FITformer® – Siemens' Liquid-Immersed Distribution Transformers (LiDT)

Distribution transformers by Siemens Transformers are designed for superior reliability, efficiency and environmental performance. A modular architecture paired with design options ensure cost efficiency and easy minimal maintenance.

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Combining cutting-edge technology with decades of experience

Distribution transformers can be both the last step in the conversion chain that bring electrical energy to the consumer as well as the first transformation step to feed non-centrally-generated power into the power grid. Siemens brings over 120 years of experience in transformer technology to its LiDT product line.

Improving quality of service and increasing utility revenues

For over a half century Siemens has led voltage regulator technology, continuously refining and improving its range of reliable, sturdy and innovative liquid-immersed distribution transformers.

LiDTs differ from dry-type distribution transformers in more ways than their names implies. Dry-type units are more limited in size and voltage, use air forced cooling and are often installed indoors, closer to the load. LiDTs allow for higher MVA ratings and voltages. They use oil as the coolant and are generally installed outdoors for safety reasons. LiDTs are custom-built to deliver optimized performance for a very specific consumer application.

Areas of application

Why Siemens

Performance you can rely on – anytime and anywhere

Siemens distribution transformers demonstrate high systematic quality: EN ISO 9001, harmonized design, environmental protection from production to finished transformer, daily savings with efficient transformers.

Customers worldwide trust in Siemens tried-and-tested quality – and with good reason. Siemens distribution transformers are among the most reliable in the world.    

Whether pole-mounted, installed in buildings, in residential areas, in solar or wind power stations, or in industry, distribution transformers are always located in the immediate vicinity of people. This means they must operate safely, reliably, efficiently, and quietly. Siemens offers a range of features and materials to ensure the environmental performance of their distribution transformers.

Built for sturdiness and efficiency

Tank & Cooling

Whether during transport or operation, the tank must remain sealed tight under mechanical stress and regardless of wind or weather. Corrosion protection is especially important. The surface is sandblasted and then multicoated. Upon request, hot-dip galvanization can provide even better protection.


The distribution transformer’s tank must dissipate the entire heat loss. In hermetically sealed transformers, the corrugated walls absorb the changes in the insulation liquid’s volume. Alternatively, the transformer can be designed as an open system or fitted with an oil conservator that compensates for the additional volume.


Some regions also use smooth-walled tanks and built-in radiators. Hermetically sealed units sometimes have an air or gas cushion to compensate for oil expansion. The sheet-steel lid is bolted – or, upon request, welded – to the tank. The steel thickness and the bracing are dimensioned to ensure that the lid withstands all necessary stress.


High-efficiency transformers for daily savings

Siemens Transformers offers two types of liquid-immersed distribution transformers – FITformers® and voltage regulators. They are used to convert electrical energy of higher voltage; usually up to 36 kV, to a lower voltage, usually 250 or 450 V, with an identical frequency before and after the transformation.

FITformer® IND for industrial applications

Siemens builds resilient and customizable distribution transformers which not only deliver reliable and superior performance in harshest conditions, but also perfectly fit the needs of customers in industry. Siemens’ FITformers® IND are designed to supply energy for heavy-duty drives for steel mills, oil rigs, offshore installations, and conveyance facilities, and for the complete range of uses for drives in industry.

Static converter facilities with appropriate valves are required for transforming and controlling electric energy for these applications. Static converter transformers provide the link to the supply network. They must endure heavier dynamic and thermal stress due to rapid changes in the load and allow for frequent start-uploads. Siemens’ special winding design achieves a high short-circuit withstand capability making the transformer insusceptible to the stress caused by frequent drive peak loads. Another positive factor is the great heat capacity and high overload capability of this type of transformer.

Siemens has developed a laboratory-tested painting system and corrosion protection (e.g. salt spray tests) for Siemens FITformers® IND used for application or in chemical environment.    


FITformer® REN for wind applications

Wind turbine operators need reliable and safe transformers so that the turbine never fails. With their expertise in transformers since 1892, and about 5,000 units built for wind farms in the last 10 years, Siemens Transformers has been at the frontline of wind application transformers technology. An extensive research and development budget and senior engineering experts have contributed to making Siemens Transformers the leading supplier for this application.

Transformers for wind applications convert MV to LV with identical frequency.

Ratings: ≤15MVA and ≤72,5 kV

Benefits of FITformers® REN

  • High-efficiency – low losses
  • Environmentally friendly
  • Largely maintenance free
  • Low weight, high efficiency and reliability
  • Global availability
  • Customized design


FITformer® REN for photovoltaics

Installed next to the solar panels in a transformer substation, FITformer® REN for solar application come with a rating of up to 5 MVA and a rated voltage of up to 36kV. Thanks to Siemens Transformers’ touch-proof design, FITformer® REN can be installed both outside and inside without extra housings.

Solar farms face harsh weather conditions and still need operate at all times. Its design options make FITformer® REN a highly reliable solution – resistant to high corrosion, harsh weather conditions and temperature variations.

FITformer® REN converts MV to LV with identical frequency
Ratings: ≤ 15 MVA /  ≤ 72,5 kV

Download Transformers for solar power brochure

Voltage regulators reduce energy loss from long cables and extended grids. They are used for integrating renewables into the grid. Voltage regulators are predominantly used in grids which comply with IEEE standards.


  • Cost-saving alternative to grid expansion
  • Easily integrated into existing grid structure
  • Easy installation
  • Extensive regulating range
  • Flexible regulation models for optimum operation

Siemens invented the voltage regulator in 1932. These tapped autotransformers maintain a desired voltage level, which means that their reliability is of primordial matter. Voltage regulators are a highly reliable solution for stabilizing voltage fluctuation in the customer’s grid. They are a notably more cost-efficient for customers than a medium-voltage grid expansion.

Voltage regulators and come in 1-phase or 3-phase models. Different cooling systems are available. They can be applied to any electrical system to improve voltage quality.    

The standard voltage regulator provides approximately 10% adjustment. However, in some designs, regulations of 15% and 20% are also available.

Available at 50 or 60 Hz, their ratings are calculated according to the voltage level of the transformer they are connected to (i.e., 10%). 

Voltage level ratings for 1-phase voltage regulators vary between 2.5kV and 19.9 kV and between 31.8kVA and 889kVA. 3-phase units are available at 13.2kV, 34.5kV, or from 500kVA up to 4,000kVA.

A global manufacturing and services network

Fifteen Siemens factories worldwide manufacture distribution transformers, and six of these production plants on various continents offer oil-immersed distribution transformers. Thanks to this network, Siemens customers enjoy very prompt preparation of bids, optimized end-to-end project management and order processing, noticeably shorter production and very high delivery reliability as well as accelerated, standardized documentation.

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A leader in liquid-immersed distribution technology

With over 100 years of experience in designing and building transformers, Siemens has emerged as a leader in liquid immersed distribution technology. Siemens offers the highest quality and reliability in its comprehensive portfolio of liquid-immersed distribution transformers, from renewable application to voltage regulators. Siemens creates tailored solutions that best fits customer needs.

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