List of Titles

Quick View

Strategy for power quality improvement and maximum demand smoothing

- Siti, Willy M., Jimoh, Adisa A., Nicolae, Dan-Valentin

Authors: Siti, Willy M. , Jimoh, Adisa A. , Nicolae, Dan-Valentin
Date: 2005
Subjects: Electric power transmission , Data transmission modes , data switching methods
Language: English
Type: Conference proceedings
Identifier: http://hdl.handle.net/10210/21725 , uj:16154 , ISBN;0780392531 , Citation: Siti,W.M., Jimoh, A.A. & Nicolae, D.V. 2005. Strategy for power quality improvement and maximum demand smoothing,“IECON’05 Conference”, Raleigh, USA, November 2005. 31st Annual conference of IEEE. pp6. DOI:10.1109/IECON.2005.1568907
Description: Abstract: In this paper, a distributed strategy for improving the power quality and maximum demand smoothing is presented. Many authors have presented the power quality improvement as a centralized issue, which implies high power capability of compensators. Based on multi-functionality of specific switching-mode converters, a decentralised model is presented. A discussion of simultaneity of different functions is presented in details. The results of this paper are intended to be a guideline for application designers
Full Text:

Quick View

Optimization of resources for H.323 endpoints and terminals over VoIP networks

- Nlend, Samuel, Swart, Theo G., Clarke, Willem A.

Authors: Nlend, Samuel , Swart, Theo G. , Clarke, Willem A.
Date: 2011
Subjects: VoIP Networks , Statistical multiplexing , Telecommunications
Language: English
Type: Conference paper
Identifier: http://hdl.handle.net/10210/139763 , uj:15455 , S. Nlend, T. G. Swart and W. A. Clarke, "Optimization of resources for H.323 endpoints and terminals over VoIP networks," in Proceedings IEEE Africon, Livingstone, Zambia, September 13-15, 2011, published on CD (5 pages)
Description: We suggest a method of optimizing resource allocation for real time protocol traffic in general, and VoIP in particular, within an H.323 environment. There are two options in the packet network to allocate resources: aggregate peak demand and statistical multiplexing. Statistical multiplexing, our choice for this case, allows the efficient use of the network resources but however exhibits greater packet delay variation and packet transfer delay. These delays are often the result of correlations or time dependency experienced by the system’s queue due to the variations observed in different point processes that occur at a point of time. To address these issues, we suggest a queuing method based on the diffusion process approximated by Orstein-Ulenbeck and the non-validated results of Ren and Kobayashi.
Full Text:

Quick View

Control algorithm of a smart grid device for optimal radial feeder load reconfiguration

- Nicolae, Dan-Valentin, Jordaan, J. A.

Authors: Nicolae, Dan-Valentin , Jordaan, J. A.
Date: 2013
Subjects: Voltage stabilizers , Electronic power system stability , Voltage regulators
Language: English
Type: Conference proceedings
Identifier: http://ujcontent.uj.ac.za8080/10210/376485 , http://hdl.handle.net/10210/18155 , uj:15966 , ISBN: 978-1-4673-5769-2 , Citation: Nicolae, D.V. & Jordaan, J.A. 2013. Control algorithm of a smart grid device for optimal radial feeder load reconfiguration. Proceedings of the 9th Asian Control Conference, 23-26 June, 2013, Istanbul, Turkey. DOI: 10.1109/ASCC.2013.6606240
Description: Abstract: Secondary distribution network, generally speaking, performs as well as the performance of its LV feeders. The main problem a feeder is experiencing is the load unbalancing due to the stochastic nature of its individual single-phase loads: bigger losses in certain phase accompanied with bed voltage regulation and voltage unbalance. The aim of this paper is to address the issue of automatic balancing as progressing from the end of the feeder towards the front using smart device based on three-ways switch selector and artificial intelligence algorithm to minimize the neutral current.
Full Text:

Quick View

Multilevel high power converters for reversible power flow between utilities and power pool transmission corridor

