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Parameter Study and Calibration of SPH–DEM Coupling Simulations for Fluid–Granular Solid Systems
No full textThe presence of fluid–granular solid flows can be found in a wide range of industrial applications such as pneumatic conveying, wet ball milling, and slurry transport. The majority of such fluid–granular solid flows are too intricate to be sufficiently modelled by fundamental theories. As a result, there has been a research effort conducted on using computer-aided engineering (CAE) tools to model industrial systems that handle fluid–granular solid flows. Apart from using conventional methods, some researchers have explored the coupling between smoothed particle hydrodynamics (SPH) and discrete element method (DEM) to model specific fluid–granular solid flows with free surfaces, complex geometries, mobile interfaces, large deformations, and fast dynamics. However, even though many feasibility studies have been conducted on SPH–DEM simulations, there is still a general lack of standardised methodologies to conduct parameter study and calibration of this newer simulation tool.With this motivation, this thesis aims to develop a dedicated model parameter study and calibration framework for new SPH–DEM coupling models using bench-scale experiments. The developed framework is utilised to construct an SPH–DEM model to simulate the mixture between water and irregularly shaped cohesionless dark peach pebbles. In this framework, length scale refinement strategies are investigated to see if they can help a standard SPH implementation make accurate predictions of 3D free-surface fluid flows. Experimental test rigs are designed to accommodate for both a dry mode granular solid sample and a submerged mode fluid–granular solid mixture on the same system. Using the experimental data as the validation reference, a manual calibration process followed by a comprehensive calibration process are performed to obtain an understanding of how SPH length scales and DEM contact parameters affect the SPH–DEM simulation model.While the research indicates a considerable challenge in using length scale refinement strategies to achieve simulation convergence only with a standard SPH implementation, it also illustrates that SPH length scale sizes, along with the DEM contact parameter values, have a substantial impact on the SPH–DEM results. The conducted manual and comprehensive calibration studies demonstrate the potential of a dedicated calibration framework to develop a fully calibrated SPH–DEM model. These studies also emphasise the need to treat dry mode DEM calibration and submerged mode SPH–DEM calibration independently.</p
Investigation of the underlying energy-regulating mechanisms of nuts: implications for nutrition labelling and strategies to promote nut consumption
No full textChronic disease is an ongoing source of poor health, and conditions such as cardiovascular disease and overweight and obesity are highly prevalent in Australia. Nuts are a core food associated with a range of health benefits; however, global consumption, including in Australia, is low. Previous research acknowledges consumer concern regarding the potential impact of nut consumption on body weight as a barrier to nut intake. While nuts are an energy-dense food, the evidence suggests that regular consumption is not associated with weight gain. Some proposed energy-regulating mechanisms of nuts include lower metabolisable energy (due to some fats within nuts being encapsulated within thick cell walls and not easily accessed and digested), reduced subsequent energy intake due to post-consumption appetite regulation (energy compensation), and increased energy expenditure. Currently, the energy content on nutrition labels in Australia is estimated based on Atwater factors, which do not account for the lower energy availability, hence may over-represent the available energy from nuts, and potentially deter the inclusion of nuts in habitual diets. Furthermore, energy intakes from nuts may be overestimated among consumers and other stakeholders. The aim of this thesis is, therefore, to synthesise evidence on the energy-regulating mechanisms of tree nuts and peanuts, and to explore the potential influence of these mechanisms on population energy intakes and strategies for labelling and promotion of nut intake. The research hypothesised that the metabolisable energy of nuts will consistently be lower than energy predicted using Atwater factors and that nut consumption will reduce subsequent energy intake and increase energy expenditure. Furthermore, energy intakes estimated using metabolisable energy values of nuts will be lower than the conventional Atwater method in Australian nut consumers, and while knowledge and practices regarding nuts will vary among consumers and other stakeholders, promoting the metabolisable energy of nut products may encourage nut consumption.</p
