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64-575: Abbreviations referring to organisations: Pacific DC Intertie , also known as Path 65 Democratic Party of Côte d'Ivoire - African Democratic Rally, (in French: Parti Démocratique de la Côte d'Ivoire), a political party in Côte d'Ivoire Partners for Democratic Change International , an international NGO network promoting democracy and civic education Partito dei Comunisti Italiani ,
128-497: A vector product , decreases. Since DC power has no phase, the phase shift cannot occur in the DC case. HVDC transmission may also be selected for other technical benefits. HVDC can transfer power between separate AC networks. HVDC power flow between separate AC systems can be automatically controlled to support either network during transient conditions, but without the risk that a major power-system collapse in one network will lead to
192-554: A 12 kV DC transmission line, which also served to convert 40 Hz generation to serve 60 Hz loads, at Mechanicville, New York . In 1941, a 60 MW, ±200 kV, 115 km (71 mi) buried cable link, known as the Elbe-Project , was designed for the city of Berlin using mercury arc valves but, owing to the collapse of the German government in 1945 , the project was never completed. The nominal justification for
256-452: A circuit that is effectively an ultra-high-voltage motor drive. More recent installations, including HVDC PLUS and HVDC MaxSine, are based on variants of a converter called a Modular Multilevel Converter (MMC). Multilevel converters have the advantage that they allow harmonic filtering equipment to be reduced or eliminated altogether. By way of comparison, AC harmonic filters of typical line-commutated converter stations cover nearly half of
320-452: A collapse in the second. The controllability feature is also useful where control of energy trading is needed. Specific applications where HVDC transmission technology provides benefits include: Long undersea or underground high-voltage cables have a high electrical capacitance compared with overhead transmission lines since the live conductors within the cable are surrounded by a relatively thin layer of insulation (the dielectric ), and
384-410: A distance of 200 kilometres (120 mi), including 10 kilometres (6.2 mi) 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
448-468: A given transmission line to operate with a constant HVDC voltage that is approximately the same as the peak AC voltage for which it is designed and insulated. The power delivered in an AC system is defined by the root mean square (RMS) of an AC voltage, but RMS is only about 71% of the peak voltage. Therefore, if the HVDC line can operate continuously with an HVDC voltage that is the same as the peak voltage of
512-446: A high resistance when conducting, wasting energy and generating heat in normal operation. The ABB breaker combines semiconductor and mechanical breakers to produce a hybrid breaker with both a fast break time and a low resistance in normal operation. Generally, vendors of HVDC systems, such as GE Vernova , Siemens and ABB , do not specify pricing details of particular projects; such costs are typically proprietary information between
576-460: A metal sheath. The geometry is that of a long coaxial capacitor . The total capacitance increases with the length of the cable. This capacitance is in a parallel circuit with the load. Where alternating current is used for cable transmission, additional current must flow in the cable to charge this cable capacitance. Another way to look at this is to realize, that such capacitance causes a phase shift between voltage and current, and thus decrease of
640-405: A much lesser extent. Nevertheless, for a long AC overhead transmission line, the current flowing just to charge the line capacitance can be significant, and this reduces the capability of the line to carry useful current to the load at the remote end. Another factor that reduces the useful current-carrying ability of AC lines is the skin effect , which causes a nonuniform distribution of current over
704-695: A political party in Italy Perth District Collegiate Institute , a secondary school in Perth, Ontario, Canada. Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with the title PDCI . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=PDCI&oldid=544879971 " Category : Disambiguation pages Hidden categories: Short description
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#1732771932691768-482: A result of a civil war in Mozambique . The transmission voltage of ±533 kV was the highest in the world at the time. Line-commutated converters have some limitations in their use for HVDC systems. This results from requiring a period of reverse voltage to affect the turn off. An attempt to address these limitations is the capacitor-commutated converter (CCC). The CCC has series capacitors inserted into
832-401: A similar concept HVDC PLUS ( Power Link Universal System ) and Alstom call their product based upon this technology HVDC MaxSine . They have extended the use of HVDC down to blocks as small as a few tens of megawatts and overhead lines as short as a few dozen kilometers. There are several different variants of VSC technology: most installations built until 2012 use pulse-width modulation in
896-413: A three-phase bridge rectifier known as a six-pulse bridge , containing six electronic switches, each connecting one of the three phases to one of the two DC rails. A complete switching element is usually referred to as a valve , irrespective of its construction. However, with a phase change only every 60°, considerable harmonic distortion is produced at both the DC and AC terminals when this arrangement
