Reduction stray loss on transformer tank wall with optimized widthwise electromagnetic shunts Atabak Najafi 1 , Okan Ozgonenel 2 , Unal Kurt 3 1 Electrical and Electronic Engineering, Ondokuz Mayis University, Samsun, Turkey atabaknajafi@omu.edu.tr 2 Electrical and Electronic Engineering, Ondokuz Mayis University, Samsun, Turkey okanoz@omu.edu.tr 3 Electrical and Electronic Engineering, Amasya University, Amasya, Turkey unal.kurt@amasya.edu.tr Abstract This paper presents an optimized widthwise electromagnetic shunt as a cost-effective way to reduce the stray losses in transformer tank walls. A 1000 KVA, 10/0.4 kV oil immersed distribution transformer is used. 3-D finite element method (FEM) has been used to analysis and study the impact of proposed magnetic shunt on the reduction of tank losses. In this paper different combinations of optimized magnetic shunt have been studied. The paper compares the performance of proposed optimized magnetic shunt with the available conventional shunts. Considerable reductions in stray losses on the transformer tank wall are obtained by using the combinations of electromagnetic shunt with optimal thickness. Compared with aluminum shields and conventional electromagnetic shunt, the proposed optimized widthwise magnetic shunt reduces stray losses by 13.96%. 1. Introduction Stray losses in the distribution transformers tank wall, due to high eddy currents near the low voltage bushes have received relatively little attention. Nowadays, we have seen those contributions and suggested the use of small inserts in the transformer to reduce the stray losses in tank walls [1]. In that paper, two-dimensional (2D) finite-element have been used to estimate the reduction of stray losses in transformer tank wall with low-cost plate inserts. In order to reduce the overheating of the flange–bolt region the copper links have been used to ensure the connection of both the cover and tank body in [2]. The failures that caused by the hot spot in transformer tank wall are included in the 13% of the total failures that happens in power transformers due to other causes [3]. Accordingly, it is important to analyze the growth of leakage flux and stray losses in the tank walls. To reduce the stray losses in the region of the tertiary voltage bushings (TVBS) of the transformer an L-shape non-magnetic stainless steel insert (SSI) has been proposed in the literature [4]. A T-shaped stainless steel plate was used in [5] for the elimination of hot spots and reduction of eddy current losses in the cover plates of distribution transformer. Based on results of that paper, T-shaped plate significantly reduces the load loss. C-shape electromagnetic shield has been proposed in [6] to protect a clamping frame of stray fluxes produced by high current leads (HCLs) of low voltage bushings. In [7], the influence of magnetic shunt geometry on the transformer leakage field is examined. The shape optimization of power transformer magnetic shunts, causes the significantly reduction in stray losses in the tank wall. Suitable magnetic shunts placed on the walls of the transformer tank, causes the increase of magnetic leakage field and also can increase the winding leakage inductance [8,9]. The stochastic-deterministic approach is used in [10], to optimal placement of a wall-tank magnetic shunt. In our previous article [11], leakage losses and leakage currents in the structural component of the transformer based on the surface impedance method have been carefully investigated. So, this paper presents the optimized magnetic shunt to reduce the stray losses in transformer tank wall, with taking into account the results of previous article. This paper is organized as follows. Section II briefly presents the estimation of stray losses on transformer tank wall. In the Section III, conventional magnetic shunt has been used in order to reduce the stray losses on transformer tank wall. Section IV introduced an optimized widthwise magnetic shunt to reduction of stray loss on transformer tank wall. Section v concludes this paper. 2. Calculation of stray losses in tank wall based on finite element method without magnetic shunts FEM is a numerical technique to solve the differential and integral equations such as electromagnetic, magneto static, thermal conductivity, solid and structural mechanics and fluid dynamics. The basic idea of FEM is sub dividing physical problems with complicated differential equations into a number of sub-problems and dissolving these equations in the linear systems [7]. In order to calculate the stray loss in the transformer tank wall, using of vector potentials methods need to a great deal of elements (mesh) whereas the skin depth of the tank wall is small when compared with their geometry dimensions. Because of this, the magnetic field does not penetrate deep into the conductor. In this paper for accurate calculation of stray loss, the surface impedance boundary condition with the following relation between the tangential component of the electric and magnetic fields is applied [11].