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Strategy for power quality improvement and maximum demand smoothing

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

A study of insulation failure in a high voltage current transformer

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

Aspects of the ratio of reactive to real powers as input to transmission network control

- Swart, Sarica Meyer

  • Authors: Swart, Sarica Meyer
  • Date: 2012-06-05
  • Subjects: Electric power transmission , Electric power system stability
  • Type: Thesis
  • Identifier: uj:2383 , http://hdl.handle.net/10210/4838
  • Description: D.Ing. , Transmission networks change continuously when new supply requests are made, network reinforcements are installed and equipment configuration changes. Therefore, network design, operation and control requirements change. To manage this, controllers are being developed to assist human network controllers who might not always be specialists in equipment operation and characteristics. A transmission network comprises multiple variables, some dependent on others. The resistive portion of a load (PLoad) and the total reactive power (Q) installed close to the load can be set in relation to each other. This relationship forms the basic concept of the QP ratio for a transmission network. This ratio is not standardly used as a variable in network operation or control. This thesis explores this new QP ratio in more depth for application in different networks. This concept is developed and investigated in detail and equations are derived from first principles. The usability of the QP ratio is described and calculations are done for existing networks. It is shown that each network has its own unique QP ratio that can be used as information for human operators or as part of a controller device. This information can assist in determining actions required to be taken by controllers and operators. This thesis investigates aspects related to the use of a QP ratio in transmission networks as far as system operation and network control is concerned. The information provided in this thesis could be developed further to assist in implementing of the QP ratio in transmission network control rooms or systems. This will contribute to the provision of more reliable, robust and controlled electrical networks.
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Effective coupling for power-line communications

- Janse van Rensburg, P. A.

  • Authors: Janse van Rensburg, P. A.
  • Date: 2009-04-28T07:26:35Z
  • Subjects: Electric power transmission , Telecommunication lines , Electric lines carrier transmission
  • Type: Thesis
  • Identifier: uj:8314 , http://hdl.handle.net/10210/2442
  • Description: D.Ing. , The technique of using a live power cable to simultaneously transport a communication signal, has been practiced since the early 1900’s. In most cases, power-line communications has been implemented as a retrofit technology, with its main benefit being the utilization of a ‘free’ existing network. This driving force of power-line communications is typical for high-, medium-, and low-voltage distribution networks, as well as intra-building networks currently targeted for home automation and home networking. Researchers have thus focused on the optimum use of these existing power-line channels, often accepting the inherent drawbacks of this hostile communication channel. Apart from unpredictable noise sources, two main disadvantages of the low-voltage powerline network as a communication channel, are i) the unknown power cable characteristics and topology and ii) time-dependent fluctuation of the power-line impedance level as loads are unpredictable switched into, and out of the network. These two factors have obscured the requirements for proper coupling and impedance adaptation to the degree that most researchers and manufacturers have merely accepted this typical ≈ 20-dB coupling loss as one of the inherited disadvantages of the power-line channel. Most researchers and manufacturers have thus defaulted to a guessed power-line impedance level, and have used one fixed coupler winding ratio under all circumstances, regardless of power-line conditions. This study has shown that proper coupling and impedance adaptation can yield significant transmission gains even with limited (qualitative) knowledge of a power-line channel and its topology. After formulating design steps for an impedance-adapting coupler that facilitates bidirectional transmission, the impact of the fluctuating power-line impedance on coupler bandwidth was investigated. Next, impedance adaptation strategies were considered and the tradeoff between series cable requirements and parallel load requirements was explored. A model of sufficient simplicity was developed to facilitate qualitative description and classification of power outlets – functioning as communication nodes. Very interesting simulation results were obtained and these were verified using a laboratory setup of characterized power cables and calibrated loads. Next, these simulation results were employed to improve power-line transmission over a live, uncharacterized 220-V residential network by means of i) classifying typical residential rooms qualitatively in order to choose proper coupler winding ratios and ii) using an innovative dual coupler for dedicated on-off switching with harsh loads, thereby mitigating the fluctuating impact of said loads on low-voltage power-line communications.
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The reliability and maintainability of the transmission transformers in South Africa

- Molabe P.P.

