Monte Carlo procedure used for the case of a multi-conductor line above ideal and
lossy ground
Classification of ground flash locations
With n the number of events generating induced voltages larger than the insulation
level, here assumed equal to the line critical flashover voltage (CFO) multiplied by a
factor equal to 1.5, the number of annual insulation flashovers per 100 km of
distribution line Fp is obtained as:
Annex B (informative) Technical modeling and assumptions
p max 200 g
tot
F n N y
n
(B.11)
where
Fp is the number of flashovers from induced voltage per 100 km of distribution line
per year
Ng is the annual lightning ground flash density (flashes per km2 per yr)
ymax is the dimension defined in Figure B.1
ntot is the total number of flashes considered to fall in the zone of ±ymax
In order to obtain Figure 5 results, this procedure was applied to a 2 km long line matched at
both terminations with surge impedance Zo, with flash locations equidistant from the line ends,
giving a configuration equivalent to an infinitely long line.