Dry Type Transformers – VPI FDUEG

Since its foundation in 1995 FDUEG has specialized in producing dry type transformers, insulated in resin through VPI (Vacuum Pressure Impregnation) technique. Products are built as series or custom, up to the power of 16 MVA and medium voltage insulation levels of 52 kV.

Three-phase transformers are destined to all sectors somehow connected to electrical energy, from production to distribution, from industry to naval applications, to the railway sector and power electronics.

Each dry-type transformer’s design aims at attaining a long lifespan, high efficiency, low losses and footprint reduction.

Dry-type VPI LV-MV transformers with power rating up to 16 MVA: an excellent alternative to cast resin

Vacuum Pressure Impregnated (VPI) transformers are alternatives to liquid insulated and cast resin transformers.

Dry-type VPI transformers offer better characteristics with respect to the other two types: mechanical compactness and dielectric stability due to resin impregnation, together with the usage of an insulating fluid, air, which does not show aging nor has needs in terms of maintenance.

This technique involves impregnating the transformer with polyester or epoxy resin under a vacuum atmosphere, so that air bubbles, dust and small particles are substituted with dielectric resin, this way eliminating any possible cause of local weakening in the insulation system. The subsequent polymerization in oven, through controlled thermal cycles, solidifies conductor materials, insulation and resin in a single piece, to attain superior mechanical and electrical characteristics.

The insulating structure obtained this way generates the best compromise between resin impregnated paper (within the windings) and air (separating windings and earthed parts). The dielectric strength is, for its major part, sustained by air, greatly reducing the quantity of material that may be subjected to fire hazard. The solid materials used (aramid paper or mica and fiberglass) are carefully selected for their self-extinguishing properties and represent a small percentage of the electrical machine weight, especially in comparison with cast coil transformers.

All of FDUEG transformers built through this technique are certified F1 class for what involves flammability and combustion gas emissions.

Another advantage of VPI technology resides in noise emission limitation, given by magnetostriction in the transformer’s core: the insulating resin, in fact, notably reduces vibrations while the primary winding is fed, both in no-load working condition and under the effect of relevant currents.

Special dry type transformers

FDUEG answers to diverse requests from multiple application sectors with specific solutions, made possible by the versatility of a constructive technology that is simple and of proved efficacy. The many solutions available for the construction of iron core, primary and secondary windings allow to use different cooling media and systems (natural or forced air, water) to drive the design stage. Two decades of cooperation with the largest players in the sector of energy distribution permit to deeply understand the needs of every application area for dry-type transformers and to offer the best solution in both technical and economic terms.

The offer from the Engineering Department is complete and continuously evolving, with a technical office ready to analyze and solve any of the customers’ needs. The criteria for compactness, efficiency and trustworthiness in time of the product stand still as guidance for the company’s production, being it in series or for a single piece.

Dry type transformer, application sectors

FDUEG recommends its dry type transformers to the whole energy sector: from production to usage, through transmission.

• Power electronics: transformers used to feed converters, rectifiers, inverters and UPS. Models with more than one secondary winding are available, with integrated choke and functioning in medium frequency.
• Electrical distribution: MV/LV dry type distribution transformers, with power ranging from a few tens of kVA to some MVA. They are available also for PV plants and wind farms. The company, moreover, sports a line dedicated to the EcoDesign EU standard.
• LV transformers: signal or insulation transformers, or used to feed auxiliaries in all industry sectors, steelworks, the IT sector (data centers) and transportation (being it naval, through railways or airports). Special machines, deputed to marine propulsion, are produced.
• Testing Lab: LV and MV transformers bearing special load profiles or adapt to sustain high current and stress tests of electrical equipment.

For every model, protection boxes sporting IP degrees from 21 to 44 are available, even with special finish for harsh environments or high ambient temperature.

Dry type transformers: durability and reliability

Bearing no moving parts and a precise design, FDUEG transformers can easily last more than twenty years in service.

The electrical, thermal and mechanical effects are thoroughly considered. Air sustains the dielectric strength, while the insulation resin is applied through vacuum impregnation in a fine layer, that is extremely resilient to local breakdowns.

Air, besides, grants a constant heat exchange, limiting the temperature rise and preventing the formation of hot spots, thus slowing down the thermal aging of the static machine. A careful design stage allows to avoid local high temperatures, which, on the long run, may reduce the transformers’ lifespan. The complete structure of the machine must be conveniently pressed through tie-rods, so that the noise is reduced and the resistance to electrodynamic effects is insured in time, granting mechanical strength.