用戶:JC1/twenty-second

電塔，又名輸電塔或輸電鐵塔，是用來承托架空電纜的結構物，通常為鋼製鐵塔-。輸電網絡中的輸電系統主要用於大規模從發電廠輸送電力至負載中心，使用架空電纜相對地底電纜成本較低，故需要輸電塔將電纜抬高以避免高壓電力影響地面活動。較低電壓的配電系統的則常用電線杆作支撐物。電塔有各種不同形狀和大小，高度通常為15至55米之間，但最高可見於舟山島架空電纜，當中有兩座370米高的輸電塔。除鋼鐵以外，亦有見以混凝土或木材作為建築材料。

電塔可主要分為三大類：懸吊塔、張力塔以及轉置塔。有些電塔則同時有以上數項塔種的功能。電塔和架空電纜為一種視覺污染，故亦為管線地下化的其中一種理由。

結構

電塔結構的建設費用通常佔該條輸電線路的三成至四成。其設計會因應地貌、氣候，以及架空電纜的電壓、線路數等參數而有所不同。跨臂

特殊設計

Sometimes (in particular on steel lattice towers for the highest voltage levels) transmitting plants are installed, and antennas mounted on the top above or below the overhead ground wire. Usually these installations are for mobile phone services or the operating radio of the power supply firm, but occasionally also for other radio services, like directional radio. Thus transmitting antennas for low-power FM radio and television transmitters were already installed on pylons. On the Elbe Crossing 1 tower, there is a radar facility belonging to the 漢堡 water and navigation office.

For crossing broad valleys, a large distance between the conductors must be maintained to avoid short-circuits caused by conductor cables colliding during storms. To achieve this, sometimes a separate mast or tower is used for each conductor. For crossing wide rivers and straits with flat coastlines, very tall towers must be built due to the necessity of a large height clearance for navigation. Such towers and the conductors they carry must be equipped with flight safety lamps and reflectors.

Two well-known wide river crossings are the Elbe Crossing 1 and Elbe Crossing 2. The latter has the tallest overhead line masts in Europe, at 227米（745英尺） tall. In Spain, the overhead line crossing pylons in the Spanish bay of Cádiz have a particularly interesting construction. The main crossing towers are 158米（518英尺） tall with one crossarm atop a 錐台 framework construction. The longest overhead line spans are the crossing of the Norwegian Sognefjord (4,597米（15,082英尺） between two masts) and the Ameralik Span in Greenland (5,376米（17,638英尺）). In Germany, the overhead line of the EnBW AG crossing of the Eyachtal has the longest span in the country at 1,444米（4,738英尺）.

In order to drop overhead lines into steep, deep valleys, inclined towers are occasionally used. These are utilized at the 胡佛水壩, located in the United States, to descend the cliff walls of the Black Canyon of the Colorado. In Switzerland, a pylon inclined around 20 degrees to the vertical is located near 薩甘斯, St. Gallens. Highly sloping masts are used on two 380 kV pylons in Switzerland, the top 32 meters of one of them being bent by 18 degrees to the vertical.

Power station chimneys are sometimes equipped with crossbars for fixing conductors of the outgoing lines. Because of possible problems with corrosion by flue gases, such constructions are very rare.

A new type of pylon, called Wintrack pylons, will be used in the Netherlands starting in 2010. The pylons were designed as a minimalist structure by Dutch architects Zwarts and Jansma. The use of physical laws for the design made a reduction of the magnetic field possible. Also, the visual impact on the surrounding landscape is reduced.

Two clown-shaped pylons appear in Hungary, on both sides of the M5 motorway, near 烏伊豪爾詹.

The Pro Football Hall of Fame in Canton, Ohio, U.S., and 美國電力公司 paired to conceive, design, and install goal post-shaped towers located on both sides of Interstate 77 near the hall as part of a power infrastructure upgrade.

The Mickey Pylon is a 米老鼠 shaped transmission tower on the side of 4號州際公路, near 華特迪士尼世界度假區 in 奧蘭多 (佛羅里達州).

