The correct answer is C. Cylindrical type.
A 3-phase shell-type transformer is a type of transformer that has three windings arranged in a cylindrical shape. The windings are typically made of copper wire and are insulated with a material such as paper or varnish. The transformer is housed in a metal case that protects the windings from damage.
The cylindrical type of winding is the most common type of winding used in 3-phase shell-type transformers. This type of winding is efficient and has good cooling properties. It is also relatively easy to manufacture.
The other options are incorrect because they are not types of windings that are typically used in 3-phase shell-type transformers.
- Option A: Circular type. This type of winding is not typically used in 3-phase shell-type transformers because it is not as efficient as the cylindrical type of winding.
- Option B: Sandwich type. This type of winding is not typically used in 3-phase shell-type transformers because it is not as easy to manufacture as the cylindrical type of winding.
- Option D: Rectangular type. This type of winding is not typically used in 3-phase shell-type transformers because it is not as efficient as the cylindrical type of winding.