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| HVDC Hokkaido-Honschu |
HVDC Hokkaido-HonschuThe HVDC Hokkaido-Honshu is a 193 kilometers long high voltage direct current transmission line for the interconnection of the power grids of Hokkaido (static inverter station Hakodate) and Honshu (static inverter station Kamikita), Japan. The project went into service in 1979. A 149 kilometer long overhead line and a 44 kilometer long submarine cable connects the terminals. The HVDC Hokkaido Honshu is a monopolar HVDC line with an operating voltage of 250 kV and rated power of 300 megawatts. This HVDC system uses thyristor static inverters.
External links
- http://www.transmission.bpa.gov/cigresc14/Compendium/HOKKAIDO.htm
- http://www.transmission.bpa.gov/cigresc14/Compendium/Hokkaido%20Pictures.pdf
Hokkaido-Honshu
High-voltage direct currentHVDC or high-voltage, direct current electric power transmission systems contrast with the more common alternating-current systems as a means for the bulk transmission of electrical power. The modern form of HVDC transmission uses technology developed extensively in the 1930s in Sweden at ASEA. Early commercial installations include one in the USSR in 1951 between Moscow and Kashira, and a 10-20 MW system in Gotland, Sweden in 1954. [1]
Advantages of high voltage transmission
Early electric power distribution schemes used direct-current generators located near the customer's loads. As electric power became more widespread, the distances between loads and generating plant increased. Since the flow of current through the distribution wires resulted in a voltage drop, it became difficult to regulate the voltage at the distribution circuit extremities.
Higher voltages reduce the transmission power loss or reduce the cost of conductors when transmitting a given quantity of power since a smaller current is required. Conductor cost is roughly proportional to the current carried, and conductor loss is roughly proportional to the square of the current, so higher transmission voltages improve the efficiency of transmission.
Low voltage is convenient for customer loads such as lamps and motors. The principal advantage of AC is that it allows the use of transformers to change the voltage at which power is used. No equivalent of the transformer exists for direct current, so the manipulation of DC voltages is considerably more complex. With the development of efficient AC machines, such as the induction motor, AC transmission and utilization became the norm (see War of Currents).
History of HVDC transmission
An early method of high-voltage DC transmission was developed by the Swiss engineer Rene Thury [5]. This system used series-connected motor-generator sets to increase voltage. Each set was insulated from ground and driven by insulated shafts from a prime mover. An early example of this system was installed in 1889 in Italy by the Society Acquedotto de Ferrari-Gallieri. This system transmitted 630 kW at 14 kV DC over a distance of 120 km.[6] Other Thury systems operating at up to 100 kV dc operated up until 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[7].
The grid controlled mercury arc valve became available for power transmission during the period 1920 to 1940[9]. In 1941 a 60 MW, +/- 200 kV,115 km buried cable link was designed for the city of Berlin using mercury arc valves (Elbe-Project), but owing to the collapse of the German government in 1945 the project was never completed [8]. The nominal justification for the project was that, during wartime, a buried cable would be less conspicuous as a bombing target. The equipment was removed to the Soviet Union and was put into service there [9].
Introduction of the fully-static mercury arc valve to commercial service in 1954 marked the beginning of the modern era of HVDC transmission. Mercury arc valves were common in systems designed up to 1975, but since then, HVDC systems use only solid-state devices.
Advantages of HVDC over AC Transmission
In a number of applications HVDC is often the preferred option.
- Undersea cables. (e.g. 250 km Baltic Cable between Sweden and Germany [3]).
- Endpoint-to-endpoint long-haul bulk power transmission without intermediate 'taps', for example, in remote areas.
- Increasing the capacity of an existing power grid in situations where additional wires are difficult or expensive to install.
- Allowing power transmission between unsynchronised AC distribution systems.
- Reducing the profile of wiring and pylons for a given power transmission capacity.
- Connection of remote generating plant to the distribution grid, for example Nelson River Bipole.
