What is Core Type Transformer : Construction & Its Working

In this industrial period, transformers are an important discovery as they help for multiple requirements and essentials of various industries. The principle of transformer lies entirely in the energy transformation. Depending on the theory of electromagnetic induction, Faraday extended this theory to a transformer, and also this machine almost operates on the same theory. So, the essential type of transformer which was discovered is the induction coil. While the initial alternating current transformers were developed in the year 1870 and from there the innovation got extended to invent various types of transformers like the core type and shell-type transformers, and many others. This article mainly focuses on the explanation of core type transformer, its working, construction, types, and benefits.

What is Core Type Transformer?

In the core type transformer, the magnetic core is constructed with laminations where creates a rectangle-shaped frame. These laminations are in the shape of L strips as depicted in the below picture. To prevent the high level of reluctance that is formed at the junctions where the laminations are joined across each other, the other layer is piled differently so as to remove continual junctions. The core type transformer diagram is:

Core Type Transformer
Core Type Transformer


Any type of transformer is mainly constructed with three parts and those are core, a primary winding, and secondary winding.

The core part is the important one where it provides a continual magnetic way having an air gap at the minimum level. This is constructed with plastic-coated steel sheets where have a high amount of silicon. And also the laminated sheets hold increase permeability and minimal hysteresis losses.

In order to less down the losses happened by eddy currents, the steel sheet is protected using a light coated core-plate polish material or by covering it with an oxide layer on the surface. The width of the lamination is varied in the range between 0.35 mm with a frequency of 50 Hz to 0.5 mm with a frequency of 25 Hz.

Also, to avoid minimal gaps in between the layers, the steel sheeted later are placed in one order, And these staggered joints are termed to be imbricated joints. And coming to the transformer’s construction, here two types of constructions are there one is core type and the other is shell type. Here, we focus on the core type construction.

In the core type transformer, some part of the core section is protected by windings. In general, the core section of the core-type transformer will be rectangular shaped and the coils will be in either rectangular or circular shape. Both the windings are positioned on the opposing limbs of the core section.

In the huge sized core type transformer’s, either round or cylindrical shaped coils are used due to the reason that the mechanical ability of the circular shaped coils is more than that of rectangular ones. These windings are protected with a helical layer having multiple layers shielded from one other using a paper, cloth, cooling channels, or micarta boards. For minimizing the flux leakages, both the windings are located one after the other by using a high insulated cylinder that is shown in the picture.

Core Type Transformer Types

Based on the lamination used in the transformer, the core type transformer is classified as two types and are

  • L-L Laminations
  • U-I Laminations

When both the stamping laminations are soldered collectively, this forms the required core shape of the transformer. The shape of the transformer is selected depending on the transformer’s rating. In a minimal rating level of the transformer, the winding is either in a rectangle or square shape.

So, a square or rectangular-shaped cross-section is used. The transformer with minimal rating also has lesser current holding capacity conductors and it is simple to cover the conductor in these shapes. Also, using these shapes is economic for minimal rated transformers.

Core Type Laminations
Core Type Laminations

In the case of huge, rated transformers, the thick level winding conductor is utilized to handle huge current levels. It is somewhat complicated to twist the conductor into the desired rectangle or square shape. The circle-shaped winding is the appropriate selection for the huge, rated transformer so that it augments the usage of copper conductor.

Whereas the corresponding amount of the space is left unused in between the core and winding when the round winding on a square cross-sectional core winding is used. To minimize this, the speed type of cross-sectional core is employed. The protection of various shapes takes place to construct an almost cross-sectional core. And this might be of single, double, or multi-stepped

Advantages and Disadvantages

The merits and demerits of core and core type of transformer are explained as follows:


Good Mechanical Ability

The cylindrical-shaped windings in the core type transformers are protected all through the symmetrical core part. The approach they are built-in will provide the benefit of enhanced mechanical ability when compared with other kinds of windings. As stated, this core transformer is constructed using a one-half portion of each winding which is covered all around each winding of its magnetic circuit.

Prevention of Iron Losses

The lamination of core type transformer is usually organized so as to construct an intersecting joint having an additional pair of protections and this enhances the preciseness of the core width. The stacking of the laminations also offers the benefit of minimizing iron losses and flux leakage also.

Appropriate for High Frequencies

As there are multiple levels of steel lamination those are protected using a non-conducting insulation substance in between each layer, the eddy currents are present and the magnetizing effects are minimized. As the thin laminations are so complicated to construct and economical also, these make the device to be suitable for a high range of frequencies.


The demerits of the core type transformer include the following.

Not suitable for External Applications

Considering the other dry type of transformers, a core type transformer is not absolutely suitable for external applications. Not Like oil transformers, these are not safeguarded from corrosion and also these have no protection from external atmospheric factors as they can gradually destroy their inner components, particularly those are constructed of metal. It is especially suitable for household appliances and small scales manufacturing appliances, like indoor power exchanges and plants.


A core type transformer and other dry transformers produce have high noise levels. It can even produce audible noise discharges from the tin work or electrical noise that happens from arcing on the laminations.


The applications of the core-type transformer are:

Used in high-voltage level applications such as distribution transformers, auto, and power transformers.

This is all about the concept of a core-type transformer. This article has provided a clear explanation of the core-type transformer, its working, construction, types, and advantages. Know what are the real-life applications of core transformer?

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