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  128 meters high Hyperboloid pylon in Russia
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  River 易北河 Crossing 2 in Germany
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  Colorful "設計師" tower titled Steps of Antti in Finland
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  Wintrack pylons in the Netherlands
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  The Mickey Pylon in Florida, U.S.

其他設置

Markers

A typical tower identification tag

The 國際民用航空組織 issues recommendations on markers for towers and the conductors suspended between them. Certain jurisdictions will make these recommendations mandatory, for example that certain power lines must have overhead wire markers placed at intervals, and that warning lights be placed on any sufficiently high towers, this is particularly true of transmission towers which are in close vicinity to 機場s.

Electricity pylons often have an identification tag marked with the name of the line (either the terminal points of the line or the internal designation of the power company) and the tower number. This makes identifying the location of a fault to the power company that owns the tower easier.

Transmission towers, much like other steel lattice towers including broadcasting or cellphone towers, are marked with signs which discourage public access due to the danger of the high voltage. Often this is accomplished with a sign warning of the high voltage. At other times, the entire access point to the transmission corridor is marked with a sign.

絕緣子

Arcing horns. Designs may vary.

架空電纜需與大地及電塔隔離以免短路，然而由於電塔需承托電纜無法使用空氣作為絕緣體，故需於承托處額外加上絕緣，通常為玻璃或陶瓷碟，稱之為絕緣子或礙子。絕緣子的材質除上述的玻璃或陶瓷以外，亦有矽氧樹脂或EPDM橡膠等複合材料。絕緣子以串聯型式將架空電纜連接至電塔，而其數量會因電壓和環境因素而增加，例如11千伏線路會有一至兩隻絕緣子，400千伏線路則可達20隻絕緣子。絕緣子的形狀增加了絕緣體表面的長度，由此減少了潮濕時短路或漏電的機會。

架空線減震器

Stockbridge damper bolted to line close to the point of attachment to the tower. It prevents mechanical vibration building up in the line.

架空線減震器s are added to the transmission lines a meter or two from the tower. They consist of a short length of cable clamped in place parallel to the line itself and weighted at each end. The size and dimensions are carefully designed to damp any buildup of mechanical oscillation of the lines that could be induced by mechanical vibration most likely that caused by wind. Without them its possible for a standing wave to become established that grows in magnitude and destroys the line or the tower.

Arcing horns

Arcing horns are sometimes added to the ends of the insulators in areas where voltage surges may occur. These may be caused by either lightning strikes or in switching operations. They protect power line insulators from damage due to arcing. They can be seen as rounded metal pipework at either end of the insulator and provide a path to earth in extreme circumstances without damaging the insulator.

Physical security

Towers will have a level of physical security to prevent members of the public or climbing animals from ascending them. This may take the form of a security fence or climbing baffles added to the supporting legs. Some countries require that lattice steel towers be equipped with a 有刺鐵絲網 barrier approximately 3米（9.8英尺） above ground in order to deter unauthorized climbing. Such barriers can often be found on towers close to roads or other areas with easy public access, even where there is not a legal requirement. In the United Kingdom, all such towers are fitted with barbed wire.

High voltage AC transmission towers

Single-circuit three-phase transmission line

三相電 systems are used for high voltage (66- or 69-kV and above) and extra-high voltage (110- or 115-kV and above; most often 138- or 230-kV and above in contemporary systems) AC transmission lines. In some European countries, e.g. Germany, Spain or Czech Republic, smaller lattice towers are used for medium voltage (above 10 kV) transmission lines too. The towers must be designed to carry three (or multiples of three) conductors. The towers are usually steel lattices or 桁架 (工程)es (wooden structures are used in Canada, Germany, and 斯堪的納維亞 in some cases) and the insulators are either glass or porcelain discs or composite insulators using silicone rubber or EPDM rubber material assembled in strings or long rods whose lengths are dependent on the line voltage and environmental conditions.

Typically, one or two ground wires, also called "guard" wires, are placed on top to intercept lightning and harmlessly divert it to ground.