  • Authors: Molabe P.P.
  • Date: 2018
  • Subjects: Eskom (Firm) , Electric transformers - South Africa - Maintenance and repair , Electric insulators and insulation , Electric power transmission , Electric power supplies to apparatus
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/286013 , uj:30941
  • Description: M.Phil. (Engineering Management) , Abstract: The power utilities have the challenging task of supplying electricity and meeting stakeholders expectations with constrained resources. Like other power utilities, Eskom has a mandate of generating and distributing electricity in a safe, reliable and cost-effective ways. The success and failure of the South African power utility are depended on the capabilities of the transformers and the maintenance strategies adopted to support the systems. This study presents the finding of the reliability and maintainability analysis of the transmission transformers in Eskom from the period of 2014 to 2016. The study used statistical methods to analyse secondary data from Eskom operational records and reports. During the period of analysis, Eskom experienced twenty-nine failures related to transmission transformers. The study shows that Eskom was operating with the ageing transmission transformers, the protection system and bushings came out as dominating causes for malfunctions. It is recommended that Eskom change the maintenance strategy and focus on replacing the high failing component or systems to improve reliability.
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The use of support vector machine for phase balancing in the distribution feeder

- Siti, M. W., Jimoh, A. A., Jordaan, J. A., Nicolae, Dan-Valentin

Electromagnetic interference in balanced converters

- Burford, Steven Trefor

  • Authors: Burford, Steven Trefor
  • Date: 2014-09-17
  • Subjects: Electromagnetic interference , Electromagnetic compatibility , Electric power transmission
  • Type: Thesis
  • Identifier: uj:12335 , http://hdl.handle.net/10210/12121
  • Description: M.Ing. (Electrical And Electronic Engineering) , In this dissertation, an investigation into reducing Electromagnetic Interference (EMI) through design is presented. Root generation mechanisms of Electromagnetic Interference are often neglected during the design process and later treated symptomatically. Mitigation of Electromagnetic Interference at source often reduces cost and physical size of electronics. This dissertation demonstrates the process and results by which schematic balance mitigates EMI. In addition, the introduction of Geometric Balance and physically designing circuits to be Geometrically Symmetrical are presented and tested to determine whether the design produces mitigating EMI results. Multiple Printed Circuit Boards (PCB’s) were developed and tested against each other to demonstrate schematic balance and other EMI generation mechanisms. The final PCB was designed to be Geometrically Symmetrical and the test results compared. The results illustrate the varying performance of each PCB due to their differing design. The Geometrically Symmetrical PCB presented the best results due to various improvements which include physical layout size and semiconductor placement. An additional important phenomenon discovered was the amount of EMI generated during MOSFET Driver operation. This contributed to a significant amount of EMI during the no-load phase of testing.
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On mercury vapor lamps and their effect on the smart-grid PLC channel

- Emleh, A., De Beer, A. S., Ferreira, Hendrik C., Han Vinck, A. J.

Aspects of the ratio of reactive to real powers as input to transmission network control

- Swart, Sarica Meyer

  • Authors: Swart, Sarica Meyer
  • Date: 2014-02-18
  • Subjects: Electric power system stability , Electric power transmission
  • Type: Thesis
  • Identifier: uj:4136 , http://hdl.handle.net/10210/9483
  • Description: M.Ing. (Electrical Engineering) , Induction heating has been used in practice for many years. The main goal of this study is to investigate the use of a single-turn coil in a typical induction heater. The work starts off with a background study of elecrroheat and specifically high-frequency induction heating. Finite element simulations were conducted on different coil shapes and compared with each other. The converter. with control and driver circuits. used in the, experimental setup, as well as the experimental construction and results are described. The work is concluded with an evaluation of the project.
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Another case of discrepancies when evaluating power theories using real data

- Cornelius, Jurgens J. J., Janse van Rensburg, J. F., Nicolae, Dan-Valentin

Evaluating an empirical relationship between recloser placement and reliability improvement in distribution networks

- Thomas, Ponny

  • Authors: Thomas, Ponny
  • Date: 2016
  • Subjects: Electric networks , Electric power distribution , Electric power transmission , Eskom (Firm)
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/213003 , uj:21065
  • Description: Abstract: The National Energy Regulator of South Africa (NERSA) has implemented an Incentive- Based Regulation (IBR) scheme that either rewards or penalizes distributors on the System- Average Interruption-Duration Index (SAIDI) and other network performance indices [1]. The optimal placement of automatic reclosers (auto-reclosers) is seen as a cost-effective measure to reduce the system-average interruption-duration index (SAIDI) impact along a medium voltage (MV) feeder. An auto-recloser is seen as a function of distribution automation (DA), thus reducing customer impact. A great advantage of a correctly implemented and operated DA system can improve network reliability significantly. This dissertation evaluates the empirical relationship between recloser placement and reliability from the perspective of control and instrumentation within ESKOM. It also puts forward an additional performance-improvement framework that can be implemented to achieve RAM (Reliability, Availability and Maintainability) management. Loop automation functionality is also under discussion; this is a Distribution-System Automation-scheme that restores the supply to the fault-free sections of a network, if they have been disconnected, because of a fault in another section of the network. Loop automation can also restore the normal network configuration automatically, when the faulty section is repaired. The process of isolating the faulty section and re-configuring the network to restore supply back to the fault-free sections is the first capability of Loop Automation. This research investigation assesses two different scenarios, namely: A conventional implementation of auto-reclosers on MV networks using Eskom reliability standard; and (ii.) the findings of a case-study using this recloser implementation (loop automation) to improve the reliability and the system’s performance. Results obtained are presented and discussed. , M.Phil. (Engineering Management)
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The technology of nonlinear resonant pole converters

