SOLUTION

Shell Type Transformer

• When the primary and secondary windings are encircled by the magnetic material, the transformer is referred to as a shell-type transformer.
• In shell-type construction, there are two parallel magnetic paths into which the flux from the central limb can divide.
• The primary and secondary windings are wound on the central limb one above the other. This provides a better magnetic coupling between the primary and secondary windings and reduces the magnetic leakage from the core.
• In the case of shell-type transformers, sandwich-type windings are used.
• The high voltage and low voltage windings are split into a number of sections where each high voltage section lies between two low voltage sections. Such type of sandwich windings is shown in Fig.

• Shell-type transformer construction features a short magnetic path and a longer mean length of the electrical turn.
• The shell-form transformer has a larger core area and a smaller number of winding turns than the core-form of the same output and performance.
• Additionally, the shell form generally has a larger ratio of steel to copper than an equivalently rated core-form transformer.
• The core type has a longer mean length of the magnetic flux but a shorter mean length for the winding coils and so it is better suited for very high voltage transformers which require a large number of turns in their windings and also, it offers better scope for insulation and its inspection.