All transformers have the following essential elements:
- Two or more electrical windings insulated from each other and from the core (except in auto transformers).
- A core, which in case of a single-phase distribution transformers usually comprises cold-rolled silicon-steel strip instead of an assembly of punched silicon-steel laminations such as are use in the larger power-transformer cores. The flux path in the assembled core is parallel to the direction of steel’s grain or ‘orientation’. This results in a reduction in core losses for a given flux density and frequency, or it permits the use of higher core densities and reduced size of transformers for given core losses.
Other necessary parts are:
- A suitable container for the assembled core and windings.
- A suitable medium for insulating the core and its windings from each other and from the container.
- Suitable bushings for insulating and bringing the terminals of the windings out of the case
The two basic types of transformer construction are:
- The core type.
- The shell type.
The above two types differ in their relative arrangements of copper conductors and the iron cores. In the ‘core type’, the copper virtually surrounds the iron core, while in the ‘shell type’; the iron surrounds the copper winding.