Use of Anti-P2X7 Biologics to Reduce Graft-Versus-Host Disease
No full textP2X7 is an adenosine 5'-triphosphate (ATP)-gated ion channel involved in various health and disease processes. P2X7 is present on many cell types, most notably leukocytes, and its activation promotes inflammatory and immune responses. Thus, P2X7 is a potential therapeutic target for inflammatory disorders, including graft-versus-host disease (GVHD), a major complication of donor blood stem cell transplantation. A speciesspecific anti-human (h) P2X7 monoclonal antibody (mAb) is available but its use to date has been limited. Moreover, anti-P2X7 nanobodies (Nbs) are available. Neither anti-P2X7 mAbs or Nbs have been examined in GVHD. Therefore, this thesis aims to investigate anti-P2X7 biologics in the reduction of GVHD in a humanised mouse model.Chapter 3 involved the purification and in vitro testing of the anti-hP2X7 mAb (clone L4). This chapter confirmed the ability of the anti-hP2X7 mAb to bind and block human, but not mouse, P2X7. Moreover, this mAb could prevent the loss of human regulatory T cells (Tregs) and human natural killer (NK) T cells during serum starvation. Consequently, the results in this chapter validated the investigation of the anti-hP2X7 mAb in an in vivo model of GVHD (Chapter 4) and in other chapters of this thesis.Chapter 4 examined if the anti-hP2X7 mAb could reduce GVHD in a humanised mouse model. This mAb impaired clinical and histological liver and lung GVHD development but had no significant effect on survival. The reduction in GVHD severity corresponded to an increase in proportions of hTregs, hNK T cells, and hNK cells and a decrease in the proportions of human T helper (Th)17 cells and the hTh17:hTreg ratio. Collectively, these results demonstrated for the first time that a biologic targeting P2X7 can reduce GVHD and that donor (human) P2X7 can contribute directly to GVHD progression.Chapter 5 explored if two different anti-P2X7 Nbs, delivered via an adeno-associated viral vector, could reduce GVHD in a humanised mouse model. The anti-mouse (m)/hP2X7 Nb (1C81) and to a lesser extent the anti-mP2X7 Nb (13A7) reduced clinical and histological GVHD, in the liver, lung and skin. These effects corresponded to, most notably, a decrease in liver hTh17 cells, and to a lesser extent, splenic hTregs and human invariant (i)NK T cells. Further, the presence of circulating anti-P2X7 Nbs in mice was confirmed.Chapter 6 examined P2X7 expression on human blood leukocyte subsets and whether the anti-hP2X7 mAb could mediate complement-dependent cytotoxicity (CDC) of these cells. This chapter confirmed the expression of cell surface P2X7 on various human blood leukocytes and revealed the presence of P2X7 on human blood MDSCs. Further, it demonstrated that this mAb can mediate CDC in human leukocytes expressing relatively high cell surface P2X7.Chapter 7 focused on the use of the anti-hP2X7 mAb in mass cytometry while also comparing the expression of P2X7 or CD39 on human blood leukocyte subsets in peripheral blood mononuclear cells (PBMCs) isolated by Ficoll-Paque and SepMate Tube density gradient centrifugation. The suitability of the anti-hP2X7 mAb for mass cytometry was validated by demonstrating P2X7 expression on blood leukocytes. Further, this chapter indicated there are minor but significant differences in P2X7 or CD39 expression between paired hPBMC samples isolated by either Ficoll-Paque or SepMate tube density gradient centrifugation, with the most notable difference with CD39 on hTregs.In summary, this thesis has identified possible anti-P2X7 biologics to reduce GVHD. Moreover, this thesis further characterised an anti-hP2X7 mAb (clone L4). Collectively, this thesis continues to support evidence that P2X7 blockade is a potential therapeutic for GVHD also providing new biologics that could potentially be used in clinical trials in the future.</p
Use of non-admitted geriatric and allied health services by people living with dementia in community and residential aged care
No full textIntroduction
Post-diagnostic care guidelines for people with dementia recommend supports such as physiotherapy, occupational therapy, speech therapy, psychology and memory clinics. There is evidence that healthcare pathways differ between people living in the community and aged care.
