Power transmission line supports are structures that serve to support live wires and lightning protection cables above the earth's surface. They are various forms and sizes. The supports can be reinforced concrete, wood, metal or even composite materials. The main elements of power transmission line support are racks, foundations, traverses (crossbars on which the wires are held), cable stands and guy wires are also often used.
ANCHOR SUPPORTS FOR POWER LINES
There are anchor and intermediate supports for power lines. The robust design of the anchor supports can withstand significant forces from wire tension; anchor supports of power lines are installed at the beginning and end of power lines, at turns, when power lines cross small rivers, railways, roads and bridges.
A type of anchor supports - transition supports are used when crossing power lines of rivers and other large obstacles. It is the transition supports that bear the heaviest loads and can themselves reach a height of 300 meters! These poles are the heaviest and tallest of all power line poles; they are often painted in bright colors For example, red and white supports are often found, and orange, gray and other colors are also used. For more details about transition supports, see the corresponding essay http://io.ua/s73072.
INTERMEDIATE POWER LINE SUPPORTS
Intermediate supports have less robust construction than anchor ones; they usually serve to support wires and cables on straight sections of power line routes. Most of the supports on the routes are intermediate. As a rule, an intermediate support can be distinguished from an anchor support by the following feature: if the garlands of insulators hang perpendicular to earth's surface, which means the support is intermediate. And on the anchor supports, the wires are fixed in the clamps of tension garlands; these garlands are like a continuation of the line and are located at an acute angle to the surface of the earth, and sometimes almost parallel.
Also, power line supports are divided into:
- transposition (to change the order of phases),
- branch,
- cross,
- increased, decreased, etc.
Based on the number of suspended wires (circuits), supports are divided into single- and multi-circuit; by design - single-post, A- and AP-shaped, U-shaped, V-shaped (for example, “Nabla” type), “shot glass” type, etc.
WOODEN POWER LINE SUPPORTS
Today, mainly reinforced concrete and metal power line supports are used. Wooden transmission line supports were installed on power lines with voltages up to 220 kV. Power line supports were usually made from pine and larch poles impregnated with an anti-rotten compound (antiseptic). Often wooden supports were strengthened on reinforced concrete attachments (stepchildren) or piles. Wooden power line supports were cheap, relatively easy to manufacture and reliable in operation. The first large Soviet power transmission line - Kashirskaya State District Power Plant - Moscow - with a voltage of 110 kV and a length of 120 km was built precisely on wooden supports Oh. Today, power lines with wooden poles are no longer built.
REINFORCED CONCRETE POWER LINE SUPPORTS
Reinforced concrete power transmission line supports, the designs of which were developed in the USSR in 1933, have higher mechanical strength. However, due to the lack of an industrial base, their mass use in the construction of power lines of all voltages began only in 1955. The advantages of reinforced concrete transmission line supports are simplicity of design and manufacturability of factory production. Such power line supports are usually ring or rectangular section, they are made mainly from prestressed reinforced concrete.
The most common are intermediate single-post reinforced concrete power line supports with metal crossarms, which are installed directly in the ground. In addition, on power lines with a voltage of 110-500 kV, intermediate and anchor-corner reinforced concrete transmission line supports with guy wires were widely used.
METAL POWER LINE SUPPORTS
Metal transmission line supports have less weight than reinforced concrete ones and high mechanical strength. This allows you to create supports of considerable height, designed for heavy loads. They are used on power lines of all voltages, often in combination with reinforced concrete intermediate supports. Metal transmission line supports are indispensable on lines with heavy loads (for example, on crossings).
Metal power transmission line supports are made mainly from steel, in some cases from aluminum alloys. According to the manufacturing method, metal transmission line supports are divided into welded ones, which come from factories in the form of finished sections, and bolted ones, which are assembled on the route from individual elements(braces, rods, chords) on bolts.
