436 research outputs found
Naidoo et al. Nature Ecology & Evolution (2021)
No full textData used in Naidoo et al. Nature Ecology & Evolution (2021)
Naidoo et al. Nature Ecology & Evolution (2021)
No full textData used in Naidoo et al. Nature Ecology & Evolution (2021)
Writing women in solitary: shifting narratives to make research count by Shanthini Naidoo
No full textAuthor Shanthini Naidoo reflects on her decision to change the focus of her Master’s dissertation in order to uncover the narratives of anti-apartheid women activists in South Africa. This research formed the basis of her recently published book Women in Solitary: Inside the Female Resistance to Apartheid, which focuses particularly on four women: Joyce Sikhakhane-Rankin, Shanthie Naidoo, Nondwe Mankahla and Rita Ndzanga. As the UK celebrates Black History Month in October, Naidoo reflects on the importance of uncovering stories that not only evidence bravery and courage, but also the power of love and friendship in daily life
Book review: Women in solitary: inside the female resistance to apartheid by Shanthini Naidoo
No full textIn Women in Solitary: Inside the Female Resistance to Apartheid, Shanthini Naidoo offers a new account based around the narratives of four women – Joyce Sikhakhane-Rankin, Shanthie Naidoo, Rita Ndzanga and Nondwe Mankahla – who experienced detention and torture in South Africa in the late 1960s when the regime tried to stage a trial to convict leading anti-apartheid activists. This timely book not only accords the four women and others their place in the history of the struggle for freedom in South Africa, but also weaves their experiences into the historical development of the anti-apartheid movement, writes Tony Trew. If you are interested in this book review, you may also like to read an LSE RB essay by author Shanthini Naidoo on her decision to change the focus of her Master’s dissertation to uncover the narratives of anti-apartheid women activists in South Africa
In Conversation with Beverley Naidoo: On Crossing Boundaries through Reading and Writing
No full textBorn into a white, middle-class family in Johannesburg, South Africa, children's author Beverley Naidoo grew up under the oppressive apartheid regime until the age of twenty-one. She has written a variety of children’s and young adult novels, picturebooks, collections of short stories, plays, and adult nonfiction. Her books have won many awards, including the Carnegie Medal for The Other Side of Truth, and she also published her PhD, called Through Whose Eyes? Exploring Racism, Reader Text and Context, which investigated the possibilities of challenging racism through reading in a school context. In this article Julia Hope, Head of the MA Children's Literature at Goldsmiths College, asks Beverley to talk about her own education, school themes that arise in her writing, her PhD, and wider perceptions of the educative power of literature
Determining transmission line parameters from time-stamped data
No full textDissertation (MEng (Electrical))--University of Pretoria, 2008.The main aim of this project was to find a practical and accurate method to determine the parameters of a transmission line by using current and voltage measurements. The term line parameters refer to the inherent series resistance and inductance that is found on transmission lines. The line parameters were determined by using the voltage and current measurements from either side of the transmission line. An accurate reference signal is needed to precisely compare the measured signals. The timing signals from GPS units were used to reference the measurements. In a field implementation data transfer of the measured signals would be a necessity which can be accomplished by GPRS modems. Three methods are proposed for determining line parameters. These methods were thoroughly tested in the following ways: 1. A model was built in SIMULINK with known elements and values. The three methods were then applied to the model and simulations were run. The results from the simulations are compared to the known values. 2. A system was built in the laboratory with known parameters. The results gathered from testing the system on all three methods are compared to known values. 3. Finally, the methods were applied to field data from recorders of a utility. This was done to see how well the methods would perform on a real system. Accuracy was determined from what the utility accepts as the correct values. Another focus of the project was to determine the surge impedance loading (SIL) curve from measured data. This curve can be used to determine the loadability limit of the transmission line as well as to visually show at what point the line is operating at any given time. The curve is also useful as it provides insight into the additional reactive power needed for a certain active power transfer. The concept of drawing a SIL curve from actual measurements was first tested by means of simulation. The drawing of the proposed curve is also tested on actual measurements from a transmission line. This investigation posed many challenges. These challenges are discussed in detail in the dissertation. Some of these challenges have easily implementable solutions while others still leave room for further research. The results and findings are published in this document.Electrical, Electronic and Computer EngineeringMEngunrestricte
A method of voltage tracking for power system applications
