Sweden Made DC Great Again

TL;DR

Sweden's ASEA revived DC power transmission through HVDC technology, solving AC's submarine cable limitations and enabling long-distance power links impossible with AC.

Key Points

• 1.Edison's DC system was fatally limited by transmission range. Pearl Street's low-voltage DC could only economically serve customers within half a mile, making it viable only in dense cities, while AC transformers enabled power transmission 40+ kilometers from Turin to Lanzo as early as 1884.
• 2.AC won the 'Battle of the Currents' decisively by 1892. Edison's PR campaign labeling AC 'dangerous' failed; his company merged with Thomson-Houston to form General Electric, and Oscar Von Miller's 176km Frankfurt-to-Lauffen AC line in 1891 settled the long-distance debate permanently.
• 3.AC has a fundamental weakness in subsea cables due to capacitance. Underground cables act as giant capacitors; at 50–100km, most AC current is wasted charging the cable rather than delivering power, making DC the only viable option for long submarine links.
• 4.Swedish engineer Uno Lamm spent 40 years solving the arc-back problem in mercury arc rectifiers. Joining ASEA in 1929, he invented grading electrodes to suppress destructive reverse arcs, achieving a commercially viable 60kV rectifier by 1944 and enabling the world's first HVDC subsea link.
• 5.The 1954 Gotland HVDC link was the pivotal moment DC returned. Led by Lamm, the $4.5M project ran a 98km subsea cable at 100kV and 20MW from Vastervik on the Swedish mainland to the island of Gotland, attracting international attention and spawning 11 ASEA HVDC projects worldwide.
• 6.The thyristor replaced mercury arc valves and transformed HVDC reliability. Introduced in 1957 and first installed at Gotland in 1967, this solid-state semiconductor eliminated arc-backs, was sturdier, and eventually gave way to the even more advanced IGBT for modern HVDC systems.
• 7.HVDC has scaled massively since Gotland, with China and Brazil leading modern projects. ABB delivered the 3.1GW, 600kV, 785km Itaipu HVDC line in Brazil in 1985; China's Xiangjiaba link surpassed it in 2010, proving AC and DC are complementary tools rather than rivals.