Browsing by Author "Dingley, Charles"

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    Comparison and evaluation of South African poletop designs for 11kV and 22kV rural distribution lines
    (1992) Scott, R A; Dingley, Charles
    The ultimate purpose of this thesis is to compare and evaluate. South African poletop designs for 11kV and 22kV rural distribution lines. However, a frame of reference is first established from the literature and from construction practice before the analytical stage is tackled. In 1989, when the work for this thesis was started, it was quite apparent that there existed a proliferation of configuration designs for rural overhead lines at 11 kV and 22kV in South Africa. The electricity supply industry did not use a universal configuration. Eskom supplied over 97 of South Africa's electricity in 1990 (Eskom, 1990). It was also operating 160 280km of lines at 22kV and below in that year and was largely responsible for this situation. Local supply authorities or distributors S!JCh as municipalities either bought components from Eskom or used an Eskom design, or developed their own designs internally or via consultants. In any event, the designs they used are not considered to be a significant portion of the total. Historically, Eskom developed on a strongly regionalised basis, the separate Undertakings joining up (electrically) to form the national grid in 1973. Prior to 1985 there were six Regions distributing the electricity generated by the power stations. Each Region developed its own designs, independently or based on designs imported from Britain.
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    The electrification of underdeveloped areas : a case study in Ciskei
    (1989) Tobich, Ralf Georg; Dingley, Charles
    More than 20 million people in South Africa live without electricity in the household. Perhaps half of them live in underdeveloped rural areas in the 'homelands', which comprise about 14% of South Africa's land area. While considerable work has been done on methods of electrifying underdeveloped urban areas, little research has gone into the need for, and especially the cost of, electrifying the rural homeland areas. This dissertation documents an investigation into this question, using Ciskei as a sample area. The study is based on research that was carried out between July 1987 and January 1989. This research included a literature review of rural electrification and development, two field trips to Ciskei to gather relevant information, two questionnaire surveys to assess people's perceptions of electricity, and the design and costing of distribution and reticulation networks for a rural sample area in Ciskei.
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    Laboratory investigation into the radio interference produced by artificially polluted 22 KV distribution line insulators
    (1990) Cunliffe, C. J; Dingley, Charles
    Although it is known that polluted power line insulators can, under certain conditions, cause interference with radio communication networks, there is little useful practical data as to the extent of the problem. This is mainly due to the difficulties associated with quantifying and measuring this interference. There are various test procedures to measure radio noise characteristics of hv insulators, set out in recommendations published by the International Electrotechnical Commission (IEC). These however, only apply to clean and dry conditions. The IEC has also recommended methods for the laboratory simulation of natural pollution conditions in insulator flashover tests. This project involved combining the two techniques into a laboratory procedure for measuring RN produced by artificially polluted insulators. The investigation was concentrated on 22 kV line insulation and RN in AM frequency bands. Initial tests were done to develop a repeatable pollution simulation method based on the IEC 507 clean fog artificial pollution test. This method was then combined with the IEC 437 RN measurement test circuit to form the basis of two different types of test procedure. The first test procedure was a prolonged or constant voltage method. It consisted of monitoring the insulator RN with time while it was subjected to a pre-determined pollution condition and a constant voltage for the test duration. This is representative of the field situation but makes it a very time consuming process to obtain interference values over a range of test voltages. The second, accelerated type, procedure was to record RN as the voltage was varied within any one test run. This is not representative of a practical case where large voltage variations are rare, but it did have time saving implications. The accelerated procedure generally gave lower RIV values than those indicated by the prolonged procedure at the same voltage and pollution severity. Nonetheless, it was concluded that, by paying particular attention to wetting rates and voltage step durations, the accelerated procedure could also be further developed into a standard polluted insulator RN test. Two different insulator types - a porcelain line post insulator and a glass disc insulator - were used in 153 clean fog test runs. The results showed that clean, or polluted but dry insulators, operating at practically used specific creepages, produce insignificant levels of interference. Only at impractically low specific creepage were unacceptably high ranges of RN emitted. When the insulators were polluted and dampened with the clean fog, the RN increased rapidly with voltages above 1 kV. For the line post insulator the curve reached a knee point at about 8 kV, beyond which very little or no RIV increase with voltage was observed up to 18 kV. For the glass disc units, although the slope of the curve decreased at the higher voltages the same knee point was not so evident. For both insulators, except at very low voltages, little variation in RN level with pollution severity at fixed voltage was observed. These results are in general agreement with the conclusions of previous work. It would be useful to further refine the test methods, both to develop a RN measurement standard and to obtain more data pertaining to specific insulator types. A standard procedure would also permit investigating the correlation of both polluted insulator leakage current and the practical nuisance value of the RN, with laboratory measured RIV values.
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    The optimal placement of switching devices on rural medium-voltage systems
    (2001) Pitamber, Neemesh; Dingley, Charles
    Electricity is supplied to rural areas by radial networks operating for example at 11 or 22 kV. A problem with radial networks is that faults on the feeders result in the loss of electricity supply to all customers if they are not sectionalised. Some radial networks emanating from one feeder from the sub-station may consist of up to 300 km of line, taking into account spurs, which makes fault detection difficult and increases customer outage time. Protective devices such as reclosers, sectionalisers and fuses are place on distribution systems to reduce the number of customers that will not have service at one time or another due to any fault on the system. There do not appear to be clear rules with regard to the placement of these protective devices. With the installed cost of devices such as sectionalisers bieng over fifty thousand rand, this is naturally of concern to a power utility.
