The History of High Voltage Direct Current Transmission*
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47 The history of high voltage direct current transmission* O Peake† Power Systems Electrical Engineer, Collingwood, Victoria SUMMARY: Transmission of electricity by high voltage direct current (HVDC) has provided the electric power industry with a powerful tool to move large quantities of electricity over great distances and also to expand the capacity to transmit electricity by undersea cables. The fi rst commercial HVDC scheme connected the island of Gotland to the Swedish mainland in 1954. During the subsequent 55 years, great advances in HVDC technology and the economic opportunities for HVDC have been achieved. Because of the rapid development of HVDC technology many of the early schemes have already been upgraded, modernised or decommissioned. Very little equipment from the early schemes has survived to illustrate the engineering heritage of HVDC. Conservation of the equipment remaining from the early projects is now an urgent priority, while the conservation of more recent projects, when they are retired, is a future challenge. 1 INTRODUCTION technology for the valves to convert AC to DC and vice versa. At the beginning of the electricity supply industry there was a great battle between the proponents In the late 1920s, the mercury arc rectifi er emerged of alternating current (AC) and direct current as a potential converter technology, however, it was (DC) alternatives for electricity distribution. This not until 1954 that the mercury arc valve technology eventually played out as a win for AC, which has had matured enough for it to be used in a commercial maintained its dominance for almost all domestic, project. This pioneering development led to a industrial and commercial supplies of electricity number of successful projects. However, at the same to customers. time a new technology, the silicon semiconductor thyristor, began to emerge as a viable technology As the size of electricity supply systems increased for the valves of HVDC systems. The thyristor valve several major challenges for AC systems emerged. fi rst came into use in HVDC applications in 1970 There were major difficulties in increasing the and from that time forward the limitations of HVDC voltage (and hence capacity) and the range of were largely eliminated (Asplund et al, 2003). undersea cables. Also the development of very large hydroelectric projects in areas quite remote from their The technology is now mature and experiencing load centres became an increasing challenge for AC rapid increases in the voltage, power carrying systems to transport vast quantities of electricity over capacity and length of transmission lines. This very great distances. For very large transmission has occurred at a time when the efficiency of schemes, high voltage direct current (HVDC) is both electricity supply systems is under great pressure more effi cient and has a greater capability than AC due to greenhouse gas considerations, while the systems. It was recognised as early as the 1920s that development of large hydroelectric schemes is an there were advantages in the use of DC transmission imperative to decrease the reliance on fossil fuel systems for these more challenging applications. power generation, which produces a large proportion Hence the concept of HVDC emerged, however, of the planet’s greenhouse gases. development was held back by the lack of a suitable * Paper presented at the 3rd Australasian 2 TERMINOLOGY Engineering Heritage Conference, “Engineering in the Development of a Region – Heritage and The following terminology and abbreviations are History”, 22-25 November 2009, University of used in this paper: Otago, Dunedin, New Zealand. • AC (alternating current) – a system of electrical † Corresponding author Owen Peake can be energy where the voltage fl uctuates around earth contacted at [email protected]. potential in the form of a sine wave at a frequency © Institution of Engineers Australia, 2010 Australian Journal of Multi-disciplinary Engineering, Vol 8 No 1 NN10-H0710-H07 PPeake.inddeake.indd 4747 116/11/106/11/10 2:232:23 PPMM 48 “The history of high voltage direct current transmission” – Peake of 50 Hz or 60 Hz in typical electricity distribution valves using IGBT technology. The IGBT is a and transmission systems throughout the world. fairly recent development, fi rst appearing in the • DC (direct current) – a system of electrical energy 1980s. Third-generation devices were available where the voltage remains constant over time in the 1990s and quickly gained a reputation for and is either positive or negative with respect to excellent ruggedness and tolerance of overloads. earth. This system is used universally in motor In HVDC applications, many devices are placed vehicle electrics, small devices operated from in series/parallel confi gurations to achieve the batteries and in many industrial applications. desired voltage and current ratings. It is also used in HVDC systems for specialised high-power, long-range