Abstract

In large power transformers, more than 20% of the total load loss is the stray loss in structural components. The biggest part of stray loss takes place in the transformer tank. As the ratings of transformer increase, the stray loss problem also increases significantly resulting in higher temperatures and local hot spots that reduce the transformer life. Due to the heavy current flow in Low Voltage (LV) windings, the strong magnetic flux linking the transformer tank causes over heating of the tank walls and particularly, if there is loose contact between the wall and tank cover it may leads to hot spot in flange bolts which are near the high current bushings of transformer. So in order to ensure a good contact between cover and tank body we use copper links thus significantly reducing the overheating of flange bolt region. This work presents a 3-D Finite Element Analysis of the geometry of interest to verify the copper link solution for the overheating of flange bolts. The overheating results are analyzed and discussed for the case of a 315MVA, 400/220/33KV Autotransformer.