Types of Transformers

A transformer is a static device that is used to transfers power from one circuit to another circuit. The transformer transfers power with the desired change is voltage and current without any change in the frequency.

It consists of two or more winding that are linked to each other by a common magnetic field.

Types of Transformers

The transformer consists of two winding; namely primary winding and secondary winding.  These winding are wound on a magnetic core and they are electrically insulated from each other and core.

The classification of the transformer is based on the relative arrangement of the core and the winding. According to the construction of the transformer, the transformers are classified into two main types.

• Core type transformer
• Shell type transformer

Core Type Transformer

In this type of transformer, winding covers the large portion of the core. Winding (LV and HV) are wound on the limb of the core that is made up of lamination.

The lamination which connect two vertical limbs is called as a yoke. Depending upon the materials used for the core its area may be larger than the limb area or equal to the limb area.

Area of yoke = 1.15 to 1.25 times gross iron area for hot rolled steel.

                        = gross iron area for grain-oriented steel

Generally, low voltage winding is placed near the core to save the insulation cost. And high voltage winding is placed over the low voltage winding.

Spacers of some insulating materials like wood, mica is placed between high voltage winding and low voltage winding. It creates ducts to help to cool the winding.

Also, the maintenance coil can be easily removed by removing the yoke portion. Due to ease of manufacturing, increased cooling effect, and easy maintenance, this type of construction is more common in practice. 

Shell Type Transformer

In this type of transformer, the core covers a larger portion of winding. As shown in the figure, winding are wound on the center portion of the limb. It carries total flux and side limbs to complete the flux path and carry half of the total flux.

In this type of transformer, high voltage and low voltage winding are divided into several coils. And these coils are placed alternatively. This type of winding is called sandwich winding.

the coils are more readily braced this type of construction achieves mechanical robustness. Compare to core transformer, under short circuit conditions winding in a shell type transformer withstand forces to a greater extent. Because winding are supported by the core over a larger portion of the length.

Due to sandwich coils leakage reactance is reduced. As the core is exposed, better cooling is achieved in the core than winding.

Difference between Power and Distribution Transformer 

A power transformer is used in the transmission system. Hence, in this case, the load fluctuations are not much more. Hence, it is designed to have maximum efficiency at about full load.

They are designed for high greater leakage reactance. But the distribution transformer is connected in the distribution lines in which case there is a load fluctuation throughout the 24 hours of a day. Iron loss is taking place all the 24 hours of a day irrespective of load variation.

Hence, they are designed for low iron loss and designed for maximum efficiency at about 50% of full load. They are to be designed for a small value of leakage reactance.