bed for both balanced and unbalanced conditions. Moreover, it can be easily applied to model different size machines and drives. The information required includes: the motor parameters, drive dc-link parameters, modulation ratio (ma) and the switching frequency. The impact of voltage unbalance in drives with long cables between the inverter and motor is examined. A 36m long, 4-core, PVC insulated cable is used on the low voltage test bed for a case study. The model used for the cable is a lumped parameter model. The 1M model is also taken from the literature to include a high frequency branch, to model the reflected voltage wave phenomenon. A basic analysis of energy savings in pumps and fans load associated with the application of variable speed drives is also done. Boiler feed-pumps from Tutuka power station are used as a case study that may be replicated for other applications in utilities or industry. The developed Excel Spreadsheet program to project the value of savings and determine the payback period is compared to an ABB program. The two results agree within an acceptable range. Therefore, the knowledge of the pumping system specifications and the cost of energy in kWh with the Energy Savings Program would enable one to project energy savings.
Open Access
Medium voltage petrochemical drives : soft start and adjustable speed systems
(2010) Endrejat, Frieder; Pillay, Pragasen
Medium voltage synchronous machines are used for large petrochemical compressor motor drives (>13 MW) at high application voltages (e.g. +-11 kV). Limited research exists on the application of Voltage Source Inverters (VSIs) for these petrochemical loads. An application concept is described where the converter is used to start several motors and to drive one at adjustable speed. Associated benefits in terms of availability, hazardous areas and switching surge overvoltages are outlined. A technology feasibility study illustrates that new VSI Cascaded H Bridge (CHB) technology and the application concept is economically feasible. Ultimately the research illustrates how and where new VSI technology can economically be applied with a significantly lower risk level.
Open Access
Monthly expenditure category fluctuations and trade-off in South Africa bottom of the pyramid households
(2017) Lappeman, James; Chigada, Joel; Pillay, Pragasen
This exploratory study investigated changes in the allocation of household expenditure between various product or service categories in a sample of South African low-income or 'bottom of the pyramid' (BoP) households. First, the mixed methods research quantified the monthly income and expenditure fluctuations in the sample of households over a period of four months. In addition, study identified and quantified expenditure category trade-offs in the target households. Finally, a qualitative inquiry explained the reasons for the fluctuations and the trade-offs identified in the first two components. The study was based on the existing BoP proposition and specifically focused on BoP consumer decision-making theory. Methodologically, the study was a monthly longitudinal panel over four months. The quantitative component employed a once-off baseline questionnaire to gather household data. The participating households then completed monthly self-complete financial diary questionnaires that recorded both income and expenditure. The qualitative component involved interviews with representatives from the participating households and provided details to explain the underlying causes for changes in monthly expenditure patterns. The study was conducted in four provinces with eighty BoP households participating in the research. The study found significant variation in both household income and expenditure between months. The variation and consequent trade-offs between expenditure categories was caused by calendar-related phenomena (such as the festive season), income shocks, unforeseen expenses and spreading the household budget over multiple months. In addition, large fluctuations in income resulted in a constantly shifting allocation of expenditure to categories that required the most attention at a particular point in time. Informal savings (stokvels) and micro-enterprise expenses also contributed to fluctuations in income and expenditure. This study provides unique insights that fill a vacuum in the current body of academic and industry knowledge for this segment of close to forty million BoP South Africans. No study of this nature has been published in either South African or international journals.
Open Access
A nonlinear adaptive filter for improved operation and protection of power systems
(2008) Naidoo, R M; Pillay, Pragasen
This thesis presents the application of a nonlinear adaptive filter to selected areas in power systems. The filter has demonstrated excellent performance against con-ventional methods in biomedical applications. The algorithm is robust in structure and highly immune to noise. Applications in this thesis include (1) sag detection, (2) symmetrical component estimation, (3) phase and frequency estimation, (4) sag analysis and (5) distributed generation synchronisation and protection. The appli-cations were chosen such that the amplitude, phase and frequency tracking ability are thoroughly tested.
Open Access
Operation of induction machines in the presence of unbalanced supplies
(2001) Manyage, Marubini J; Pillay, Pragasen
Three-phase induction machines are widely used in South Africa for industrial, commercial and residential applications because of their simple construction and low maintenance. The manufacturers design these motors to provide their nameplate ratings when supplied with balanced sinusoidal voltages. However, the power system experiences unbalanced voltages, overvoltages, undervoltages, etc, which are seen at the motor terminals. The South African Electricity Supply Utility (Eskom) supplies the commercial and industrial systems with a line voltage range of 400V +- 10%. An Induction motor rated at 380V or 400V will therefore experience overvoltages or undervoltages depending on the location of the motor from the supply. Besides overvoltages and undervoltages, unbalanced voltages exist on the power system. The tolerable level of voltage unbalance on the South African three-phase networks is 2%, and may be up to 3% in the rural areas. In practice, induction motors experience a combination of overvoltages or undervoltages with unbalanced voltages. This affects motor life. NEMA has done research on induction motors operating under unbalanced voltages. They defined voltage unbalance and produced a derating curve, assuming the average voltage applied to the motor is equal to the rated voltage. The EEC has another definition of voltage unbalance based on the positive and negative sequence voltages. The IEC definition is referred to as the true definition. Two formulas that approximate the true definition also exist. An analysis was done in order to understand the implications of using these definitions of voltage unbalance in the South African power system. It was found that the NEMA definition and the true definition do not differ significantly below a 5% unbalance. in order to estimate motor life when a motor is supplied with unbalanced voltages, in combination with over or undervoltages, electrical and thermal models were developed to predict the temperature. The electrical model was based on the positive and negative sequence equivalent circuits. The thermal model used, separated stator and rotor thermal circuits. The thermal parameters were obtained from simple tests rather than from motor design data. The predicted temperature values agree closely to the measured values. The interaction between the electrical model, thermal model and the thermal ageing equation were used to estimate motor life when the motor is supplied with unbalanced voltages, in combination with over or undervoltages. Motor life is reduced when the operating temperature exceeds the rated. In order to restore motor life, new derating curves were developed since the NEMA derating curve is limited to rated average voltage. Motor life can be restored by applying the new derating curves developed here.