- Stabilising a predominantly AC power-grid,without increasing maximum prospective short circuit current
Long undersea cables have a high capacitance. While this has minimal effect for DC transmission, the current required to charge and discharge the capacitance of the cable causes additional power losses when the cable is carrying AC. In addition, AC power is lost to dielectric losses.
HVDC can carry more power per conductor, because for a given power rating the constant voltage in a DC line is lower than the peak voltage in an AC line. This voltage determines the insulation thickness and conductor spacing. This allows existing transmission line corridors to be used to carry more power into an area of high power consumption, which can lower costs.
Increased stability of power systems
Because HVDC allows power transmission between unsynchronised AC distribution systems, it can help increase system stability, by preventing cascading failures from propagating from one part to another of a wider power transmission grid, whilst still allowing power to be imported or exported in the event of smaller failures. This has caused many power system operators to contemplate wider use of HVDC technology for its stability benefits alone.
Possible health advantages of HVDC over AC transmission
A high-voltage DC transmission line would not produce the same sort of extremely low frequency (ELF) electromagnetic field as would an equivalent AC line. It is speculated by those who believe that ELF radiation is harmful that such a reduction in EM fields would be beneficial to health. The benefits would extend only to those near the transmission lines, as the electric and magnetic fields associated with high current AC transmission lines do not travel far beyond the actual lines themselves. These fields are, however, also associated with electrical equipment and household appliances. It should be noted that the current scientific consensus [http://www.greenfacts.org/power-lines/index.htm] does not consider ELF sources and their associated fields to be particularly harmful, and that deployment of HVDC equipment would not completely eliminate electric fields, as there would still be DC electric field gradients between the conductors and ground.
Disadvantages
The required static invertors are expensive and cannot be overloaded very much. At smaller transmission distances the losses in the static inverters may be bigger than in an AC powerline, and the cost of the inverters may not be offset by reductions in line construction cost.
In contrast to AC systems, realizing multiterminal systems is complex, as is expanding existing schemes to multiterminal systems. Controlling power flow in a multiterminal DC system requires good communication between all the terminals.
AC network interconnections
AC transmission lines can only interconnect synchronized AC networks that oscillate at the same frequency and in phase. Many areas that wish to share power have unsynchronized networks. The power grids of the UK, Northern Europe and continental Europe all operate at 50 Hz but are not synchronized. Japan has 50 Hz and 60 Hz networks. Continental North America, while operating at 60Hz throughout, is divided into regions which are unsynchronised: East, West, Texas and Quebec. Brazil and Paraguay, which share the massive Itaipu hydroelectric plant, operate on 60Hz and 50Hz respectively. However, HVDC systems make it possible to interconnect unsynchronized AC networks, and also add the possibility of controlling AC voltage and reactive power flow.
A generator connected to a long AC transmission line may become unstable and fall out of synchronization with a distant AC power system. An HVDC transmission link may make it economically feasible to use remote generation sites. Wind farms located off-shore may use HVDC systems to collect power from multiple unsynchronized generators for transmission to the shore by an underwater cable.
In general, however, an HVDC power line will interconnect two AC regions of the power-distribution grid. Machinery to convert between AC and DC power adds a considerable cost in power transmission. The conversion from AC to DC is known as rectification, and from DC to AC as inversion. Above a certain break-even distance (about 50 km for submarine cables, and perhaps 600-800 km for overhead cables [3]), the lower cost of the HVDC electrical conductors outweighs the cost of the electronics.
The conversion electronics also present an opportunity to effectively manage the power grid by means of controlling the magnitude and direction of power flow. An additional advantage of the existence of HVDC links, therefore, is potential increased stability in the transmission grid.
Rectifying and inverting
Rectifying and inverting components
Early static systems used mercury arc rectifiers, which were unreliable. Nevertheless some HVDC systems using mercury arc rectifiers are still in service in 2005. The thyristor valve was first used in HVDC systems in the 1960s. 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. The insulated-gate bipolar transistor (IGBT) is now also used and offers simpler control and reduced valve cost.