Metal supports are divided into two broad groups - lattice and MGS (multifaceted bent racks). If the first ones are well known to everyone, then IGUs are just beginning to become widespread in the CIS countries. A lot of useful information You can find out about these supports on the website www.energobud.com.ua
By voltage, power lines within the CIS are divided into 35 kV, 110 kV, 154 kV (150 kV), 220 kV, 330 kV, 400 kV, 500 kV, 750 kV, 800 kV, 1150 kV and 1500 kV. The majority of all power lines in the world operate on alternating current, but there are also lines that operate on a permanent basis, for example, power lines direct current Volgograd-Donbass (you can read about these power lines here http://io.ua/s91331).
POWER LINE VOLTAGE CLASSES
It can be difficult for a non-specialist to accurately determine the voltage in power lines, but, as a rule, this can be done in a simple way- count how many insulators in the garland are suspended on the traverse. So 35 kV power lines have three to five insulators in each garland. But in the garlands of 110 kV power lines there are already six to ten insulators. If there are ten to fifteen insulators, then it is a 220 kV power line.
If the power line wires are split into two (this is called splitting), then the line can have a voltage of 330 kV. If there are three wires in each phase, then 500 kV, if there are four wires, then 750 kV.
There are exceptions to every rule. Thus, 220 kV and 150 kV lines have splitting, although this is typical for 330 kV lines. Power lines 330 kV, in special cases, can work without splitting.
35 kV -110 kV power lines are used everywhere as distribution networks (for example, a 110 kV power line can supply a substation that powers a small village or microdistrict). The 150 kV class is a more advanced analogue of the hundred-tens; this voltage is used in the Dneproenergo power system and some adjacent areas, as well as in the Kola power system (Kola Peninsula). This voltage class came to the USSR in the early 30s, along with the American equipment of the General Electric company for the Dnieper Hydroelectric Power Station.
220 kV power lines are mainly used to connect power plants with substations and large consumers. 330 kV lines are often built over long distances, for communication between powerful power plants and substations (interconnections), and sometimes for the needs of very energy-intensive enterprises. Lines with voltages of 400 kV, 500 kV, and 750 kV and higher are also used for intersystem connections and for transmitting electricity over long distances, including to neighboring countries.
UNIFICATION OF POWER LINE SUPPORTS IN THE USSR
In 1976, in connection with the unification of power transmission line supports in the USSR, the following system for designating metal and reinforced concrete supports of 35-330 kV was adopted:
the letters P and PS indicate intermediate supports,
PVA—intermediate with internal connections,
PU or PUS - intermediate corner,
PP - intermediate transitional,
AN US - anchor-corner,
K or KS - end ones.
The letter B indicates reinforced concrete supports, and its absence indicates that the supports are steel. The numbers 35, 110, 150, 220, etc., following the letters indicate the line voltage, and the numbers behind them indicate the standard size of the supports. The letters U and T are added respectively to the designation of intermediate supports used as corner supports and with cable support. And in modern power grid construction, “de-unification” is observed, new original supports are being developed, designed for the conditions of a specific power line route. Thus, in developed countries they have already abandoned mass use standard projects. Each line must be built taking into account all the nuances of the relief, climate, etc.
CLASSIFICATION OF POWER LINE SUPPORTS BY GENERAL APPEARANCE
Tower supports
Classic, the most common of all high voltage power line supports. They can have from one to 9 parallel traverses, and are used for single-, double- or multi-circuit power lines. All lattice tower supports are united by common feature- their trunk narrows from the base to the top. Divided into two families:
- wide-barreled lattice (if the base of the mast is wider than a freight car, see photo 1). These are the most common supports. They can be single-chain (“Crimean type”), double-chain (“barrel” type) and multi-chain.
The most interesting representatives of single-circuit tower supports are T-shaped supports for DC lines.
- narrow-base lattice (accordingly, their base is somewhat narrower in size than the base of a freight car).
Portal supports
Supports made of metal, wood or reinforced concrete, resembling the letter “P” or the letter “N”. They are widely used on 330-750 kV power lines. As a rule, single-chain.
AP-shaped supports
Single-chain supports created using welded metal pipes, MGS or a tree, in profile resembling the letter “A”, in front the letter “P”. The cross-section of pipes in these supports can reach 1300 mm, and the height can be over 80 m.
