Measurement and Assessment of Exposure Limits for the Static Magnetic Field Generated by Large Inductors for Railway Applications

A measurement system and a procedure for the postprocessing of the measurement data are designed and implemented for onsite characterization of the static magnetic field generated by large inductors installed along the railway infrastructure. The measurement procedure allows for simultaneous monitoring of the dc current through the inductor and the resulting magnetic flux density on a radial spatial grid, during normal operating conditions of the railway system. Linear regression is used to identify the parameters of a field model that correlates the magnetic field with the current through the coils. A field map in the space region around the inductor is derived and used both to assess exposure limits for individuals and to identify exclusion zones to prevent inadvertent harmful exposure. Particularly, the minimum distance from the coil axis, complying with the ICNIRP safety requirements for people with implanted electronic medical devices (e.g., pacemakers), is determined and related to the dc current through the filter.