There are invisible points dotted along the power lines criss-crossing Italy, at which energy changes. These points are transformers, devices that enable connection and energy transfer between grids of different voltages. Without them, the national power grid would be nothing but a patchwork of isolated fragments: power plants would produce medium-voltage energy, cities would require low-voltage energy, and nothing would match up. Transformers are, quite literally, the bridge between different electrical worlds.
Italy has one of the most extensive electricity transmission infrastructures of all countries in Europe. Terna manages over 75,000 kilometres of power lines and more than 900 electrical substations. And it’s right here inside these substations that the real stars of energy continuity are found: 781 large transformers that increase or decrease the voltage according to the network’s needs. All Italy’s electrical energy, from hydroelectric plants in Alpine valleys to street lamps on seaside promenades, passes through these transformers.
In the energy sector, transformers are electrical devices that play a crucial role: they facilitate the connection and transfer of energy between grids of different voltages.
How transformers work and what makes them crucial. The principle is as elegant as it is simple: two separate copper windings (or in aluminium, as an alternative for smaller transformers) around a core of laminated magnetic sheet, immersed in an insulating fluid, exchange energy electromagnetically. This way, the electrical voltage rises or falls without the circuits touching each other. When energy must travel hundreds of kilometres, it is stepped up to 220 or 380 kV: the higher the voltage, the less energy is lost due to dissipation along the cables. Upon arrival close to urban centres or industrial areas, the voltage is stepped down again. The true efficiency of the electrical transmission system lies in this continuous "up and down".
Transformer technology has always had a dual purpose: reliability and longevity. In Italy, many of the plants currently in operation were built between the 1980s and 1990s, and continue to operate thanks to targeted maintenance and the installation of digital monitoring systems, such as smart sensors that detect vibrations, thermal variations, and insulating oil quality, allowing for fault prevention before failures occur.
The Tamini industrial hub, where giants are made. The transformers of the Italian electric grid represent another big name in the nation’s industrial history: Tamini Transformers. Founded in 1916 in Milan, it is now part of Terna Energy Solutions, the Terna Group’s market-facing company. It is among the few companies in Europe to design and manufacture power transformers of up to 900 MVA and 500 kV. A strong tradition of Italian technical and engineering expertise, serving both the domestic market and exports.
Each transformer can weigh over 300 tonnes and operate continuously for decades under extreme temperature and load conditions. At its factories in Legnano, Ospitaletto, Valdagno, Novara, and Rodengo Saiano, Tamini tests next-generation insulating materials and oils, with an increasing focus on sustainability. These are places where technological developments go hand-in-hand with manufacturing tradition, as many phases of constructing and assembling the transformers, such as the delicate winding of copper cables, are still performed by hand.
The new green frontier: the Calenzano case study. The most interesting innovation in recent years has been the “green” transformers. Terna has started experimenting with Tamini at the Calenzano electrical substation, in the province of Florence, where the first Green ATR went into operation in 2024: a large transformer immersed in natural ester instead of traditional mineral oil. The idea is simple but revolutionary: to reduce the risk of fire and environmental impacts in the event of leaks, while simultaneously improving the biodegradability of the fluid.
The use of natural esters allows the flash point to be raised above 300 °C and reduces toxicity. In the event of a failure, there is almost zero risk to the environment and to groundwater. For infrastructure operating 24 hours a day, 365 days a year, this is a crucial advantage. The Calenzano prototype, which comes in the wake of the Demetra project carried out in Travazzano (Lodi) a few years earlier, was developed by Tamini in collaboration with the Italian Electrotechnical Experimental Centre (CESI) and is one of Europe’s first "green" power transformers on the primary grid. It is one piece in the puzzle of the Group's broader strategy for the sustainability of the electrical system, which aims to reduce grid losses and indirect CO₂ emissions.
Infrastructure transforming. Transformers are an issue that impacts not only efficiency, but resilience, too. Over the next ten years, the Italian grid will need to integrate a growing share of renewable energy from widely scattered solar and wind plants. These intermittent flows require more flexible transformers, capable of managing rapid load variations and energy flow reversals. This is the principle of the "bidirectional grid": energy no longer flows simply from power plants to homes, but also from homes back into the grid, through small plants and storage systems.
In its latest Development Plan, Terna has allocated over 23 billion euros in investments for the 2025-2034 period to modernise and digitalise the national transmission grid. Part of this sum will also be dedicated to replacing older transformers and introducing systems for real-time digital control. The goal is to build transformers that do not merely transform energy, but interpret it: sensors that measure and monitor various operating parameters and signal load variations before they become critical issues.
