a es r up to ± 300 kV and lOOOMW 1. lntroduction The electricity networks of today increasingly need control and stability at high levels of loading. lncreasing the stability through adding more lines is not always an option due to restrictions in right-of-way or limits to acceptable short circuit current. Here, HVDC transmission solutions using undergrounding through extruded cables systems offer unique advantages. For instance, voltage source converters (VSC) do not add to the short-circuit power while extruded cables systems offer easy installation for both land and submarine applications. Recent developments in four major fıelds; valves, cable system, system design and HVDC control has opened the possibility to the increase the power rating of VSC based HVDC and greatly expand the area of application. 2. Valves Adding more components in series increases DC-voltage handling in a fairly straightforward manner. Current handling may be improved in several ways, whereof the most important are to increase semi- conductor active area in the IGBT-modules, improve cooling and optimize switching. 1 Converter Valves DC Capacitors (Volage Source) Cables Phase Reactors AC Harmonic Filters 7 AC Transformers, breakers/disconnectors Figııre 1. Siınplifiedcircııit diagraınfor 2-level VSC HVDC slıowing tlıe ıııajor coıııponenıs of t/ıe ;ysteııı. - -1
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