Transformer core Materials

In order to increase the efficiency of the transformer various core materials are being used during the developmental processes of transformer. The following are some of the popular core materials that are being used.

Air core transformer:

air core transformer circuit

It is the simplest form of the transformer without any core material or a non-magnetic core material. The two coils primary and secondary are placed near to each other and as the alternating current flows through primary conductor, a magnetic field is established around it and as this field links the second conductor, emf is induced in it. The percentage of the flux linking the secondary coil is small due to absence of low reluctance path. So such a transformer is inefficient.

Iron or steel solid core transformer:

The ability of iron or steel to carry flux is much higher than air. The ability to carry flux is called Permeability. Electrical steels have permeability in the order of 1500 compared to 1.0 for air. This means, the ability of a steel core to carry magnetic flux is 1500 times than air core. Steel core were used in transformers when alternating currents for distribution of electrical energy was first introduced. But still the no load losses, especially the eddy current losses are higher in these transformers and the efficiency is less with solid iron or steel core.

Laminated carbon steel core transformer:

In order to overcome the disadvantage of solid steel core transformers laminated carbon steel cores were introduced, to decrease the no load losses. The laminated carbon steel core gives about 6 watts/kg of core loss at a flux density of 1 tesla.

Hot rolled silicon steel core for transformer:

Switching, over further to hot rolled silicon steel core, it gave substantial reduction to core losses to 2 watts/kg at a flux density of 1.5 Tesla. The core material will have more permeability when magnetised in rolling direction and thus reduces the core losses.

Cold rolled grain oriented silicon steel core transformer:

Presently this is the most widely used core material and is highly efficient. It the cold rolled grain oriented silicon steel further reduced the core losses to 0.75 to 0.85 watt/kg at maximum flux density of 1.92 tesla.

Chemical composition of CRGO:

A part from the primary element (Fe) the other elements are as follows:

Carbon = 0.01% max
Manganese = 0.2% max
Phosphorus = 0.03% max
Sulphur = 0.01% max
Silicon = 2.8% to 3.5%

Amorphous core transformers:

Energy efficiency in power sector has become even more relevant today than ever before due to increasing gap between demand and supply. This lead to the invention of new core material called amorphous core. The word “Amorphous” means lacking of symmetrical structure. This material has non crystalline molecular structure and often referred to as glassy metal. They exhibit very low hysteresis losses and are highly efficient and longer life. But these are expensive but can recover in the form of energy savings.

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