Shell Type Transformer- Construction, Working & Applications

Shell type transformer winding is positioned on the middle limb of the core and other limbs are used for mechanical support.The transformer can be categorized into core type transformer and shell  type transformer depending on the construction of the magnetic core and arrangement of the winding of the transformer.

Table of contents

  • Shell Type Transformer Construction
    • Main Parts of the Transformer
    • Core
    • Lamination
    • Winding
    • Cooling System
  • Working of Shell Type Transformer
  • Applications of Shell Type Transformer
  • Merits and Demerits of Shell Type Transformer
    • Advantages
    • Disadvantages

Shell Type Transformer Construction

Main Parts of the Transformer

Core

The core of the shell type transformer is made from the E-I and E-E type laminated sheet.

Lamination

The core of the single phase transformer has three limbs.This arrangement increase the mechanical strength of the core. In addition to this, the winding remain protected from the mechanical shock.

Winding

The HV and LV winding is wound around the central limb. The central limb carries the entire flux (Ф ). The flux (Ф ) divides into two equal part and thus each side limbs carries the half (Ф/2 ) of the total flux(Ф ). As a result, cross section area of the central limb is two times of the side limbs area.The arrangement of the winding around the central limb is as given below.

The magnetic flux flows through two closed magnetic path, and therefore the iron core losses reduce. And, the efficiency of the transformer improves. This transformer gives more output as compared to similar core type transformer.

The core of the transformer has good mechanical strength. The electromagnetic force developed during charging and short circuit condition cause less adverse effect on winding.

The HV and the LV winding fixes around the central limb in the sandwich arrangement. The HV winding is in between the two LV winding.

The amount of conductor required for the shell type transformer is less because both the winding has its position on the central limb. However, the amount of insulation requirement is more as compared to the core type transformer.

It is because HV and LV winding fixes alternatively on the same limb. The design of the transformer is complex as compared to the core type transformer.

In case of any defect in the inner winding, the outer winding removal is must.

Cooling System

In case of core type transformer natural air cooling may be sufficient. However, we need forced air or forced oil cooling for a shell type transformer. The reason is that the yoke and limbs surrounds the core.

Working of Shell Type Transformer

Two coils are mounted in the central leg. First one winding is wound and above it one more winding is wound. This arrangement ensures no flux leakage. On excitation of the primary winding, it generates flux & voltage is induced in the secondary winding.The working principle of shell type and core type transformer is based on the Farady’s law of electromagnetic induction.

Read More: Core Type Transformer- Its working & Application

Applications of Shell Type Transformer

Transformer is most suitable for the low voltage applications. We use shell type transformer for low voltage electronics circuits. The cost of the transformer is less because we can use the square or rectangular cross section area core.

Merits and Demerits of Shell Type Transformer

Advantages

  1. Good mechanical strength
  2. Compact size
  3. Low leakage magnetic flux
  4. It has a high seismic-withstand ability

Disadvantages

  • Needs special fabrication facilities for transformer designing
  • More Iron in the core
  • Complex in design
  • Manufacturing cost high
  • Force cooling required
  • Repairing needs removal of all the outer winding