How transformer is constructed

What is a transformer

A transformer is a device that transfers electrical power from one electrical circuit to the other with the help of electric induction. The electrical power transfer is done without changing the frequency. It can step up or step down the level of AC or DC current and voltage. Transformers can amplify the electrical power, without transformers the electrical energy generated at the generating stations won’t be sufficient enough to power up a city.

Transformer working principle and parts of transformer

Core and shell-type transformer

Transformer types

How is a transformer constructed

A transformer has the following main parts core, winding, cooling material and terminal.


A core is a flux carrying part of the transformer around which the windings are wound. It has high permeability so that the maximum amount of flux passes through it. There are certain types of core they are, solid core, laminated steel core, toroidal core, and air core. The composition of the transformer core depends on voltage, current, frequency, size limitations, and construction costs. Air core is produced by simply placing the winding in closed proximity to each other. They have high bandwidth and are mostly used for radio-frequency applications, air-core transformers are used when the voltage source has a high frequency which would be above 20 kHz. In solid core type solid iron is used to make the core, to maximize the flux high permeable silicon steel is used, iron core transformers are mostly used when the frequency is below 20 kHz.

In the solid core type, the losses are high like eddy current losses so in order to reduce this problem, laminated cores can be used. The laminations will reduce the magnitude of their magnitude and thinner lamination can reduce losses, so in laminated cores thin layer of steel, laminations are stacked over one another to make the core. Laminated sheets of steel dissipate heat readily, thus it provides for the efficient transfer of power. Toroidal cores are ring-shaped cores they are made from a long strip of silicon steel wound into a coil. In this type, the grain boundaries are optimally aligned and they have high efficiency. Primary and secondary coils are often wound concentrically to cover the entire surface of the core and this will minimize the length of wire needed, other advantages of this type include smaller size, lower weight, less noise.


Winding is the conductive part of the transformer and they are meant to carry current and they are wound on the core. According to the transformer applications, the conducting material on the winding is selected and the individual turns are electrically insulated from each other to make sure that the current travels through each turn. The coils are wound by enameled magnet wire for small power and signal transformers. The coils could be wound with copper rectangular strip conductors in case of large power transformers that operate at high voltages. High-frequency transformers that operate in tens to hundreds of kilohertz have windings that are made of braided Litz wire to minimize the skin and proximity effect losses. The type of insulation decides the allowable minimum temperature.

Cooling arrangement

The heat generated due to the heavy losses in the core and winding has to be dissipated quickly so that the excessive temperatures won’t be reached, which could rupture the insulation. Small transformers do generate a large amount of heat so it can be cooled by air circulation and radiation of heat. Power transformers that are rated up to several hundred KVA can be cooled by natural convective air cooling. There are coolants that can insulate and cools the windings of transformers and they are used in some power transformers. There are oil and air-cooled transformers and the coolants are chosen according to their environment and working conditions. The coolants which are used are liquid nitrogen, helium…

Terminals and bushing

Only the small transformers will have wire leads connected directly to the ends of the coils and bought out to the base of the unit for circuit connections. Larger transformers may have bolted terminals, bus bars, or high-voltage insulated bushings which are made of polymers and porcelain. At higher voltage, air-filled bushings are used.

Other accessories of transformer

Transformer tank, radiator, and transformer tap

The transformer tank is a vessel that is filled with oil and is connected to the transformer tank. Its function is to ensure that the transformer tank is always filled with oil. Radiators are used in the transformer to cool the transformer oil through natural air or forced air. By the help of transformer tap, a certain number of turns can be selected transformer tap is a connection point