Reduction of stray losses in Tertiary Voltage Bushings in power transformer tanks

This paper presents an analysis and computation of stray losses in the tank cover of a 75 MVA three-phase core-type transformer. Stray losses in the region surrounding high current bushings are estimated using 3D Finite Element (FE) simulations. In the considered region the stray losses are high and its reduction is important to avoid the presence of hot spots in the tank cover of power transformer. In this paper, an L-shape non-magnetic Stainless Steel Insert (SSI) is utilized to reduce the stray losses in the region of the Tertiary Voltage Bushings (TVBs) of the transformer. Stray losses in the tank cover are estimated for a level of overload of 30% considering two cases: 1) When there is no SSI and 2) When the SSI is considered. The reduction of stray losses in the tank cover of power transformers helps to avoid the presence of dangerous high temperature spots. Hot spots can degrade the transformer oil and they can produce a potential failure of the equipment during operation.