- Nnachi, A. F., Jimoh, A. A., Nicolae, Dan-Valentin

Authors: Nnachi, A. F. , Jimoh, A. A. , Nicolae, Dan-Valentin
Date: 2007
Subjects: Circuit breakers , Wind-powered generation , Power transmission
Language: English
Type: Conference proceedings
Identifier: http://hdl.handle.net/10210/20003 , uj:16066 , ISBN 078038606x , Citation: Nnachi, A.F., Jimoh,A.A. & Nicolae, D.V. 2007. Multilevel high power converters for reversible power flow between utilities and power pool transmission corridor. IEEE AFRICON'07, Windhoek, Namibia, 26-28 September 2007:1-8. DOI:10.1109/AFRCON.2007.4401473
Description: Abstract: Multilevel converters have emerged as the state of the art high power conversion for applications in reversible power flow. Electric power could be tapped from or injected to the grid regardless of the discrepancies in voltage levels, frequency, phase number and different modes of operation of the grid and the system. This paper presents an overview of different topologies of multilevel converters and modulation strategies with a verification of back-to-back neutral point converter for bidirectional power flow application
Full Text:

Quick View

Low-complexity SOCPBFSK-OOK interface between PLC and VLC channels for low data rate transmission applications

- Ndjiongue, A. R., Ferreira, Hendrik C., Ouahada, K., Han Vinck, A. J.

Authors: Ndjiongue, A. R. , Ferreira, Hendrik C. , Ouahada, K. , Han Vinck, A. J.
Date: 2014
Subjects: Frequency shift keying , Power line communications , Visible light communications
Type: Book
Identifier: uj:4747 , http://hdl.handle.net/10210/11733
Description: This paper studies and proposes a low cost low complexity interface between power line communications (PLC) and visible light communications (VLC) for low data rate transmission applications. The discussion presents the performance of a spread orthogonal continuous phase binary frequency shift keying (SOCPBFSK) receiver combined with an on-off keying (OOK) modulator to relay low data transmission between PLC and VLC channels. The characteristics of the interface are presented. The results of an experimental test using the proposed interface over the European Committee for Electrotechnical Standardization (CENELEC) bands C and D are presented. The eye diagrams of the combined error are presented as well.
Full Text:

Quick View

A study of insulation failure in a high voltage current transformer

- Jimoh, A. A., Mahlasela, V. S., Nicolae, Dan-Valentin

Authors: Jimoh, A. A. , Mahlasela, V. S. , Nicolae, Dan-Valentin
Date: 2005
Subjects: Electric power transmission
Language: English
Type: Conference proceedings
Identifier: http://hdl.handle.net/10210/22348 , uj:16190 , ISBN: 9075815085 , Citation: Jimoh, A.A., Mahlasela, V.S. & Nicolae, D.V. 2005. A study of insulation failure in a high voltage current transformer. EPE 2005 Conference, Dresden, Germany, 11-14 September 2005. DOI:10.1109/EPE.2005.219752
Description: Abstract: The ageing and deterioration of insulation in high voltage (HV) plants have been a source of concerns to utilities. Breakdown of insulation leads to failures of HV equipment. The ageing and eventual failure of insulation in a high voltage curTent transformer (JHVCT) is the subject of investigation in this paper. A lumiiped parameter model ofHVCT is developed. This model is used to study the influlence of deteriorating and failed iinsulation on the state variables of the HVCT. Somie possible scenarios that could lead to a CT failure are investigated in this paper. For all the scelarios considered, steady alid transient equations relating the state variables of the mlodel have been developed and analyzed. The objectives of these analyses are to establish the behavioural claracteristics of the state variables, establish the interactions between these variables, and investigate the possible generations of harmonics under the various scenarios of deteriorating and outright failure of insulation in the CT. The paper concludes with a discussion of the results obtained
Full Text:

Quick View

ATE : anti-malware technique evaluator

- Corregedor, Manuel, Von Solms, Sebastiaan

Authors: Corregedor, Manuel , Von Solms, Sebastiaan
Date: 2012
Subjects: Anti-malware evaluation
Type: Article
Identifier: uj:6051 , ISBN 978-1-4673-2159-4 , http://hdl.handle.net/10210/10462
Description: Current commercial anti-malware products fail to guarantee a 100% detection and prevention of malware. This paper proposes an evaluation framework called ATE (Anti-malware Technique Evaluator) that can be used to evaluate commercial anti-malware products. ATE identifies the vulnerabilities in anti-malware products by providing a set of requirements that must be fulfilled by the anti-malware product being evaluated. The ATE requirements used for evaluating anti-malware products go beyond the usual false positives, false negative, performance etc requirements employed by current anti-malware product evaluations.
Full Text:

Quick View

Power supply from the high voltage transmission lines part 2 : tapping from HVDC lines, design and system interactions

- Nicolae, Dan-Valentin, Jimoh, Adisa A.

