An accurate numerical method to compute the effects of the protections against direct lightning on charged liquid tanks

This paper presents a method for the simulation of lightning protection systems for charged oil tanks. The presented procedure allows to compute the reduction of the electric voltage and field at the inner of the container due to the adopted protections. Three kinds of lightning protection systems are considered in which the distances between the down conductors and between the interconnecting rings and the container are varied. The ionization phenomena in the soil is considered and represented by a nonlinear current-dependent electrical model, function of the electrode´s shape and the ground resistivity. The analysis of the equivalent lumped-constant network is carried out by the circuit simulator SPICE. The obtained electric voltage values at the surface of the vessel are used as boundary conditions for the field equation system valid at the Inner of the charged oil metal tank. The reductions of the electric voltage inside the vessel are analyzed in order to detect possible hazards and to identify the better lightning protection system. In absence of liquid, the proposed method is validated against measurements. The agreement is good, demonstrating that the proposed method can accurately predict all the features in the simulation of lightning protection systems for charged oil tanks.