Because the voltages in HVDC systems, up to 800 kV in some cases, exceed the breakdown voltages of the semiconductor devices, HVDC converters are built using large numbers of semiconductors in series.
The low-voltage control circuits used to switch the thyristors on and off need to be isolated from the high voltages present on the transmission lines. This is usually done optically. In a hybrid control system, the low-voltage control electronics sends light pulses along optical fibres to the high-side control electronics. Another system, called direct light triggering, dispenses with the high-side electronics, instead using light pulses from the control electronics to switch light-triggered thyristors (LTTs).
A complete switching element is commonly referred to as a 'valve', irrespective of its construction.
Rectifying and inverting systems
Rectification and inversion use essentially the same machinery. Many substations are set up in such a way that they can act as both rectifiers and inverters. At the AC end a set of transformers, often three physically separate single-phase transformers, isolate the station from the AC supply, to provide a local earth, and to ensure the correct eventual DC voltage. The output of these transformers is then connected to a bridge rectifier formed by a number of valves. The basic configuration uses six valves, connecting each of the three phases to each of the DC rails. However, with a phase change only every sixty degrees, considerable harmonics remain on the DC rails.
An enhancement of this configuration uses 12 valves (often known as a twelve-pulse system). 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, the other a delta secondary, establishing a thirty degree phase difference between each of the sets of three phases. With twelve valves connecting each of the two sets of three phases to the two DC rails, there is a phase change every 30 degrees, and harmonics are considerably reduced.
In addition to the conversion transformers and valve-sets, various passive resistive and reactive components help filter harmonics out of the DC rails.
Configurations
Monopole and earth return
In a common configuration, called monopole, one of the terminals of the rectifier is connected to earth ground. The other terminal, at a potential high above, or below, ground, is connected to a transmission line. The earthed terminal may or may not be connected to the corresponding connection at the inverting station by means of a second conductor.
If no metallic conductor is installed, current flows in the earth between the earth electrodes at the two stations. The issues surrounding earth-return current include
- Electrochemical corrosion of long buried metal objects such as pipelines
- Underwater earth-return electrodes in seawater may produce chlorine or otherwise affect water chemistry.
- An unbalanced current path may result in a net magnetic field, which can affect magnetic navigational compasses for ships passing over an underwater cable.
These effects can be eliminated with installation of a metallic return conductor between the two ends of the monopolar transmission line. Since one terminal of the converters is connected to earth, the return conductor need not be insulated for the full transmission voltage which makes it less costly than the high-voltage conductor. Use of a metallic return conductor is decided based on economic, technical and environmental factors[4].
Modern monopolar systems for pure overhead lines carry typically 1500 MW. If underground or seacables are used the typical value is 600 MW.
Bipolar
In bipolar transmission a pair of conductors is used, each at a high potential with respect to ground, in opposite polarity. Since these conductors must be insulated for the full voltage, transmission line cost is higher than a monopole with a return conductor. However, there are a number of advantages to bipolar transmission which can make it the attractive option.
- Under normal load, negligible earth-current flows, as in the case of monopolar transmission with a metallic earth-return; minimising earth return loss and environmental effects.
- When a fault develops in a line, with earth return electrodes installed at each end of the line, current can continue flow using the earth as a return path, operating in monopolar mode.
- Since for a given power rating bipolar lines carry only half the current of monopolar lines, the cost of the second conductor is reduced compared to a monopolar line of the same rating.
- In very adverse terrain, the second conductor may be carried on an independent set of transmission towers, so that some power may continue to be transmitted even if one line is damaged.
A bipolar system may also be installed with a metallic earth return conductor.
Bipolar systems may carry as much as 3000 MW at voltages of +/-533 kV. Submarine cable installations initially commissioned as a monopole may be upgraded with additional cables and operated as a bipole.
