ETRA HYDRO Oil-filled power transformer

Description

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).

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

Additional information

Scope of application	Hydroelectric stations
Conditions of use	outside

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 (R_P0,2 ) 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.

 

 

Oil-Immersed Power Transformer for Hydroelectric Power Plants

What is the role of the ETRA HYDRO transformer in a hydroelectric power plant?

The ETRA HYDRO oil-immersed power transformer is specifically designed to step up voltage at the generator output of hydroelectric facilities, between the powerhouse and the grid connection substation.

It adapts the voltage generated by the turbo-generator set to the required transmission grid voltage levels, ensuring:

• High operational safety margins
• Excellent electrical stability
• Long-term reliability under continuous load

Engineered from the outset for the specific constraints of hydropower plants, ETRA HYDRO combines electrical performance, mechanical robustness, acoustic control and integration flexibility — both for new hydroelectric projects and like-for-like transformer replacement.

Distributed by SYNERDIS®, the commercial entity of the SANERGRID® Group, this product benefits from full French technical support and turnkey commissioning assistance provided by SONEC – KESF (KOLEKTOR ETRA Service France) teams.

Why choose an ETRA HYDRO power transformer for a hydropower project?

Can it handle high power and high voltage ratings?

Yes. The ETRA HYDRO transformer range covers a wide spectrum of configurations:

• Power ratings typically from 10 to 500 MVA
• Voltage levels up to 420 kV, depending on grid connection schemes

Available configurations include:

• One or two HV windings
• Optional auxiliary tertiary winding
• Multiple vector groups (YNd11, YNyn0, Dyn, etc.)

Options include:

• On-Load Tap Changer (OLTC)
• HV bushing extensions
• Josse expansion systems
• SF6 cable terminations
• Remote conservators

This flexibility enables seamless integration in both new hydropower plants and refurbishment projects, without major modification of existing interfaces, while optimizing losses and footprint.

Is it designed to withstand hydropower operating stresses?

Yes. Windings are dimensioned to withstand:

• Generator start-up transients
• Rapid load variations
• Thermal stresses specific to hydraulic alternators

High-conductivity Cu-ETP copper windings are manufactured using Continuously Transposed Conductors (CTC) or foil windings depending on voltage levels. This design:

• Reduces hot-spots
• Minimizes skin effect
• Enhances short-circuit withstand capability

Axial and radial clamping, core compression systems and anti-buckling structures ensure mechanical strength compliant with the most demanding international standards.

Loss reduction and acoustic performance

How does ETRA HYDRO reduce electrical losses?

The magnetic core is built from grain-oriented low-loss silicon steel laminations, assembled using step-lap joints. This design provides:

• Significant reduction in no-load losses
• Improved overall efficiency throughout the transformer lifecycle

On request, fine loss optimization can be performed to match the plant’s operational profile:

• Base load operation
• Load modulation
• Seasonal variations

Result: reduced total cost of ownership (TCO), controlled temperature rise, and extended oil and insulation lifetime.

How is noise level controlled?

Hydroelectric plants are often located near residential areas or environmentally sensitive zones. Therefore, low acoustic emissions are integrated at the design stage.

The optimized magnetic core reduces electromagnetic vibrations, while core clamping and leakage flux optimization minimize sound emissions.

Cooling systems are selected to balance thermal performance and noise reduction. Silencers and acoustic enclosures can be provided where strict regulatory thresholds apply.

Available cooling modes

Cooling selection impacts transformer compactness, acoustic performance and overload capability.

ETRA HYDRO is available in:

• ONAN – Oil Natural Air Natural
• ONAF – Oil Natural Air Forced
• OFAF – Oil Forced Air Forced
• OFWF – Oil Forced Water Forced

In powerhouse buildings, OFAF and OFWF solutions allow heat containment while controlling acoustic impact through remote heat exchangers and variable speed drives.

Pumps and fans can be redundant and thermally controlled. Flow and pressure sensors facilitate diagnostics and predictive maintenance while increasing operational margins during peak load periods.

