Browsing by Author "Gaunt, Trevor"

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    Open Access
    An investigation into 88 KV surge arrester failures in the Eskom east grid traction network
    (2022) Mzulwini, Mduduzi Comfort; Awodele, Kehinde; Gaunt, Trevor
    The Eskom East Grid Traction Network (EGTN) supplying traction loads and distribution networks has experienced at least one surge arrester failure over the past ten years. These failures results in poor network reliability and customer dissatisfactions which are often overlooked. This is because reliability indices used in the reliability evaluation of transmission and distribution networks are different. It is suspected that fast transient faults in this network initiate system faults leading to surge arrester design parameter exceedances and poor network insulation coordination. Preliminary investigations in network suggest that transient studies were not done during network planning and design stages. This may have resulted in the lack of surge arrester parameter evaluations under transient conditions leading to improper surge arresters being selected and installed in this network resulting in surge arrester failures that are now evident. These failures may also have been exacerbated by the dynamic nature of traction loads as they are highly unbalanced, have poor power factors and emit high voltage distortions. Poor in-service conditions such as defects, insulation partial discharges and overheating, bolted faults in the network and quality of supply emissions can also contribute to surge arrester failures. To address problems arising with different reliability indices in these networks the reliability of the EGTN is evaluated. In this work the reliability evaluation of the EGTN is done by computing common distribution reliability indices using analytic and simulation methods. This is done by applying the analytic method in the EGTN by assessing network failure modes and effects analysis (FMEA) when the surge arrester fails in this network. The simulation method is applied by applying and modifying the MATLAB code proposed by Shavuka et al. [1]. These reliability indices are then compared with transmission reliability indices over the same period. This attempts to standardize reliability evaluations in these networks. To assess the impact of transient faults in the surge arrester parameter evaluation the EGTN is modelled and simulated by initiating transient faults sequentially in the network at different nodes and under different loading conditions. This is done by using Power System Blockset (PSB), Power System Analysis Toolbox (PSAT) and Alternate Transient Program (ATP) simulation tools and computing important surge arrester parameters i.e. continuous operating voltage, rated voltage, discharge current and energy absorption capability (EAC). These parameters are assessed by in the EGTN by evaluating computed surge arrester parameters against parameters provided by manufacturers, the Eskom 88 kV surge arrester specification and those parameters recommended in IEC 60099-4. To assess the impact and contribution of in-service conditions, faults and quality of supply emissions in surge arrester failures these contributing factors are investigated by assessing infra-red scans, fault analysis reports, results of the sampled faulted surge arrester in this network and quality of supply parameters around the time of failures. This study found that Eskom transmission and distribution network reliability indices can be standardized as distribution reliability indices i.e. SAIDI, SAIFI, CAIDI, ASAI and ASUI indices are similar to Eskom transmission indices i.e. SM, NOI, circuit availability index and circuit unavailability index respectively. Transient simulations in this study showed that certain surge arresters in the EGTN had their rated surge arrester parameters exceeded under certain transient conditions and loading conditions. These surge arresters failed as their discharge currents and EACs were exceeded under heavy and light network loading conditions. This study concluded that surge arresters whose discharge currents and EACs exceeded were improperly evaluated and selected prior to their installations in the EGTN. This study found the EAC to be the most import parameter in surge arrester performance evaluations. The Eskom 88 kV surge arrester specification was found to be inadequate, inaccurate and ambiguous as a number of inconsistencies in the usage of IEEE and IEC classified systems terminology were found. It was concluded that these inconsistencies may have led to confusions for manufacturers during surge arrester designs and selections in the EGTN. The evaluation of fault reports showed that two surge arrester failures in this network were caused by hardware failures such as conductor failure and poor network operating as the line was continuously closed onto a fault. There was no evidence that poor in-service and quality of supply emissions contributed to surge arrester failures in this network. PSB, PSAT and ATP simulation tools were found adequate in modelling and simulating the EGTN. However the PSB tool was found to be slow as the network expanded and the PSAT required user defined surge arrester models requiring detailed manufacture data sheets which are not readily available. ATP was found to be superior in terms of speed and accuracy in comparison to the PSB and PSAT tools. The MATLAB code proposed by Shavuka et al. [1] was found to be suitable and accurate in assessing transmission networks as EGTN's reliability indices computed from this code were comparable to benchmarked Eskom distribution reliability indices. The work carried out in this research will assist in improving surge arrester performance evaluations, the current surge arrester specification and surge arrester selections. Simulation tools utilized in this work show great potential in achieving this. Reliability studies conducted in this work will assist in standardizing reliability indices between Eskom's transmission and distribution divisions. In-service condition assessment carried out in this work will improve surge arrester condition monitoring and preventive maintenance practices.
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    Beyond free electricity: The cost of electric cooking in poor households and a market-friendly alternative
    (Elsevier, 2006) Howells, Mark; Victor, David G; Gaunt, Trevor; Elias, Rebecca J; Alfstad, Thomas
    The South African government is introducing a poverty-reduction policy that will supply households with a monthly 50kWh “Free Basic Electricity (FBE)” subsidy. We show that FBE distorts the energy choices of poor households by encouraging them to cook with electricity, whereas alternatives such as liquefied petroleum gas (LPG) can deliver a similar cooking service at a much lower cost to society. An alternative energy scheme, such as providing households with clean energy credits equivalent in value to the FBE’s cost, could deliver additional energy services worth at least 6% of total household welfare (and probably much more) at no additional public cost; those benefits are so large that they would cover the entire cost of LPG fuel needed to implement the scheme. The analysis is extremely sensitive to the coincidence of electric cooking with peak power demand on the South African grid and to assumptions regarding how South Africa will meet its looming shortfall in peak power capacity. One danger of FBE is that actual peak coincidence and the costs of supplying peak power could be much less favorable than we assume, and such uncertainties expose the South African power system to potentially very high costs of service.
