Анализ результатов натурных испытаний сосредоточенных заземлителей при импульсных токах

Abstract

The extent to which an overhead power line is protected from lightning strokes depends to a considerable degree on the values of surge impedances of line support grounding conductors rather than on their impedances at the power frequency that are specified in the Electrical Installations Code (PUE). Hitherto, the results from calculations of grounding conductor surge impedances had to be compared with the results of tests carried out with currents around 20 kA, whereas the lightning stroke current design value is 100 kA. Such an approach would be valid provided that the grounding conductor parameters were similar to those under the conditions of lightning currents. A method for calculating a rod type grounding conductor parameters under the conditions of real lightning currents is developed. The calculation results have shown that the grounding conductor surge impedance is essentially lower under lightning current conditions; moreover, its qualitative characteristics differ from those obtained from the tests. For example, with currents around 100 kA, the surge impedance increases with increasing the grounding conductor sizes instead of decreasing as is the case with currents equal to 20 kA.