Analysis of 500Â kV OHTL polluted insulator string behavior during lightning strokes

In this paper, the lightning overvoltage in the El-Kuorimate - Cairo 500-kV transmission line single circuit is discussed. The leakage current and its harmonic spectrum on clean and polluted 500-kV string insulators are determined under normal condition and lightning strokes. Furthermore, the relation between back flashover and insulator surface condition are discussed under different magnitude of lightning strokes. The results show that the leakage current, thermal losses magnitudes in case polluted insulator are higher than in case clean insulator by about 97.2%. For polluted insulator, less lightning strokes peak will increase leakage current to above 60 mA, and lead to serious insulator flashover faster than clean insulator. This study based on an equivalent electrical model by using Alternative Transients Program (ATP-EMTP) software.