Photo 4 shows an example of such a tubular support when crossing a 330 kV line across the Dnieper, in Ukraine. Inside its racks there are stairs for climbing to the top, and in total the support has four knees, each 21 meters high (they are painted in different colors), the total height of the mast is about 85 meters. You can read more here - http://io.ua/s93360.
Three-post freestanding lattice supports
Three-post lattice supports, as a rule, stand at turns and transitions of 500 kV and 750 kV power lines and are used as anchors (photo 5).
L-shaped supports
They are flat L-shaped lattice structures, articulated with two foundations. At the top of the support there is a traverse for attaching 4 load-bearing cables that hold the support in a vertical position. Below there are three more (rarely two) traverses for hanging wires. L-shaped towers were used, in particular, as transition towers for two 110 kV or 220 kV overhead line circuits. Their use allowed us to save metal and simplify the foundation. It was advisable to use such supports in areas flooded with water during floods. Design features prevented these supports from becoming widespread.
Y-shaped supports, "shot glasses"
Single-chain masts resembling the letter “Y” or a glass (photo 6). Exist different types and have been used for quite a long time both here and abroad, including as transitional ones (for example, PS-101). These supports are always made of metal, usually lattice, less often they consist of multifaceted bent posts.
V-shaped,"Nabla"
Intermediate pores with guys are used on power transmission line routes of 330-1150 kV, for example, Nabla type supports for 750 kV. They resemble an inverted triangle - nablu. Exclusively single-chain.
Class: "Cat" type supports
Very interesting original supports, are very popular in countries Western Europe, especially in France (photo 10).
Pillar supports(i.e. not lattice)
These are supports based on wood, metal or reinforced concrete pillars. There are single-post and portal ones. Single-post reinforced concrete supports are the most widely used intermediate power transmission line supports at voltages of 35-220 kV. Relatively recently, a progressive type of metal single-column pole supports has become widespread - using MGS. To be more precise, in the USA such supports have been used for quite a long time, but in the CIS they are just beginning to gain popularity. The use of MGS made it possible to create multi-chain pillar supports (see photo 8).
Portal pillar supports consist of two pillars (wooden, reinforced concrete or MGS) connected by a common crossbeam. Particularly widespread in our country are pole-mounted single-circuit portal reinforced concrete supports (with internal connections) for 220 and 330 kV lines (photo 9).
Non-standard supports
These include various non-standard supports and exotic ones that do not belong to this classification, for example, numerous decorative supports.
2011 "POWERLINER"
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When laying air lines For power transmission, in addition to selecting the cable, it is also necessary to select the supports on which it will be fixed, as well as insulators. We will devote this article to overhead power line supports.
For the installation of overhead lines, metal, reinforced concrete and wood are used, as they are often called in ordinary life, electrical supports.
Wooden supports
They are usually made from pine logs with the bark removed. For power lines with supply voltages up to 1000 V, it is also possible to use other tree species, for example, fir, oak, cedar, spruce, and larch. Logs that will subsequently become power line supports must comply with certain technical requirements. The natural taper of the trunk, in other words, the change in its diameter from the thick lower end (butt) to the upper cut should not exceed 8 mm per 1 meter of log length. The diameter of the log on the upper cut for lines with voltage up to 1000 V is taken to be at least 12 cm, for lines with voltage above 1000 V, but not higher than 35 kV - 16 cm, and for lines with more high voltage not less than 18 cm.
Wooden supports can be used for the construction of overhead lines with a voltage not exceeding 110 kV inclusive. Wooden supports are most widely used in overhead lines with voltages up to 1000 V, as well as in communication lines. The advantage of wooden supports is their relatively low cost and ease of manufacture. However, there is a minus, a significant minus - they are susceptible to rotting and the service life of pine supports is about 4-5 years. To protect wood from rotting, it is impregnated with special antiseptics against rotting, for example anthracene or creosote oil. Those parts that will be dug into the ground, as well as cutting ends, braces and traverses, lend themselves to especially careful processing. Thanks to antiseptics, the service life increases by about 2-3 times. For the same purpose, quite often the legs of a wooden electrical support are made of two parts - the main stand and the chair (stepchild):
Where – 1) the main stand, and 2) a chair (stepchild)
If the lower part is severely rotted, it is enough to replace only the stepson.
