The South — West scheme: A new HVAC and HVDC transmission system in Sweden

The South West scheme is an important part of the development of the Swedish national grid and is a key facility to enable the production of renewable energy, in accordance with Swedish and EU energy policy. It will reinforce the AC network, increase operational reliability, and deal with transmission limitations in southern Sweden and between Sweden and Norway. The paper describes the first phase of the project, which will consist of a new AC transmission line from Hallsberg, in central Sweden, to Barkeryd and a HVDC link from Barkeryd to Hurva, close to Malmo in southern Sweden. The HVDC scheme consists of two parallel links, each of 720MW capacity, operating at a DC voltage of ±300kV. The DC transmission system of each link comprises 190 km of XPLE underground cables plus 60km of overhead line, supplied under separate contracts. The paper describes the design of the converter stations, which are being built using Voltage Sourced Converter (VSC) technology. Each station will be configured as a symmetrical monopole, thus each circuit has two HV conductors (+ve and -ve), but there is no neutral or ground conductor. Phase 2 of the project will see a western extension of the HVDC line from Barkeryd to Tveiten in Norway to create a multi-terminal DC system. The design of the Barkeryd station allows for the future connection of underground cables, with minimal disruption to the operation of Phase 1. As part of the Phase 1 contract, Alstom Grid is designing the control and protection system suitable for multi-terminal operation when the future Tveiten station is brought into service, even if built by another vendor.