Shielding of field produced by lighting type current pulse through metallic cylinders

The paper presents a method of estimation of field in a metallic conductor excited by lightning type current pulse for (i) when the return path is provided through a single conductor and (ii) when the return path is provided by the conductors forming the cage in which the excited conductor is enclosed. In the first case, analysis is carried out by replacing the current loop by an equivalent dipole, and solving the Helmholtz equation satisfied by the magnetic type Hertz vector. In the second example, when the excited conductor is enclosed in an axis symmetric cage, the entire circuit is replaced by an equivalent magnetic current loop, and the expressions for the field components are derived using the principle of duality. Analysis presented for this example is applicable to restricted case of axially symmetric cage. Numerical data on components of electric and magnetic fields are presented.