Metal supports
Plus - durable and reliable in operation. Minus - necessary high consumption metal, which entails a significant increase in cost (compared to wood). Metal supports of overhead power lines are used, as a rule, at voltages from 110 kV, since the operation of metal supports is caused by high expenses to perform very labor-intensive and expensive work on periodic painting to protect against corrosion.
Reinforced concrete supports
In the industrial manufacturing process, the most the best option for overhead lines both up to 1000 V and above 1000 V. The use of reinforced concrete supports dramatically reduces operating costs, since they practically do not require repairs. Currently, almost everywhere, reinforced concrete supports are used in the construction of overhead lines of 6-10 kV and up to 110 kV. They are especially widespread in urban networks up to and above 1000 V. Reinforced concrete supports can be made either monolithic (cast) or in the form of assemblies, which are assembled directly at the installation site. Their strength depends on the method of concrete compaction, of which there are two - centrifugation and vibration. When using the centrifugation method, a good density of concrete is obtained, which subsequently has a good effect on the finished product.
On overhead power lines, special anchor, corner, end, and intermediate supports are used.
Their purpose is to rigidly secure wires and lines to them. The location for their installation is determined by the project. By design, the anchor support must be strong, since if a wire breaks on one side, it must withstand the mechanical load of the wires on the other side of the line.
Anchor spans are the distance between anchor supports. On straight sections (depending on the cross-section of the wires), anchor spans are up to 10 km long.
Intermediate supports
Serve only to support wires on straight sections of line between anchor supports. Of the total number of electrical supports installed on the line, intermediate ones occupy about 80-90%.
Corner supports
Designed for installation in places where power line routes turn. If the angle of rotation of the line is up to 20 0, then the electrical support can be manufactured as an intermediate one, and if the angle is about 20-90 0, then as an anchor type.
They are of an anchor type and are installed at the beginning and end of lines. If in anchor electrical supports the force of one-sided tension of the wires can only arise in emergency situation, if the wire breaks, it always operates in the end electrical supports.
Special supports
They are electric poles of increased height and are used at the intersection of power lines with highways and highways. railways, rivers, intersections between power lines themselves and in other cases when standard height the electrical support is not enough to provide the required distance to the wires. Intermediate electrical supports for lines with voltages up to 10 kV are made single-post (candle-shaped). On networks low voltage single-post supports perform the functions of corner or end supports, and are also equipped additionally with guy wires attached to the side opposite to the tension of the wires, or with struts (supports) that are installed on the side of the tension of the wires:
For lines with a voltage of 6-10 kV, electrical supports are made A-shaped:
Air lines are also characterized by their main dimensions and dimensions.
Overhead line dimension is the vertical distance from the lowest point of the wire to the ground or water.
The sag is the distance between the imaginary straight line between the wire attachment points on the support and the lowest point of the wire in the span:
All dimensions of power lines are strictly regulated by the PUE and directly depend on the value of the supply voltage, as well as the terrain through which the route passes.
The PUE also regulates other dimensions when crossing and approaching power lines, both among themselves and between communication lines, highways and railways, overhead pipelines, and cable cars.
To check the designed power line to the requirements of the PUE, mechanical strength calculations are performed, the methods of which are given in special courses on electrical networks.
Designed to hold wires suspended. These include lattice and multifaceted racks, traverses, and foundations. They may have different sizes and shape. The production of power transmission poles involves the use various materials. These structures are made of reinforced concrete and metal. By purpose they are allocated following types supports:
- Anchor;
- Intermediate;
- End;
- Angular.
Anchor wires are installed to limit anchor spans and in places where the number or type of wires changes. Installation of intermediate supports is carried out on straight sections of the electrical wiring route. Corner structures are used where it changes its direction. End - used at the beginning and end of the line. The plant for the manufacture and installation of power transmission poles JSC PK "StalKonstruktsiya" produces intermediate supports of rigid and flexible construction in Moscow.
