Consider the distribution system given in Problem 7 and assume
that most transformers are shielded from lightning to some extent
by buildings or trees. Therefore, use a “reasonable estimate” of
70% for the average shielding factor. It is assumed that the total
expected number of strikes to the transformer poles is 174
strikes/year and that 5% of lightning return strokes exceed 100 kA.
Determine the following:
(a) The total number of strikes per year to the transformers if
shielding is taken into consideration
(b) The total number of expected transformer failures per year due
to lightning
(c) The annual expected transformer failure rate due to
lightning
(a)
answer = (70/100)*174 = 121.8 strikes per year
(b)
answer = (5/100) * 121.8 = 6.09 failures per year
(c)
answer = 6.09/174 = .035
in percentage = .035*100 = 3.5 %
Consider the distribution system given in Problem 7 and assume that most transformers are shielded from lightning to some extent by buildings or trees. Therefore, use a “reasonable estimate” of 70% fo...