Authors: Nicolae, Dan-Valentin , Jimoh, Adisa A.
Date: 2007
Subjects: Transmitting electricity , Voltage-frequency converters
Language: English
Type: Conference proceedings
Identifier: http://hdl.handle.net/10210/21325 , uj:16140 , ISSN:1609-3224 , Citation: Jimoh, A.A. & Nicolae, D.V. 2007. power supply from the high voltage transmission lines part 2 : tapping from HVDC lines - design and system interactions. Quantum - The Journal for Professionals:5-9, December 2007.
Description: Tapping tools , Abstract: Electric power may be tapped straight from the high voltage transmission lines either for consumption to meet the needs of rural and remote areas, and telecommunication establishments located in remote sites; or as a scheme to enhance the capacity of another utility or grid along a trans-national or trans-continental transmission corridor. The importance and interests the technologies to accomplish this has generated necessitate the need for a review of the state of the art of this subject so as to delimit research actions and allow research interests to be appropriately promulgated. In the first part of this work the principle, conditions and methods for tapping from HVAC lines have been discussed. This paper completes the study by looking at tapping from the HVDC transmission systems. The principles on which tapping methods from HVDC system is based are presented; and various methods, existing and novel, for multiterminal operation or integrating small tapping into HVDC links are reviewed. The paper ends with a general discussion of tapping from HVDC, and concludes with a presentation of the future direction.
Full Text:

Quick View

Active power control for capacitive divider tapping method

- Nicolae, Dan-Valentin, Jimoh, Adisa A., Britten, Anton C.

Authors: Nicolae, Dan-Valentin , Jimoh, Adisa A. , Britten, Anton C.
Date: 2006
Subjects: Power systems , Captive divider systems , Tapping electric power
Language: English
Type: Conference proceedings
Identifier: http://hdl.handle.net/10210/22404 , uj:16197 , ISSN: 1-4244-0121-6 , Citation: Nicolae, D.V., Jimoh, A.A. & Britten, A.C. 2006. Active power control for capacitive divider tapping method. EPE-PEMC, 12th International Power Electronics and Motion Control, 30 August-1 September, 2006, Portorož, Slovenia.
Description: Abstract: Capacitive divider systems for tapping electric power from high voltage transmission lines are known to exhibit certain detrimental problems of stability, sub-resonance harmonic oscillations, and ferroresonance when coupled with non-linear loads. On the other hand, they can improve reactive power flow, power factor and contribute to improved harmonic filtration of the larger power system. This paper, therefore, proposes a controlled power flow conditioner as an essential integral component of a capacitive divider system to control power transfer between the high voltage transmission line, capacitive divider system, and the load. The ultimate objective of this conditioner is to mitigate or minimize the attendant problems associated with coupling the system to the load, and optimize the derivable benefits to the larger network.
Full Text:

Quick View

A statistical analysis of metal oxide varistor current under distorted supply voltage conditions

- Bokoro, Pitshou, Hove, Miidzo, Jandrell, Ian

Authors: Bokoro, Pitshou , Hove, Miidzo , Jandrell, Ian
Date: 2014
Subjects: Metal oxide varistor , Third harmonic current , Large-sample statistical test of hypothesis
Language: English
Type: Conference proceedings
Identifier: http://hdl.handle.net/10210/20201 , uj:16079 , Citation: Bokoro, P., Jandrell, I. & Hove, M. 2014. A statistical analysis of metal oxide varistor current under distorted supply voltage conditions. Proceedings of the 2014 IEEE Electrical Insulation Conference, Philadelphia, Pennsylvania, USA, 8 to 11 June 2014. p. 493-496. ISBN: 978-1-4799-2789-0
Description: Abstract: Leakage current monitoring is still relied upon when on-site condition assessment or stability analysis of metal oxide varistors is to be conducted. The non-availability of adequate testing equipment, capable of directly measuring resistive component of varistor current, has paved the way to indirect diagnostic techniques which makes use of third harmonic component of varistor-arrester leakage current. The major shortcoming related to this method consists of high probability of measurement errors and subsequent misinterpretation of actual condition of varistor units should third harmonic-frequencies not be compensated in the supply voltage, prior to measurement. In this study, 90 identical low voltage varistor samples acquired from three leading manufacturers are subjected to distorted and non-distorted ac supply voltage. The magnitude of third harmonic currents observed in both measurement conditions, is deduced from the decomposition of time-domain leakage current waveforms into the frequency-domain using the flattop window algorithm of the Fast Fourier Transform. The large-sample statistical test of Hypothesis methodology is invoked to analyse the difference between the mean third harmonic currents of the varistor samples before and after harmonic injection in the supply. The average percentage of third harmonic injected in the supply voltage is 5%. However, the results obtained suggest over 95 % confidence that the measurement deviation in the third harmonic current-based assessment of varistor-arresters upon 5% third harmonic distortion in the supply voltage lies between 32%and 67%.
Full Text:

Quick View

Torque ripple analysis of three-phase induction machines with non-uniform coil groups distribution

- Muteba, M., Jimoh, A. A., Nicolae, Dan-Valentin

Authors: Muteba, M. , Jimoh, A. A. , Nicolae, Dan-Valentin
Date: 2013
Subjects: Electronic motors , Electrostatic induction , Electric machinery induction
Language: English
Type: Conference proceedings
Identifier: http://hdl.handle.net/10210/18069 , uj:15956 , ISBN: 978-1-4673-4974-1 , Citation: Muteba, M., Jimoh, A.A., & Nicolae, D.V. 2013. Torque ripple of three-phase induction machines with non-uniform coil groups distribution. IEEE International Electric Machines and Drives Conference (IEMDC2013), 12-15 May 2013, Chicago, USA. DOI: 10.1109/IEMDC.2013.6556313
Description: Abstract Please refer to full text to view abstract
Full Text:

Quick View

On-line remote and automatic switching of consumers' connection for optimal performance of a distribution feeder

- Popoola, O., Jimoh, A. A., Nicolae, Dan-Valentin

Authors: Popoola, O. , Jimoh, A. A. , Nicolae, Dan-Valentin
Date: 2007
Subjects: Phase transformations , Voltage-frequency converters
Language: English
Identifier: http://hdl.handle.net/10210/20144 , uj:16073 , ISBN:078038606x , Citation: Popoola, O., Jimoh, A.A. & Nicolae, D. 2007. On-line remote and automatic switching of consumers' connection for optimal performance of a distribution feeder, IEEE AFRICON’07, Windhoek, Namibia, 26-28 September, 2007:1-6. DOI:10.1109/AFRCON.2007.4401536
Description: Abstract: Load balancing on phases is performed using a conventional trial and error approach. With this approach, service interruption is unavoidable; hence rearrangement of consumers load distribution points on phases cannot be performed frequently. Also phase voltage and current imbalances might improve using this approach but the change does last for too long. To get the secondary distribution to operate at its optimal performance, a technique in the form of remote and automated technology is needed. This paper contributes such a technology at the low voltage side of the distribution network. The proposed static transfer switching technology is based on the open-transition switch that enables transfer or arrangement of consumer loads in a three-phase system within milliseconds and supervisory control system for effective co-ordination, computational and control of other intelligent units
Full Text:

Quick View

Small world network based dynamic topology for particle swarm optimization

- Liu, Qingxue, Van Wyk, Barend Jacobus, Sun, Yanxia

Authors: Liu, Qingxue , Van Wyk, Barend Jacobus , Sun, Yanxia
Date: 2015
Subjects: Particle swarm , Small world network , Neighborhood topology , Global model , Local model
Language: English
Type: Conference proceedings
Identifier: http://hdl.handle.net/10210/22381 , uj:16196 , Citation: Liu, Q, Van Wyk, B.J. & Sun, Y. 2015. Small world network based dynamic topology for particle swarm optimization. 11th International Conference on Natural Computation (ICNC 2015). p. 289-294. ISBN: 978-1-4673-7678-5. DOI: 10.1109/ICNC.2015.7378005
Description: Abstract: A new particle optimization algorithm with dynamic topology is proposed based on ‘small world’ network. The technique imitates the dissemination of information in a ‘small world network’ by dynamically updating the neighborhood topology of particle swarm optimization. The proposed dynamic neighborhood strategy can effectively coordinate the exploration and exploitation ability of particle swarm optimization. Simulations demonstrated that convergence of the swarms is guaranteed. Experiments demonstrated that the proposed method maintained the population diversity and enhanced the global search ability.
Full Text:

Quick View

DC current source to voltage source CT-based converter

- Nicolae, Dan-Valentin, Jimoh, A. A., Van Rensburg, J. F. J.