Back to back
A back-to-back station is a plant in which both static inverters are in the same area, usually even in the same building and the length of the direct current line is only a few meters. HVDC back-to-back stations are used for
- coupling of electricity mains of different frequency (as in Japan)
- coupling two networks of the same nominal frequency but no fixed phase relationship
- different frequency and phase number (for example, as a replacement for traction current converter plants)
- different modes of operation (as until 1995/96 in Etzenricht, Dürnrohr and Vienna).
In contrast to HVDC long-distance lines, the DC voltage in the intermediate circuit can be selected freely at HVDC back-to-back stations because of the short conductor length. The DC voltage is as low as possible, in order to build a small valve hall and to avoid parallel switching of valves. For this reason at HVDC back-to-back stations the strongest available static inverter valves are used.
Tripole - Current Modulating Control
A newly patented scheme [http://www.patentstorm.us/patents/6714427.html|(US Patent 6714427))] is particularly applicable to conversion of existing AC transmission lines to HVDC. Two of the three circuit conductors are operated as a bipole. The third conductor is used as a
parallel monopole, equipped with reversing valves (or parallel valves connected in reverse polarity). The parallel monopole periodically relieves current from one pole or the other, switching polarity over a span of several minutes. The bipole conductors would be loaded to
either 1.37 or 0.37 of their thermal limit, with the parallel monopole always carrying +/- 1 times its thermal limit current. The combined RMS heating effect is as if each of the conductors was always carrying 1.0 of its rated current. This allows heavier currents to be carried by the bipole conductors, and full use of the installed third conductor for energy transmission. The higher current compared to AC operation may also help prevent ice build-up during winter storms. The system can be arranged to circulate high currents through the line conductors even if load demand is low.
Combined with the higher average power possible with a DC transmission line for the same line to ground voltage, a tripole conversion of an existing AC line could allow up to 80% more power to be transferred using the same transmission right-of-way, towers, and conductors. Some AC lines
cannot be loaded to their thermal limit due to system stability, reliability, and reactive power concerns, which would not exist with an HVDC link.
The system operates without earth-return current. Since a single failure of a pole converter or a conductor results in only a small loss of capacity and no earth-return current, reliability of this scheme would be high. No time would be lost in switching if a conductor broke. The valves
would inherently have an emergency overload rating in bipole mode. This would possibly allow great increase in power transmission with significant effect in congested transmission systems, where consequences of a single line failure limit the allowed loading of other parallel transmission lines. While capital costs are higher than for a bipole conversion operating at the same voltage class, the extra power capability reduces incremental cost per megawatt. Depending on transmission line physical configuration, replacement of insulators may be required to achieve
the highest power rating, to insure proper line-to-line clearance distances.
As of 2005 no tri-pole conversions are in operation, although a transmission line in India has been converted to bipole HVDC.
See
[http://202.149.37.7/PGNEW/docs/HVDC2005/EPRI-Adapa-Current%20Modulated%20HVDC%20Transmission%20-%20Lionel%20Barthold.pdf Presentation on Current-Modulated Control]
[http://www.electricity.doe.gov/documents/neitb_noi_comment_final_apnd.pdf United States Department of Energy comments received on an inquiry into power transmission bottlenecks]
Corona discharge
Corona discharge is the creation of ions in a fluid (such as air) by the presence of a strong electric field. Electrons are torn from un-ionised air, and either the positive ions or else the electrons are attracted to the conductor, whilst the charged particles drift. This effect can cause considerable power loss, create audible and radio-frequency interference, generate toxic compounds such as oxides of nitrogen and ozone, and lead to arcing.
