Scielo RSS <![CDATA[Journal of Energy in Southern Africa]]> vol. 30 num. 4 lang. es <![CDATA[SciELO Logo]]> <![CDATA[<b>Potential for grid efficiency based on a combination of leakage reactances of transformers of a transmission interconnecting line: Application of an exhaustive search algorithm</b>]]> Transmission interconnecting lines (called interconnectors in this study) are built to facilitate the exchange of active and reactive power between two areas of a network. Step-up and step-down transformers are required at the ends of the interconnector when interconnectors are at a different voltage, usually higher, than the networks to be connected. A study was carried out to examine the impact on active power losses of a combination of leakage reactances of the transformers at the ends of an interconnector. The study assessed whether combinations can lead to different levels of active power losses and can thus affect the efficiency of the system. It was found that the combinations of reactance have a tangible impact on the power that flows through the inter-connector and, consequently, on the sharing of apparent power between the interconnector and the rest of the network. The total active power losses varied appreciably with the various combinations of reactances, resulting in the life-cycle cost of active power losses also varying with the combinations. The study showed that the combination needs to be carefully made, considering that such a choice can have a significant impact on techno-economic aspects of the power system.Highlights • Active power losses in power networks reduce power transfer efficiency. • Impact of coordinated choice of transformer reactances on active power losses is assessed. • Combinations of settings affect the power flow values in various lines. • Further, active power losses and costs vary as combinations of settings change. • Careful choice of reactances can enhance efficiency and reduce cost of active power losses. <![CDATA[<b>A statistical exploration of interval-deficient wind speed data for application to wind power assessments</b>]]> Gathering quality wind speed data can be time-consuming and expensive. The present study established whether interval-deficient wind speed data could be rendered useful for wind power assessments. The effect of interval deficiency on the quality of the wind speed data was investigated by studying the behaviour of the Weibull scale and shape factors as the interval size between wind speed measurements increased. Five wind speed data sets obtained from the Southern African Universities Radiometric Network (Sauran) were analysed, based on a proposed procedure to find the true Weibull parameters from an interval-deficient wind speed data set. It was found that the relative errors in the Weibull parameters were, on average, less than 1%, compared with the Weibull parameters computed from a wind speed data set that complies with the IEC 61400-12-1:2005(E) standard. This finding may contribute to time and cost reduction in wind power assessments. It may also promote the application of statistical methods in the renewable energy sector.Highlights • Sauran data is used to test whether interval-deficient wind data is useful for wind power assessments. • Simulated interval-deficient wind speed datasets provide for better insight into the behaviour of Weibull parameters as interval size is increased. • A proposed statistical procedure was used to render interval-deficient wind data useful. <![CDATA[<b>Holistic analysis of the effect on electricity cost in South Africa's platinum mines when varying shift schedules according to time-of-use tariffs</b>]]> In the past the cost of electricity was not a significant concern and was not common practice for mining companies to consider peak time-of-use (TOU) tariffs for their shift schedules. It has become more prevalent, as TOU tariffs continue increasing, to consider energy saving important. A study was carried out to analyse the mining operation of a South African deep-level platinum mine in respect of integrated load management, shift changes and TOU schedules. This was achieved by thoroughly analysing energy consumers, mine operational schedules and their interconnectedness. A specific mining system was analysed as a case study and a maximum savings scenario was determined, using the methodology formulated. The maximum savings scenario schedule change resulted in a 1.3% cost reduction. System improvements had an additional potential reduction effect of 8.4%, which was primarily the result of a reduction in compressors' power consumption. The implications of the proposed schedule adjustments necessitated a realistic scenario. The realistic scenario had an effective financial reduction of 0.7%. The realistic schedule change, however, opened the door for large system operational improvements, which could increase the reduction potential by 7.6%. The study methods described illustrate the potential implications of integrated load management and operational schedule optimisation on the power demand and cost savings in the mining industry, specifically focusing on deep-level platinum mines.Highlights • Integrated load management and schedule adjustment savings potential • Case study of a deep-level platinum mine • Significant energy reductions possible considering method discussed • Includes comprehensive literature review of load management studies and effects <![CDATA[<b>Recloser based energy exposure assessment of a distribution network</b>]]> The optimised placement of reclosers on a distribution network is known to improve the reliability of a power system. Furthermore, the protection settings on distribution systems rely heavily on the number and placement of such reclosers. This study examined the effect of using protection settings methodology with the placement of reclosers to ameliorate the damage sustained during faults on a distribution network. The aim of the study was to determine whether this 'damage control factor' should be a future consideration for recloser placement. It has been found that the determination of the number and placement of reclosers, which are the function of the energy exposure of feeder, helped to optimise the operation and reliability of a distribution network. This could benefit both energy users and energy suppliers, who often face different challenges during the fault levels on the network.Highlights • Assesses energy exposure to avoid damage to the system during a given fault conditions. • Develops the effect of using protection settings methodology with the number and replacement placement of reclosers. • Alleviate damage sustained during faults into an electrical distribution network. • Assesses an optimal relationship between the number and replacement of reclosers in the network and the energy exposure of the feeder. <![CDATA[<b>Quality control of solar radiation data within the South African Weather Service solar radiometric network</b>]]> This study reports on the performance results of the Baseline Surface Radiation Network (BSRN) quality control procedures applied to the solar radiation data, from September 2013 to December 2017, within the South African Weather Service radiometric network. The overall percentage performance of the SAWS solar radiation network based on BSRN quality control methodology was 97.79%, 93.64%, 91.60% and 92.23% for long wave downward irradiance (LWD), global horizontal irradiance (GHI), diffuse horizontal irradiance (DHI) and direct normal irradiance (DNI), respectively, with operational problems largely dominating the percentage of bad data. The overall average performance of the surface solar radiation dataset - Heliosat data records for the GHI estimation for all stations showed a mean bias deviation of 8.28 Wm-2, a mean absolute deviation of 9.06 Wm-2 and the root mean square deviation of 11.02 Wm-2. The correlation, quantified by the square of correlation coefficient (R²), between ground-based and Heliosat-derived GHI time series was ~0.98. The established network has the potential to provide high quality minute solar radiation data sets (GHI, DHI, DNI and LWD) and auxiliary hourly meteorological parameters vital for scientific and practical applications in renewable energy technologies.Highlights • Atmospheric conditions inadvertently influence the quality of ground-based measurements of solar irradiances. • South African Weather Service's solar resource database exhibits good quality and has both scientific and practical applications. • Satellite-derived irradiance compares favourably with ground measurements across South African Weather Service's solar radiation network.