Special transformers

Where numerous and diverse industry applications are required, the need for a complete system design approach is prevalent. Since its beginning, FDUEG developed strong bonds with its customers in order to select new solutions and propose competitive special transformers, compliant in all their aspects to the needs of the clients.

Earthing special transformer - Rated for 125 kV basic impulse level (BIL) FDUEG
Three Phase Special Transformer with on load tap changer (OLTC) and six secondary windings 2700 kVA 11000- 204 up to 725 V Yd1 50 Hz AF 5800 kg FDUEG

Special transformers manufacturers, the quality of made in Italy for every type of grounding transformers and transformers for converters

Special transformers for converters

Converters exploiting power electronics components do need, for most of their applications, a transformer for galvanic insulation of the apparatus, also ensuring the correct damping of disturbances and enough decoupling from the power transmission network.

FDUEG has been, for more than 20 years, in the market of transformers designed for controlled and natural bridge rectifiers, inverters, UPS (Uninterruptible Power Supply) and similar applications.

Both single and three phase models are available, all sporting compactness and efficiency, adapt to be installed inside cabinets. The Engineering Department designs power transformers with integrated chokes on their primary windings, whose secondary voltage can be compensated in its on-load drop to feed the cascaded load with its rated parameters.

Moreover, the following is manufactured:

  • Non-standard frequency models for avionic appliances, working at 400 Hz, or special devices for which a high frequency (kHz) is needed.
  • Special application transformers, bearing particular prescriptions. These include particular conditions of acceleration during the service life (naval applications, apparatus for seismic areas or off-shore oil rigs)
  • Transformers operating with high current, for industrial plants with important rated power. Dry type rectifier transformers supporting any number of pulses are available, with the possibility to handle a few Volt and some kA-range currents, to be connected to high power AC/DC bridges.


Power electronics is a sector characterized by adaptability and flexibility, thus claiming its share in any technology application. To ensure this, FDUEG offers its experience and know-how in order to provide transformers that are perfectly compliant to any field of application.

Custom design


High performance

Grounding and protection special transformers

This kind of transformers allows to create stable earth connection points, so that overcurrents induced by a fault are channeled from the three-phase power transmission line towards ground.

Relevant features for grounding apparatus include mechanical stability (because of the high currents that may appear), a sufficiently long time constant to avoid overheating before the protection devices intervention, and a limited footprint.

Grounding transformers do not convey relevant power during a distribution system’s normal operation. However, they become fundamental in case of line malfunctions. In a fault condition, the entire structure needs to be sufficiently solid and massive in order to withstand the current variation without any damage. FDUEG proposes a solution which makes use of the least possible space within the facility, while granting its security.

Grounding transformers remain transparent with respect to positive and negative sequence voltages, while offering a low-impedance path to homopolar currents and third harmonics, improving the global power quality of their system. This means that, besides a power supply that remains undisturbed, the cascaded appliances are loaded less severely, resulting colder and extending their service life.

FDUEG produces grounding transformers for power lines up to 36 kV, built on three wound columns or on five columns of which the two on either side lack a winding. Models that are insulated in air or oil are available for both setups.

Special transformers for testing facilities

This category is the most variable with respect to the specific needs of a customer. Each test room or laboratory is different from others, thus requiring precise features for its operations. A transformer is essential for the current management of the power supply, and needs to be carefully designed based on duty cycle and loading profile of its actual usage.

FDUEG boasts numerous deliveries of its special type transformers to testing facilities with specific needs, designed to analyze and validate electromechanical switches, magnetic cores, motors or even other transformers.

In particular, the following utilization categories can be distinguished:

  • Service life tests
  • Overload tests
  • Insulation tests and power frequency withstand voltage tests
  • No load losses measurements

The offered products are solid and durable, able to effectively manage the currents and high voltages in use at the laboratory the are installed in, with any kind of service and loading profile. Each device can be equipped with transformer steps to attain a wide voltage regulation.

The construction aims at the best result in performance and quality for the machine, since exploiting a power supply whose high-level output is constant in time is a crucial aspect for a testing facility.

Vector groups Dyn11 and upon request

Besides the usual vector groups, as delta – star (Dyn11) and vice versa, FDUEG can exploit all available solution in turns combination in order to cover any need in terms of amplitude and phase shifting of primary and secondary voltages.

A system in need of a nice stability in power supply, without heavy influence from third harmonics in current, while contemporarily keeping no phase shift between primary and secondary side voltage, may use the vector group delta – zig-zag (with or without neutral). In addition to the desirable properties already listed above, it has to be considered how a zig-zag transformer connection offers a nice rejection of star point displacement, an essential quality in case of heavily unbalanced single-phase loads.

In some cases, a certain phase angle with respect to the supply is needed for the voltage output, different from the usual 30° lagging or leading. The interval between 0° and 30° can be covered by transformers with phase-shifting windings, configured either as delta with appendices or as non-symmetrical zig-zag. This kind of construction may be used, without restrictions, both as primary or secondary winding of the transformer under scope.

Systems without a specific need for galvanic separation might make use of the custom autotransformers produced by FDUEG. Models for continuous usage or for intermittent service can be designed upon request. A prominent application of these involves induction motor starting service.

Additional information at: info@fdueg.com.


Technical data

Type Power Features Protection
Transformers for converters Up to 16 MVA Up to 36 kV AN – AF – ANWF
Grounding transformers Up to 10 MVA Up to 10 kHz WF


Industrial electric power supply
Power Plants
Public, Medical and Commercial Buildings
Renewable Energies
fdueg applicazioni steelworks
Test Lab & Research Institutes
Offshore Plants
Data Centers


    Contact us
    +39 0321 824131

    Related products

    • Italian
    • English
    • French
    • German
    • Russian