Interlaminar Magnetic Flux Assessment of a Transformer Core Measured by an Extra-Thin Printed Foil Detector

Abstract

Transformer cores represent complex 3-D magnetization systems with balancing off-plane fluxes, normal to magnetization plane. Therefore, for optimizations of core performance, not only the information about the local induction distributions in the plane, but also perpendicular to it is highly essential. The conventional sensors for detections of off-plane inductions $B_{Z}$ ( ${t}$ ) are either of very high thicknesses, causing significant air gaps between laminations, or require extremely laborious preparations and are not reusable. In this paper, we developed an extra-thin ( $\approx 50~\mu \text{m}$ ), reusable foil detector with handles for easy and precise insertion and positioning in the interior of a laminated core. The detector was assembled by a low-cost 3-D printer, equipped with a micro-dispersing system for printing of conductive ink, controlled by in-house developed software. The manufactured foil sensor, due to its high mechanical stability, enables detections of off-plane flux at many different locations within an entire core. The detector was effectively tested in a three-phase model transformer core, stacked from three packages of different width. The results prove the important role of sensor thickness for precise detection of off-plane induction. Peak induction $B_{Z}$ increases in a strong non-linear way with increasing nominal magnetization $B_{\mathrm{ NOM}}$ . Maxima of $B_{Z}$ arise close to border regions of packages. $B_{Z}$ ceases for $B_{\mathrm{ NOM}} T, favoring low level of audible noise.