Towers for high- and extra-high voltage are usually designed to carry two or more electric circuits (with very rare exceptions, only one circuit for 500-kV and higher). If a line is constructed using towers designed to carry several circuits, it is not necessary to install all the circuits at the time of construction. Indeed, for economic reasons, some transmission lines are designed for three (or four) circuits, but only two (or three) circuits are initially installed.

Some high voltage circuits are often erected on the same tower as 110 kV lines. Paralleling circuits of 380 kV, 220 kV and 110 kV-lines on the same towers is common. Sometimes, especially with 110 kV circuits, a parallel circuit carries traction lines for 電氣化鐵路.

High voltage DC transmission towers

HVDC distance tower near the terminus of the Nelson River Bipole adjacent to Dorsey Converter Station near Rosser, Manitoba, Canada — August 2005

高壓直流輸電 (HVDC) transmission lines are either monopolar or bipolar systems. With bipolar systems, a conductor arrangement with one conductor on each side of the tower is used. On some schemes, the ground conductor is used as electrode line or ground return. In this case, it had to be installed with insulators equipped with surge arrestors on the pylons in order to prevent electrochemical corrosion of the pylons. For single-pole HVDC transmission with ground return, towers with only one conductor can be used. In many cases, however, the towers are designed for later conversion to a two-pole system. In these cases, often conductors on both sides of the tower are installed for mechanical reasons. Until the second pole is needed, it is either used as electrode line or joined in parallel with the pole in use. In the latter case, the line from the converter station to the earthing (grounding) electrode is built as underground cable, as overhead line on a separate right of way or by using the ground conductors.

Electrode line towers are used in some HVDC schemes to carry the power line from the converter station to the grounding electrode. They are similar to structures used for lines with voltages of 10–30 kV, but normally carry only one or two conductors.

AC transmission towers may be converted to full or mixed HVDC use, to increase power transmission levels at a lower cost than building a new transmission line.

Railway traction line towers

Tension tower with phase transposition of a powerline for single-phase AC traction current (110 kV, 16.67 Hz) near 巴托洛梅, Germany

Towers used for single-phase AC 鐵路運輸 traction lines are similar in construction to those towers used for 110 kV three-phase lines. Steel tube or concrete poles are also often used for these lines. However, railway traction current systems are two-pole AC systems, so traction lines are designed for two conductors (or multiples of two, usually four, eight, or twelve). These are usually arranged on one level, whereby each circuit occupies one half of the cross arm. For four traction circuits, the arrangement of the conductors is in two levels and for six electric circuits, the arrangement of the conductors is in three levels.

Towers for different types of currents

Pylon in Sweden about 1918.

AC circuits of different frequency and phase-count, or AC and DC circuits, may be installed on the same tower. Usually all circuits of such lines have voltages of 50 kV and more. However, there are some lines of this type for lower voltages. For example, towers used by both railway traction power circuits and the general three-phase AC grid.

Two very short sections of line carry both AC and DC power circuits. One set of such towers is near the terminal of HVDC Volgograd-Donbass on Volga Hydroelectric Power Station. The other are two towers south of Stenkullen, which carry one circuit of HVDC Konti-Skan and üne circuit of the three-phase AC line Stenkullen-Holmbakullen.

Towers carrying AC circuits and DC electrode lines exist in a section of the powerline between Adalph Static Inverter Plant and Brookston the pylons carry the electrode line of HVDC Square Butte.

The electrode line of HVDC CU at the converter station at Coal Creek Station uses on a short section the towers of two AC lines as support.

The overhead section of the electrode line of Pacific DC Intertie from Sylmar Converter Station to the grounding electrode in the Pacific Ocean near Will Rogers State Beach is also installed on AC pylons. It runs from Sylmar East Converter Station to Southern California Edison Malibu Substation, where the overhead line section ends.

In Germany, Austria and Switzerland some transmission towers carry both public AC grid circuits and railway traction power in order to better use rights of way.

Tower designs

Shape

Guyed "Delta" transmission tower (a combination of guyed "V" and "Y") in 內華達州.

Different shapes of transmission towers are typical for different countries. The shape also depends on voltage and number of circuits.