960-512: A total of 42 valves in each converter. The valves had a width of 7.1 feet (2.15 m), a height of 10 feet (3.2 m) and a length of 11 feet (3.5 m) and weighed 14,000 pounds (6,400 kg). Each valve contained 1.1 litres (37 US fl oz) mercury, with a weight of 33 pounds (14.9 kg). High voltage direct current A high-voltage direct current ( HVDC ) electric power transmission system uses direct current (DC) for electric power transmission, in contrast with
1024-454: A valve becoming positive (at which point the valve would start to conduct if it were made from diodes) and the thyristors being turned on. The DC output voltage of the converter steadily becomes less positive as the firing angle is increased: firing angles of up to 90° correspond to rectification and result in positive DC voltages, while firing angles above 90° correspond to inversion and result in negative DC voltages. The practical upper limit for
1088-462: A wider power transmission grid to another. Changes in load that would cause portions of an AC network to become unsynchronized and to separate, would not similarly affect a DC link, and the power flow through the DC link would tend to stabilize the AC network. The magnitude and direction of power flow through a DC link can be directly controlled and changed as needed to support the AC networks at either end of
1152-406: Is also ideal for connecting two AC systems that are not synchronized with each other. HVDC lines can help stabilize a power grid against cascading blackouts since power flow through the line is controllable. The Pacific Intertie takes advantage of differing power demand patterns between the northwestern and southwestern US. During winter, the northern region operates electrical heating devices while
1216-440: Is also known as line-commutated converter (LCC) HVDC. On March 15, 1979, a 1920 MW thyristor based direct current connection between Cabora Bassa and Johannesburg (1,410 km; 880 mi) was energized. The conversion equipment was built in 1974 by Allgemeine Elektricitäts-Gesellschaft AG (AEG) , and Brown, Boveri & Cie (BBC) and Siemens were partners in the project. Service interruptions of several years were
1280-475: Is complex (especially with line commutated converters), as is expanding existing schemes to multi-terminal systems. Controlling power flow in a multi-terminal DC system requires good communication between all the terminals; power flow must be actively regulated by the converter control system instead of relying on the inherent impedance and phase angle properties of an AC transmission line. Multi-terminal systems are therefore rare. As of 2012 only two are in service:
1344-613: Is different from Wikidata All article disambiguation pages All disambiguation pages Pacific DC Intertie The Pacific DC Intertie (also called Path 65 ) is an electric power transmission line that transmits electricity from the Pacific Northwest to the Los Angeles area using high voltage direct current (HVDC). The line capacity is 3.1 gigawatts , which is enough to serve two to three million Los Angeles households and represents almost half of
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#17327719326911408-467: Is left over from £750M for the installed works. Add another £200–300M for the other works depending on additional onshore works required. An April 2010 announcement for a 2,000 MW, 64 km (40 mi) line between Spain and France is estimated at €700 million. This includes the cost of a tunnel through the Pyrenees. At the heart of an HVDC converter station , the equipment that performs
1472-625: Is no potential difference. DC will never cross zero volts and never self-extinguish, so arc distance and duration is far greater with DC than the same voltage AC. This means some mechanism must be included in the circuit breaker to force current to zero and extinguish the arc, otherwise arcing and contact wear would be too great to allow reliable switching. In November 2012, ABB announced the first ultrafast HVDC circuit breaker. Mechanical circuit breakers are too slow for use in HVDC grids, although they have been used for years in other applications. Conversely, semiconductor breakers are fast enough but have
1536-440: Is one of two HVDC lines serving Los Angeles; the other is Path 27 . The idea of sending hydroelectric power to Southern California had been proposed as early as the 1930s, but was opposed and scrapped. By 1961, US president John F. Kennedy authorized a large public works project, using new high voltage direct current technology from Sweden . The project was undertaken as a close collaboration between General Electric of
1600-531: Is referred to as the rectifier and the station that is operating with power flow from DC to AC is referred to as the inverter . Early HVDC systems used electromechanical conversion (the Thury system) but all HVDC systems built since the 1940s have used electronic converters. Electronic converters for HVDC are divided into two main categories: Most of the HVDC systems in operation today are based on line-commutated converters (LCCs). The basic LCC configuration uses
1664-443: Is that DC current penetrates the entire conductor as opposed to AC current which only penetrates to the skin depth . For the same conductor size, the effective resistance is greater with AC than DC, hence more power is lost as heat with AC. In general, the total cost for HVDC is less than an AC line if the line length is over 500–600 miles, and with advances in conversion technology, this distance has been reduced considerably. A DC line
