Core Type vs Shell Type Transformer: Key Differences
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This article compares core type transformers with shell type transformers, highlighting their key differences.
Introduction:
Transformers are categorized based on several factors, including the number of phases, their construction, voltage level, and applications. Based on construction, transformers are primarily classified into:
- Core type
- Shell type
- Berry type
Core Type Transformer
Core Type Transformer
- The core can be either square or rectangular.
- It’s typically made of silicon steel sheets (around 4% silicon). The laminations help to minimize eddy current losses.
- The vertical portions where the coils are wound are called limbs. The top and bottom parts are known as the yoke.
- The core material needs high permeability, ideally with a relative permeability (µr) greater than 1000.
- Core Type Transformer have a single magnetic circuit, featuring two limbs/arms as shown in the image above. The primary and secondary windings are wound on these two limbs.
Shell Type Transformer
Shell Type Transformer
- Shell Type Transformer have a double magnetic circuit.
- The core has a rectangular shape and consists of three limbs/arms and two yokes.
- The core surrounds the windings.
- Both the primary and secondary windings are wound on the central limb.
- The core is constructed from very thin laminations of high-grade silicon steel to minimize eddy current and hysteresis losses within the core.
Core Type Transformer vs. Shell Type Transformer: Key Differences
The following table summarizes the main differences between core-type and shell-type transformers:
Parameters | Core Type Transformer | Shell Type Transformer |
---|---|---|
Construction | Winding encircles the core. | Core encircles most of the winding. |
Number of magnetic circuits | Only one | Two |
Number of limbs in a core (for single phase type) | Two | Three |
Construction complexity | Simple | Difficult |
Cooling | Better, as more surface is exposed to atmosphere. | Not very effective. |
Repairing/Maintenance | Easy to repair as coils are easy to remove. | Difficult to repair, requires removing many laminations. |
Application | Preferred for low voltage transformer. | Used for very high voltage transformer. |
Type of coils | Cylindrical coils | Multilayer disc type or sandwich coils |
Losses | More | Less |
Insulation | More | Less |
Copper requirement | More | Less |