Methods
Retrospective matched cohort study was carried out using linked mortality, admitted and non-admitted data. Study participants were residents living in a regional area, aged 65 or older with a first inpatient diagnosis of dementia. Transition from community to aged care (where applicable) was estimated using mode of separation, transfers to/from facility IDs, source of referral and type of usual accommodation. Time in study was censored for deaths and hospital admissions. A propensity matched cohort (admission date, socio-demographics, admission characteristics and comorbidities but without history of dementia) was used to compare rates of service use by setting.
Results
The study cohort included 4,786 people with a total of 4,937 person-years observed in the community and 3,734 in aged care. Non-admitted geriatric services 0.91 per year in the community compared to 0.35 in aged care. Non-admitted services involving an occupational therapist 0.61 per year in the community in contrast to 0.13 in aged care, involving a physiotherapist 0.84 per year in the community in contrast to 0.14 in aged care.
The matched cohort included 4,909 people with a total of 7,205 person-years observed in the community and 3,251 in aged care. Non-admitted geriatric services 0.16 per year in the community compared to 0.12 in aged care. Non-admitted services involving an occupational therapist 0.51 per year in the community in contrast to 0.26 in aged care, involving a physiotherapist 0.88 per year in the community in contrast to 0.41 in aged care.
Implications
Despite having a similar demographic and clinical profile, people living with dementia in aged care received less support occupational therapy and physiotherapy than people without dementia.</p
Moral Motivation in Early Childhood: Measurement, Relations to Social Conduct, and the Role of Socialisation
No full textMoral motivation is a key component of young children’s moral development that provides crucial insights into their propensity to engage in positive (and negative) social behaviours. This thesis explores the measurement of moral motivation in children between 4 and 8 years of age, examines its relations to their social conduct, investigates its developmental trajectory, and explores how it can be nurtured by parental socialisation.Study 1 compared two measures of moral motivation, the Moral Emotion Attribution (MEA) task (Nunner-Winkler & Sodian, 1988) and the Moral Self-Concept (MSC) task (Kochanska et al., 1997), in a sample of 59 elementary school children aged 6-8 years. Findings revealed an agentive identification effect for the MEA task such that children provided more mature moral emotion responses when they were asked to imagine how they themselves would feel in a given moral situation (MEA-self), rather than how a story protagonist would feel (MEA-other). Additionally, the MEA-self and MSC tasks demonstrated a significant association, particularly with morally-themed stories, which remained significant when children’s verbal abilities and theory of mind (ToM) were controlled for. Further analyses showed that, in comparison to the MEA-self tasks, the MSC task more consistently predicted children’s social behaviour in ways that were independent of the influence of ToM on children’s social behaviour. The MEA-self task did not significantly predict social behaviour after controlling for the simpler MSC task, and ToM. This finding highlights the robustness of the MSC task in measuring children’s moral motivation and predicting their social conduct.Study 2 focused on 67 preschool children aged 4-6 years to investigate whether the relations observed in Study 1 extended to younger children during a period of rapid development in social cognition (i.e., ToM). Like Study 1, Study 2 compared the MEA and MSC tasks, and explored relations with ToM. Unlike the older children in Study 1, preschool children did not exhibit a significant difference in moral emotion attributions when asked to consider how they themselves (MEA-self) would feel versus how a story protagonist (MEA-other) would feel, although a non-significant trend emerged. This suggests that children become better at self-other emotion differentiation as they get older. A hierarchical regression analysis was used to test whether children’s performance on the MSC task and their ToM was related to their performance on the MEA task. Results broadly supported Study 1, showing that there was a robust but modest association between MSC and MEA task performance, independent of children’s verbal abilities, ToM, and effortful control. Furthermore, as in Study 1, ToM was not independently related to children’s performance on the MEA (or the MSC) task.Together, the findings of Studies 1 and 2 suggested that both the MSC and MEA tasks tap into similar aspects of children’s