How does hvdc work

Thus, the majority of transmission lines carrying power around the world are of the AC type. However, there are instances when high-voltage direct current HVDC transmission systems offer significant benefits.

The challenge, however, is that to transmit via HVDC, two converter stations are needed. First, the AC power must be converted to DC to begin the transmission process, and then when it gets to the desired tie-in destination, the DC power must be converted back to AC to be utilized on the grid.

Conversion technology is well-established. Electrical pioneers were working on the building blocks for HVDC-links back in the late s. Conventional HVDC converter technology is based on the use of line-commutated or phase-commutated converters.

The original Gotland link could transfer 20 MW over a kilometer km -long submarine cable with a voltage of kV. The service was re-engineered in , increasing capacity to 30 MW at a voltage of kV through the addition of a thyristor valve bridge. VSC technology uses gate turn-off switching devices, such as insulated-gate bipolar transistors IGBTs , to perform the conversion. An IGBTs high switching frequency capability allows more-precise VSC control and less-complex circuit configuration through the use of pulse width modulation techniques.

MMC technology offers excellent harmonic performance and reduced power losses compared to previous VSCs. Vince Curci, underground transmission project manager with HDR, said one of the advantages of VSC technology is that it is very compact. That makes them a good choice for offshore wind farms. So, the advantage of this new technology is that you can put them at sea on a small footprint and transfer power to land via submarine cables.

One example of that is the DolWin2 project Figure 1. Thus, the conversion and inversion equipment are also needed at the two ends of the line.

HVDC transmission is economical only for long distance transmission lines having a length more than kms and for underground cables of length more than 50kms. In generating substation, AC power is generated which can be converted into DC by using a rectifier. In HVDC substation or converter substation rectifiers and inverters are placed at both the ends of a line. The DC is flowing with the overhead lines and at the user end again DC is converted into AC by using inverters, which are placed in converter substation.

Hundreds of HVDC converter transformers are in successful operation all over the globe. Active in the field since the s, we benefit from a 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.

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.

However, to ensure high HVDC converter transformer reliability, Siemens Energy implements in-house prototype design and manufacturing. HVDC transformers are used as coupling elements between AC grids and high-power rectifiers to carry power onshore or bridge long distances. Back-to-back links are an easy solution for connecting two AC networks with deviating frequencies. Grid operators not only strengthen and optimize the performance of their grids with back-to-back links.

They also allow both: network users to balance varying loads and generation caused by different time zones or usage patterns. With about one third of HVDC lines worldwide past the year mark, operators need to decide — invest in repairs that will give them an as-good-as-new transformer from the s, or benefit from the latest technology?

Our engineers excel in replacing HVDC transformer originals, producing units that replicate performance, capacities and dimensions of the original unit, but offer the latest in transformer innovation.

HVDC transformers are subject to operating conditions that set them apart from conventional system or power transformers. These conditions include:. Two or three high or ultra-high voltage windings but no low voltage winding inside of the transformer. GE has designed, delivered and supports an installed HVDC capacity of more than 35 GW globally in a broad range of applications and environments. The below details are a selected representation of HVDC projects.

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