Guide for upgrading transmission systems with HVDC transmission

Following the installation of the first HVDC transmission scheme between Sweden and the Island of Gotland in 1954, over 60 HVDC schemes throughout the world have been installed. Since their initial installation many of the HVDC schemes have been upgraded in various ways. By reviewing both what has been achieved in terms of upgrading and what potentially is possible to accomplish in an upgrade, this guide provides direction and the latest information on the subject.