moral motivation despite the stark methodological difference between them; specifically, children’s self-referential emotions and the process of moral self-identification. When compared directly, however, the MEA task did not provide any additional information about children’s moral motivation in relation to their social behaviour over and above the MSC task. Contrary to many interpretations of the MEA literature, this finding suggests that, in so far as the MEA task provides a window on young children’s moral motivation, it is likely to do so in the same way as the simpler MSC task.In Study 3, therefore, a longitudinal design was employed with 106 children between 6. and 7. years of age, focusing on the developmental trajectory of their moral self (as measured on the MSC task), and its relationship with their social behaviour and ToM. Results revealed longitudinal stability of MSC, but with an asymmetrical and counter-intuitive influence: past social behaviour predicted future MSC, while past MSC did not predict future social behaviours. This asymmetry suggests that the MSC task is sensitive to children’s behavioural track record, which shapes the development of a child’s moral self in this age-window. This direction of influence aligns with theories of moral socialisation (Blasi, 1999; Grusec, 2006) and suggests that, even at an age when children can reliably pass the MEA task, their moral self is best conceived in terms of their consistent experience of themselves as a social actor rather than in terms of their attempts to achieve moral consistency in their activity or their sense of self. Study 3 also underscored the distinctive developmental trajectories of children’s moral self and their ToM.Study 4 explored the role of socialisation through a systematic review of parenting practices on children’s moral emotions (guilt, sympathy, and empathy) from birth to 7 years. The review highlighted the significant influence of parenting, particularly the quality of the parent-child relationship, responsive parenting, secure attachment, and moral discourse, in nurturing children’s moral emotions. However, methodological variations in the measurement of parenting practices and moral emotions, along with the small number of studies addressing guilt and sympathy specifically, posed challenges to synthesising the findings. These inconsistencies suggest the need for more precise methodologies to capture the nuanced effects of parenting on moral emotion development.Collectively, the studies presented in this thesis advance our understanding of children's moral motivation, particularly in its measurement, relationship to social behaviour, and the influence of parenting practices. The findings speak to the reliability and validity of the MSC task as a measure of young children’s moral self, and highlight the developmental complexity of the MEA task. The thesis also contributes to the broader literature on moral self-concept, emphasising the pivotal role of past behaviour in shaping children’s moral self. Future research should continue to refine methodological approaches in measuring moral motivation. Additionally, these insights can guide parents and educators in better supporting children’s moral development.</p
Spatio-temporal Trends, Multilevel Correlates and Impacts of Public Policy and other factors on Trajectories and Inequalities in Road Traffic Mortality in China
No full textRoad traffic injury is one of the leading causes of death in China, according to the results from Global Disease of Burden 2017. The Chinese Government has taken steps to reduce the incidence of road traffic mortality (RTM), including punitive measures (e.g. increasing the severity of punishments for speeding and drinking while under the influence of alcohol) and strategies to limit the number of cars on the road (e.g. number plate lotteries). The implementation of these policies constitutes ‘natural experiments’ that may influence trajectories of, and inequalities in, RTM across mainland China. However, RTM in China has so far only been analyzed in descriptive terms, without any substantial evaluation of these natural experiments using suitably advanced and robust statistical methodologies (e.g. multilevel modelling). The overall aim of my PhD research is to address this gap in knowledge. This research will explore trends in RTM across different areas of China and over time using the best data available, before and after the policy changes, to understand their potential impacts on RTM trajectories and inequalities.Through multilevel modeling, we analyze the spatio-temporal variation trends of road traffic injury deaths at the county level, while exploring influencing factors at the regional level. Using cohort data, we establish a multilevel model at the individual level to analyze the impact of personal