II. ELECTRICALEQUIVALENTMODEL
The cylindrical metal structure can be considered as a
grid of conductors electrically connected to each other
forming a cage as shown in Fig. l(a). The cage has
been simulated by means of an electric equivalent
network. The equivalent model takes into account that
the lightning current flowing into the conductors, as
an effect of a direct lightning stroke, presents
significant harmonic components not exceeding 10
MHz. This upper limit does not allow the
representation of conductor elements using simple
lumped parameters. The condition
were 1 min is the minimum wavelength associated to
the maximum frequency of the spectrum and D is the
maximum dimension of the structure, is not generally
observed and it is therefore necessary to use an
equivalent network representation with distributed
parameters. Each conducting element has been divided
into an appropriate number of elementary cells in
order to minimize the discretization error and to bear
in mind the propagation phenomena. Each cell is
made up of resistances and inductances placed in