ETRA HYDRO Oil-filled power transformer


Kolektor ETRA power transformer, elevator, oil immersed, for hydroelectric power stations

Range of mineral oil power transformers from 10 to 500 MVA and up to 420 kVA, for hydroelectric power stations; custom-made power transformers manufactured in Europe.




Kolektor ETRA supplies oil-filled power transformers up to 500 MVA and voltage up to 420 kVA.

For step-up power transformers, as for production transformers in hydroelectric power stations, we pay particular attention to reducing the transformer’s noise level, as well as ensuring very low load and no-load losses. We also take into account the sizing of conductors and insulating materials to cope with production peaks linked to hydroelectric turbine output, and the effects of overheating linked in particular to sunshine or the use of the transformer in confined areas.

Low levels of no-load and on-load losses require the use of the best materials and a great deal of technological know-how, which KOELKTOR ETRA® has at, enabling us to offer you the transformer that will cost you the least throughout its life cycle, whether it is on-load or no-load. The noise levels achieved for the transformers are low enough to considerably reduce the cost of building anti-noise devices.

For hydroelectric applications, we can offer transformers equipped with ONAN, ONAF, ODAF, OFAF, ODWF or OFWF cooling systems.

Finally, thanks to our EDF-ISATION programme launched in 2016 with the SANERGRID Group and our power transformer experts SYNERDIS® , you benefit from service and technical support in French from the sales department, to the design office, via factory project management, and site project management in France thanks to our subsidiary SONEC® (see Accessories and options tab).

Accessories and options

Thanks to our SONEC® entity, for your hydraulic projects we are able to offer you essential services such as :

  • Measure and 3D scan your transformer box for a customised design to suit your constraints
  • Reconnaissance and marking out the “last kilometre”.
  • Unloading and positioning of the transformer, by ride-on truck, turtle, rigging or craning
  • Creation of a temporary storage area in flexible berms TRFLEX-ECO or TRFLEX-REFOR, or in watertight concrete with PETRO PIPE drainage skid.
  • Replacement of the remote conservatory and installation of a secure maintenance platform with climbing ladder
  • Removal of polluted pebbles from the pit of the old transformer, cleaning, lining of the pit, installation of fireproof covers for EXTICOV-CCF or EXTICOV-LHD transformers and installation of an SPI rainwater drainage system at the bottom of the retention pit.
  • Recharge your metal structures and high and medium voltage gantries with galva at ambient temperature using our unique GALVAGRID galvanic coating.
  • Protect your low and medium voltage installations from animal or plant intrusion with MIDSUN AVIFAUNE protective covers, which are plastic-free, heat-free and glue-free.
  • Installation of the SANERVIB SP high-performance anti-vibration system

Technical data

Additional information

Scope of application

Hydroelectric stations

Conditions of use


Additional information

Generic design data, which may vary according to the needs of each design:


Three grades of laminations are used:

  • Conventional C.G.O. class oriented laminations
  • HI-B high magnetic orientation steel sheets
  • Laser-treated laminations


The magnetic core, with 2, 3 or 5 legs, is stacked by overlapping individual steel sheets. The core laminations are securely held in place by heat-shrink polyglass strips and anti-magnetic steel clamps. The lower yoke and limbs are coated with glue varnish. Oscillations and vibrations caused by magnetostriction forces are thus reduced to a minimum.


The frame formed by the clamp and the legs is fixed around the magnetic core and enables the transformer to be transported safely with adequate resistance to electromagnetic short-circuit forces.


The windings are made of high-purity electrolytic copper, Cu-ETP. Single or multi-layer windings are used for phase currents up to 1000 A and nominal voltages up to 72.5 kV. Disc windings are used for higher voltage classes: helical, continuous or interlaced discs.


The specific electrical conductivity is 58 Sm/mm2.


The conventional yield strength (RP0,2 ) of conductors is 90 to 160 N/mm2.


Three thermal insulation classes are used:

  • Enamel insulation (PVA), thermal class E (120°C), compliant with IEC 60317-0-2 standard
  • 5A2-1M3 paper insulation, thermal class A (105°C), compliant with IEC 554-3-5.
  • Thermally improved paper insulation 5B1-2M3, thermal class E (120°C), compliant with IEC 554-3-5.


The transformers are equipped with a cooling system that can effectively dissipate the heat generated during operation. The cooling system is designed and tested for continuous operation with a declared capacity within the specified temperature limits. If there are no overload requirements, the cooling system is designed in accordance with IEC 60076-7. It includes radiators, various types of oil coolers or heat exchangers.

They can be separated from the reservoir and divided into several batteries or coolers, which means that installations can be assembled or dismantled quickly.

The cooling system can be separated from the reservoir and located in separate installations for better heat dissipation. In this case, the system is fitted with pumps for faster oil circulation. Only types OF and OD can be used.


Our archives contain over 4,000 different models. Most of them are currently in use in our service activities, and represent a unique source of tradition, innovation, experience and excellence.


Thanks to its team of highly experienced and trained staff, Kolektor ETRA can carry out all types of routine and special tests required by international industry standards, including IEC, EN and ANSI.

  • IEC 60076 : Recommendations on temperature rise, insulation levels and dielectric tests, short-circuit resistance and an application guide
  • IEC 60354 : Loading guide for oil-immersed power transformers
  • NF C13-200: Rules relating to the design and implementation of electrical installations whose nominal voltages are greater than 1 kV and less than or equal to 245 kV in alternating current and preferential frequencies of 50 Hz and 60 Hz.


Each core, winding, reservoir and other parts are subjected to mechanical and electrical inspection before assembly. The following operations are carried out during the assembly procedure:

  • Voltage ratio interphase measurement
  • Measurement of insulation resistance
  • Measurement of short-circuit loss before the drying process
  • Monitoring the drying process and transformer oil

Thanks to our SONEC® service business, we are qualified and able to support you in your projects with repair work, rebuilds and various overhauls of transformers, their components and equipment.

Contact us with details of your site and project requirements.


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