Scielo RSS <![CDATA[SAIEE Africa Research Journal]]> http://www.scielo.org.za/rss.php?pid=1991-169620190003&lang=pt vol. 110 num. 3 lang. pt <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>Guest Editorial</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1991-16962019000300001&lng=pt&nrm=iso&tlng=pt <![CDATA[<b>Supply and Demand Side Flexibility Options for High Renewable Energy Penetration Levels in South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1991-16962019000300002&lng=pt&nrm=iso&tlng=pt This paper presents a study on supply and demand side flexibility resources assessed for two South African power system expansion scenarios with high penetrations of variable renewable energy. The demand response opportunities associated with residential water heating as well as plug-in electric vehicles are included in order to demonstrate demand-side flexibility options. Supply-side options are based on existing and optimally deployed new-build generation technologies. The scenario based results indicate that the combination of cost reductions in wind, solar PV and stationary storage (batteries), results in economic deployment of batteries in South Africa. Battery storage complements flexibility provided by demand response and supply-side options. A notable outcome is the displacement of gas-fired turbines by batteries when assuming cost reductions for batteries in the future. Finally, despite the extensive deployment of battery storage, a significant 55 TWh of energy from solar PV and wind is curtailed. Therefore, effective sector-coupling could make extensive use of this curtailed energy in a number of ways to be identified as part of future research. <![CDATA[<b>Electrical Model of Phase-to-Woodpole Bird Electrocution</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1991-16962019000300003&lng=pt&nrm=iso&tlng=pt The electrocution of large birds such as eagles and vultures when making simultaneous contact between a phase conductor and the top of a pole on medium voltage woodpole distribution lines is addressed. System (phase-to-phase) voltages of 11 kV, 22 kV and 33 kV are covered. This phenomenon has been investigated by measurement of the resistance of poles used in the field, as well as measurement of the impedance of recently deceased birds. This has previously been used to compile a simple electrical model for 22 kV systems. This paper compiles a detailed model that is used to estimate the risk posed to large birds by this mode of electrocution for all three voltage levels. The results show that only a few scenarios exist whereby a bird may be at risk, which ties in with field experience. Details of how the wood and bird resistance was measured are also included, as are details of calculations performed. <![CDATA[<b>Measured and simulated time-evolution PD characteristics of typical installation defects in MV XLPE cable terminations</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1991-16962019000300004&lng=pt&nrm=iso&tlng=pt In condition monitoring of medium voltage (MV) power cable accessories, there are still challenges in the recognition of partial discharge (PD) defects. In the present paper, typical installation defects were deliberately introduced into MV XLPE power cable terminations. Accelerated ageing under PD activity was achieved by applying voltage at elevated frequency for 900 hours. At suitable time intervals, off-line PD measurements were conducted for each test specimen at 50 Hz test voltage. The results show that the initial PD signatures in the form of Partial Discharge Phase-Resolved-Patterns (PDPRP) are unique for each defect type. The signatures in turn evolve uniquely under continuous voltage application. A modified 3-Capacitor PD model based on the physiochemical processes in the discharge area was implemented in MATLAB Simulink™. The measured initial PD characteristics and the subsequent time-dependent changes were interpreted by comparison with the computer numerical simulation results. It is confirmed that the conductivity of the discharging surface area as well as the voltage at which the cavity breaks down, both change with ageing under PD activity, are the dominant parameters that influence the time-evolution of the PD signatures. Furthermore, the geometry and ventilation of the discharge area is a function of the installation defect type and therefore each defect type gives a unique PD signature. The ability to recognise installation defect through PD tests immediately after installation as well as during the course of on-line PD monitoring is desirable in condition monitoring of power cables. The findings strengthen the credibility of PD diagnosis as an after-installation test as well as in-service condition monitoring technique of MV power cable terminations. <![CDATA[<b>Distribution Pole Monitoring Using Magnetic Field Characterization</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1991-16962019000300005&lng=pt&nrm=iso&tlng=pt This paper outlines methodologies for monitoring the supporting structures of distribution power lines by characterizing the rotating magnetic field established by the current carrying conductors. This is achievable since the resultant magnetic field is a function of phase currents and pole geometry. The resultant magnetic field vector (measured using 3-axis magnetic field sensors) rotates with time and forms an ellipse. The formation of an ellipse provides an expedient mechanism for data compression and comparison between pole geometries, which is achieved by wireless communication between two adjacent poles. A detected change in geometric state between poles can be sent to the substation at the end of the line. This data can be used to detect, locate, mitigate, prevent, or repair damage caused by a fallen power line. An experiment was performed to demonstrate the working principal of the single-sensor design methodology. A prototype instrument is under development to be field tested. A simulation was performed to show the effects that nearby metal structures have on the resultant magnetic field. The solution is realizable through the low-cost implementation of existing technologies and practices. A preliminary version of this paper was presented at the South African Universities Power Engineering Conference, SAUPEC 2018. <![CDATA[<b>A Comparative Study on High-Voltage Spacer-Damper Performance and Assessment: Theory, Experiments and Analysis</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1991-16962019000300006&lng=pt&nrm=iso&tlng=pt This paper reports on the experimental analysis of commercially available spacer-dampers used to suppress wind induced Aeolian vibrations on transmission lines with bundle conductors. Three spacer-dampers w'ith different bushing-shaft designs, overall mass, and fabrication technology have been selected for this evaluation. Spacer-damper performances have been examined in a temperature-controlled testing facility by measuring their frequency and force-displacement response, in order to determine whether the bushing-shafting design meets the prerequisite to withstand the undesirable motions of the coupled sub-conductors. The tests showed that the hysteresis force-displacement test gives a better indication of an efficient spacer-damper and its energy absorption but is not consistent enough to describe the entire list of needed features against wind induced vibrations, i.e., its mobility or impedance, admittance and receptance vs. frequency. However, to investigate the working range of the spacer-damper in terms of the relative amplitudes between the frame and the arm of the spacer-damper, an analytical and experimental sensitivity model was developed. Analytically, the sensitivity models are based on the partial differential of an explicit dynamic model of the arm-rubber-frame and arm-rubber while the transfer functions have been experimentally established from the identification technique of force response frequency. In both approaches, the same conclusion was observed, although, analytically some assumptions have been made. In addition, a sensitivity analysis of the energy absorbed with variation of the ambient temperature was conducted during the hysteresis test. <![CDATA[<b>Maximum Demand Comparison of Aggregated Load Profiles for Vertical and Horizontal EWHs Due to a Fixed Draw Event</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1991-16962019000300007&lng=pt&nrm=iso&tlng=pt This paper shows a comparison of the vertical and horizontal tank orientation and the associated maximum demands from synthesized aggregated load models for various grid scenarios. Aggregated load profiles are produced by replicating a 50 litre (50% capacity) draw event for a 100-litre dual-mountable electric water heater (EWH) for each orientation. A total of 416 load profiles are produced containing 208 sets of horizontal and vertical aggregated profiles for comparison. Two factors are varied, (1) total EWH population from 1 to 1 million in various increments and (2) peak time window for initiating EWH draws ranging from 1 to 12 hours, where a Gaussian distribution is applied to the times each EWH starts participating on the grid. The resulting aggregated load profiles show that EWHs in the vertical orientation produce a higher aggregated maximum demand whereas the horizontal orientation can have a much lower aggregated maximum demand to a ratio of 0.58. A maximum demand ratio Ph/Pv of 0.80 is determined for a scenario similar to normal grid operation for a peak time window of 4 hours. The significance of this work is to quantify the difference in maximum power demand of a population of EWHs due to tank orientations in a controlled simulated environment.