Currents and Electric Field Characteristics at Structure during Direct Lightning Strike and Issue of Separation Distance

In present study, distributions of currents, potentials and electric field intensities at structure during direct lightning strikes are simulated (Comsol Multiphysics, frequency domain). Conditions at down conductors and inner components of the structure are explored for the cases of a simple 5-m vertical air-termination rod and of a frame structure (5x6x10 m) having four down conductors. As inner components of the structure, there were considered 4-m or shorter vertical conductor (connected at bonding level or isolated) and rectangular loop (1x3 m, single and of grid type). Simulations were performed for separation distances (SD) selected according to standards and for other determined values, for the first (10/350 mu s; 1/200 mu s) and subsequent (0.25/100 mu s) lightning strokes current impulses, for ideal and real ground (permittivity of 15 and conductivity of 1.10(-3) S/m), for chosen materials (including permeability mu not equal 1) and radiuses of the conductors (4 to 30 mm). Current distributions at structure components and induced currents in loops are compared to values estimated according to standards. Obtained scalar electric potentials (thousands of kV) and electric field intensities (tens and hundreds of kV/cm) at conductors are extremely large, both for first and subsequent strokes, especially for real ground, and can cause significant ionization processes in dielectric media. These issues can be considered for SD determination.