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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/5276 |
| Date | January 2001 |
| Creators | Taylor, Paul. |
| Contributors | Hoch, Derek A. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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