High-voltage direct-current (HVDC) converter transformers
Highly efficient power transmission meets huge energy demands
Expertise and experience at Siemens Energy produce superior transformers in different HVDC schemes like HVDC Classic and HVDC Plus. HVDC converter transformers are indispensable, where highly efficient bulk power transmission for offshore and onshore grid connections is neccessary.
Interview with Stefan Klaassen, Siemens Energy’s Vice President for Power Transformers
Transformers are the important link within the energy value chain towards achieving a successful energy transition. Today, the energy landscape is changing rapidly, and our customers need to respond flexibly to power fluctuations due to renewable energy generation. Therefore, the requirements for power dissipation and continuous and reliable power transmission are higher than ever.
Worldwide availabilityAt the lead center in Nuremberg we pool an extensive know-how and make sure that the same technology and quality are available to our customers around the world, while two additional HVDC facilities in China and Brazil can keep distances for transport to a minimum. Where transmission power capability of HVDC systems is steadily increasing, our customers can rely on our experienced design teams to help master transmission and grid challenges around the globe.
HVDC makes a difference - attention to every detail
As a world-class leader synonymous with top quality and reliability, Siemens Energy enables the successful implementation of HVDC transmission systems with dedicated research and development programs.
- DC voltages: 500 kV, 800 kV, 1100 kV
- Line ratings: 3 GW, 6,4 GW 8 GW, 10 GW and 12 GW
- AC voltages: 525 kV, 765 kV,1050 kV
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 Energy delivers HVDC converter transformers including all main components to facilitate its reliable and safe operation.
Reliability lowers total cost of ownership
For operators, assessing reliability risks is crucial for evaluating the total cost of ownership of a HVDC transformer. HVDC transformers from Siemens Energy have an extremely high mean-time-between-failure (MTBF) rate, compared to our competitors. HVDC transformers from Siemens Energy reach a failure rate well below 0.5. 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 years of operation. Including failure rate (FR) and MTBF of a HVDC transformer in purchase considerations lowers your risk potential and ensures savings over the entire transformer lifecycle.
Covering the HVDC transformer market with leading competence
Hundreds of HVDC converter transformers are in successful operation all over the globe, which are active in the field since the 1970s. Challenges like in-time delivery for large order volumes or building record-setting units that meet highest technical specifications, are proof, beeing the marked leader in designing and manufacturing HVDC converter transformers .
A strong factory network around the globe creates leading HVDC converter transformer technology and pre-manufactured components. To meet public local content requirements, Siemens Energy enables and supports local transformer manufacturers to produce HVDC converter transformers based on our technology and make sure that our extensive quality standards for manufacturing processes are implemented.
Increase transformer reliability
The impact of transformer outages on the application in which they are used can be severe because outage costs may not be limited to the cost of transformer repairs. An outage of a HVDC converter transformer may result in loss of reliable energy transmission and partly outage of the grid. An effective way to minimize this risk is the continuous monitoring of key parameters during transformer operation.
Therefore, HVDC converter transformers from Siemens Energy are produced as Sensformer per default. This means they are equipped with sensors, that are transmitting operational status data to a secure storage and analytics tool. Operators can optimze operations based on customized data analytics and minimize outage times.
Bringing stability and security to the gridHVDC transformers are key components of HVDC stations for long-distance DC transmission lines or DC sea cables, off- and onshore. As coupling elements between AC grids and high-power rectifiers, they adapt the voltage, insulate the rectifier itself from the AC grid and generate the necessary phase shift.
HVDC technologies for long distances and low lossesSiemens Energy offers two HVDC technologies: HVDC Classic and HVDC Plus. HVDC transformers of Siemens Energy 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.
HVDC transformers are subject to operating conditions that set them apart from conventional system or power transformers. These conditions include:
- Combined voltage stresses with both AC and DC
Two or three high or ultra-high voltage windings but no low voltage winding inside of the transformer
- High harmonics content of the operating current
- DC pre-magnetization of the core
- Very narrow tolerances in between units, especially in terms of impedance voltage
Siemens Energy delivers line-commutated converters (LCC) for transmission lines up to 12 GW, up to 1,100 kV DC with connections to AC grids up to 1,050 kV.
The high harmonics content of the operating current results from the virtually quadratic current blocks of the power converter. The odd-numbered harmonics with the ordinal numbers of 5, 7, 11, 13, 17 cause additional losses in the windings and other structural parts. Furthermore, additional DC currents on the valve and/or neutral terminals need to be considered and managed. The high bulk power ratings also require a high rating of HVDC classic converter transformers which must share specific performance parameters, e.g. short circuit impedance.
Siemens Energy delivers voltage-sourced converters (VSC) for transmission lines up to 3000 MW, up to 800 kV DC with connections to AC grids up to 525 kV.
In HVDC Plus mono-pole applications, no DC voltage stresses occurs at the transformer valve terminals. In HVDC Plus, bi-pole applications the valve windings which are connected to the HVDC Plus rectifier/ converter circuit are subject to the combined load stress of DC and AC voltage. The harmonics content of the operating current is much lower than in HVDC Classic applications. It usually meets grid code requirements. Additional DC currents on the valve and/or neutral terminals have to be considered. They are much lower than in HVDC Classic applications.