Cast resin transformers

A cast resin insulated transformer represents the best compromise between the simple realization of an air insulated machine and the dielectric strength qualities of solid insulation. It is compact, easy in construction and relatively cheap: thus, dry type transformers, insulated with cast resin windings, have become the most common and widespread solution in the market of distribution MV-LV substations.

FDUEG designs and produces cast resin transformers with power ratings up to 3150 kVA and voltage transformation from low (usually the typical 400 V three-phase voltage) up to medium (24 kV). Since efficiency is one of the most important parameters while describing this kind of static machines, FDUEG supplies products that completely satisfy the limits imposed by international standards IEC 60076-11 and UE 548/2014 (the so-called “EcoDesign” norm), remaining within the allowed temperature rise for the whole transformer, without heat concentration spots beyond what is allows by the standards and advised for a full functionality of the apparatus.

This kind of product finds its most common usage as distribution transformer for power plants or small industries and factories, public facilities, hospitals, airports and other similar applications.

Three Phase Cast Resin Transformer 500 kVA 20000-400 V 50 Hz AN 1600 kg FDUEG
Three Phase Cast Resin Transformer 630 kVA 15000-400 V 50 Hz AN 1850 kg FDUEG

Cast resin MV LV transformers: small footprint, low operational and maintenance costs

As mentioned above, the main application for the cast resin technology is distribution. A typical model features a transformer with a low voltage winding, whose rating depends on the system of installation, and another, bearing medium voltage, that is connected to the local distribution grid. This last one is encapsulated in epoxy resin to safely manage the applied voltage.

This feature represents the prominent advantage with respect to an oil immersed transformer with the same rating and duty: managing the MV side with solid insulation instead of a liquid one allows for a simpler, faster and cheaper installation, while offering better performances in terms of safety and, especially, maintenance costs. There is no need to filter or replace oil from time to time, while the number of auxiliary equipment pieces is reduced as much as possible, thus minimizing the chances of random faults and stops.

The right compromise between solid insulation material (resin) and air permits the realization of dry type transformers that are both electrically safe and small in dimensions if compared to products that are equivalent in functionality and power rating. Being the air portion of insulation continuously replaced and, thus, not affected by aging, a high level of dielectric strength and a long service life are granted.

The reduction in dimensions and weight directly leads to lower purchase prices, together with smaller operational costs. Restrained dimensions correspond, in terms of mass, to a lower quantity of ferromagnetic material and electrical conductors, which scale in proportion with both no-load and load losses.

A smaller magnetic core also makes the installation easier, and causes the noise level to decrease while the transformer is fed with the rated voltage.

All these reductions do not impact on the mechanical stability of the whole structure, which is designed to withstand both normal electrodynamical stresses and short circuit forces.

The conductor material that is usually exploited is aluminum, for its compatibility with resin on what concerns the cycles of thermal expansion and shrinkage due to a possibly intermittent service of the device.

At last, the fire risk is kept under control: all FDUEG dry type transformers are certified F1 class, which involves self-extinguishing materials and low gas emission, in compliance with IEC standards.

Reduced maintenance

Low prices

Small dimensions and weight

Cast resin transformers manufacturers: custom solutions

The Engineering Department of FDUEG develops a wide range of special transformers upon customers’ requests. The features of compactness and easy maintenance, offered by the cast resin insulation, are exploited to be able to install the machine in the harshest environments. The transformers can be delivered in protection boxes featuring IP degrees up to 66, equipped, if needed, with heat exchange and conditioning systems for an enhanced cooling capability. Temperature monitoring and control devices are also available upon request: the usual set comprehends PT100 thermal resistance sensors, and a control unit to give alarm and trip signals to the auxiliary circuitry. The final product can be customized for naval, industrial and railway applications, while keeping the same performances as described above.

The experience FDUEG has grown on designing cast resin transformers allows to adapt these machines to approach other sectors of application. Transformers that are completely encapsulated in resin that can be either epoxy or silicone make up for the ideal solution to be exploited for any voltage ratio in medium frequency systems, where high currents and mechanical resistance to electrodynamical stress are needed. Applications that make use of power electronics converters, as induction heating or soldering, need medium frequency machines for their reduced dimensions and great performance: FDUEG’s expertise includes the ability to design such machines while taking into account all their critical aspects and weaknesses.

Power transformer windings design and R&S

Inside the company there is a team of engineers dedicated to the research and development of power transformers, reactors and passive filters.

The engineers and technicians of the R&D Department work in team and they are able to carry out feasibility studies and cost analysis quickly. They use the best softwares for 2D and 3D modeling.

The research and development department actively collaborates with several international university institutions and research’s center.

The company’s Quality System is certified ISO 9001:2015. It has obtained ISO 9001:2008 certification in 2012.


Technical data

Distribution transformer UP TO 16 MVA UP TO 24 kV AN – AF
Medium frequency (MF) transformer UP TO  10 MVA UP TO 10 kHz WF


Industrial electric power supply
Public and commercial buildings
Renewable energies


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