behavior on traffic accident mortality. Finally, we analyze the impact of regional road traffic policies(car plate lottery policy) and national road traffic regulations(criminalizing drunk driving) on road traffic injury deaths and evaluate policy effectiveness.This study outlines the temporal and spatial variation of road traffic mortality in China. The mortality rate decreased during 2006-2015, with males consistently having a higher rate than females. Northwest China had the highest rates compared to other regions, even after adjusting for demographic factors. Improvements in socioeconomic status and urbanization may help reduce road traffic mortality.All four behaviors (not using seat belts, driving under the influence of alcohol, fatigue driving, and driving without a license) increased the risk of death from traffic injuries to varying degrees, with drunk driving significantly increasing the risk (RR=3.22). Lower education levels were linked to vulnerable road user roles, such as pedestrians, bicyclists, and motorcyclists, which increased their risk of road traffic injuries. Our findings provide evidence that risky driving behavior, particularly drunk driving, is a major factor in traffic injury deaths.We used interrupted time-series models to assess the car plate lottery policy in Beijing, implemented in 2011, in reducing road traffic mortality. Since the policy's implementation, the growth rate of motor vehicle data volume and the traffic injury death rate in Beijing have significantly decreased. However, the traffic injury death rate in the control group also started declining in 2011, suggesting that the lottery policy may not be the sole reason for the decrease in Beijing's death rate.This research also evaluated the effectiveness of three traffic policy revisions in improving road safety from 2007 to 2015. These revisions included criminalization of drunk driving and increased penalties for license suspension and fines in 2011, as well as revisions to the driving points penalty system in 2010 and 2013. The implementation of the drunk driving law in May 2011 led to a significant reduction in daily and monthly road traffic mortality rates. However, the increase in driving points penalty did not contribute to reducing mortality. This research found an annual decrease of 28.46% in the road traffic mortality rate after the implementation of stricter punishments for drunk driving. It is estimated that before the policy, over 300,000 people died annually from road traffic incidents in China, and this policy would save 88,000 lives every year.In conclusion, this PhD thesis employed a multi-level temporal-spatial model and an interrupted time series model to analyze nationally representative data. The findings reveal a gradual decline in road traffic injury mortality in China. However, this decline varies across different regions of the country. Additionally, the research highlights the significant role of risky driving behaviors as risk factors for traffic injury mortality. It suggests that individuals who engage in dangerous driving practices are more susceptible to fatal road accidents. Moreover, the study emphasizes that the implementation of stricter national penalties for drunk driving has proven to be highly effective in reducing traffic injury deaths in China. It is imperative for policymakers to continue prioritizing and reinforcing such measures, given the evidence of their significant success.</p
Artificial Muscles as Cardiac Assist Devices
No full textMuscle-like actuators can function in various medical applications, such as heart failure, where the gold standard of treatment is currently heart transplantation with further research. With limited donors and strict criteria for suitable donors, the emergence of superior or similar-effect cardiac support devices is a welcome development, as currently available devices are large and cause undesired effects like thrombosis. Direct mechanical cardiac compression eases such burdens using miniature materials, such as coiled muscle-like actuators, which are noiseless and provide good actuation, similar to natural heart muscles.Twisted and coiled artificial muscles have twenty times the power-to-weight ratio of skeletal muscles and are made from everyday materials, making them quite affordable. However, a major limitation to their exploration is the low output to input power ratio which is lower than the ratio for human muscles and implies that they operate at higher than desired temperatures. In a bid to improve the output, this research work focuses firstly on the exploration of and the effect of coil geometry on their actuation properties. Secondly, to find ways to make them operate at lower temperatures by incorporating thermosensitive gels into the yarns to induce volume change actuation.Initially, twisted, and