transmission of electric 3 THE PIONEER WORK – energy. In this paper when the symbol ± is used MECHANICVILLE in association with DC voltages, it signifi es that the system operates with one pole above earth In 1932, the General Electric Company built an potential and one pole below earth potential with experimental HVDC scheme between a hydroelectric the mid-point (zero voltage) at earth potential. powerstation at Mechanicville, New York, and • kV (kilovolt) – the volt (V) is the SI unit of Schenectady, New York, a distance of 37 km. This electromotive force. The kilovolt is 1000 V and system used mercury arc rectifi ers to create the DC is the commonly used unit for voltage in high- voltage, but the load at Schenectady was DC motors, voltage electricity supply systems. Domestic so in a sense it was only half of a full HVDC scheme, electricity supplies operate between 120 and which typically consists of a connection between two 240 V, depending on national standards. AC systems. The line operated at 12 kV and had a • MW (megawatt) – the watt (W) is the SI unit for capacity of 5 MW. The General Electric Company power. The megawatt (one million watts) is the did not, surprisingly, pursue this technology and the measure commonly used for large systems in the scheme was dismantled after World War II without electricity supply industry. One MW is equivalent further development. to 1340 horsepower. Three types of converter devices have been used 4 THE EARLY ENGINEERS in HVDC schemes to date and are referred to in this paper: In Sweden in 1929, Uno Lamm, working for the • Mercury arc valves – a mercury arc valve consists Swedish electromechanical company ASEA, took of an evacuated chamber containing a pool of out a patent on the high-voltage mercury arc valve. mercury at the bottom forming the cathode. An experimental valve, tested in 1933, confi rmed The anode is a carbon electrode at the top of the the validity of Lamm’s earlier patent, although it chamber. When the mercury pool is heated, an arc had only a very short life. Research then continued can be struck within the chamber that conducts to improve materials to give the valves a longer life. electrons from the cathode to the anode, but not In 1944, a test rig of 2000 kW capacity operating at in the other direction. Hence the device operates 60 kV proved successful. Lamm continued in the as a rectifi er. The device was invented by Peter fi eld working systematically towards the goal of a Cooper Hewitt in 1902. The mercury arc valve was commercially-viable system for HVDC. the technology used to convert AC to DC and vice August Uno Lamm was born on 22 May 1904 at versa in HVDC schemes, until the introduction Gothenburg on the Swedish west coast (Gould, of the semiconductor thyristor was applied to 1992). He studied at the Swedish Royal Institute of HVDC schemes from 1970. Technology in Stockholm and obtained a degree in • Thyristor valves – the thyristor is a silicon solid- Electrical Engineering in 1927. After military service state semiconductor device with four layers of he joined ASEA and in 1929 was made the manager alternating N and P type materials. They act of a project to develop the high voltage mercury arc as bi-stable switches, conducting when their valve. He obtained his PhD from the Royal Institute gate receives a current pulse, and continuing in 1943, studying part-time, while he continued his to conduct as long as the voltage across the work on the mercury arc valve. device is not reversed. In HVDC applications, many devices are placed in series/parallel In 1955 he was made head of the project to build confi gurations to achieve the desired voltage and Sweden’s fi rst nuclear power reactors. In 1961 he current ratings. was appointed to head the ASEA team in the joint venture with General Electric in the United States to • Insulated-gate bipolar transistor (IGBT) – the IGBT build the Pacifi c DC Intertie and moved to Southern is a three-terminal silicon semiconductor device, California in 1964. noted for high effi ciency and fast switching. The IGBT is a voltage source converter, meaning that During his career, Lamm took out 150 patents and it can be switched off as well as on by gate control. wrote 80 technical papers. He wrote extensively This brings advantages to the control of HVDC and was published widely in the Swedish press Australian Journal of Multi-disciplinary Engineering Vol 8 No 1 NN10-H0710-H07 PPeake.inddeake.indd 4848 116/11/106/11/10 2:232:23 PPMM “The history of high voltage direct current transmission” – Peake 49 on subjects as diverse as societal commentary, site is therefore the most signifi cant heritage site in education, technology, political commentary and the development of HVDC for several reasons. economics. He was strongly anti-communist and From the commissioning of the Gotland scheme, anti-Nazi, which got him into some difficulties ASEA (later to become ABB) pursued commercial during World War II when he was required to work success with the HVDC technology and has remained on ASEA projects in Germany.