3D Finite Element analysis of magnetic shunts and aluminum shields in clamping frames of distribution transformers

This paper presents a 3D Finite Element (FE) analysis of stray losses in core-type distribution transformers, where a magnetic shunt and a C-shape electromagnetic shield are utilized to protect a clamping frame of stray fluxes produced by high current leads (HCLs) of low voltage bushings. A real clamping frame of a three-phase core-type oil distribution transformer is utilized to study the electromagnetic behaviour of the shields and magnetic shunts. The electrical steel of the magnetic shunt is modelled utilizing anisotropic properties and aluminum is employed for the electromagnetic shield. Impedance boundaries were utilized in the frame and in the aluminum shield to compute the stray losses. Stray losses in the clamping frame are computed for three cases: 1) frame without any shielding method, 2) frame with a magnetic shunt, and 3) frame with a C-shape aluminum shield. The current in the HCLs were varied from 2 kA to 20 kA. The results obtained between the use of electromagnetic shield and magnetic shunts in frames of distribution transformers are also discussed in this paper.