Authors: Nicolae, Dan-Valentin , Jimoh, A. A. , Van Rensburg, J. F. J.
Date: 2007
Subjects: Energy storage , Transformer substations
Language: English
Type: Conference proceedings
Identifier: http://hdl.handle.net/10210/20504 , uj:16106 , Citation: Nicolae, D.V., Jimoh, A.A. & Van Rensburg, J.F.J. 2007. DC current source to voltage source CT-Based converter,International Aegean Conference on Electric Machines and Power Electronics & Electromotion Joint Conferences, Bodrum, Turkey, September 10-12, 2007:665-670. DOI10.1109/ACEMP.2007.4510587
Description: Abstract: As generally known there is no energy transfer between a dc current and a current transformer. After a brief overview of other methods for tapping energy from the high voltage direct current transmission line, this paper presents the concept of a new dc to ac current source converter utilizing a current transformer. The advantage of this converter is that it is connected in series to the dc line and that at any moment in time the current flow is kept continuous. This paper presents the concept of the converter and simulation results.
Full Text:

Quick View

Power supply from the high voltage transmission lines Part 1: conditions, principles and tapping from HVAC lines

- Jimoh, Adisa A., Nicolae, Dan-Valentin

Authors: Jimoh, Adisa A. , Nicolae, Dan-Valentin
Date: 2007
Subjects: Powerline ampacity , Voltage-frequency converters , Transmitting electricity
Language: English
Type: Conference proceedings
Identifier: http://hdl.handle.net/10210/21283 , uj:16134 , ISSN: 1609-3224 , Citation:Jimoh, A.A. & Nicolae, D.V.2007. Power supply from the high voltage transmission lines Part 1: Conditions, principles and tapping from HVAC lines. Quantum-The Journal for Professionals:23-27, September 2007.
Description: Abstract: Electric power may be tapped straight from the high voltage transmission lines either for consumption to meet the needs of rural and remote areas, and telecommunication establishments located in remote sites; or as a scheme to enhance the capacity of another utility or grid along a trans-national or trans-continental transmission corridor. The importance and interests the technologies to accomplish this has generated necessitate the need for a review of the state of the art of this subject so as to delimit research actions and allow research interests to be appropriately promulgated. This paper therefore reviews, in two parts, the state of the art of tapping electric power from HV and EHV ac and dc transmission lines. Part one focuses on the general conditions for tapping, presents the principles on which tapping methods are based, reviews methods for tapping from HVAC transmission systems, and concludes with a general discussion on tapping from HVAC. The companion paper completes the study, by presenting the part two of the work.
Full Text:

Quick View

Codes for correcting three or more adjacent deletions or insertions

- Cheng, Ling, Swart, Theo G., Ferreira, Hendrik C., Abdel-Ghaffar, Khaled A. S.

Authors: Cheng, Ling , Swart, Theo G. , Ferreira, Hendrik C. , Abdel-Ghaffar, Khaled A. S.
Date: 2014
Subjects: Correction codes
Type: Article
Identifier: uj:4750 , ISSN 978-1-4244-7891-0 , http://hdl.handle.net/10210/11736
Description: Codes are presented that can correct the deletion or the insertion of a predetermined number of adjacent bits greater than or equal to three. This extends the constructions of codes beyond those proposed by Levenshtein fifty years ago to correct one or two adjacent deletions or insertions.
Full Text:

Quick View

Narrowband PLC channel modeling using USRP and PSK modulations

- Familua, A. D., Ogunyanda, K., Swart, Theo G., Van Olst, Rex, Cheng, L.

