The operation of the transformer

Discover the principle of electromagnetic induction, key components, and the differences compared to oil-immersed transformers.

How does a dry-type transformer work?

Principle of electromagnetic induction

A transformer is a static device that transfers electrical energy between two or more circuits through the phenomenon of electromagnetic induction, adjusting voltage and current levels while maintaining a constant frequency.

Main components

The operation of a transformer is based on the principle of electromagnetic induction. When an electric current flows through the primary winding, it generates a magnetic field around it. This magnetic field, in turn, induces an electric current in the secondary winding, which is wound around the same magnetic core.

The ratio between the number of turns in the primary and the secondary determines the voltage and current transformation. If the primary winding has more turns than the secondary, the secondary voltage will be lower than the primary, while the current will be higher. Conversely, if the secondary has more turns than the primary, the secondary voltage will be higher while the current will be lower.

The operating mechanism is divided into three main stages based on Faraday–Lenz’s Law:

• Flux generation: an alternating current flows through the primary winding, producing a variable magnetic flux in the ferromagnetic core.
• Flux linkage: the core channels the magnetic field lines toward the secondary winding.
• Electromagnetic induction: the variation of magnetic flux across the secondary turns induces an electromotive force (voltage), enabling current to flow to the connected load.

Difference between dry-type and oil-immersed transformers

Transformers can also be classified according to their insulation and cooling system. The two main technologies are dry-type resin transformers and oil-immersed transformers, which primarily differ in the insulating materials used and their cooling method.

Dry-type transformers

In dry-type transformers, the windings are insulated using solid materials, such as epoxy resin or vacuum pressure impregnation (VPI) systems. Cooling is achieved through natural air circulation or forced ventilation, without the use of insulating liquids.

Thanks to the absence of oil, dry-type transformers are ideal for indoor installations and environments where safety and sustainability are key requirements, such as:

• commercial buildings
• data centers
• transport infrastructure
• industrial plants
• renewable energy facilities

The absence of flammable liquids also reduces fire risk and simplifies maintenance operations.