Construction of Three Phase Transformer

Construction of Three Phase Transformer

• The three phase transformers can be core type or shell type. The three core type single phase transformers can be combined to get three phase core type transformers. Similarly three single phase shell type transformers can be combined together to form a three phase shell type transformer.

1. Core Type Construction

• Core type three phase transformer has three limb construction as shown in the Fig. 7.3.1.

• The core consists of three legs with the magnetic circuit completed through two yokes, one at the top and the other at the bottom. Each limb has primary and secondary winding arranged concentrically. The core type transformers usually wound with circular cylindrical coils.

• A primary and a secondary winding of one phase are wound on one leg. Flux flows up each leg in turn and down the other two legs in general so that the magnetic circuits of different phases are in series and therefore independent. The transformer is having only two windows each of which is containing two primary and two secondary sale windings.

2. Shell Type Construction

•  In shell type transformer the three phases are more independent than they are in the core type of three phase transformer. This is because each phase has an individual magnetic circuit which is independent of the other. The construction of shell type three phase transformer is shown in the Fig. 7.3.2 (a), while the arrangement of the windings is shown in the Fig. 7.3.2 (b). While showing the winding arrangement only one winding is shown for the simplicity.

• The three phase shell type of transformer has construction similar to that of single phase shell type transformer built on top of one another. This type of transformer is rarely used.

Review Question

1. Explain the construction of three phase transformers