This thesis discusses the results of an investigation that was initiated in January 1996 to determine the root cause of the increasing fault trend in respect of transient earth faults on the 275 kV transmission grid in KwaZulu-Natal, South Africa. Historically it was thought that the persistently poor performance of this network was caused by pollution faults. This network was reinsulated with silicone composite insulators, and cane fire as well as veld fire management programmes were introduced. These projects did not result in a consistently decreasing fault trend on this 275 kV transmission grid. The burn marks caused by the power arcs, which were identified in this study, appeared to indicate that air gap breakdown was occurring. Birds were also observed in close proximity to the faulted towers. Consequently it was thought that bird streamers caused the transmission line faults. Welded rod bird guards designed to prevent bird streamer faults were installed on eighteen 275 kV transmission lines. The accumulative length of these transmission lines is 932 km. The implementation of this initiative coincided with a 73% reduction in the total number of transient earth faults. This improvement in performance indicates a strong statistical correlation showing that a large number of the transient earth faults on the transmission grid are related to bird streamers. Bird streamer induced faults were identified by means of the following diagnostic techniques: • Burn mark analysis • Time-of-day analysis Bird streamer line faults have been observed on I string, V string and strain jumper assemblies on the 275 kV power lines. However, on the 400 kV power lines bird streamer faults have only been observed on V string assemblies. Experimental work involved simulated bird streamers and determining the minimum flashover distance for AC system voltages. Electric field measurements by means of a capacitive probe were undertaken at the ground plane. The electric field measurements at the ground plane under bird streamer intrusion confirm that if the streamer is moved away from the live tower hardware, the electric field enhancement at the ground plane decreases below the background streamer propagation field. This case study determined that in order to prevent bird streamer faults the bird streamer must be moved away from the live tower hardware. The distance it must be moved is at least 900 mm for 275 kV power lines and 1 100 mm for 400 kV lines. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2001.

The Eskom Transmission Network experiences an exceptionally high number of line faults, the cause of which, may not be correctly identified. This thesis analyses a number of all the possible factors responsible for causing these faults. The objective is to assign probable causes of these faults and that the correct preventative or corrective measures may be planned. The percentage of unexplained line faults is estimated to be 35 % of the total system faults. It is important for the Transmission Group of Eskom to minimise the number of faults. Major efforts to minimise identified faults such as bird streamers, veld fires, sugar cane fIfes, lightning and a hypothesised light pollution, light wetting mechanism has been undertaken by the transmission grid authority. This thesis presents an analysis of the statistical data of the unknown faults (unknown faults is defined as lines that trip due to a reason which could not be identified) that has been undertaken. This analysis takes into account a number of categories of causes of line faults. The period, for which the performance of the lines was analysed for was the years inclusive of 1993 to 1997. The investigation has focused on the identification of the under-performing lines of the main Transmission Network. The identified poorly performing lines have been compared with each other from the perspective ofthe following variables: • Region • Voltage (System Voltage) • Climatic Data Line faults - Time ofDay analysis • Line Faults - Time of Year analysis. The analysis indicates that the majority of unexplained flashovers occur between 22 :00 and 07:00 the following morning (Britten et al, 1999). Almost all of the under performing lines in South Africa fall in the sub-tropical/humid climatic area. All the lines studied are insulated with standard glass disc insulators. The analysis indicated that most of the unexplained line faults occur during the months when the seasons change, e.g. from autumn to winter. The analysis further indicates that most unexplained line faults occurred during the months of April to May and August to September. Of note is that during the period of this investigation bird guarding was performed on some lines. Installing bird guards may reduce those line faults that are caused by bird streamers. However, the bird pollution (deposited on glass disc insulators) that is not washed off at the same time as the bird guard installation may cause the line to trip due to the combination of the pollution and wetting resulting in a pollution type flashover. This is a possible cause of some unexplained line faults that occur from April to May. Bird streamers are also identified as the most probable cause of the unexplained faults which occur during the late evening periods (22:00 - 00:00). Pollution (with wetting) during the early morning periods may result in faults for the period 00:00 to 02:00. Line faults in the early morning periods (04:00 - 7:00) could be due to bird streamers or pollution and wetting, depending on the time of year in which the faults occurs. / Thesis (M.Sc.)-University of Natal, Durban, 2003.