No full textDissertation (MSc)--University of Pretoria, 2010.An algorithm that is capable of estimating the parameters of non-stationary sinusoids in real-time lends application to various branches of engineering. Non-stationary sinusoids are sinusoidal signals with time-varying parameters. In this dissertation, a nonlinear filter is applied to power system applications to test its performance. The filter has a structure which renders it fully adaptive to tracking time variations in the parameters of the targeted sinusoid, including its phase and frequency. Mathematical properties of the differential equations which govern the proposed filter are presented. The performance of the proposed filter in the field of power systems is demonstrated with the aid of computer simulations and practical experimentations. The filter is applied to synchronous generator excitation control, voltage dip mitigation as well as the real-time estimation of symmetrical components. The parameter settings of the filter are tested and optimized for each of the applications. This dissertation demonstrates the simulation and experimental results of the filter when applied to the various power system applications. AFRIKAANS : 'n Filter wat bevoeglik is met die beraming van die parameters van beweeglike sinusoïdale in ware-tyd, kan bruikbaar aangewend word in verskeie takke van ingenieurswese. Beweeglike sinuskrommes is sinusoïdale seine met tyd-wisselende parameters. In hierdie verhandeling word `n nie-liniêre filter aangewend in verskeie kragstelseltoepassings om die werksverrigting van die filter te toets. Die filter het 'n struktuur wat dit toelaat om wisselende tydvariasies in die parameters van die teikensinusoïdaal op te spoor, insluitende die fase en frekwensie. Wiskundige eienskappe van die differensiaalvergelykings wat die voorgestelde filter beheer is ondersoek. Die werksverrigting van die voorgestelde filter in die veld van kragstelsels is gedemonstreer met die hulp van rekenaarsimulasies asook praktiese eksperimente. Die filter is toegepas tot opgewekte, sinkrone eksitasie-beheer, spanningsverlaging versagting, asook die ware tyd estimasie van simmetriese komponente. Die parameter verstellings van die filter is getoets en geoptimeer vir elk van die toepassings. Hierdie verhandeling demonstreer die simulering en eksperimentele resultate van die filter wat aangewend is vir verskeie kragstelseltoepassings. CopyrightElectrical, Electronic and Computer Engineeringunrestricte
Adaptive protection for renewable-based ac microgrids in low-voltage radial networks
No full textDissertation (MEng (Electrical Engineering))--University of Pretoria, 2020.By placing clusters of renewable-based AC microgrids in low-voltage radial distribution networks,
emergent energy demands can be met. However, this leads to fundamental changes and challenges in
the topology and protection coordination performance. Protection challenges such as bi-directional
current flow, sympathetic tripping, protection blinding, unwanted islanding, system stability, nuisance
tripping and prohibition of unsynchronised reclosing may occur. This is due to the complex operation
and control of the embedded renewable-based microgrid, causing increased penetration of dynamic
fault currents in the radial distribution network. The aforementioned protection challenges prove that
existing South African low-voltage protection philosophy standards are unreliable and need to be
re-evaluated. It is expected that by optimally sizing and selecting renewable distributed generators,
alongside using communication-based intelligent electronic devices and adaptive protection strategies,
a hybrid adaptive protection scheme can be outlined and developed for embedded renewable-based AC
microgrids in South African low-voltage radial distribution networks.
The developed adaptive hybrid protection philosophy should be able to successfully clear high- and
low-impedance faults in a selective, sensitive, speedy and reliable manner. This investigation looks into
the various short-circuit fault current levels experienced in a low-voltage radial distribution network,
(namely three-phase, phase-phase, phase-to-ground, and phase-phase-to-ground) when embedded
renewable-based AC microgrids are integrated. Three various types of renewable energy sources
(namely solar photovoltaic, wind generation and energy storage systems) are modelled and designed
to in accordance with the South African grid code requirements for renewable power plants and
SANS 10142-1: Wiring of premises standards, and NRS 097-2-1: Grid interconnection of embedded
generation. The renewable energy sources and proposed adaptive protection schemes are simulated and
validated in a low-voltage radial distribution network with the use of DIgSILENT PowerFactory 2017.
The results obtained are used to outline and develop an adaptive hybrid philosophy standard to assist in
maintaining the protection coordination between the embedded renewable-based AC microgrid and inline
protection intelligent electronic devices. Additionally, an optimisation function is used to optimise
the renewable-based AC microgrid’s capacity and power flow, in-turn reducing losses, fault limits,
bi-directional power flow, initial cost investments and increasing the voltage profile of the low-voltage
radial distribution system. Through this implementation and investigation network efficiency and
protection selectivity, sensitivity, stability and reliability of the existing radial low-voltage distribution
network, will improve when renewable-based AC microgrids are integrated. This will correct major
limitations in the South African low-voltage protection philosophy standards for the development
and future introduction of independent power producers in low-voltage radial networks in the utility
grid.Electrical, Electronic and Computer EngineeringMEng (Electrical Engineering)Unrestricte
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