Mitigation of Low Frequency Magnetic Field Emitted by 10/0.4 kV Substation in the School

Abstract

The article is related to mitigation of magnetic field emitted by a 10/0.4 kV substation located in a primary school in Belgrade, Serbia. During the first testing in the classroom located directly above the substation, the measured values of magnetic flux density significantly exceeded the reference level of 40 μT prescribed by Serbian legislation, and it was concluded that the field levels at the transformer rated load could exceed the reference level of 100 μT prescribed by European Council Recommendation 1999/519/EC. For that reason, the 0.4 kV busbars located near the ceiling of the substation were removed and replaced with cables that were placed on the floor of the substation. The testing was repeated and the measured values as well as the values at the rated load were lower than 40 μT. However, above the locations where the cables were connected to the transformer and to the 0.4 kV switchboard, the field levels were still higher than in the rest of the classroom. The focus of this article is to analyze different solutions based on passive shielding for the reduction of magnetic field in these two areas. Seven solutions based on conductive shields with different geometries are analyzed. The substation and the shields are modeled by using appropriate software tools to determine which shield is the most effective. In the case of Solution 7, the lowest field values were obtained. The highest value of magnetic flux density in this case was 6.95 μT at the transformer rated load.