coiled polymer samples of varying indices were made using the mandrel wrapping technique. The tensile actuation parameters were obtained by stretching the samples at a certain preload force in the actuated (80oC) and unactuated state (30oC) to generate their load-unload force-extension curves in both states. Torsional actuation was evaluated by tethering a twisted but not coiled sample to a torsional sensor and inserting manual turns. Like linear actuation, twist-untwist curves of torque versus twist were obtained in both actuated and unactuated states.Samples were analysed for their tensile and torsional properties for samples prepared with coil indices from 1.8 to 2.9 and produced measured tensile strains from 15% to 85%. The tensile strains were reliably predicted as 20% to 96% using spring mechanics calculations. Stiffnesses of 0.04 N/mm to 0.22 N/mm was also measured in the samples with spring mechanics prediction of 0.03 N/mm to 0.20 N/mm.Next, yarn gel composites of thermosensitive poly (MAA-coOEGMA), iron chloride gel and polyester yarn were successfully developed. The gel and polyester yarn composites produced reversible and repeatable volume changes in the form of swelling and deswelling with small temperature changes, first as a gel and when incorporated into yarns to form a composite. The yarn composites were subjected to a 7.5% stretch at 50oC (unactuated) and 27oC (actuated) to obtain tensile actuation data from samples made using various quantities of the crosslinker- iron chloride (0-2 M). Isotonic strains up to 39% were measured in the gel-yarn composites with the 1 M iron chloride concentration selected as the optimum crosslinking concentration. The maximum operation temperature of gel-yarn twisted, and coiled composites was 50oC which is lower than the 80oC operating temperature for actuators made from twisted and coiled nylon 6 fibres.Lastly, an attempt was made to assess whether the low temperature activated actuators of yarn and gel could be successfully developed and applied to a prototype cardiac assist device. A simple model of a water-filled balloon with actuators wrapped around it and a transparent tube fixed to the balloon top to read the difference in water levels was used. The model did not show discernible differences in the water level when the actuators were stimulate. Another model using a pair of silicone tongs with actuators fixed to the handle and the balloon supported by the grips of the tong demonstrated pumping action when twisted and coiled nylon-6 fibres were used as the actuator. There was no discernible effect when the low-temperature composite yarn and poly (MAA-coOEGMA) gel actuators were used. In order to explain the lack of pumping in the tongs experimental prototype, the force generated by each set of actuators was calculated, and the lack of visible pumping action by the low-temperature composite actuators was attributed to the low force generation during the heating and cooling of the gel composite samples.Overall, this thesis has contributed to the understanding of how coil geometry influences the actuation of twisted and coiled polymer fibres and how to a reasonable extent, spring mechanics can be used to predict actuation properties. A low temperature activated actuator was also developed from poly (MAA-coOEGMA) iron chloride gel and yarn to produce low temperature actuation at 50oC.</p
The multi-semiotic expression of emotion in storytelling performances of Cinderella: A focus on verbal, vocal and facial resources
No full textIt is widely recognised that emotion in spoken communication is conveyed multimodally; not only through wordings but also through a diverse range of other communicative resources such as vocal features, gesture, facial expression and posture (Abercrombie, 1968; Burns & Beier, 1973; Mehrabian, 1972; Ngo et al., 2022; Scherer & Ellgring, 2007; Scherer et al., 1984; Wallbott, 1998). Effective multimodal expression and interpretation of emotion in spoken English can be a challenge, especially when speakers of English as an additional language (EAL) are involved (Brown, 1977/1990; Dewaele & Moxsom-Turnbull, 2019; Lorette & Dewaele, 2019; Rintell, 1984; Roach, 2009; Unsworth & Mills, 2020). This study thus aims to explore the division of labour and interplay of multi-stratal and multi-semiotic meaning across verbal, vocal and facial resources in the expression of emotion in spoken English.The study deploys a Systemic Functional Semiotic (SFS) perspective (e.g., Halliday, 1978; Halliday & Matthiessen, 2014; Jewitt et al., 2016; Kress, 2010; Matthiessen, 2007, 2009; Ngo et al., 2022; van Leeuwen, 1999) to explore and establish how wordings, vocalisations and facial expressions construe emotion, both separately and synergistically, in eight storytelling performances of Cinderella. While emphasis