Both AC and DC transmission lines can generate coronas, in the former case in the form of oscillating particles, in the latter a constant wind. Due to the space charge formed around the conductors, an HVDC system may have about half the loss per unit length of a high voltage AC system carrying the same amount of power. With monopolar transmission the choice of polarity of the energised conductor leads to a degree of control over the corona discharge. In particular, the polarity of the ions emitted can be controlled, which may have an environmental impact on particulate condensation (particles of different polarities have a different mean-free path). Negative coronas generate considerably more ozone than positive coronas, and generate it further downwind of the power line, creating the potential for health effects. The use of a positive voltage will reduce the ozone impacts of monopole HVDC power lines.
Applications
Overview
The controllability of current-flow through HVDC rectifiers and inverters, their application in connecting unsynchronized networks, and their applications in efficient submarine cables mean that HVDC cables are often used at national boundaries for the exchange of power. Offshore windfarms also require undersea cables, and their turbines are unsynchronized. In very long-distance connections between just two points, for example around the remote communities of Siberia, Canada, and the Scandinavian North, the decreased line-costs of HVDC also makes it the usual choice. Other applications have been noted throughout this article.
The development of insulated gate bipolar transistors and gate turn-off thyristors has made smaller HVDC systems economical. These may be installed in existing AC grids for their role in stabilizing power flow without the additional short-circuit current that would be produced by an additional AC transmission line. One manufacturer calls this concept "HVDC Light", and has extended the use of HVDC down to blocks as small at a few tens of megawatts and lines as short as a few score kilometres of overhead line.
System configurations
A HVDC link in which the two AC-to-DC converters are housed in the same building, the HVDC transmission existing only within the building itself, is called a back-to-back HVDC link. This is the common configuration for interconnecting two unsynchronised grids or for changing frequency or for stabilizing an AC network.
HVDC back-to-back stations can also be designed to deliver single phase AC. This is required for Traction current converter plants.
The most common configuration of an HVDC link is a station-to-station link, where two inverter/rectifier stations are connected by means of a dedicated HVDC link. This is also a configuration commonly used in connecting unsynchronised grids, in long-haul power transmission, and in undersea cables.
Multi-terminal HVDC links, connecting more than two points, are rare. The configuration of multiple terminals can be series, parallel, or hybrid (a mixture of series and parallel). Parallel configuration tends to be used for large capacity stations, and series for lower capacity stations. An example is the 2000 MW Quebec - New England Transmission system opened in 1992, which is currently the largest multi-terminal HVDC system in the world. [3]
Realized HVDC systems
Systems that use (or used) mercury arc rectifiers
Systems that used thyristors from first power-on
Systems that used IGBTs from first power-on
See also
- Static inverter plant
- Valve hall
- Electrode line
- Electrical pylon
- Submarine cable
- Uno Lamm
References
:[1] Narain G. Hingorani in [http://www.spectrum.ieee.org/publicaccess/9604teaser/9604pow1.html IEEE Spectrum] magazine, 1996.
:[2] Siemens AG "[http://www.siemens.com/page/1,3771,261226-1-12_2_261226-0,00.html HVDC Basics]" page.
:[3] [http://www.abb.com/hvdc ABB HVDC] website
:[4] [http://www.rpdc.tas.gov.au/projects_state_signif/Basslink Basslink] project
:[5] Donald Beaty et al, "Standard Handbook for Electrical Engineers 11th Ed.", McGraw Hill, 1978
:[6] http://www.myinsulators.com/acw/bookref/histsyscable/
:[7] Shaping the Tools of Competitive Power http://www.tema.liu.se/tema-t/sirp/PDF/322_5.pdf
:[8] http://www.rmst.co.il/HVDC_Proven_Technology.pdf
:[9] http://www.ieee.org/organizations/history_center/Che2004/DITTMANN.pdf
- [http://www.abb.co.uk/global/gad/gad02181.nsf/0/5950ab82df908d0cc1256e89002f3e6f?OpenDocument History of HVDC]
- [http://www.worldbank.org/html/fpd/em/transmission/technology_abb.pdf World Bank briefing document about HVDC systems]
Category:Electric power transmission systems
Hakodate
Hakodate (函館市; -shi) is a city and port located in Oshima, Hokkaido, Japan. It is the capital city of Oshima Subprefecture and the sister city of Halifax, Nova Scotia, Canada.