1728-542: Is used, the cable capacitance is charged only when the cable is first energized or if the voltage level changes; there is no additional current required. DC powered cables are limited only by their temperature rise and Ohm's law . Although some leakage current flows through the dielectric insulator , this effect is also present in AC systems and is small compared to the cable's rated current. The capacitive effect of long underground or undersea cables in AC transmission applications also applies to AC overhead lines, although to
1792-422: Is used. An enhancement of this arrangement uses 12 valves in a twelve-pulse bridge . The AC is split into two separate three-phase supplies before transformation. One of the sets of supplies is then configured to have a star (wye) secondary, and the other a delta secondary, establishing a 30° phase difference between the two sets of three phases. With twelve valves connecting each of the two sets of three phases to
1856-793: The Los Angeles Department of Water and Power (LADWP) electrical system's peak capacity. The intertie originates near the Columbia River at the Celilo Converter Station of Bonneville Power Administration 's grid outside The Dalles, Oregon and is connected to the Sylmar Converter Station north of Los Angeles , which is owned by five utility companies and managed by LADWP . The Intertie can transmit power in either direction, but power flows mostly from north to south. The section of
1920-592: The Quebec – New England Transmission between Radisson, Sandy Pond, and Nicolet and the Sardinia–;mainland Italy link which was modified in 1989 to also provide power to the island of Corsica . HVDC circuit breakers are difficult to build because of arcing : under AC, the voltage inverts and in doing so crosses zero volts dozens of times a second. An AC arc will self-extinguish at one of these zero-crossing points because there cannot be an arc where there
1984-776: The 1930s in Sweden ( ASEA ) and in Germany . Early commercial installations included one in the Soviet Union in 1951 between Moscow and Kashira , and a 100 kV, 20 MW system between Gotland and mainland Sweden in 1954. Before the Chinese project of 2019, the longest HVDC link in the world was the Rio Madeira link in Brazil , which consists of two bipoles of ±600 kV, 3150 MW each, connecting Porto Velho in
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2048-516: 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
2112-493: The AC equivalent line, then for a given current (where HVDC current is the same as the RMS current in the AC line), the power transmission capability when operating with HVDC is approximately 40% higher than the capability when operating with AC. Because HVDC allows power transmission between unsynchronized AC distribution systems, it can help increase system stability, by preventing cascading failures from propagating from one part of
2176-479: The AC line connections. CCC has remained only a niche application because of the advent of voltage-source converters (VSCs) which more directly address turn-off issues. Widely used in motor drives since the 1980s, voltage-source converters (VSCs) started to appear in HVDC in 1997 with the experimental Hellsjön–Grängesberg project in Sweden. By the end of 2011, this technology had captured a significant proportion of
2240-432: The DC link. The disadvantages of HVDC are in conversion, switching, control, availability, and maintenance. HVDC is less reliable and has lower availability than alternating current (AC) systems, mainly due to the extra conversion equipment. Single-pole systems have availability of about 98.5%, with about a third of the downtime unscheduled due to faults. Fault-tolerant bipole systems provide high availability for 50% of
2304-592: The HVDC market. The development of higher rated insulated-gate bipolar transistors (IGBTs), gate turn-off thyristors (GTOs), and integrated gate-commutated thyristors (IGCTs), has made HVDC systems more economical and reliable. This is because modern IGBTs incorporate a short-circuit failure mode, wherein should an IGBT fail, it is mechanically shorted. Therefore, modern VSC HVDC converter stations are designed with sufficient redundancy to guarantee operation over their entire service lives. The manufacturer ABB Group calls this concept HVDC Light , while Siemens calls
2368-682: The US and ASEA of Sweden. Private California power companies had opposed the project but their technical objections were rebutted by Uno Lamm of ASEA at an IEEE meeting in New York in 1963. When completed in 1970 the combined AC and DC transmission system was estimated to save consumers in Los Angeles approximately US$ 600,000 per day by use of cheaper electric power from dams on the Columbia River . One advantage of direct current over AC
2432-634: The commissioning of replacement thyristor converters. The development of thyristor valves for HVDC began in the late 1960s. The first complete HVDC scheme based on thyristor was the Eel River scheme in Canada, which was built by General Electric and went into service in 1972. Since 1977, new HVDC systems have used solid-state devices , in most cases thyristors . Like mercury arc valves, thyristors require connection to an external AC circuit in HVDC applications to turn them on and off. HVDC using thyristors
2496-436: The conversion between AC and DC is referred to as the converter . Almost all HVDC converters are inherently capable of converting from AC to DC ( rectification ) and from DC to AC ( inversion ), although in many HVDC systems, the system as a whole is optimized for power flow in only one direction. Irrespective of how the converter itself is designed, the station that is operating (at a given time) with power flow from AC to DC
