The evolution of electrical transformers

October 31, 2023

Introduction to electrical transformers

Electrical transformers are fundamental devices for the operation of electrical systems. They make it possible to change the values of alternating voltage and current while keeping power constant.

Transformers perform several essential functions:

  • Adjust voltage levels for the efficient transport of electricity on transmission and distribution networks
  • Provide electrical isolation between circuits of different voltages
  • Transforming alternating voltage for end use in electrical appliances

In essence, electrical transformers enable the efficient adjustment of electricity production and consumption.

Selective Focus Greyscale Shot of Powerlines, Connections, and Transformers.

How does an electrical transformer work?

The operation of a transformer is based on the principle of electromagnetic induction. It consists of two or more windings of conducting wire around a magnetic iron core.

One winding, called the primary winding, is connected to the power source. The varying alternating current in this winding generates a variable magnetic field in the core.

This field induces an electromotive force in the other windings, called secondary. The voltage at the ends of each secondary winding depends on the ratio of turns to the primary winding.

Usually, the primary has fewer turns than the secondary to obtain a higher output voltage (elevating transformer). Conversely, to get a lower output voltage, the secondary has fewer turns than the primary (reducing transformer).

Historical evolution of electrical transformers

Since the first applications of alternating current in the late 19th century, transformers have played a key role. Their evolution has enabled the development and improvement of electrical systems.

The first transformers

In 1876 Pavel Yablochkov invented a primitive transformer to power arc street lamps.
In 1878 Lucien Gaulard and John Gibbs made an iron-core transformer with a more efficient primary and secondary.

Tesla and Westinghouse transformers.

In 1884 Nikola Tesla designed the first working high-frequency transformer.
In 1885 William Stanley built the first commercial transformers for the Westinghouse Electric Corporation.

Diffusion of alternating current systems

In the late 1800s the War of Currents saw Westinghouse’s AC systems with transformers prevail over Edison’s DC systems.
In the early 1900s, electrification with AC grids and transformer substations became widespread.

Transformers for industrial uses

Electrical transformers are essential for supplying power to industrial electrical systems that require different voltages and currents.
The main types of industrial transformers are:

  • Power transformers – for adapting the supply voltage to the needs of industrial electrical machinery. They can be elevated or reducers.
  • Isolation transformers – provide insulation and protect equipment from surges.
  • Autotransformers – have one common winding with intermediate sockets. They allow different voltages to be obtained with a small footprint.
  • Variac – adjustable transformers to have a variable DC voltage. Useful for gradual switching on of loads.
  • Welding transformers – designed to provide the high current required by arc welding processes.
High voltage post or High voltage tower

Transformers and renewable energy

Transformers also play a crucial role in harnessing renewable energy and distributed microgeneration.

  • They enable the integration of the grids of energy produced by wind, photovoltaic, hydroelectric plants, etc.
  • They enable the connection of small domestic systems to the grid.
  • They provide isolation and protection for DC generation systems and batteries.

With their essential functionality, transformers facilitate the transition to more sustainable and efficient electricity grids.


In more than a century, transformers have evolved from experimental devices to indispensable components in the production, transmission and use of electricity.

Technological innovations have improved the efficiency, power, quality and reliability of these electrical machines. Transformers will continue to play an irreplaceable role in the flexible utilization of traditional and renewable energy resources.

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