Magnetic Field Problems when Planning Indoor Distribution Substation with Dry-type Transformers

T. Keikko, T. Sauramäki, S. Kuusiluoma, and L. Korpinen (Finland)


Magnetic Fields; Indoor DistributionSubstation; Dry-type transformer.


The need for magnetic field reduction in some indoor distribution substation cases comes from disturbances caused by power frequency magnetic fields in some sensitive appliances and EMC standards, which set immunity levels for magnetic fields. The aim of this work is to study magnetic field problems when planning a MV/LV indoor distribution substation with dry-type transformer. Indoor distribution substation in this case was in design stage, thus final form of the secondary conductor system was not decided. The only claim for the indoor distribution substation was a dry-type transformer, that was required because the indoor distribution substation was above a bomb shelter. Dry-type transformer is known to cause higher magnetic fields than oil insulated transformer, thus magnetic fields were decided to be reduced in the new indoor distribution substation construction. To support the planning, magnetic fields in similar indoor distribution substation structure were measured and calculated to better understand the need for the reduction. The difference between highest measured and calculated magnetic field results was 12.0% at the height of 1 meter. Considering present study, magnetic fields were intended to reduce with placing secondary cables on the floor of the substation, and installing aluminum plate above the transformer.

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