2560-402: The converter station area. With time, voltage-source converter systems will probably replace all installed simple thyristor-based systems, including the highest DC power transmission applications. A long-distance, point-to-point HVDC transmission scheme generally has lower overall investment cost and lower losses than an equivalent AC transmission scheme. Although HVDC conversion equipment at
2624-428: The cross-sectional area of the conductor. Transmission line conductors operating with direct current suffer from neither constraint. Therefore, for the same conductor losses (or heating effect), a given conductor can carry more power to the load when operating with HVDC than AC. Finally, depending upon the environmental conditions and the performance of overhead line insulation operating with HVDC, it may be possible for
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2688-407: The energy lost as heat in the wires is directly proportional to the square of the current ( energy lost as heat = current 2 ⋅ resistance ⋅ time ) , {\textstyle ({\text{energy lost as heat}}={\text{current}}^{2}\cdot {\text{resistance}}\cdot {\text{time}}),} using half the current at double the voltage reduces
2752-427: The firing angle is about 150–160° because above this, the valve would have insufficient turnoff time. Early LCC systems used mercury-arc valves , which were rugged but required high maintenance. Because of this, many mercury-arc HVDC systems were built with bypass switchgear across each six-pulse bridge so that the HVDC scheme could be operated in six-pulse mode for short maintenance periods. The last mercury arc system
2816-745: The last mercury arc HVDC system (the Nelson River Bipole 1 system in Manitoba , Canada) having been put into service in stages between 1972 and 1977. Since then, all mercury arc systems have been either shut down or converted to use solid-state devices. The last HVDC system to use mercury arc valves was the Inter-Island HVDC link between the North and South Islands of New Zealand, which used them on one of its two poles. The mercury arc valves were decommissioned on 1 August 2012, ahead of
2880-567: The line in Oregon is owned and operated by Bonneville Power Administration, while the line in Nevada and California is owned and operated by Los Angeles Department of Water and Power. The transition is at the Oregon–Nevada border, at 41°59′47″N 119°57′44″W / 41.9964°N 119.9623°W / 41.9964; -119.9623 ( Pacific Intertie ownership boundary ) . This
2944-678: The line losses by a factor of 4. While energy lost in transmission can also be reduced by decreasing the resistance by increasing the conductor size, larger conductors are heavier and more expensive. High voltage cannot readily be used for lighting or motors, so transmission-level voltages must be reduced for end-use equipment. Transformers are used to change the voltage levels in alternating current (AC) transmission circuits, but cannot pass DC current. Transformers made AC voltage changes practical, and AC generators were more efficient than those using DC. These advantages led to early low-voltage DC transmission systems being supplanted by AC systems around
3008-662: The link capacity, but availability of the full capacity is about 97% to 98%. The required converter stations are expensive and have limited overload capacity. At smaller transmission distances, the losses in the converter stations may be bigger than in an AC transmission line for the same distance. The cost of the converters may not be offset by reductions in line construction cost and power line loss. Operating an HVDC scheme requires many spare parts to be kept, often exclusively for one system, as HVDC systems are less standardized than AC systems and technology changes more quickly. In contrast to AC systems, realizing multi-terminal systems
3072-462: The more common alternating current (AC) transmission systems. Most HVDC links use voltages between 100 kV and 800 kV. HVDC lines are commonly used for long-distance power transmission, since they require fewer conductors and incur less power loss than equivalent AC lines. HVDC also allows power transmission between AC transmission systems that are not synchronized . Since the power flow through an HVDC link can be controlled independently of
3136-450: The phase angle between source and load, it can stabilize a network against disturbances due to rapid changes in power. HVDC also allows the transfer of power between grid systems running at different frequencies, such as 50 and 60 Hz. This improves the stability and economy of each grid, by allowing the exchange of power between previously incompatible networks. The modern form of HVDC transmission uses technology developed extensively in
3200-542: The project was that, during wartime, a buried cable would be less conspicuous as a bombing target. The equipment was moved to the Soviet Union and was put into service there as the Moscow–Kashira HVDC system. The Moscow–Kashira system and the 1954 connection by Uno Lamm 's group at ASEA between the mainland of Sweden and the island of Gotland marked the beginning of the modern era of HVDC transmission. Mercury arc valves were common in systems designed up to 1972,
3264-402: The same voltage. This is because direct current transfers only active power and thus causes lower losses than alternating current, which transfers both active and reactive power . In other words, transmitting electric AC power over long distances inevitably results in a phase shift between voltage and current. Because of this phase shift the effective Power=Current*Voltage, where * designates
