The shell-type transformer is a simple rectangular form and the core surrounds the considerable portion of the windings which is shown in fig. Both the primary & secondary windings are placed in one limb. And the coils are wound in from of multi-layer disc type. The different layers of the multi-layer disc are insulated from each other by paper.

Each winding is subdivided into sections. Low voltage (lv) and High voltage (hv) subsections are alternatively placed in the form of a sandwich that is why this winding is also called the sandwich or disc winding.

Shell type transformers are often used where a limited amount of space is available. Typical applications include the railway industry, where it is beneficial to lay the transformers on top or underneath the carriages without increasing the overall height of the carriage considerably. Height is a particular concern for trains due to aerodynamic considerations and other considerations such as passing under bridges.