Power transformers for high-voltage direct-current (HVDC) transmission systems

Tailored-to-fit and delivered fully-assembled, HVDC transformers by Siemens enable reliable and highly-efficient HVDC power transmission systems

Siemens expertise and experience produces superior transformers for the HVDC schemes, HVDC Classic and HVDC Plus, in bulk power transmission, offshore and onshore grid connections, back-to-back systems and other HVDC use cases. Portfolio: transformers, upgrades, replacement, repair, refurbishment, and the supply of selected components HVDC ratings: up to 12 GW and up to 1,100 kV DC AC grid connections: up to 1,050 kV AC Features: Compact designs, high reliability, and proven technology from Siemens’ global manufacturing network

Find out how to best specify an HVDC transformer for your application

Download the HVDC design checklist

Innovation, nov 7, 2017 - ene 24, 2019

Direct-current electricity can now be transmitted at gigantic 1,100 kilovolts

The world´s first transformer, which has been designed and manufactured for the HVDC transmission line with the highest direct-current electricity of ± 1,100 kilovolt (kV) has been dispatched from Nuremberg, Germany. The transformer is now on its way to its Chinese destination. This will take approx. three months. In the future the transformer will enable low-loss and extremely efficient high-voltage direct-current (HVDC) power transmission over a record distance of 3,284 kilometers with a transmission capacity of twelve gigawatts.

Power Grids of the Future

Smarter, more sustainable power grids with HVDC

Deregulation, privatization, growing demand, and environmental considerations have grid operators facing a new challenge: building secure and efficient power grids that delivers clean, reliable, and affordable power over long distances to increasingly urbanized societies. Innovative HVDC transformers play a key role in shaping environmentally sustainable power grids while offering economic efficiency.

Smart grids are emerging as a necessary response to the environmental, social and political demands placed on energy supply.


With their capacity to increase transmission efficiency, innovative HVDC solutions will play a key role in making sustainable low-loss AC/DC hybrid grids a reality. With the transmission power capability of HVDC systems steadily on the rise, requirements for converter transformer technology and design have greatly increased. Customers rely on Siemens’ experienced design teams to help them master transmission and grid challenges around the globe.

HVDC Technologies

Bringing stability and security to grid and transmission

HVDC transformers are key components of HVDC stations for long-distance DC transmission lines or DC sea cables. As coupling elements between AC grids and high-power rectifiers, they adapt the voltage, insulate the rectifier itself from the AC grid, and generate a phase shift.
Download: “Ensuring efficient flow of bulk energy”

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HVDC technologies for long distances and low losses

Siemens offers two HVDC technologies: HVDC Classic and HVDC Plus. Siemens transformers meet all requirements for power, voltage, mode of operation, low-noise, connection types, types of cooling, transport, and installation. They also comply with specific national design requirements.
Why Siemens

Siemens HVDC transformers make a difference

As a world-leading manufacturer, systems integrator, and provider of transformer solutions and services with a strong local presence, Siemens experts are there wherever and whenever you need them to assist, consult, and provide service. The lead center in Nuremberg ensures that the same extensive know-how and the same technology and quality are available to our customers around the world, while four HVDC facilities across the globe can keep distances for transport to a minimum.    

Experience in project execution and operational excellence

Hundreds of Siemens HVDC Converter transformers are in successful operation all over the globe. Active in the field since the 1970s, Siemens Transformers has huge experience in designing and manufacturing HVDC units. Rising to challenges, from in-time delivery for large order volumes to building record-setting units that meet highest technical specifications, Siemens stands out for trademark reliability and customer focus.


Reliability lowers total cost of ownership

For operators, assessing reliability risks is crucial for evaluating the total cost of ownership of an HVDC transformer. Including failure rates (FR) and mean-time-between-failure rates (MTBF) of a Siemens HVDC transformer in purchase considerations lowers your risk potential and ensures savings over the entire transformer lifecycle.


Siemens transformers reach a failure rate well below 0,5 percent. According to the international standard defined in IEEE C 57.117 this translates into excellent product reliability. It equals an MTBF rate of more than 200 service years.    


Attention to every detail, from design to delivery

Siemens has been pioneering transformer technology, since the dawn of HVDC converter transformer production. As a world-class leader synonymous with top quality and reliability, Siemens enables the successful implementation of HVDC transmission systems with dedicated research and development programs.


-       DC voltages: 500 kV, 800 kV, 1100 kV

-       Line ratings: 3GW, 6,4GW 8GW, 10GW and 12 GW

-       AC voltages: 525kV, 1050kV


Designing and building a HVDC transformer is a complex process. The insulation to ground and between line and valve winding has to withstand AC and DC stresses. Valve windings need to be tested with voltages determined by the protection level of the DC side. Harmonics in currents cause losses in various parts and DC currents influence the magnetization of the core.


Siemens ensure that the quality of the core sheet, the lamination of the sheets, and the nominal induction all conform to rigorous requirements covering losses, noise level, overexcitation, etc.


Siemens Transformers delivers HVDC converter transformer including all main components to facilitate transportation, installation, and safe operation.


Leading competence at the local doorstep

A strong Siemens transformer factory network around the globe creates leading HVDC Converter transformer technology and pre-manufactured components.


To meet public local content requirements, Siemens enables and supports local transformer manufacturers to produce HVDC converter transformers based on Siemens technology. However, to ensure high HVDC converter transformer reliability, Siemens Transformers implements in-house prototype design and manufacturing.


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Success stories and case studies

Learn more about latest applications of Siemens’ HVDC transformers

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For your convenience, we have gathered relevant downloads in one spot. If your question is still unanswered, please feel free to contact our Energy Support Team.    

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Ready to meet any challenge

With a superior track record for meantime-between-failure, on-time delivery, and for first-pass-yield, Siemens’ experience, expertise, and dedication to excellence reflect in a wealth of milestone references.        

Pioneering transformers for the world's largest HVDC transmission project



500 kV

DC transmission voltage

0 GW

transmission capacity

With local partners Siemens will deliver the HVDC link between Changji and Guquan, operated by State Grid Corporation of China. It is the world's largest and first HVDC transmission link with a 1,100-kV transmission voltage.    

Transmission losses of less than 4 percent for TenneT

0 million

households supply capacity

0 kV

AC input offshore

100 kV

DC HVDC link

The German-Dutch network operator TenneT contracted Siemens for its North Sea grid connection, SylWin 1. The AC produced offshore is converted to DC power and transported by 205-km subsea cables to the German mainland. 

Connecting Texas to the Southwest power pool

0 kV

DC transmission voltage    

100 MVA

DC capacity

200 MW

power rating

The 170 kV DC Welsh Converter Station in Texas links the network of the Energy Reliability Council of Texas with the Southwest Power Pool of the eastern US network. The back-to-back tie is equipped with 7 Siemens transformers. It operates at a power rating of 600 MW at a voltage level of 345/345 kV, 60/60 Hz.    


Find out how to best approach specification of your HVDC transformer custom-built by Siemens specialists

Do you need a tailored HVDC solution to tackle challenges in transmission or connecting power grids? Tell us your requirements and we will find the right product for you. The Siemens HVDC design checklist helps you make the process quick and efficient.