Dry cast resin transformers have important benefits over oil cooled transformers

ELECTRICAL specialists Legrand’s range of Cast Resin Transformers (CRT) has been designed for high-efficiency, enhanced safety and low environmental impact during energy distribution in diverse applications. Typical installations include data centres, shopping malls, hospitals and residential buildings. CRTs are also suitable for photovoltaic (PV) installations and wind power, as well as offshore applications, the railways, shipping and airport facilities.

Legrand CRTs – which efficiently transfer electrical power between two different voltage systems, at the same frequency – ensure reduced electricity consumption and minimal energy waste.

According to Legrand specialists, there are important advantages of CRT transformers over traditional oil cooled units. The major benefits are reduced environmental impact, easy installation, low maintenance requirements, flexibility in use and efficient operational costs.

Unlike conventional oil cooled transformers, which are highly flammable, these eco-friendly transformers have no risk of insulating fluid losses and are a low fire hazard – even in harsh environments, like the mines and chemical and petrochemical plants. The robust construction of these units can withstand high thermal shocks and enables safe operation in damp, salty and polluted environments.

The compact CRT system has been designed for low maintenance requirements, which significantly reduces operational costs. Because no cooling fluids are necessary in the system, no oil analysis, refilling or oil purifications are needed. In addition, the absence of flammable insulation liquids, the use of self-extinguishing materials that are exempt of toxic gas emissions, reduced noise levels and low electromagnetic emissions, ensure greater safety and enhanced environmental protection in all sectors.

As cast resin units operate on the principle of air cooling and take longer to reach operation temperature, they are particularly well suited to feed loads with frequent current breakaway starting current.

Lower installation costs

Dry type cast resin units have smaller weight, size and dimensions than oil transformers and with the absence of cooling fluids, they can be safely installed inside commercially occupied buildings. CTR’s installed inside the building can be closer to the loads, with the advantage of minimising connection costs and reducing losses in the supply line. Civil costs are also lower, as there is no need to cater for the construction of oil containment bunions.

Legrand CRTs have notable features for enhanced efficiency and optimum safety. Rubber inserts alleviate the transmission of vibrations between core and windings, also reducing operating noise levels and absorbing thermal expansion of components. Sockets on the MV side adapt the primary voltage to the mains, which can be set with the transformer switched off.

Class F insulating material, at 155°C, allows for a temperature rise of 100°C and the epoxy resin insulation means low maintenance. The carriage of these units, which allow safe movement, is pre-equipped for the mounting of IP reinforced enclosures.

Legrand’s standard distribution transformers have rated power between 100 and 3 150 kVA, primary rated voltage up to 36 kV and secondary rated voltage up to 433 V. Special transformers have rated power up to 17 000 kVA. The variable impedance level selection enhances the options on the fault level requirements and various tap settings are also available.


Accessories include thermal sensors or thermistors, electronic units for temperature control and forced ventilation systems to increase transformer power in temporary overloads or at high environmental temperatures. Legrand can also supply MV terminations for plug-in connections, surge arrester kits and anti-seismic supports. Various enclosure options are available, with different degrees of protection against the environment, as well as for human protection.

The synergy of products from Legrand group companies facilitates seamless integration between power distribution systems, to provide the guarantee of a certified distribution system.

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