ABB Review Special Report - ABB - ABB Group

The problem was solved in 1929 by aproposal to insert grading electrodesbetween the anode and cathode. Subsequentlypatented, this innovative solutioncan in some ways be considered asthe cornerstone of all later developmentwork on the high-voltage mercury-arcvalve. It was during this time that Dr.Uno Lamm, who led the work, earnedhis reputation as ‘the father of HVDC’.The Gotland linkThe time was now ripe for service trialsat higher powers. Together with theSwedish State Power Board, the companyset up, in 1945, a test station at Trollhättan,where there was a major powerplant that could provide energy. A 50-kmpower line was also made available.Analog simulator used in the design of the early HVDC transmission systemsTrials carried out over the followingyears led to the Swedish State PowerBoard placing, in 1950, an order forequipment for the world’s first HVDCtransmission link. This was to be builtbetween the island of Gotland in theBaltic Sea and the Swedish mainland.over which AC at ever-higher voltagesflowed. To bridge expanses of water,submarine cable was developed.Neither of these transmission media waswithout its problems, however. Specifically,they were caused by the reactivepower that oscillates between the capacitancesand inductances in the systems.As a result, power system plannersbegan once again to look at thepossibility of transmitting direct current.Back to DCWhat had held up high-voltage directcurrent transmission in the past was,first and foremost, the lack of reliableand economic valves that could convertHVAC into HVDC, and vice versa.The mercury-arc valve offered, for a longtime, the most promising line of development.Ever since the end of the 1920s,when the Swedish ASEA – a foundingcompany of ABB – began making staticconverters and mercury-arc valves for voltagesup to about 1000 V, the possibilityof developing valves for even higher voltageshad been continually investigated.This necessitated the study of new fieldsin which only a limited amount of existenttechnical experience could beapplied. In fact, for some years it wasdebated whether it would be possibleat all to find solutions to all the variousproblems. When HVDC transmissionfinally proved to be technically feasiblethere still remained uncertainty as towhether it could successfully competewith HVAC in the marketplace.Whereas rotating electrical machinesand transformers can be designed veryprecisely with the aid of mathematicallyformulatedphysicallaws, mercury-arcvalve designdepends to alarge degreeon knowledgeacquiredempirically.As a result, attempts to increasethe voltage in the mercury-vaporfilledtube by enlarging the gap betweenthe anode and cathode invariablyfailed.Following on this order, the companyintensified its development of the mercury-arcvalve and high-voltage DC cable,while also initiating design work onother components for the converter stations.Among the equipment that benefitedfrom the increased efforts weretransformers, reactors, switchgear andthe protection and control equipment.Even when HVDC transmissionfinally proved technically feasible,it was doubted for a long timewhether it could compete withHVAC in the marketplace.Only some of the existing AC systemtechnology could be applied to the newDC system. Completely new technologywas thereforenecessary.SpecialistsinLudvika,led byDr. ErichUhlmannandDr. HarryForsell, set about solving the many verycomplex problems involved. Subsequently,a concept was developed for the Gotlandsystem. This proved to be so successfulthat it has remained basically unchangedright down to the present time!Since Gotland is an island and thepower link was across water, it was62Special ReportABB Review