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    The protection of high-voltage shunt capacitor banks
    (1999) Van der Toorn, Sean; Dingley, Charles
    The use of shunt capacitor bank equipment is essential if a utility wishes to control the flow of reactive power effectively. The most significant results stemming from this will be lower losses on the system and an increased power transfer capability. Thus it is important that the methods used to protect a shunt capacitor bank will ensure that the bank is available when required. While the more common shunt capacitor problems are related to capacitor unit failures, conditions such as bank over currents, surge voltages and harmonics can cause extended undesired conditions. Today's protection methods are able to remove a shunt capacitor bank from service before extensive damage is done, although the location of the faulty capacitor units will not be known (if this was in fact the reason for the protection tripping the bank). This thesis explores the subject of improving the protection of high-voltage shunt capacitor banks, specifically with respect to the detection of unhealthy fuseless capacitor units. An extensive literature search was carried out on the theory pertaining to the protection of shunt capacitor banks, and a model of a fuse less shunt capacitor bank was built in the laboratory to better understand the failing process of an element within a capacitor unit. The changes in the capacitor unit's current and voltage profiles, as well as those of the remaining healthy capacitor units, were monitored as an element failure was simulated (whereby the element forms a solid weld, or short circuit).Stemming from these experiments, it was found that where a bank consists of strings of units with no interconnection between the units of different strings, an element failure in a capacitor unit would cause a significant decrease in voltage across the affected unit. This voltage change could be used to identify when elements are failing in capacitor units, and the location of the unhealthy unit could also be determined. One potential method would be to have capacitor units with built-in voltage transformers attached across each element section in the unit. As element failures occur either send this information to ground level, where it can be read by a microprocessor relay device, or have a display on the outside of the capacitor unit. In the case of the change in unit current, it was found to be very small and thus had no function for detecting unhealthy capacitor units.
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    Public and private sector involvement in the provision of electricity in urban areas of South Africa
    (1991) Theron, Paul Richard; Eberhard, Anton A; Dingley, Charles
    This study examines the involvement of public and private sector institutions in the provision of electricity in urban areas of South Africa. Access to electricity in South Africa is highly unequal and little progress is currently being made to bring electricity to all, mainly due to institutional and financial problems. The focus on public and private sector roles is adopted because of the social importance and economic nature of electricity provision, the global and national significance of privatisation policies, and the current importance of allocating appropriate roles to the public and private sectors in widening access to services, including electricity, in South Africa. The distribution sector of the South African electricity supply industry (ESI) is highly fragmented. Municipal electricity departments, which mostly serve white residential, commercial and industrial areas, are generally highly profitable and provide an effective service, but are not highly efficient by international standards. These departments are self-sufficient in the implementation of electrification projects, and have access to adequate capital to finance such projects. Electricity distribution authorities set up to serve black areas, especially electricity departments of black local authorities, are ineffective, and often financially unsound. Due to the weakness of public authorities charged with the task of undertaking electrification projects in black areas, the implementation of these projects is dependent on the involvement of private electrical consultants and contractors. However, few such projects are currently being undertaken due to inappropriate planning and shortages of concessionary finance. After close consideration of the benefits and drawbacks of public and private involvement in range of activities that arise from electricity provision, it is concluded that the key challenges facing the ESI in South Africa will best be met if the distribution sector is restructured on a regional basis in order to utilise existing expertise, and retained within the public sector. Accelerated electrification initiatives, planned and co-ordinated by these distribution authorities, would draw upon the experience and capabilities of private electrical consultants and contractors. Public sector leadership in mobilising both public and private investment would also be necessary. Thus, whilst public institutions would be dominant, important roles would remain for the private sector in the provision of electricity in urban areas. The results of this study suggest that far from privatising service provision in South Africa, it will be essential to allocate a dominant role to the public sector in widening access to services to all.
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    A review of the emergency electric power supply systems at PWR nuclear power plants
    (1989) Smyth, Thomas Paton; Dingley, Charles
    The Emergency Electric Power Supply Systems at Pressurized Water Reactor Nuclear Power Plants are reviewed, problem areas are identified, and recommendations are made for existing and future Nuclear Power Plants. A simplified introduction to a typical Pressurized Water Nuclear Reactor is given and the problems associated with the commercial use of nuclear power are discussed. An overview of the Nuclear industry's solutions is presented and covers the Reliability of equipment and the American Regulatory requirements. The alternating and direct current power supply systems are examined in terms of plant operational state and equipment type (Diesel generators, Grid network, Lead-acid batteries, Battery chargers, Inverters, and Power Distribution networks). The trends in the design of Emergency Electric Power supply systems at Nuclear Power Plants are presented. The loss of all alternating current power, known as Station Blackout, is discussed and the American and European response to this. problem is presented. Problems experienced in the direct current systems are discussed and solutions are presented. The experience at Koeberg Nuclear Power station with Lead-acid batteries is included in the discussion. The thesis concludes with recommendations for designers and operators of the Electric Power Supply Systems at Nuclear Power Stations.