As of 2004, the city has an estimated population of 299,737 and the density of 442.24 persons per km². The total area is 677.77 km². Hakodate's size nearly doubled on December 1, 2004 when the neighboring municipalities of Toi, Esan, Todohokke and Minamikayabe were merged into it.
The port of Hakodate was opened to American trade on March 31, 1853 under the conditions of the Treaty of Kanagawa, as negotiated by Commodore Matthew Perry. A mariner of his fleet died during cruising and his body was buried in Hakodate cemetery for foreigners. He was the first U.S. citizen to be buried in Japan. Hakodate was later awarded the status of city on August 1, 1922.
Soon several countries settled their consulates in Hakodate. One of them, the Russian one, had a chapel, from where Eastern Orthodoxy arrived in Japan, now the Japanese Orthodox Church. The Orthodox church is neighbored by several other churches, including Anglican and Catholic.
Catholic
The city is overlooked by Hakodateyama (Mount Hakodate), a lumpy, totally forested mountain. The summit of the mountain is easily reached by either hiking trail, cable car, or car. The nighttime view from the summit is renowned all over Japan as one of the loveliest sights in the country. An obscure local nickname of the bumpy mountain is Gagyuzan ("Mount Cow's-back"), which alludes to the way the mountain's shape resembles that of a resting bovine.
Hakodate is home to the famous European-style Goryokaku fort, which was built in the shape of a five-pointed star in 1866. During the last phase of the Meiji Restoration, the shogunate loyalists occupied the fort, declaring the establishment of the Republic of Ezo. A handful of French soldiers,who had served as military advisers for the shogunate army, joined the rebellion led by Enomoto Takeaki. After battles with the government forces, the secessionists surrendered the fort in 1869. It is now used as a public park. The park is a popular spot in Hokkaido for hanami (cherry blossom viewing).
The small but bustling city is also famous as the site of Hijikata Toshizo's last stand.
Hijikata Toshizo
The city is also known for Hakodate Shio Ramen, where instead of having a pork cutlet placed inside the soup, sliced squid is used. On a similar note, Hakodate's city fish is the squid. Every year (around July) the city gets together for the Hakodate Port Festival. Hordes of citizens gather in the streets to dance a wiggly dance known as the Ika-odori (Squid Dance), the name of which describes the dance appropriately. The glowing lights of squid-catching boats can be seen in the waters surrounding the city.
Near Hakodate, Hokkaido there is the static inverter plant of the HVDC Hokkaido-Honshu.
Famous People
- GLAY members - rock band
- YUKI - singer (Judy and Mary)
- Goro Naya - actor
See also
- Foreign cemeteries in Japan
The fish of Hakodate is the ika, Japanese for cuttlefish.
External link
- [http://www.city.hakodate.hokkaido.jp/kikaku/english/ Official website] in English
- [http://wikitravel.org/en/article/Hakodate Wikitravel: Hakodate]
Category:Cities in Hokkaido Prefecture
ja:函館市
ko:하코다테 시
th:ฮาโกดาเตะ
HonshuHonshū (本州) is the largest island of Japan, called the Mainland; it is south of Hokkaido across the Tsugaru Strait, north of Shikoku across the Inland Sea, and northeast of Kyushu across the Kanmon Strait. It is the seventh largest island, and the second most populous island in the world after Java (see the list of islands by size, population).
The island is roughly 1300 km long and ranges from 50 to 230 km wide, and its total area is 230,500 km², around 60% of the total area of Japan. It is larger than the island of Great Britain, and ranks between the states of Minnesota and Michigan in area. Honshu has 5450 km of coastline.