One circuit

Delta pylons are the most common design for single circuit lines, because of their stability. They have a V-shaped body with a horizontal arm on the top, which forms an inverted Delta. Larger Delta towers usually use two guard cables.

Portal pylons are widely used in Ireland, Scandinavia and Canada. They stand on two legs with one cross arm, which gives them a H-shape. Up to 110 kV they often were made from wood, but higher voltage lines use steel pylons.

Smaller single circuit pylons may have two small cross arms on one side and one on the other.

Two circuits

One level pylons only have one cross arm carrying 3 cables on each side. Sometimes they have an additional cross arm for the protection cables. They are frequently used close to airports due to their reduced height.

Typical T-shaped 110 kV tower from the former 東德.

Danube pylons or Donaumasten got their name from a line built in 1927 next to the 多瑙河. They are the most common design in central European countries like Germany or Poland. They have two cross arms, the upper arm carries one and the lower arm carries two cables on each side. Sometimes they have an additional cross arm for the protection cables.

Ton shaped towers are the most common design, they have 3 horizontal levels with one cable very close to the pylon on each side. In the United Kingdom the second level is often (but not always) wider than the other ones while in the United States all cross arms have the same width.

A close up of the wires attached to the pylon, showing the various parts annotated.

Four circuits

Christmas-tree-shaped towers for 4 or even 6 circuits are common in Germany and have 3 cross arms where the highest arm has each one cable, the second has two cables and the third has three cables on each side. The cables on the third arm usually carry circuits for lower high voltage.

Support structures

Danube pole for 110 kV in Germany, built in the 1930s

Towers may be self-supporting and capable of resisting all forces due to conductor loads, unbalanced conductors, wind and ice in any direction. Such towers often have approximately square bases and usually four points of contact with the ground.

A semi-flexible tower is designed so that it can use overhead grounding wires to transfer mechanical load to adjacent structures, if a phase conductor breaks and the structure is subject to unbalanced loads. This type is useful at extra-high voltages, where phase conductors are bundled (two or more wires per phase). It is unlikely for all of them to break at once, barring a catastrophic crash or storm.

A guyed mast has a very small footprint and relies on guy wires in tension to support the structure and any unbalanced tension load from the conductors. A guyed tower can be made in a V shape, which saves weight and cost.

Materials

Tubular steel

Steel tube tower next to older lattice tower near 沃加沃加, Australia

Poles made of tubular 鋼 generally are assembled at the factory and placed on the right-of-way afterward. Because of its durability and ease of manufacturing and installation, many utilities in recent years prefer the use of monopolar steel or concrete towers over lattice steel for new power lines and tower replacements.

In Germany steel tube pylons are also established predominantly for medium voltage lines, in addition, for high voltage transmission lines or two electric circuits for operating voltages by up to 110 kV. Steel tube pylons are also frequently used for 380 kV lines in France, and for 500 kV lines in the United States.

Lattice

參見：Lattice tower

A lattice tower is a framework construction made of steel or aluminium sections. Lattice towers are used for power lines of all voltages, and are the most common type for high-voltage transmission lines. Lattice towers are usually made of galvanized steel. Aluminium is used for reduced weight, such as in mountainous areas where structures are placed by helicopter. Aluminium is also used in environments that would be corrosive to steel. The extra material cost of aluminium towers will be offset by lower installation cost. Design of aluminium lattice towers is similar to that for steel, but must take into account aluminium's lower 楊氏模量.

A lattice tower is usually assembled at the location where it is to be erected. This makes very tall towers possible, up to 100米（328英尺） (and in special cases even higher, as in the Elbe crossing 1 and Elbe crossing 2). Assembly of lattice steel towers can be done using a crane. Lattice steel towers are generally made of angle-profiled steel beams (L- or T-beams). For very tall towers, 桁架 (工程)es are often used.

Wood

Wood and metal crossbar

Wooden lattice transmission tower in 茵萊湖 (緬甸).

