Development of HVDC thyristor valves and HVDC transmission technologies in the last two decades makes the electric power transmission by HVDC more economical and reliable nowadays. Using of HVDC for bulk power transmission becomes even blooming. Modern HVDC thyristor valves are characterized in the module design

high power and water-cooled thyristors

intelligent thyristor control unit

comprehensive computer valve control and rigorous tests. The use of capacitor commutated converters

digital optical instrument transformers

active DC filters and continuously turned AC filters enhances the HVDC power transmission quality significantly and yields a more robust HVDC transmission system as a consequence. Voltage source converter as a new generation of HVDC makes the small power transmission economically feasible.