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Microwave relay stations are key components in controlling power grids and maintaining their stability, but lightning strikes to the stations may cause faults, malfunctions, or even physical damage to microwave radio equipment. To protect equipment from lightning, it is necessary to predict surge phenomena in a microwave relay station, and design effective lightning protection methodologies. Recently, numerical electromagnetic field computation methods to solve Maxwell's equations have entered widespread use for analyzing surge phenomena in 3-D structures such as buildings and towers and in grounding structures such as grounding grids. In this paper, we apply the finite-difference time-domain (FDTD) method to the surge analysis of a microwave relay station. First, to validate the applicability of the FDTD method, we set up a reduced-scale model of a microwave relay station. Using this model, we measured the distribution of the currents flowing through the station and compared the measured results with those simulated by the FDTD method. Second, through FDTD-based surge simulations, we analyzed the effects of the reinforcing bars of a building, the route of the ground wire of a waveguide, and the layout of a deep earth electrode on the lightning current distribution. [ABSTRACT FROM AUTHOR]