- De Beer, Arnoldus Stephanus

Analysing the propagation of fast time-varying electromagnetic disturbances along power-transmission structures

- Sinclair, Andrew John

  • Authors: Sinclair, Andrew John
  • Date: 2012-08-28
  • Subjects: Electric power transmission , Electromagnetic interference
  • Type: Thesis
  • Identifier: uj:3301 , http://hdl.handle.net/10210/6705
  • Description: D.Ing. , The propagation of fast disturbances along power transmission structures depends on the parameters of the excitation for the disturbance, the characteristics of the power transmission structure, and eventually on the characteristics of the electrical load connected to the structure. This thesis will therefore target the determination of the parameters of transmission structures in Chapter 2, applicable transmission-line theory in Chapter 3, modelling the load in Chapter 4, and apply this knowledge to the specific problem of over-voltages on the terminals of machines fed via cables from inverters in Chapter 5. The rest of this chapter is devoted to explaining the introductory aspects of this application problem.
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Reliability assessment of medium voltage underground cable network using failure prediction methods

- Mehlo, Nqaba A.

  • Authors: Mehlo, Nqaba A.
  • Date: 2018
  • Subjects: Electric power distribution , Electric power transmission , Underground electric lines , Electric cables
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/293865 , uj:31962
  • Description: M.Phil. (Engineering Management) , Abstract: In recent years, electricity supply has become the driving force behind economic growth in many cities, urban areas and businesses around the world. As a result, utilities are under pressure to supply reliable electricity to their customers at all times. Most power outages take place in the distribution network, and the most used distribution network in the city and urban areas is Medium Voltage (MV) underground cable distribution network is due to space constraint. The power disruption statistics in Europe and South Africa indicates that the rate of power outages is high in the MV network adding up to 80% of the entire electrical distribution network. However, the national regulator expects the City of Tshwane to manage these interruptions effectively and to improve network reliability. This dissertation will begin by giving a detailed description of the City of Tshwane MV underground cable network. Thereafter, the research will identify, quantify and characterize factors that cause cable failures and poor reliability of this network. It is very important for the municipality to understand these causes before making any asset management decisions in the network since condition assessment or replacement of underground cables is very difficult and restoration times are long due to the complexity of cable access. The research also looked at the available solutions in various literatures that can benefit the municipality in terms of knowledge. Some of the solutions include different network configurations. The research methodology used in this paper is a quantitative approach, which applies statistical analysis methods for failure prediction, and a qualitative method is also applied for in-depth explanation of the data. The focus of this research is a case study about the City of Tshwane municipality, using secondary data. MV underground cable failure data evaluation was divided into four stages so that important network behaviour characteristics could be analysed. The first stage was MV network data and information acquisition. The second stage consisted of cable failure analysis, where equipment failure was the highest. The main cause of equipment failure is insulation failure. In the third stage, Pearson’s linear correlation method is used to evaluate the relationship between cable failure behaviour and various climatic seasons (temperature and rainfall). The findings were not...
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Impact of parameters of transmission line interconnecting transformers on power system performance

- Dyantyi, Ayanda Theophilus

  • Authors: Dyantyi, Ayanda Theophilus
  • Date: 2016
  • Subjects: Electric transformers , Electric power systems , Electric power transmission , Data transmission systems
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/57230 , uj:16371
  • Description: Abstract: Power transformers are used to form a connection between distribution, sub-transmission and transmission power lines in order to allow electric power to flow between networks of different voltages. Thus, the desired value of transformer reactance value is determined at the design stage. In most cases, once a transformer is commissioned, its tap changer setting is fixed at a particular position, and the position is likely to be changed only during maintenance. In this dissertation, an investigation into the impact of parameters of high voltage transmission line interconnecting transformers on power system on the performance of the power system is being done. The specific transformer parameters that are considered are reactance and tap changer settings. The performance aspects that are investigated are active power flow, system losses, and voltage stability. From the findings of the investigation, it is observed that the reactance value of a transformer has an influence on power flow, system losses, and voltage stability. Therefore, in networks where the likelihood of fault current occurrence is low, the reactance of the transformer can be varied in order to improve the performance of the power system. Moreover, transformer tap changer positions have a higher influence on power flow, system losses, and voltage stability. It is concluded that at the design stage, transformer reactance values need to be carefully selected for the improvement of power system performance. During the commissioning and maintenance of transformer units, there is a need for power system planners and operators to carefully select the tap changer position and fix it in a position that yields better results with regard to power flow, system losses, and voltage stability of the power system. , M.Ing. (Electrical and Electronic Engineering)
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