is placed on the definition, analysis and description of the vocal qualities deployed to express emotion and in developing a clear framework and consequent analytical approach, the study also focuses on how verbal, vocal and facial semiotic resources combine to create multi-semiotic messages that affectively colour the phases and stages of the storytelling performances. The results of this exploration are consolidated in an exploratory system network of SEMOGENIC VOCAL QUALITIES which bundle together to realise affectual meanings in spoken English. A key argument in this thesis is that affectual vocalisation interacts with verbiage and facial expression as an ensemble of resources that integrate in the discourse semantic system of AFFECT.The significance of this study is both theoretical and practical. Theoretically, it constitutes a potential contribution to the development of a systemic functional multi-stratal and multi-semiotic account of the phonological resources that inscribe affectual meaning in spoken language. Practically, it offers a foundation for developing an EAL multi-semiotic literacy toolkit to explore and describe the grammar of emotion in the context of storytelling performances. Such a recontextualisation of the multi-stratal and multi-semiotic frame proposed in this thesis could hold great value for second language teaching contexts. The results of this project could inform the practices of EAL teacher training courses, offering well-founded principles to support students’ interpretation and use of the multi-semiotic expression of emotions. In addition, a SFS analytical toolkit of this kind could advance work in and beyond the EAL pedagogical context of this study, such as in higher education interaction more generally (e.g., Hood, 2010, 2011; Hood & Hao, 2021; Macnaught, 2018; Martin & Dreyfus, 2015), in clinical interaction in healthcare (Butt et al., 2012; Henderson-Brooks, 2006; Moore et al., 2010) and in automated emotion detection as a tool for reception studies of multimodal ensembles in literary text reading (e.g., Montaña & Alías, 2016; Wegener et al., 2017), among others.</p
An on-site calibration system for high frequency harmonic voltage measurements in high voltage power systems
No full textThe power system landscape is undergoing a transformative shift due to the penetration of renewable resources, advancements in transmission and distribution infrastructure, and the use of non-linear device based consumer appliances. As a result of these developments, a significant increase in the use of power electronic converters have been observed recently. Modern power electronics employ force commutated semiconductor devices switching at relatively high frequencies, contributing to an increase in harmonic emissions beyond 2 kHz. The measurement and assessment of high-frequency harmonics ranging from 2 kHz to 150 kHz have been overlooked due to their negligible magnitudes and perceived minimal impact. However, anticipating a future growth in emissions, technical bodies are working to regulate harmonic emissions and to develop measurement techniques covering this range.Associated with the above, there is a growing interest in the accurate measurement of high frequency harmonics. State-of-the-art power quality analysers provide accurate measurements at low voltage (LV) levels. For medium voltage (MV) and high voltage (HV) levels, an instrument transducer (IT) is required to reduce the primary voltages into measurable quantities. The majority of ITs are inductive and capacitive voltage transformers, designed for the accurate voltage transformation at rated frequency. These transformers have non-linearities at higher frequencies, affecting their frequency response. Hence, an accurate calibration is required for the correction of measurement errors. Conventionally, the IT calibration is performed using an LV sinusoidal frequency sweep. However, recent work shows that ITs could demonstrate comparatively different voltage ratio and phase displacement errors when determined under distorted high voltage waveforms. However, implementation of such calibration systems for frequencies above 2 kHz has been challenging. The underlying reasons being the lack of voltage sources that can generate distorted HV waveforms with superimposed high frequency harmonics, and also the lack of reference transducers of which the frequency response have been experimentally proven not to be affected by the distorted HV waveforms. Hence, there exists a need to develop such HV sources and reference transducers along with acceptable experimental test procedures to prove their performance. Research work and outcomes presented in this thesis addresses these requirements.This thesis presents a novel IT calibration system consisting of a composite voltage source to generate HV