ABB Review Special Report - ABB - ABB Group

During the 1960s several HVDC linkswere built: Konti-Skan between Swedenand Denmark, Sakuma in Japan (with50/60 Hz frequency converters), theNew Zealand link between the Southand the North Islands, the Italy – Sardinialink and the Vancouver Island linkin Canada.Early mercury-arc valve for HVDC transmissionalso necessary to manufacture a submarinecable that could carry DC. It wasseen that the ‘classic’ cable with massimpregnated paper insulation that hadbeen in use since 1895 for operationat 10 kV AC had potential for furtherdevelopment. Soon, this cable wasbeing developed for 100 kV DC!Finally, in 1954, after four years of innovativeendeavor, the Gotland HVDC transmissionlink, with a rating of 20 MW,200 A and 100 kV, went into operation.A new era of power transmission hadbegun.The original Gotland link was to see28 years of successful service beforebeing finally decommissioned in 1986.Two new links for higher powers havemeanwhile been built between theisland and the Swedish mainland, onein 1983 and the other in 1987.The largest mercury-arc valve HVDCtransmission link to be built by thecompany was the Pacific Intertie [1] inthe USA. Originally commissioned for1440 MW and later uprated to 1600 MWat ±400 kV, its northern terminal is sitedin The Dalles, Oregon, and its southernterminal at Sylmar, in the northern tipof the Los Angeles basin. This projectwas undertaken together with GeneralElectric, and started operating in 1970.In all, the company installed eight mercury-arcvalve based HVDC systemsfor a total power rating of 3400 MW.Although many of these projects havesince been replaced or upgraded withthyristor valves, some are still in operationtoday, after 30 to 35 years ofservice!Mercury-arc valves in the first Gotland link,1954The semiconductor ‘takeover’ beginsMercury-arc valve based HVDC hadcome a long way in a short time, but itwas a technology that still harboredsome weaknesses. One was the difficultyin predicting the behavior of thevalves themselves. As they could notalways absorb the reverse voltage, arcbacksoccurred. Also, mercury-arcvalves require regular maintenance,during which absolute cleanliness iscritical. A valve that avoided thesedrawbacks was needed.The invention of the thyristor in 1957had presented industry with a host ofnew opportunities, and HVDC transmissionwas soon seen as a promising areaEarly HVDC projectsThe early 1950s also saw the British andFrench power administrations planninga power transmission link across theEnglish Channel. High-voltage DCtransmission was chosen, and the companywon its second HVDC order – thistime a link for 160 MW.The success of these early projects generatedconsiderable worldwide interest.Gotland 1 extension, with the world’s first HVDC thyristor valvesSpecial ReportABB Review63