Reduction of Transient Magnetic Field Due to Lightning by a Shielded Room in a Building

The protection of a control center from transient currents and voltages due to lightning is an important problem. This paper investigates the effect of a shielded room on transient currents and induced magnetic fields in the room. The experimental and FDTD simulation results in a scaled-down shielded room show that steel poles around the room can reduce the transient magnetic fields noticeably, and the magnetic fields inside the shielded room are reduced to about one-third. An on-site test in a skyscraper under construction is carried out, and the transient magnetic field in a server room of a control/data center is measured to show that it is reduced to nearly two-thirds by shielded meshes when lightning strikes the building. The FDTD simulations show a reasonable accuracy in comparison with the experimental and on-site test results, and can be applied to design a shielded room.