Contents 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.
