Passive and active shielding of power-frequency magnetic fields from secondary substation components

The paper presents a methodology based on effective techniques to mitigate power frequency magnetic fields originating from secondary substations. The field from sources such as transformers, busbars and cables was studied. Shielding was performed at the sources rather than at the affected areas. Experimental, analytical and numerical methods were used. It was observed that a shielded transformer gives a good field reduction when contrasted to an unshielded one. The field of busbars and its mitigation was analysed using finite elements. Geometry and shielding materials were varied, it was found out that open shielding is more effective when using conductive rather than ferromagnetic materials. Two 1-phase coils, fed by low voltage and low current, mimicked the source performing active compensation of the 3-phase busbars.