Antenna supports
They are used to secure antenna equipment at the required height. They are a rod metal structure in the shape of a regular tetrahedral pyramid. Depending on the signal strength, the level of communication lines raised may be different. Therefore, the height of these structures ranges from 30 to 80 m. They include:
- Bracket;
- Service area;
- Staircase with railing;
- Crossing area;
- Lattice support.
The main area of application is radio relay communication lines. The structures are secured using bolted connections. A vertical ladder for the movement of people is fixed in the internal shaft of the structure. The production of power line supports of this type is carried out in six standard sizes. In this case, sections 10 m long are used.
Communication towers
They are special towers that have increased bearing capacity and increased height. Their purpose is to accommodate sets of antenna equipment that provide communications. The production of metal structures of this type is carried out in 2 varieties - masts and towers.
The most popular of them are masts. They are made from rolled pipe and painted white or red. Among them are supports for cellular and radio communications, street lighting, masts for television and radio broadcasting. The most commonly used are three-section designs. Installation of radio masts is carried out in several stages using special equipment.
Power poles
Their purpose is to maintain electrical wires at the required distance from the surface of roofs, ground and wires of other lines. Such structures have to function in various meteorological conditions, so they require strength. The production of power line supports is carried out on the basis of various materials. IN rural areas For power lines with a voltage of 35 kV, coniferous wood is still widely used.
Most modern version are multifaceted steel structures galvanized by hot dip galvanizing. The design period of their operation is 70 years.
Production and installation
In order for such structures to serve for a long time and reliably, they need to be carefully designed and high quality manufacturing. Our metal structures plant produces and supplies power transmission line supports to many energy and manufacturing companies. Technological process consists of assembling the frame, conducting incoming inspection of raw materials, heat-and-wet processing of molded products, and output inspection of finished products.
The production of metal power transmission poles in Moscow uses pipe and sheet metal. It is made from high quality carbon steel. Raw materials entering production must be subjected to laboratory control in the form of chemical and spectral analysis.
After production, the products are transported on platforms in separate sections. Before installation of structures, marking of the route is carried out. Next, wells are drilled for their subsequent installation. The depth and diameter of the pit depend on the type of product and the type of soil. Installation of supports is carried out using cranes or manipulators.
Description of the presentation: Overhead power line supports. Classification of power line supports by slides.
Classification of power transmission line supports Intermediate, on which the wires are fixed in supporting clamps. Anchor type, used for tensioning wires; on these supports the wires are secured in tension clamps. Intermediate lines - on straight sections of power lines. The wires are secured in clamps on garlands or with wire knitting. Intermediate corners - at angles up to 20°. Anchor-angular - at large angles of rotation. Special - transpositional, branching, transitional.
MATERIAL OF POWER LINE SUPPORTS Reinforced concrete - made of concrete reinforced with metal. For lines 35-110 kV and above, supports made of centrifuged concrete are usually used. Metal (lattice, multifaceted) - made of special grades of steel. Connecting elements by welding or bolting. The metal is galvanized or periodically painted with special paints. Wooden - mainly pine supports and less often larch. Used in Russia for overhead lines with voltages up to 220 kV (in the USA - up to 330 kV).
Designations of supports For metal and reinforced concrete supports of VL 35-330 k. V, the following designation system has been adopted in Russia: P, PS - intermediate supports PVS - intermediate supports with internal connections PU, PUS - intermediate corner PP - intermediate transitional U, US - anchor- angular K, KS - anchor-end The designation system is sometimes violated by manufacturers.
Technology for the production of wooden poles 1. Sorting on a line with an electronic reading device. 2. Debarking on a line equipped with debarking machines, quality control of wood processing and culling. 3. Impregnation with antiseptic. Impregnation and drying in autoclaves using the “vacuum - pressure - vacuum” method. Impregnation depth of at least 85% sapwood. Fixation of impregnation in wood with superheated steam. The length of the autoclaves is 27.0 m; diameter - 2.0 m; volume - 84, 78 cubic meters. m.
Impregnation and drying of wood Impregnation with antiseptic SSA (copper, chromium, arsenic), TU 5314 -002 -05020332 -2005 Service life in contact with soil up to 40 -45 years, Power line supports can be installed directly into the ground without the use of reinforced concrete consoles (stepchildren).
