Siemens has introduced a new direct current transmission system for medium-voltage AC grids from 30kV to 150kV.
This transmission system has been developed for grid operators who have to expand their infrastructure to handle the increasing volumes of power fed into the distribution system from distributed and renewable energy sources and to keep their networks stable.
The MVDC PLUS transmission system can be used for distances up to 200km.
Siemens claims to have developed the MVDC PLUS as a compact system and is available in three variants with capacities of about 50, 100 and 150 MW at DC transmission voltages of 20 to 50 kV.
The German manufacturer says that the MVDC PLUS is best suited for connecting small communities in thinly populated regions to the grid and to connect and stabilise low-power distribution grids regardless of their voltage and frequency.
The system also provides regulated power exchange between regional medium-voltage networks and microgrids. It makes it possible to use existing routes when there is a need to increase power capacity without the need to increase to high-voltage levels.
It is claimed that the transmission system lets operators set up power links between island and offshore platforms and the mainland to avoid maintenance measures and the cost of a diesel generator for backup.
It can also be used as a backup solution for medium voltage in production industry, where it can make electricity available for machines and equipment and reduce production losses. As a backup power supply for data centers, MVDC PLUS ensures, for example, classification in a quality stage (tier).
According to Siemens, MVDC technology is based on its HVDC PLUS technology, but is reduced to its basic functions. Like the HVDC PLUS, MVDC operates with voltage-source converters (VSC) in a modular multilevel converter (MMC) design, where alternating current is converted into direct current and vice versa.
Image: Siemens introduced MVDC PLUS transmission system. Photo: Courtesy of Siemens AG.