Core Type and Shell type Transformer Basic

You may ask, where shell type and core type transformer are used and why? Simply we can say actually there is no any hard and fast rule to choose your core type or shell type transformer for a particular ranges area.

Mostly you will find some tendency to choose the core or shell type transformer used based on the practicalities; and it is a choice made by the designer.

The core transformer has one magnetic circuits; in this type transformer both the primary and the secondary windings are wound outside and surround the core ring means both windings are placed on the side limbs.

The shell transformer has one magnetic circuit; in this type transformer the primary and secondary winding pass inside the steel magnetic core which forms a shell around the winding.

In Practical core type transformer mainly uses in high voltage applications like electrical energy transmission, primary distribution, auto power transformer etc. The reasons are simple-

High voltage system deals high flux and keeping this in less iron loss the iron core need more thickly;

1.   Heavy insulation is required for high voltage system and in core type transformer it is easier and cheaper to maintain heavy insulation. In fact low voltage winding itself acts as an insulation between high voltage winding and core;

2.   The cylindrical coils used in core type transformers that remarkable construction provides the advantage of getting better mechanical strength;

    3.   The core type transformer is typically arranged to create an overlapping joint   with  an extra pair of laminations that preventing condensed flux leakage and iron loss.

  4.   The core type transformer is efficient for high frequencies because the core type transformer uses several steel laminations, which are protected by a non-conducting insulation material between layers.

The Shell type transformers are popular in Low voltage applications like transformers used in electronic circuits and power electronic converters etc. The reasons are simple-

    1.   In low voltage system normally require more volume for the copper wires than that of iron core. So, shell type transformer is a better choice in low voltage system;

   2.   In low voltage shell type transformer higher insulation is not more considerable. So, it can put the winding anyway you want in the shell;

3.   High short-circuit withstand capability;

4.   High mechanical strength and high dielectric strength as it’s special construction;

5.    The shell type transformer provides for excellent control of leakage magnetic flux to prevent against local heating inside the transformer;

6.   The shell type transformer provides efficient cooling capability;

7.    The shell type transformer also provides compact size and flexible design facility.


The difference between Core type and Shell type Transformer, we may consider the key features as windings, limbs, copper requirement, lamination, flux distribution, windings position, cooling system, repair, design, efficiency & mechanical strength etc.

Types of Transformer by Construction

Constructionally the electrical transformers are of two general types, distinguished from each other merely by the manner in which the primary and secondary coils are placed around the laminated core. 

The two types are known as 
(i) core-type and 
(ii) shelltype.

Another recent development is spiral-core or wound-core type, the trade name being spirakore transformer. In the so-called core type transformers, the windings surround a considerable part of the core whereas in shell-type transformers, the core surrounds a considerable portion of the windings as shown schematically in Fig.(a) and (b) respectively.
Types of Transformer by Construction


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