Reliability and protection systems

The ETRA HYDRO transformer complies with IEC 60076 and integrates all standard protection devices for safe operation:

• Buchholz relay
• Pressure relief device
• Oil and winding temperature indicators (OTI / WTI)
• Oil level indicator
• Silica gel air breather
• OLTC protection and monitoring (IEC 60214)

HV bushings are dimensioned according to required lightning impulse withstand levels and power-frequency voltage ratings, with site-specific configuration options.

Factory testing and quality assurance

Each transformer undergoes the full routine test sequence defined by IEC 60076:

• Loss measurements
• Ratio and vector group verification
• Insulation resistance tests
• Dielectric tests
• Noise level measurement
• Accessory verification

Type and special tests available upon request include:

• Short-circuit withstand test (IEC 60076-5)
• Thermal endurance
• SFRA diagnostics
• Lightning and switching impulse tests
• Partial discharge measurements
• Helium leak testing for specific configurations

For international projects, EN and ANSI compliant test protocols are available.

For over 10 years on the French hydropower market, KOLEKTOR ETRA HYDRO transformers have been installed for major French utilities (CNR, EDF Hydro, Hydrostadium).

At 63 kV, 90 kV and 225 kV levels, more than 30 units are currently in production and factory tested.

The strength of KOLEKTOR ETRA HYDRO: Proven engineering expertise

KOLEKTOR ETRA benefits from an extensive design database of more than 4,000 archived transformer models, developed over decades across European and international transmission networks.

This technical library accelerates transformer definition based on similar power ratings, voltage levels, vector groups and installation constraints — while maintaining fully project-specific engineering.

Result: faster design, increased robustness and perfect adaptation to the specific constraints of your hydroelectric plant.

Why contact SYNERDIS for your oil-immersed hydroelectric transformer?

A single point of contact from design to operation

SYNERDIS, commercial entity of the SANERGRID Group, coordinates your entire project:

• Technical studies
• Interface with KOLEKTOR ETRA factory
• Project management
• Logistics coordination
• Transport and on-site installation
• Oil filling under vacuum
• Site acceptance testing
• Commissioning and operational follow-up

You benefit from French-speaking technical support close to your field teams, combined with the industrial strength of a leading European transformer manufacturer.

Risk mitigation and schedule security

SYNERDIS anticipates civil engineering, handling and connection constraints:

• Road width and access
• Site altitude and climate
• Transport and delivery conditions

Environmental risk management engineering note

SANERGRID can also support compliance upgrades of transformer oil containment systems:

• Oil pit refurbishment and waterproofing
• Fire-protection systems (EXTICOV)
• Rainwater evacuation systems (SPI, PETROPIPE)
• Remote oil containment pits (DEPOSIT)
• Galvanized structure re-treatment (GALVAGRID)

Turnkey installation includes radiator and bushing assembly, vacuum treatment, oil filling and on-site acceptance testing prior to grid coupling.

Long-term service and lifecycle support

Through SONEC, the SANERGRID service entity, you benefit from long-term support:

• Preventive and corrective maintenance
• Spare parts supply
• Field interventions
• Modernization (OLTC retrofit, bushings, monitoring systems, cooling upgrades)

Additionally, the TECHNIKELEC platform facilitates online purchase and reservation of transformer parts and accessories throughout the equipment lifecycle, with available stock for emergency situations.

Contact SYNERDIS for your ETRA HYDRO transformer project

Planning the purchase or replacement of a hydroelectric power transformer?

An ETRA HYDRO transformer can be efficiently defined based on key parameters:

• Target power rating
• Generator-side and grid-side voltages
• Impedance
• Vector group
• Cooling mode
• Ambient conditions and altitude
• Target sound level
• Required accessories
• Transport and installation constraints

Even with partial data, our teams will complete the specification with you and propose a configuration fully adapted to your hydroelectric installation.

Based in Lyon, at the crossroads of the Jura, Alps, Massif Central and Pyrenees regions, SYNERDIS provides responsive local support backed by KOLEKTOR ETRA’s industrial expertise.

From design to maintenance, we stand by your side to transform hydropower into safe, reliable electricity delivered to the grid.