Simple wooden transmission tower in 蒙古國

木材 is a material which is limited in use in high-voltage transmission. Because of the limited height of available trees, the maximum height of wooden pylons is limited to approximately 30米（98英尺）. Wood is rarely used for lattice framework. Instead, they are used to build multi-pole structures, such as H-frame and K-frame structures. The voltages they carry are also limited, such as in other regions, where wood structures only carry voltages up to approximately 30 kV.

In countries such as Canada or the United States, wooden towers carry voltages up to 345 kV; these can be less costly than steel structures and take advantage of the surge voltage insulating properties of wood. 截至2012年 (2012-Missing required parameter 1=month!), 345 kV lines on wood towers are still in use in the US and some are still being constructed on this technology. Wood can also be used for temporary structures while constructing a permanent replacement.

Concrete

A reinforced concrete pole in Germany

混凝土 pylons are used in 德國國名 normally only for lines with operating 電壓s below 30 kV. In exceptional cases, concrete pylons are used also for 110 kV lines, as well as for the public grid or for the 鐵路運輸 traction current grid. In Switzerland, concrete pylons with heights of up to 59.5 metres (world's tallest pylon of prefabricated concrete at 利陶) are used for 380 kV overhead lines. Concrete poles are also used in Canada and the United States.

Concrete pylons, which are not prefabricated, are also used for constructions taller than 60 metres. One example is a 66米（217英尺） tall pylon of a 380 kV powerline near Reuter West Power Plant in Berlin. Such pylons look like industrial chimneys. In China some pylons for lines crossing rivers were built of concrete. The tallest of these pylons belong to the Yangtze Powerline crossing at Nanjing with a height of 257米（843英尺）.

Assembly

Cable riggers atop a pylon engaged in adding a fiber optic data cable wound around the top tower stay cable. The cable (SkyWrap) is wound on by a traveling machine, which rotates a cable drum around the support cable as it goes. This travels under its own power from tower to tower, where it is dismantled and hoisted across to the opposite side. In the picture, the motor unit has been moved across but the cable drum is still on the arrival side.

Before transmission towers are even erected, prototype towers are tested at tower testing stations. There are a variety of ways they can then be assembled and erected:

Temporary guyed pylon next to a commenced new tower

• They can be assembled horizontally on the ground and erected by push-pull cable. This method is rarely used because of the large assembly area needed.
• They can be assembled vertically (in their final upright position). Very tall towers, such as the Yangtze River Crossing, were assembled in this way.
• A jin-pole crane can be used to assemble lattice towers. This is also used for 電線杆s.
• 直升機s can serve as aerial cranes for their assembly in areas with limited accessibility. Towers can also be assembled elsewhere and flown to their place on the transmission right-of-way. Helicopters may also be used for transporting disassembled towers for scrapping.

Tower functions

Three-phase alternating current transmission towers over water, near 達爾文 (澳大利亞), Australia

Tower structures can be classified by the way in which they support the line conductors. Suspension structures support the conductor vertically using suspension insulators. Strain structures resist net tension in the conductors and the conductors attach to the structure through strain insulators. Dead-end structures support the full weight of the conductor and also all the tension in it, and also use strain insulators.

Structures are classified as tangent suspension, angle suspension, tangent strain, angle strain, tangent dead-end and angle dead-end. Where the conductors are in a straight line, a tangent tower is used. Angle towers are used where a line must change direction.

Cross arms and conductor arrangement

Generally three conductors are required per AC 3-phase circuit, although single-phase and DC circuits are also carried on towers. Conductors may be arranged in one plane, or by use of several cross-arms may be arranged in a roughly symmetrical, triangulated pattern to balance the impedances of all three phases. If more than one circuit is required to be carried and the width of the line right-of-way does not permit multiple towers to be used, two or three circuits can be carried on the same tower using several levels of cross-arms. Often multiple circuits are the same voltage, but mixed voltages can be found on some structures.

參見

• 電線杆
• 帶電工作

外部連結

• Pylon Appreciation Society
• Flash Bristow's pylon photo gallery and pylon FAQ
• Magnificent Views: Pictures of High Voltage Towers (also offers technical information)
• Structurae database of select notable transmission towers
• Pylons in Russia and other areas of former Soviet Union
• Meet the 'pylon spotters' – BBC News