Calculations of magnetic fields from indoor distribution substation busbars

Abstract

Magnetic fields around the 20/0.4 kV transformer busbars and their shielding was studied with different calculation methods. Three calculation methods were used. In addition, the sensitivity and suitability of the approximation of shielding effectiveness was studied. First the general situation (busbars positioned horizontally) was calculated with two programs which used FEM (finite element method) and with analytic method. Then, magnetic shielding with aluminium, copper and iron was studied. Thermal effects of the enclosing were considered for aluminium shield. The best shielding material was copper, but considering economic and technical aspects, aluminium was the best choice. Approximated shielding effectiveness calculations were quite accurate for highly conductive materials, aluminium and copper. The differences with the approximated method and finite element method were 1.8 dB with aluminium shield and 2.2 dB with copper shield. Calculations did not work for ferromagnetic iron.