Core Type Transformer

The transformer has a magnetic core and the primary and the secondary winding around the core. Types of the transformer can be categorized according  to the shape of the magnetic core. The transformer can be categorized into core type and the shell type.In a core type transformer the winding encircles the core whereas in a shell type transformer the core encircles the winding. The winding encircles the core of a transformer. The Single phase transformer has two limbs and three phase transformer has three limbs.

The core of a single phase transformer has a single window. The core of the single phase transformer has two limbs.

Both HV and LV winding is wrapped around  both the  limbs.The LV winding is placed near to the core and then the HV winding is placed after LV on the same limb. This way the  transformer size becomes compact due to less insulation requirement. The transformer cost reduces with this arrangement of placing the LV and HV winding on the same limb.

The main disadvantage of core type transformer is that all the flux produced in the primary does not link to the secondary and some parts of the flux does not link. Thus, the leakage flux in the core type transformer is more as compared to the flux utilization in shell type transformer. However, the core type arrangement is best suited for the large rating transformer because of easier access of the winding during maintenance.If there is fault in the inner winding, the inner winding can be removed after removing the outer winding.

Transformer Core Types and Applications

There are different types of lamination used in the core type transformer.

L-L and U-I stamping lamination when connected together form the requires core shape.

The transformer core shapes is chosen according to the rating of the transformer. In a small rating transformer, the winding is square or rectangular in the shape therefore, the square or rectangular cross section core is used.The small rating transformer has lower current carrying capacity conductors and it is easy to wrap the conductor in a square or rectangular shape. The square or rectangular core is economic for the small rating transformer.

For large rating transformer, the thick winding conductor is used to carry the more current. It is difficult to bend the thick conductor in a square or in a rectangular shape. The round cylindrical shaped winding is the best choice for the large rating transformer in view of optimize use of copper conductor.However, the significant amount of space between the winding and core is unused when the round cylindrical shaped winding on a square cross sectional core limb is used. To reduce this unused space, the stepped cross sectional core is used. The lamination of different shapes are staged to form nearly circular cross sectional core.The cross section of the core may be one stepped, two- stepped or multi stepped.P