Mountainous and volcanic, Honshu has frequent earthquakes (the Great Kantō earthquake heavily damaged Tokyo in September 1923); the highest peak is the active volcano Mount Fuji at 3,776 m. There are many rivers, including the Shinano River, Japan's longest. The climate is highly variable from the cool north to the subtropical south.
The population is 98,352,000 (as of 1990, in 1975 it was 89,101,702), concentrated in the available lowlands, notably in the Kanto plain where 25% of the total population reside in and around Tokyo and Yokohama. Other cities include Kyoto, Osaka, Kobe, Hiroshima, Sendai, and Nagoya. The island is nominally divided into five regions and contains 34 prefectures, including metropolitan Tokyo.
The regions are Chugoku (southern), Kansai (southern, above Chugoku), Chubu (central), Kanto (eastern), and Tohoku (northern).
Three-fourths of Japan's main, major, and modern cities are here on Honshu, including the 23 special wards of Tokyo, Yokohama, Osaka, Nagoya, Kobe, Kyoto, Akita, Sendai, Fukushima, Niigata, and Hiroshima. Cultural centers are also present, such as Kyoto (which is both modern and cultural), Nara, and Kamakura.
The island also includes important agricultural regions. Niigata is noted as an important producer of rice. The Kanto and Nobi plains produce rice and vegetables. Yamanashi is a major fruit-growing area, and Aomori is famous for its apples.
A mountain range runs along the length of Honshu from end to end. In addition to Mt. Fuji, the Japanese Alps are features of Honshu. The mountains are responsible for a marked difference in climate between the eastern or southern (Pacific or Inland Sea coast) side, and the western or northern (Sea of Japan coast) side.
The prefectures are:
- Chugoku — Hiroshima-ken, Okayama-ken, Shimane-ken, Tottori-ken, Yamaguchi-ken.
- Kansai — Hyogo-ken, Kyoto-fu, Mie-ken, Nara-ken, Osaka-fu, Shiga-ken, Wakayama-ken.
- Chubu — Aichi-ken, Fukui-ken, Gifu-ken, Ishikawa-ken, Nagano-ken, Niigata-ken, Toyama-ken, Shizuoka-ken, Yamanashi-ken.
- Kanto — Chiba-ken, Gunma-ken, Ibaraki-ken, Kanagawa-ken, Saitama-ken, Tochigi-ken, Tokyo-to.
- Tohoku — Akita-ken, Aomori-ken, Fukushima-ken, Iwate-ken, Miyagi-ken, Yamagata-ken.
Honshu is connected to the islands of Hokkaido, Kyushu and Shikoku by tunnels or bridges. Three new bridge systems have been built across the islands of the Inland Sea between Honshu and Shikoku (Akashi-Kaikyo Bridge and the Ohnaruto Bridge; Shin-Onomichi Bridge, Innoshima Bridge, Ikuchi Bridge, Tatara Bridge, Ohmishima Bridge, Hakata-Ohshima Bridges, and the Kurushima-Kaikyo Bridge; Shimotsui-Seto Bridge, Hitsuishijima Bridge, Iwakurojima Bridge, Yoshima Bridge, Kita Bisan-Seto Bridge, and the Minami Bisan-Seto Bridge), and the Seikan Tunnel connects Honshu with Hokkaido.
Category:Geography of Japan
ko:혼슈
ja:本州
Category:Submarine power cablesCategory:Power cables Buffering agentA buffering agent adjusts the pH of a solution. The function of a buffering agent is to drive an acidic or alkaline solution to a certain pH state and prevent a change in this pH. Buffering agents have variable properties -- some are more soluble than others; some are acidic while others are basic. As pH managers, they are important in many chemical applications, including agriculture, food processing, medicine and photography.
What is a buffering agent?
