Keywords:Solar flare, GIC, FDTD method
During geomagnetically disturbed conditions, geomagnetic induced currents (GICs) can cause severe damages on the power grid. Recent observation has revealed that extreme solar flares may occur in our Sun. If such an extreme solar event occurs, the impact on our life would be catastrophic. Under this circumstance, the need for GIC research is increasing for better understanding of the cause of the GIC. Previously, many researches have calculated the GICs for given geomagnetically induced electric field (GIE) by assuming an equivalent electrical circuit. The GIE is often calculated by the temporal variation of the magnetic field, and is assumed to be independent of the existence of the transmission line. However, the existence of the transmission line may alter the ambient electric field including GIE because the conductance of the transmission line is extremely high in comparison with the ground conductivity. We calculated both the GIE and GIC simultaneously by using 3-D Finite-Difference Time-Domain (FDTD) method to investigate the interaction between the ground and the transmit line. A plane of the uniform electric field is placed at 100 km altitude, and the amplitude of the source electric field varies sinusoidally with a period of 1 sec. Due to the limitation of the computational resource, the thickness of the transmission line is set to be 2 km. For this particular study, we tested (1) different conductance of the transmission line, (2) different conductance of the ground, (3) different thickness of the transmission line, and (4) different distance of the transmission line. In our simulation, when the conductivity of the transmission line increases, GIC increases linearly until a particular threshold. When the conductivity of the transmission line exceeds the threshold, GIC is saturated, and is less sensitive to the conductivity of the transmission line. We discuss the relationship between GIE and GIC in terms of the interaction between the ground and the transmission line on the basis of the simulation results.