Popularly used impedance-based methods need voltage and current waveform as well as line impedance per unit length to estimate distance to fault location. For a non-homogenous system with different line configuration, these methods assume that the system is homogenous and use the line impedance of the most frequently occurring line configuration. Load present in the system before fault is an important parameter which affects fault location accuracy. Impedance-based methods like Takagi and positive-sequence method assume that the load is lumped beyond the fault point which may not be true for a typical distribution system. As a result, accuracy of the impedance-based methods in estimating distance to fault is affected. Another short-coming of impedance-based methods are that they are unable to identify the branch in which the fault may be located. To minimize these errors, this thesis proposes a short-circuit fault current profile approach to complement impedance-based algorithms. In the short-circuit fault current profile approach, circuit model of the distribution feeder is used to place faults at every bus and the corresponding short-circuit fault current is plotted against reactance or distance to fault. When a fault occurs in the distribution feeder, fault current recorded by relay is extrapolated on the current profile to get location estimates. Since the circuit model is directly used in building the current profile, this approach takes into account load and non-uniform line impedance. Using the estimates from short-circuit fault current profile approach and impedance-based methods, the path on which the fault is located is identified. Next to improve fault location estimates, a median value of the estimates is computed. The median is a more robust estimate since it is not affected by outliers. The strategy developed above is tested using modified IEEE 34 Node Test Feeder and validated against field data provided by utilities. For the IEEE 34 Node Test Feeder, it is observed that the median estimate computed from impedance-based methods and the short-circuit fault current profile approach is very close to the actual fault location. Error in estimation is within 0.58 miles. It was also observed that if a 0.6 mile radius is built around the median estimate, the fault will lie within that range. Now the IEEE 34 Node Test Feeder represents a typical distribution feeder and has also been modeled to represent the worst case scenario, i.e. load current is around 51% of the fault current for the farthest bus. Hence the 0.6 mile radius around the median estimate will hold true for most distribution feeders and will be used when computing the fault range for field case events. For the field events, it was seen that the actual faults indeed lie within the 0.6 mile radius built around the median estimate and the path of the fault location has also been accurately estimated. For certain events, voltage waveform was not useful for analysis. In such situations, short-circuit fault current profile alone could be used to estimate fault location. Error in estimation is within 0.1 miles, provided the circuit model closely represents the distribution feeder. / text

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ESKOM has relied primarily on impedance-based measurement protection relays for the protection of transmission lines. One of the main disadvantages of distance relays is the limited fault resistance measurement capability. High-resistance faults are characterised by low fault currents, therefore the impedance calculated would be much bigger and so the fault will appear to be beyond the protected line. The main aim of the study is to gain clear understanding of the capability of the existing relays used in Eskom Transmission network, to be able to give recommendations on the refinements to the transmission line protection philosophy required to improve future protection performance. Omicron relay tests, showed that the dynamic characteristics of the three selected relays which were tested covers more fault resistance than that of the normal static impedance and also that the effect of DC offset is negligible with regards to fault resistance measurement capability. Normally the relays have built in algorithms which are able to filter nuisance signals. Theoretical case study that compared the most used relays in Eskom Transmission was done and the results are documented. Settings recommendations to improve fault resistance coverage were deduced from the above study. Fault investigation by using digital simulations (Matlab simulations) has proven the lack of capability to operate for some impedance relays in some fault conditions, as the fault resistance sometimes moves fault impedance beyond relay characteristic even when actual . polarization of the relay is considered. Analysis of the protection performance in transmission proved that high resistance faults accounts for at least half of protection equipment performance index (PEPI) incidents. Finally the author made recommendations to improve the protection performance concerning high resistance faults. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2006.

The main aim of this project was to determine the extent to which the study of electric fields and ions in a laboratory can be used to study the electrical environment below High Voltage Direct Current (HVDC) transmission lines. The focus of the study was to set up small scale laboratory experiments and to compare these results to actual line measurements and to software simulations. The laboratory tests were undertaken at the HVDC Centre at the University of KwaZulu-Natal (Westville Campus). The software simulations that were conducted as part of this study were done using EPRI TL 3.0 and Microsoft Excel. Initially tests conducted were the measurement of the induced voltage and corona leakage current on a floating object. The next set of laboratory tests conducted was the measurement of ion current density and the electric field at ground level. The ion current density was measured with a Wilson Plate (lm2) and the electric field at ground level was measured using a JCI static monitor field meter (JCI 140) and a Monroe (257D) Portable Electrostatic Fieldmeter, with an elevated earth plane. Measurements of ion current density and electric field at ground level were also taken under an operating HVDC transmission line (Cahora Bassa to Apollo), in order to compare the laboratory measurements and simulations with real line measurements. The results have shown that the electrical parameters (i.e. ion current, induced voltages, corona currents, electric field, ion density, space charge) are higher under the negative pole as compared to the positive pole. The results of the laboratory measurements show that the ion currents under the negative polarity are almost double the ion currents that were measured under positive polarity, while the electric field under negative polarity was 20 percent higher than under positive polarity. Measurements of the electric field show that the total electric field below the line is greatly enhanced when corona generated space charge is present. The results of the EPRI TL Workstation simulations show good correlation with the EXCEL® simulations. However, there was poor correlation between EPRI simulations and test line measurements in the laboratory. The EPRI simulations show good correlation to the measured electric field values below the Cahora Bassa line. The comparison between the actual measurements on the test line and the Cahora Bassa line showed poor correlation and this was attributed to factors such as scaling, laboratory size constraints, ion concentration in laboratory, line loading and wind speeds. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2008.

The power quality performance of South African utilities has been regulated through the application of NRS 048-2 standard. The earliest edition of the power quality standard (NRS 048- 2:1996) defines compatibility levels for voltage dips in the form of annual dip limits for each voltage dip type. Actual measured utility dip performance has consistently resulted in higher dip numbers than the limits imposed in the standard. On the other hand, the dip limits were considered to be less restrictive by industrial customers. The revised power quality standard addresses the difficulties in managing voltage dip performance based on dip limits as specified in the first edition of NRS 048-2. This new philosophy does not define dip limits; instead, utilities are required to develop specific strategies to manage dip performance according to customer requirements. This research work develops an alternative approach to the management of dip performance as opposed to the application of dip limits. The study analyses measured voltage dip records for a steel-processing plant and a pulp and paper plant. The supply network for each plant is modelled to define dip influence zones as a function of fault locations. The principal results of this study are critical circuits, causes of dips, dip influence zones and the key elements of the proposed approach in communicating dip performance. The optimised approach was presented to and adopted by the customers involved. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2009.

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