SHIELDING OF FIELD PRODUCED BY LIGHTNING TYPE CURRENT PULSE THROUGH METALLIC CYLINDERS

The paper presents a method of estimation of field in a metallic condu ctor excited by lightning type current pulse for (i) when the return p ath is provided through a single conductor and (ii) when the return pa th 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 He lmholtz equation satisfied by the magnetic type Hertz vector. In the s econd example, when the excited conductor is enclosed in an axis symme tric cage, the entire circuit is replaced by an equivalent magnetic cu rrent loop, and the expressions for the field components are derived u sing the principle of duality. Analysis presented for this example is applicable to restricted case of axially symmetric cage. Numerical dat a on components of electric and magnetic fields are presented.