distorted waveforms comprising of a fundamental component up to 132/√3 kV, with superimposed spectrum of harmonics up to 10 kHz. A salient feature of the developed source is its capability to superimpose multiple high frequency harmonics with sufficient amplitudes that are essential for the accurate calibration of ITs with large voltage transformation ratios. Compared to existing HV sources, whose harmonic generation capability diminishes with increasing frequencies, the developed source can generate sufficient harmonic voltage magnitudes up to 10 kHz. This enables the investigation of IT accuracy at high frequencies under different conditions and would contribute to the expansion of knowledge on both conventional and novel instrument transducer technologies.This research also addresses the limitations of reference transducers by developing a precision capacitive voltage divider of which the performance in terms of its voltage ratio and phase error was demonstrated to have a negligible impact due to distorted high voltage waveforms. Rigorous experimental procedures have been developed, which are expected to have a profound impact on the ongoing work by the various technical bodies with regard to harmonic measurement in high voltage networks, where there are existing deficiencies in transducer calibration.Employing the above calibration system and based on the case study results obtained through characterization of two inductive voltage transformers under high voltage distorted conditions, it was identified that the transformer response around resonance frequencies can exhibit significant differences in voltage ratio and phase displacement errors under high voltage distorted waveforms compared to frequency response results obtained with low voltage frequency sweep. Results also illustrate that, with lower order harmonic frequencies below 2 kHz, the transformer responses do not show a significant difference in their accuracy when subjected to distorted high voltage waveforms in comparison to those obtained using frequency sweep. This could be attributed to the fact that the tested transformers do not show resonance effects at frequencies below 2 kHz. However, the results support the fact that high frequency characterization of inductive transformer should be undertaken with distorted waveforms in place of frequency sweep.The work presented in this thesis contributes towards the linear and non-linear modelling of inductive transformers under LV sinusoidal and HV distorted waveforms. The frequency response of the investigated transformer under LV sinusoidal conditions can be successfully represented by higher order transfer functions. However, linear models fail to represent the high frequency behaviour of inductive transformers where resonance effects are observed. In contrast, the non-linear models, which have been previously used to model non-linearities of instrument transformers for harmonics below 25th order, can be successfully employed to represent the behaviour transformers at high frequencies. The development of such measurement based non-linear models at high frequencies has not been previously possible due to the limitations in the voltage sources required to generate distorted high voltage waveforms consisting of high frequency harmonics. Hence, the contributions made in this thesis are novel and significant not only in terms of investigating the accuracy performance of high frequency harmonic measurements in HV networks, but also in the expansion of knowledge with respect to high frequency harmonic measurement.</p
Characterisation of supraharmonic emissions based on phase angle representation methods
No full textPower electronic interfaces in solar PV inverters generate high-frequency harmonic emissions, also referred as ’supraharmonic’ emissions, due to the fast switching (above 2 kHz) required to create low distortion output waveforms. Measuring and evaluating these emissions is a new challenge for power quality experts, as present standards (IEC, CISPR) do not include prescriptive measurement and analysis techniques for the entirety of this range (2–150 kHz). This paper investigates supraharmonic emissions from identical solar PV inverter systems highlighting distinct frequency zones to distinguish phenomenon types. The existing high-frequency harmonic measurement method given in IEC 61000-3-6 with some enhancements has been used to characterise supraharmonic emissions. This paper proposes three methods to represent the phase angle for grouped supraharmonic emissions that assist in understanding their diversity. In terms of aggregation of emissions, field measurements indicate that a summation exponent (α) equal to 1 should be applied for resonant emissions, while for switching frequency emissions, circulation between sources leads to harmonic cancellation.</p