A new technique for reducing extremely low frequency magnetic field emissions affecting large building structures

Abstract

When large structures such as residential compounds or public buildings are under the influence of extremely low frequency (ELF) magnetic fields, such as the one generated by a system of railways fed by 16.67 Hz, standard methods of designing shielding structures by numerical methods usually fail. The latter can be explained by the difficulty posed in the computing process by the large aspect ratios involved due to thin layers of metal (a few millimetres or centimetres) in contrast to the large dimensions of the affected structure (several tens of meters). In some cases one has to utilize special approximations such as surface conductivity, which are not easy to handle when the designed shielding structure is clearly three -dimensional. Other alternatives such as experimentation in situ are very costly. Here, a new technique is presented of mitigating the field by using three-dimensional propagation of induced currents optimizing the field reduction factors and minimizing the cost of shielding material. The particular designing method is a hybrid of numerical simulations combined with lab experimentation using scaled models of the large structure. The method is rather cost-effective and flexible as various designs can be easily tested. Results are presented in the form of magnetic field values, at various locations in the buildings, before and after this mitigation technique is applied.

Some 2D–3D aspects of shielding of longitudinal sources of extremely low frequency magnetic fields

“…Unfortunately, the cross-sectional dimensions of the ribbons compared with their length yield huge aspect ratios making it very difficult to handle this problem numerically. Thus an experimental method was applied, which is based on the use of scaling rules (Chadwick et al 1998;Salinas et al 2007).…”

“…Recent studies on AC railway powering (Buccella et al 2004;Salinas et al 2007) are also related to this type of source. In this article, numerical and experimental methods are applied to study some practical properties of the shielding of the magnetic field emitted by these sources.…”

Practical solutions for ground grid circulating currents caused by air‐core reactor

“…Many accurate calculation methods for evaluating the magnetic flux of the air-core reactor are developed in the literature. They include analytical, semi-analytical and numerical methods [7][8][9]. Although the corresponded research works considerably focused on the optimisation effect of the magnetic field [9], they ignored the direct effect on the other equipment.…”

Research on Distribution and Shielding of Spatial Magnetic Field of a DC Air Core Smoothing Reactor

“…Study on the magnetic field of air core reactors is mainly concentrated in the area of AC air core reactors. The scaling rules and the equivalency of the scaled experimentation have been verified [9][10][11][12]. The magnetic field distribution of the air core reactor in a substation has been tested and numerically calculated [13].…”