Authors: Familua, A. D. , Ogunyanda, K. , Swart, Theo G. , Van Olst, Rex , Cheng, L.
Date: 2014
Subjects: Markov processes , Carrier transmission on power lines , Forward error correction , Quadrature phase shift keying , Software radio , Narrowband power line communications , Power line communications
Type: Article
Identifier: uj:4804 , http://hdl.handle.net/10210/12061
Description: The indoor narrowband power line communication (NB-PLC) suffers from noise impairments, which emanate from several end-user electrical devices connected across the PLC channel. These noise impairments result into burst errors, which consequently lead to data corruption. Therefore, in order to implement robust communication techniques that will thrive on the noisy PLC channel, a full knowledge and modeling of the noise that exists on the NB-PLC channel is inevitable. This paper thus reports a First-order Markov modeling of NB-PLC channel noise, based on experimental measurements. For the modeling, BPSK, DBPSK, QPSK and DQPSK modulation schemes were implemented using Universal Software Radio Peripheral (USRP). The resulting channel models are useful for improving the robustness of the above modulation schemes as well as designing forward error correction techniques for mitigating the effect of noise impairments. The results are also useful in optimizing NB-PLC system design, thereby, enhancing the accuracy and improving the overall PLC system performance.
Full Text:

Quick View

Double-boost DC to DC converter

- Van Rensburg, J. F. J., Case, M. J., Nicolae, Dan-Valentin

Authors: Van Rensburg, J. F. J. , Case, M. J. , Nicolae, Dan-Valentin
Date: 2008
Subjects: DC-to-DC converters
Language: English
Identifier: http://hdl.handle.net/10210/20484 , uj:16103 , Citation: Van Rensburg, J.F.J, Case, M.J. & Nicolae, D.V. 2008. Double-boost DC to DC converter. Proceedings of the 34th Annual Conference of IEEE Industrial Electronics, 10-13 November, 2008, Orlando, USA. DOI: 10.1109/IECON.2008.4758040 , ISBN: 978-1-4244-1766-7
Description: Abstract In this paper anew boost topology is proposed. The circuit is similar with two parallel boost dc-to-dc converters, but the two inductors are charged in parallel and release energy in series, thus enhancing the voltage boost ratio. After a short analysis of the circuit, a comparative study with other classic boost converter (single boost and two-cascade) is presented. The simulation results show a net improvement of the boost ratio for the new proposed topology.
Full Text:

Quick View

Study of direct energy tapping from electric field

- Nicolae, Dan-Valentin, Hofsajer, I. W.

Authors: Nicolae, Dan-Valentin , Hofsajer, I. W.
Date: 2007
Subjects: Direct energy conversion , Voltage-frequency converters
Language: English
Type: Conference proceedings
Identifier: http://hdl.handle.net/10210/20455 , uj:16100 , Citation: Nicolae, D.V. & Hofsajer, I. 2007. Study of direct energy tapping from electric field. International Aegean Conference on Electric Machines and Power Electronics & Electromotion Joint Conferences, Bodrum, Turkey, September 10-12, 2007:240-244. DOI:10.1109/ACEMP.2007.4510509
Description: Abstract: A method of extracting small amounts of power directly from the ambient electromagnetic field around a 50kV AC single phase line is described using a new approach to coupling capacitance. The amount of the power that may be extracted is limited. The proposed solution is vastly more cost effective than the alternatives of a transformer or a directly connected capacitive tap. The modelling and design limitations of the method are described and demonstrated on a scaled model
Full Text:

Quick View

Implementing rootkits to address operating system vulnerabilities

- Corregedor, Manuel, Von Solms, Sebastiaan

Authors: Corregedor, Manuel , Von Solms, Sebastiaan
Date: 2011
Subjects: Computer security , Rootkits , Operating systems - Security measures , Malware (Computer software)
Type: Article
Identifier: http://ujcontent.uj.ac.za8080/10210/373539 , uj:6251 , ISBN 978-1-4577-1482-5 , http://hdl.handle.net/10210/8205
Description: Statistics show that although malware detection techniques are detecting and preventing malware, they do not guarantee a 100% detection and / or prevention of malware. This is especially the case when it comes to rootkits that can manipulate the operating system such that it can distribute other malware, hide existing malware, steal information, hide itself, disable anti-malware software etc all without the knowledge of the user. This paper will demonstrate the steps required in order to create two rootkits. We will demonstrate that by implementing rootkits or any other type of malware a researcher will be able to better understand the techniques and vulnerabilities used by an attacker. Such information could then be useful when implementing anti-malware techniques.
Full Text:

Showing items 1 - 20 of 142