Transformer Construction and Types of Cores

Basic Transformer Construction

A transformer consists of two coils mounted in the fixed positions relative to each other. One coil is supplied by an alternating current. As current alternates, the magnetic field it produces also alternates. This alternating field induces the alternating current in the second coil, which supplies a load. A simple transformer construction consists of two coils wound on the closed iron core. The winding connected to the supply is called primary winding. The winding connected to the load is the called secondary winding.

If the transformer is used for the increasing the potential difference, it is called a step-up transformer. In this kind of the transformer low-voltage winding is the primary. If the transformer is used for the decreasing the potential difference, it is called a step-down transformer. In this case, the high-voltage winding is the primary.

Standard markings are used for transformer terminals. The terminals of the high-voltage winding are the marked H1, H2, and so on. The low-voltage terminals are marked X1, X2, and so on. Number of the turns in each winding is abbreviated TH or TX.

Construction of transformer

Simple Transformer Construction

Commercial Transformer Construction

The windings of the commercial transformers are not placed on separate “legs” of the core. The transformer can be the made more efficient by placing both windings on the same leg, or by placing both windings on both legs. Placing the two windings together enables more of the magnetic field of the primary to induce the current in the secondary.

There are two ways to the combined primary and secondary windings on a single leg of the core.

  • The windings may be cylindrical and wound one over and other with insulation between them
  • The windings may be shaped like pancakes and the stacked alternately on the core

transformer construction of the winding

Windings construction of the transformer

Notice the placement of the two windings. The low-voltage transformer winding is the wound next to the core. The high-voltage winding is the wound over the low-voltage winding.

The construction of transformers varies widely according to their size and use. One variation is arrangement of the iron core and the windings. There are two basic construction arrangements

  • the core arrangement
  • And the shell arrangement. Transformer construction of cores

Transformer Cores Types

The core-type transformer has a core made in shape of a hollow square. Half the windings are placed on each leg of the core. The core of core-type transformer passes through the center of the windings but does not surround the windings. By contrast, the shell-type transformer has a core that the surrounds the windings as well as passing through the center.

Cores Construction of Transformer

Typical transformer cores are the made of thin steel sheets, called laminations. The laminations are coated with the varnish or with some other insulating material and stacked together to form the core. The number of the laminations stacked together determines the thickness of the transformer core. The purpose of this laminated construction is to the reduce eddy currents that waste energy in a transformer.

Another kind of core is made of a steel strip or ribbon wound in a spiral on a form. When this type of core is used, power losses are the reduced, tighter construction of the transformer is possible, and the magnetic characteristics of the core are improved.

Coils Construction of Transformer

Transformer coils are the usually made of copper because of its low resistance. They are the designed to fit the required number of turns into a minimum amount of space. The cross-sectional area of the conductor must be the large enough so that conductor can carry the maximum required current without overheating. The coil must also be designed to leave enough space for insulation and for cooling ducts.

Round copper wire is used in the transformer coils that carry low current. Round wire larger than the number 10 is generally not used because of the large amount of wasted space between wires. Either square or the rectangular wire ribbon is used instead.

The wire is the insulated with cotton, enamel, paper, or a combination of materials. The insulation must have the proper dielectric strength for potential difference between it and other parts of the transformer.