Buffering agents can be either the weak acid or conjugate base (weak base) that would comprise a buffer solution. Buffering agents are usually added to water to form buffer solutions. They are the substances that are responsible for the buffering seen in this solutions. These agents are added to substances that are to be placed into acidic or basic conditions in order to stabilaze the substance. For example, buffered aspirin has a buffering agent, such as MgO, that will maintain the pH of the aspirin as it passes through the stomach of the patient. Another use of a buffering agent is in antacid tablets, whose primary purpose is to lower the acidity of the stomach.
How a buffering agent works
The way buffering agent works is seen in how a buffering solutions works. Using Le Chatelier's principle we get a equilibrium expression between the acid and conjugate base. As a result we see that there is little change in the concentrations of the acid and base so therefore the solution is buffered. A buffering agent sets up this concentration ratio by providing the corresponding conjugate acid or base to stabilize the pH of that which it is added to. The resulting pH of this combination can be found by using the Henderson-Hasselbalch equation which is
where HA is the weak acid and A is the the anion of the base.
Buffering Agents Vs. Buffering Solutions
Buffering agents are similar to buffer solutions as a result of the fact that buffering agents are the main components of a buffer solution. They both regulate the pH of a solution and resist changes in pH. A buffer solution maintains the pH for the whole system which is placed into it, whereas a buffering agent is added to an already acidic or basic solution where is then modifies and maintains a new pH.
Conclusion
Buffering agents and buffering solutions are almost one in the same except for a view differences.
1)Solutions maintain pH of a system preventing large changes in it where as agents modify the pH of what there placed into.
2)Agents are the active compenents of a buffer solutions.
Monopotassium phosphate (MKP) is an example of a buffering agent. It has a mildly acidic reaction; when applied as a fertilizer with urea or diammonium phosphate, it minimizes pH fluctuations which can cause nitrogen loss.
External links
[http://www.oshun.ca/glossary.html] Oshun - The Glossary
- [http://antoine.frostburg.edu/chem/senese/101/acidbase/faq/buffered-aspirin.shtml General Chemistry FAQ: buffered aspirin]
- [http://www.umass.edu/umext/floriculture/fact_sheets/greenhouse_management/ph_pesticides.htm Effects of pH on Pesticides and Growth Regulators]
"Chemical Principles: The Quest for Insight", Third Edition. Peter Atkins and Loretta Jones
"Quanitative Chemical Analysis", Sixth Edition. Daniel C. Harris
Category:Acid-bases
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Hood Green
Hood Green is a village in the metropolitan borough of Barnsley, in South Yorkshire, England. It is near Dodworth and Silkstone, which are also villages in the metropolitan borough of Barnsley.
Landmarks
Wentworth Castle & Gardens
This site is only a matter of metr
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Chalk horse
Numerous chalk figures have been carved into hillsides in the United Kingdom. Although they are frequently considered to be ancient monuments few can trace their origins further back then a couple of hundred years. The significant exception to this is the Uffington White Horse which seems to date from sometime in the iron age.
The reasons for the creation for the figures are varied and obscure. The Uffington Horse probably held relig
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Ferranti-Packard 6000
The FP-6000 was a second generation mainframe computer developed and built by Ferranti-Packard in the early 1960s. It is particularily notable for its support of multitasking in hardware, likely the first commercial machine to do so. Only six FP-6000s were sold before the computer division of Ferranti-Packard was sold off by Ferranti's UK headquarters in 1963, the FP-6000 becoming the basis for the mid-ran
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Bandana Square
Bandana Square is a small enclosed shopping center in the Energy Park industrial park in Saint Paul, Minnesota. It includes a Holiday Inn Express hotel and conference center and the Twin City Model Railroad Club museum, as well as a few restaurants. It was a conversion of early
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Broad Town, Wiltshire
Broad Town is a village and civil parish in the North Wiltshire district of Wiltshire, England, about 8 miles south-west of Swindon. According to the 2001 census it had a population of 584.
The parish is the site of a chalk horse, known as the Broad Town White Horse. [http://wiltshirewhitehorses.org.uk/broad
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