The factors such as weight, stray load losses and minimum cost are kept in mind while selecting the material for transformer tank. The material must be capable to withstand stresses due to jacking and lifting and must have capacity to house cores, windings and internal connections giving adequate clearance between the windings and the walls. Rolled steel plates are used for tank bodies of most of the transformers. Small tanks are generally welded from steel plates. The larger tanks are assembled from boiler plates. Usage of aluminium for transformer tank reduces the weight and the stray magnetic losses. However, it increases the cost and also needs special attention for lifting to present stressing. The aluminium tanks are usually made of cast aluminium tank parts, which are mounted on a shallow mild steel tray and are arranged to carry the main lifting.
The conductors which are responsible for producing demagnetizing and distortion effects are shown in the Fig.1. Fig. 1 The brushes are lying along the new position of MNA which is at angle θ from GNA. The conductors in the region AOC = BOD = 2θ at the top and bottom of the armature are carrying current in such a direction as to send the flux in armature from right to left. Thus these conductors are in direct opposition to main field and called demagnetizing armature conductors. The remaining armature conductors which are lying in the region AOD and BOC carry current in such a direction as to send the flux pointing vertically downwards i.e. at right angles to the main field flux. Hence these conductors are called cross magnetizing armature conductors which will cause distortion in main field flux. These conductors are shown in the Fig. 2 Fig. 2 ...
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