Numerical Simulations of Lightning Surge Responses in a Seismic Isolated Building by FDTD and EMTP

Abstract

Current distribution and overvoltages in a structure of a seismic isolated building struck by lightning are analyzed by a Finite-Difference Time-Domain (FDTD) method and by the Electromagnetic Transients Program (EMTP). The simulated results by the FDTD method show that the voltage at the first floor, which is an important factor of a design of building installation, shows a damped oscillatory wave. The transient overvoltage is caused by the multiple reflections within the structures and the resonance between a stray capacitance of the structure and an equivalent inductance of the bonding wire, which electrically shunts a rubber insulator installed for dumping earthquake tremor. The investigation shows that the transient response can be expressed by a lumped-parameter equivalent circuit. Two numerical models for circuit analysis method are proposed in this paper. A multiphase model reproduces a distribution of currents flowing through vertical pillars by mutual couplings between the pillars. A single phase model is obtained by a simplification of the multiphase model and gives the voltage at the first floor. The calculation time is remarkably reduced compared to that by the FDTD method. The accuracy of the models is discussed in comparison with the results obtained by the FDTD method.