obabilities of configurations were determined on the basis of data obtained from Electrical Power Utility, Рrelating to the ponents (Table 4). Table 5 shows the results of the insulation failure risk of transformer due to the backflashovers causing impinging overvoltages, as a function of configurations, dispositions and tower-footing resistances. The denominations in Table 5 have the following meanings: RTi Li is the insulation failure risk of transformer Ti due to the annual ightning discharges along the first two spans of transmission line Li; a is a disposition according to Fig. 4a; b is a disposition according to Fig. 4b.Р The risk of failure of at least one power transformer for discharges in month h and the considered six configurations are determined from the following expressions:
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