The paper introduces the concept of critical currents curve and uses it to assess the lightning performance of high voltage overhead lines. The line total flashover rate (ND) was selected to qualify the lightning performance of the line. The method developed to evaluate the line total flashover rate is a combination between numerical simulation in ATP-EMTP (which compute the voltage applied to the insulator strings during a lightning strike), and dedicated statistical techniques conceived to evaluate the occurrence probabilities for flashover or back flashover events. The method can be applied to establish an order of merit among different solutions intended to improve the lightning protection of the line, including line surge arresters (LSA).

Keywords: Lightning protection, Insulation flashover, Critical current, Total flashover rate, Line surge arrester