page_title: High-voltage direct current
section_title: Electromechanical (Thury) systems
hierarchical_section_title: High-voltage direct current / History / Electromechanical (Thury) systems
caption_attribution_description: English: One of the English Electric mercury arc valves (a kind of rectifier) used to convert electricity from alternating current to direct current at the Manitoba Hydro Radisson Converter Station in Gillam, Manitoba. As of 2004, all of the mercury arc valves have been replaced with thyristors. Deutsch: Einer der Quecksilberdampfgleichrichter der Stromrichterstation Radisson in Gillam, Manitoba, Kanada. Hersteller war English Electric, Betreiber Manitoba Hydro. 2004 wurden sämtliche Quecksilberdampfgleichrichter durch Thyristoren ersetzt. Français&#160;: Une des diodes à mercure English Electric utilisées pour convertir du courant alternatif en courant coutinu à la station de conversion Radisson de Manitoba Hydro à Gillam. En 2004, les diodes à mercures étaient remplacées par des thyristors.
context_page_description: A high-voltage, direct current electric power transmission system uses direct current for the bulk transmission of electrical power, in contrast with the more common alternating current systems. For long-distance transmission, HVDC systems may be less expensive and have lower electrical losses. For underwater power cables, HVDC avoids the heavy currents required to charge and discharge the cable capacitance each cycle. For shorter distances, the higher cost of DC conversion equipment compared to an AC system may still be justified, due to other benefits of direct current links, such as interconnecting power systems operating at different frequencies.
  Most HVDC links use voltages between 100 kV and 800 kV. A 1,100 kV link in China was completed in 2019 over a distance of 3,300 km with a power of 12 GW. With this dimension, intercontinental connections become possible which could help to deal with the fluctuations of wind power and photovoltaics.
  HVDC allows power transmission between unsynchronized AC transmission systems.
context_section_description: The first long-distance transmission of electric power was demonstrated using direct current in 1882 at Miesbach-Munich Power Transmission, but only 1.5 kW was transmitted. An early method of HVDC transmission was developed by the Swiss engineer René Thury and his method was put into practice by 1889 in Italy by the Acquedotto De Ferrari-Galliera company. This system used series-connected motor-generator sets to increase the voltage. Each set was insulated from electrical ground and driven by insulated shafts from a prime mover. The transmission line was operated in a 'constant current' mode, with up to 5,000 volts across each machine, some machines having double commutators to reduce the voltage on each commutator. This system transmitted 630 kW at 14 kV DC over a distance of 120 km. The Moutiers–Lyon system transmitted 8,600 kW of hydroelectric power a distance of 200 km, including 10 km of underground cable. This system used eight series-connected generators with dual commutators for a total voltage of 150 kV between the positive and negative poles, and operated from c.1906 until 1936. Fifteen Thury systems were in operation by 1913.  Other Thury systems operating at up to 100 kV DC worked into the 1930s, but the rotating machinery required high maintenance and had high energy loss. Various other electromechanical devices were tested during the first half of the 20th century with little commercial success.
  One technique attempted for conversion of direct current from a high transmission voltage to lower utilization voltage was to charge series-connected batteries, then reconnect the batteries in parallel to serve distribution loads. While at least two commercial installations were tried around the turn of the 20th century, the technique was not generally useful owing to the limited capacity of batteries, difficulties in switching between series and parallel connections, and the inherent energy inefficiency of a battery charge/discharge cycle. (A modern battery storage power station includes transformers and inverters to change energy from alternating current to direct current forms at appropriate voltages.)
caption: HVDC in 1971: this 150 kV mercury-arc valve converted AC hydropower voltage for transmission to distant cities from Manitoba Hydro generators.
exif: {"Image ImageWidth": "1536", "Image ImageLength": "2048", "Image BitsPerSample": "[8, 8, 8]", "Image PhotometricInterpretation": "2", "Image Make": "Canon", "Image Model": "Canon PowerShot S30", "Image Orientation": "Horizontal (normal)", "Image SamplesPerPixel": "3", "Image XResolution": "180", "Image YResolution": "180", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "Adobe Photoshop CS6 (Windows)", "Image DateTime": "2014:03:30 14:25:01", "Image HostComputer": "Mac OS X 10.2.6", "Image YCbCrPositioning": "Centered", "Image ExifOffset": "320", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "1094", "Thumbnail JPEGInterchangeFormatLength": "7706", "EXIF ExposureTime": "1/8", "EXIF FNumber": "14/5", "EXIF ExifVersion": "0210", "EXIF DateTimeOriginal": "2003:08:20 03:46:38", "EXIF DateTimeDigitized": "2003:08:20 03:46:38", "EXIF ComponentsConfiguration": "YCbCr", "EXIF CompressedBitsPerPixel": "5", "EXIF ShutterSpeedValue": "3", "EXIF ApertureValue": "95/32", "EXIF ExposureBiasValue": "0", "EXIF MaxApertureValue": "97349/32768", "EXIF MeteringMode": "Pattern", "EXIF Flash": "Flash did not fire, compulsory flash mode", "EXIF FocalLength": "227/32", "EXIF FlashPixVersion": "0100", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "1536", "EXIF ExifImageLength": "2048", "EXIF FocalPlaneXResolution": "1024000/139", "EXIF FocalPlaneYResolution": "1536000/209", "EXIF FocalPlaneResolutionUnit": "2", "EXIF SensingMethod": "One-chip color area", "EXIF FileSource": "Digital Camera"}