- Shell Type Transformer Definition: A shell type transformer is defined as a transformer with a magnetic core using ‘E’ and ‘L’ shaped laminations.
- Core Structure: The core has three limbs, with the central limb carrying all the flux and side limbs half the flux, enhancing strength and protection.
- Winding Design: HV and LV windings are alternately wound around the core, needing less conductor but more insulation.
- Cooling System: Requires forced air and/or oil cooling to dissipate heat effectively from the windings.
- Applications: Shell type transformers are used for low voltage applications and help optimize circuit expenditure.
Depending on the construction of its magnetic core, we can categorize transformers into two types:
- Shell Type Transformer
- Core Type Transformer
Core of Shell Type Transformer
We use ‘E’s and ‘L’s shape laminations to make the core of the shell-type transformer.
Limb of Shell Type Transformer
A single-phase shell type transformer has a core with three limbs, enhancing mechanical strength and protecting windings from shocks. The HV and LV windings are on the central limb, which carries all the flux, while side limbs carry half the flux (φ/2). Thus, the central limb’s cross-section is twice that of the side limbs.
Magnetic flux in a shell type transformer flows through two closed paths, reducing core losses and increasing efficiency of transformer. This design also provides strong support against electromagnetic forces during short-circuits, giving more output compared to core type transformers.
Winding of Shell Type Transformer
HV and LV windings are wound longitudinally along the core alternately. The HV coils are sandwiched between two LV coils as shown in the figure below.
Since both HV and LV coils are wound on the central limb, shell type transformers need less conductor material than core type transformers. However, they require more insulation due to the sandwich design, which can lead to short-circuit risks. The complex winding structure also makes maintenance difficult, as inner winding defects require removing all outer windings.
Cooling System of Shell Type Transformer
Forced air and/or forced oil cooling is essential in shell type transformer as heat generated during working, cannot get dissipated easily from windings due to surrounding yoke and limbs.
Applications of Shell Type Transformer
Shell type transformers are mainly used for low voltage applications, often in low voltage power and electronic circuits. They help optimize circuit costs due to their square or rectangular cross-sectional cores, which are less expensive.
Disadvantages of Shell Type Transformer
Special fabrication facilities are required for the construction of a shell-type transformer due to its complexity and that leads to increased manufacturing and labour cost.