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    Open Access
    Extending the Herman-Beta transform for probabilistic load flow analysis of radial feeders
    (2019) Chihota, Munyaradzi Justice; Gaunt, Trevor
    The increased penetration of distributed generation (DG) mostly derived from renewable energy sources (RES) such as wind and photovoltaic (PV) systems presents two main forms of technical issues. The system is more susceptible to voltage-rise and equipment overload conditions, while the levels of uncertainty associated with the power system’s parameters increase significantly. The resulting networks characterised by the bi-directional flow of power, uncertainty from stochastic customer load variations and the intermittent generation from DGs, require appropriate load flow assessment tools. Classic deterministic load flow (DLF) approaches which assume the input parameters are fixed, or address the associated variability using empirical factors, have been shown to be inadequate. As a result, probabilistic load flow (PLF) approaches based on statistical foundations were proposed to account for the impacts of the uncertainty. For the PLF methods, the efficiency of a specific approach is influenced by two major constraints; the accuracy of the method and the associated computational effort that affects speed. For instance, numerical methods such as the renowned Monte-Carlo simulation (MCS), offer the most accuracy (within the limits of randomness) but are very computationally demanding and undesirable for practical applications. Usually, speed is coupled with loss of accuracy. Most approaches based on analytical and approximation approaches, which offer higher computational speeds, have limited accuracy due to excessive simplifications. Consequently, a trade-off between accuracy and speed is key to a robust PLF approach. Furthermore, the model solutions must be applicable to both small and large systems, consider the dependency between random variables, and avoid complex formulations which limit the practical usefulness. This research proposes a non-iterative analytical approach referred to as the Herman-Beta extended (HBE) transform to meet the performance and scope requirements of a model PLF solution. The method is based on the beta probability density function (PDF) as a universal descriptor of inputs, and the method of moments for the computation of the output PDFs. The novel formulation of the transform with consideration of complex-type input parameters redresses the network model simplifications of unity power factor loads and resistive feeders in the original HB algorithm (HBA) and the limitation of the representation using absolute values. Further, the effects of dependence between loads and generators are incorporated directly using covariances. The proposed approach opens many possibilities for new applications, including the accurate analysis of the PLF for feeders at any voltage (LV, MV and HV), compensated feeders (shunt reactors and shunt capacitors), and systems with voltagedependent load or DG. The performance of the proposed technique is demonstrated using representative test feeders, modified IEEE 33, 34 and 69-bus test systems, as well as practical distribution networks. The results from several test cases demonstrate a good correlation between the LF outcomes from the proposed method and those from the MCS method and with significant computational advantage. The performance of the method compared with its predecessor shows advanced accuracy while maintaining high computational speed.
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    South Africa's rapid electrification programme: policy, institutional, planning, financing and technical innovations
    (Elsevier, 2008) Bekker, Bernard; Gaunt, Trevor; Marquard, Andrew; Eberhard, Anton
    This paper documents South Africa’s electrification programme from the late 1980s to the present. The primary aim of the paper is to present the reader with an overview of the policy, institutional, planning, financing and technological developments and innovations that resulted in more than 5 million households receiving access to electricity between 1990 and 2007. Key aspects include the way in which a period of political change and policy disruption were essential to the programme’s initiation, and the critical role played by organisations and individuals outside of national government in helping shape new electrification policies and strategies. In addition, the paper identifies the contribution of technology development in cost reduction and achieving the social aims of the programme. Several lessons may be drawn from the institutional and planning arrangements that the South African programme has developed, the significance of the development of appropriate cost-driven technical innovations and standards, and the acknowledgement of the social function of electrification and its funding from the fiscus (rather than through cross-subsidies).
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    Open Access
    Testing for relationship between diagnostic tests and DC BDV of in-serviced aged stator bars of a hydro generator
    (2024) Bruintjies, Mark Anthony; Gaunt, Trevor ; Barendse, Paul
    The effective management of assets currently presents a challenge to utilities. A cognisance and understanding of the actual condition of these assets will enable utilities to implement mitigation strategies and use these assets for the full duration of their lifespan. One of these assets could be hydro generators with the stator bars constituting one of the failing components. Integral to the satisfactory operation of a high voltage (HV) electrical rotating plant is the integrity of the electrical high voltage insulation of both the rotor and stator. During operation, high voltage generator components (for example stator bars), are continuously and simultaneously subjected to electrical, thermal, mechanical and ambient (environment) stresses. Subsequently, the complex interactions of these stresses degrade and deteriorate the insulation material gradually, resulting in a reduction of valuable operative life, potential forced outages and costly emergency repairs. Because both expected and unexpected stator bar in-service failures may lead to costly repairs, rotating machine users implement condition monitoring (CM), diagnostic tests and condition-based maintenance in order to mitigate risk. The contribution was executed in the form of removing aged stator bars from a generator and subjecting the bars to various diagnostic and direct current (DC) HV tests, testing for correlation. The diagnostic tests included insulation resistance (IR), polarization index (PI), partial discharge (PD), tan delta (TD) and Tennessee Valley Authority (TVA) tests. The HV breakdown tests included very low frequency (VLF) and DC tests. Despite using this wider range of tests than has been used before, the test results still confirm earlier reports that there are no clear correlations between the different diagnostic tests. There is also no clear relationship between the condition monitoring test results and physical breakdown of the insulation in the high voltage tests. Hence, it was concluded that these diagnostic tests on their own could not predict incipient insulation failure and that currently the most value derived from these tests would be to use the results as trending parameters rather than absolute values to predict insulation failure.