Sputtered search coils for flux distribution analyses in laminated magnetic cores

Abstract
Localised regions in a transformer core, such as joints, are well known to have distorted magnetisation waveforms. Earlier, 30-100µm thick search coil wires have been introduced in the joint regions to investigate the nature of flux distributions which show high relevance for the core's power losses. This thickness exceeds considerably the typical interlaminar spacing of some µm, thus affecting the interesting distribution of flux. In the present work such artifacts were overcome by means of only 1µm thick copper search coils sputtered on lamination surfaces. Crucial problems of galvanic contacts between the search coils and the SiFe material were met by 0.25 µm thick SiO2 depositions prior to sputtering. Practical applications were performed on a linearized model of a transformer joint region. The relevance of results was checked numerically using 2D finite element method. The results show that the take-over of flux may arise in a locally most concentrated way, i.e. in sheet end regions of less than 1 mm length. Air gap bridging sheet regions prove to be strongly saturated, with induction values up to 2.6 T.