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#17327719326913328-518: The scheme, completed in May 1970, used only mercury-arc valves in the converters . The valves were series connected in three six-pulse valve bridges for each pole. The blocking voltage of the valves was 133 kV with a maximum current of 1,800 amperes , for a transmission rating of 1,440 MW with a symmetrical voltage of 400 kV with respect to earth. Each converter station housed six mercury arc valves groups, consisting each of seven valves, for
3392-521: The selection. However, some practitioners have provided some information: For an 8 GW 40 km (25 mi) link laid under the English Channel , the following are approximate primary equipment costs for a 2000 MW 500 kV bipolar conventional HVDC link (excluding way-leaving , on-shore reinforcement works, consenting, engineering, insurance, etc.) So for an 8 GW capacity between Britain and France in four links, little
3456-519: The southern portion uses relatively little electricity. In summer, the north uses little electricity while the south reaches peak demand due to air conditioning usage. Any time the Intertie demand lessens, the excess is distributed elsewhere on the western power grid (states west of the Great Plains, including Colorado and New Mexico ). The Pacific Intertie consists of: The first phase of
3520-781: The state of Rondônia to the São Paulo area with a length of more than 2,500 km (1,600 mi). High voltage is used for electric power transmission to reduce the energy lost in the resistance of the wires. For a given quantity of power transmitted, doubling the voltage will deliver the same power at only half the current: power = ( voltage ) ⋅ ( current ) = ( 2 ⋅ voltage ) ⋅ ( 1 2 ⋅ current ) {\displaystyle {\text{power}}=({\text{voltage}})\cdot ({\text{current}})=(2\cdot {\text{voltage}})\cdot ({\tfrac {1}{2}}\cdot {\text{current}})} Since
3584-414: The supplier and the client. Costs vary widely depending on the specifics of the project (such as power rating, circuit length, overhead vs. cabled route, land costs, site seismology, and AC network improvements required at either terminal). A detailed analysis of DC vs. AC transmission costs may be required in situations where there is no obvious technical advantage to DC, and economical reasoning alone drives
3648-538: The terminal stations is costly, the total DC transmission-line costs over long distances are lower than for an AC line of the same distance. HVDC requires less conductor per unit distance than an AC line, as there is no need to support three phases and there is no skin effect . AC systems use a higher peak voltage for the same power, increasing insulator costs. Depending on voltage level and construction details, HVDC transmission losses are quoted at 3.5% per 1,000 km (620 mi), about 50% less than AC (6.7%) lines at
3712-435: The transmitted power, which is a vector product of voltage and current. Additional energy losses also occur as a result of dielectric losses in the cable insulation. For a sufficiently long AC cable, the entire current-carrying ability of the conductor would be needed to supply the charging current alone. This cable capacitance issue limits the length and power-carrying ability of AC power cables. However, if direct current
3776-519: 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 configurations, and the inherent energy inefficiency of a battery charge/discharge cycle. First proposed in 1914, the grid controlled mercury-arc valve became available during the period 1920 to 1940 for the rectifier and inverter functions associated with DC transmission. Starting in 1932, General Electric tested mercury-vapor valves and
3840-452: The turn of the 20th century. Practical conversion of current between AC and DC became possible with the development of power electronics devices such as mercury-arc valves and, starting in the 1970s, power semiconductor devices including thyristors , integrated gate-commutated thyristors (IGCTs), MOS-controlled thyristors (MCTs) and insulated-gate bipolar transistors (IGBT). The first long-distance transmission of electric power
3904-400: The two DC rails, there is a phase change every 30°, and harmonics are considerably reduced. For this reason, the twelve-pulse system has become standard on most line-commutated converter HVDC systems built since the 1970s. With line commutated converters, the converter has only one degree of freedom – the firing angle , which represents the time delay between the voltage across
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#17327719326913968-485: 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 kilometres (75 mi). The Moutiers–Lyon system transmitted 8,600 kW of hydroelectric power
4032-591: 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, the Thury system, 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
4096-642: Was shut down in 2012. The thyristor valve was first used in HVDC systems in 1972. The thyristor is a solid-state semiconductor device similar to the diode , but with an extra control terminal that is used to switch the device on at a particular instant during the AC cycle. Because the voltages in HVDC systems, up to 800 kV in some cases, far exceed the breakdown voltages of the thyristors used, HVDC thyristor valves are built using large numbers of thyristors in series. Additional passive components such as grading capacitors and resistors need to be connected in parallel with each thyristor in order to ensure that
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