2 BACKGROUND
Following the development of the simplified model of the last step of the lightning
stroke by Wagner [1, 21, Young [3] developed the geometric model (GM) with the
primary and indeed sole purpose of showing that shielding angles should be
decreased as tower height increases. Prior to this investigation, shielding angles of
about 30' were used with success on all lines for which tower heights were in the
range of 80 feet (24meters) [4, 51. For example, a Philadelphia Electric 230-kV line
with 80-foot towers had a shielding angle of 35' and a flashover rate of 1.4/100 mileyears,
and an Ontario Hydro 230-kV line with 80-foot towers had a shielding angle
of 32' and a flashover rate of 0.33/100mile-years. A Pennsylvania Water & Power