The valves in HVDC Light form in its basic configuration a two-level three-phase bridge with six valves.
Each valve consists of a number of series connected IGBTs. (Read more about ABB's StakPak IGBT design here. For high power ratings more than hundred are connected in series.
Even voltage distribution is achieved during all phases of operation with a special gate unit and a voltage divider for each IGBT level.
The IGBT together with voltage divider, gate unit and heat-sink is mounted in a stack (up to 30 level in a stack) as a mechanical unit. Turn on/off of each single IGBT is ordered via an optical link from the valve control on ground potential. The IGBT level is cooled with de-ionized water. ( Link to: SwedeWater )
The valve is of indoor design and normally mounted in enclosures at the factory. (See picture!)