The detection of fires under high voltage transmission lines.
Fires generate heat and propel burning material into the air above and around the core of the fire. Fires under power lines reduce the breakdown strength of the air insulation due to the influence the heat and particles have on the electric field surrounding the conductors. The result can be flashovers and undesirable power supply interruptions in the electrical transmission network with a considerable impact on Eskom's 275 kV and 400 kV MTS (main transmission system) networks. Eskom typically experiences a loss in sales, a reduction in the quality of the power supplied to consumers and disgruntled consumers who in turn experience financial losses due to a loss in production. In this thesis, the high frequency characteristics of corona and electrical discharges generated by the fire phenomena are studied. The influence of the operating voltages on the electric fields, the potential of different media to initiate ionisation and comparison of conductor construction (bundling and diameter) are all considered in the measurement of high frequency signals in the range of frequencies available in the tuned circuits connected to power lines. The propagation of these high frequency signals is studied both in isolation of other sources of high frequency signals (within controlled laboratory conditions) and in the real environment adjacent to all other interfering sources. Finally the fingerprinting of the varying high frequency signal patterns associated with fires is considered with a view to implementing an operational early detection device. Early detection of a fire allows the utility to understand the source of a system fault, manage it effectively and if possible pre-empt possible failure by means of appropriately applied standard operating guidelines (SOG) to minimise the impact.
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