Back in the Victorian era, the first power stations in Europe and the USA supplied low-voltage, direct current (DC) electricity, but the transmission systems they used were inefficient. This was because much of the generated power was lost in the cables. Alternating current (AC) offered much better efficiency, since it could easily be transformed to higher voltages, with far less power loss. This set the stage for long-distance highvoltage AC (HVAC) transmission.
As the AC systems grew and power increasingly was being generated far from where most of its consumers lived and worked, long overhead lines were built, over which AC at ever higher voltages flowed. To bridge expanses of water, submarine cable was developed. Neither of these transmission media was without its problems, however. Specifically, problems were caused by the reactive power that oscillates between the capacitances and inductances in the systems.
Power system planners therefore started to look again at DC transmission. What had held up High- Voltage Direct Current (HVDC) transmission in the past was the lack of reliable and economic valves that could convert HVAC into HVDC, and vice versa. However, since the end of the 1920s, when ABB’s forerunner ASEA began making static converters and mercury-arc valves for voltages up to about 1000 V, research focused on developing valves for even higher voltages. It was the work led by Dr Uno Lamm in this area that earned his reputation as ‘the father of HVDC’.
By the 1940s, the time was ripe for HVDC service trials. The first installation was at a test station at Trollhättan. After further successful trials, in 1950 Swedish State Power placed an order for equipment for the world’s first authority HVDC transmission link. This was built between the island of Gotland in the Baltic Sea and the Swedish mainland. The concept for that project proved so successful that it has remained basically unchanged.
In 1954, the Gotland HVDC transmission link, with a rating of 20 MW, 200 A and 100 kV, went into operation. A new era of power transmission had begun. The company’s second HVDC order, a 160 MW link across the English Channel, followed soon after. The success of these early projects generated considerable worldwide interest and in the 1960s several HVDC links were built: Konti-Skan between Sweden and Denmark, Sakuma in Japan (with 50/60 Hz frequency converters), the New Zealand link between the South and North Islands, the Italy – Sardinia link and the Vancouver Island link in Canada.
The largest mercury-arc valve HVDC transmission link to be built by ABB was the Pacific Intertie in the USA in 1970. Originally commissioned for 1440 MW and later uprated to 1600 MW at ± 400 kV, its northern terminal is The Dalles, Oregon, and its southern terminal at Sylmar, in the northern tip of the Los Angeles basin. In all, eight mercury-arc valve based HVDC systems were installed for a total power rating of 3400 MW. Although many of these projects have since been replaced or upgraded with thyristor valves, some are still in operation today, after nearly 40 years of service.