The capacity of a modern impregnation workshop is up to 200 supports per shift (2 drying and 2 impregnating autoclaves). Annual volume – up to 120,000 supports. The standard length of supports is 6.5 – 11 m. The price is about 50 -60 USD (pcs). Power transmission line supports are shipped to customers in gondola cars (loading rate is up to 4 cars per day) or by car(loading rate is up to 20 cars per day).
Advantages of wooden poles Wooden poles are 40% lighter and cheaper than reinforced concrete ones High insulating properties of wood make it possible to reduce the number of insulators on lines 35 -110 kV. The service life of wooden poles reaches 45 years, which is 20% longer than the service life of reinforced concrete poles. The operation of power lines is efficient in seismically active zones. Wooden supports work well in bending and do not break under high wind and ice loads. When wooden supports fall, there is no domino effect, since the damaged support is supported by wires. Chemical composition impregnating agents makes the supports resistant to fire. Wooden supports have exceptionally high dielectric properties.
Multifaceted conical supports (MKO power transmission lines) The supports are a multifaceted conical structure made of steel sheet. The support can consist of one, two or more sections. Section length is up to 16 meters. Typically, for ease of transportation, sections up to 11.5 m long are used. The sections can be connected to each other either flanged or flangeless (telescopic). Height of supports: up to 40 meters or more. Wall thickness: from 3 to 12 mm. Support diameter: up to 2 meters.
Installation of supports of multifaceted metal supports In the ground, supports are installed either directly into a drilled well, or are attached on flanges to a reinforced concrete foundation. A wide variety of standard sizes of multifaceted metal supports allows them to be used in the electric power industry (overhead lines 6-35 kV), in railway transport, etc.
Advantages of MKO power lines Reliability. Multifaceted conical supports are much more reliable than reinforced concrete and lattice supports, especially in difficult icy and windy conditions. In emergency mode, a multifaceted steel support can withstand loads 2-3 times greater than a reinforced concrete support. Adaptability. The multifaceted supports that make up the standard range can be easily modified by increasing or decreasing height, wall thickness, diameter, etc. Transportability. Multifaceted supports are several times lighter than concrete and lattice supports. The intermediate support VL-35 weighs about 1 ton, a similar reinforced concrete one - 4 tons, a lattice one - 2 tons. Ease of installation. Light weight and high degree of factory readiness allow you to install the support in a few hours. Durability. The service life of multifaceted supports (50 years) is twice as long as that of reinforced concrete supports. Economical. Capital costs for the construction of 1 km of power lines are 25–50% lower than when using reinforced concrete and lattice supports. Moreover, the effect is greater when constructing power lines in remote and complex regions.
The service life of reinforced concrete and metal galvanized or periodically painted supports reaches 50 years or more. The cost of metal and reinforced concrete supports significantly exceeds the cost of wooden supports. The choice of a particular material for supports is determined by economic considerations, as well as the availability of appropriate material in the area where the line is being constructed.
The arrangement of wires on the support is horizontal - in one tier, vertical - one above the other in two or three tiers, mixed - vertically located wires are offset one relative to the other horizontally, “triangle” - on single-circuit supports, “zigzag” - on intermediate single-circuit supports VL; the height of the suspension of the lower wires increases on average by half the distance between the lower and upper traverses, which allows you to increase the span between the supports.
The supports of single-circuit overhead lines 6 -220 k. V are designed for hanging three phase wires. Two parallel running circuits are suspended from the supports of double-circuit overhead lines. On the supports of overhead lines with split phases (330 kV and above), several wires are suspended per phase to eliminate the appearance of “corona”, which creates additional active losses and radio interference. If necessary, one or more lightning protection cables are suspended above the phase wires.
Overhead lines up to 1 kV - hang from 2 to 5 wires (single-phase and three-phase power lines), Overhead line 6 -220 kV - one wire per phase, Overhead line 330 kV - two wires (per phase) horizontally, 500 kV overhead line - three wires at the vertices of the triangle, 750 kV overhead line - four or five wires, 1150 kV overhead line - eight wires.
Wire markings Bare wires. M - wire consisting of one or twisted of several copper wires. A - wire twisted from several aluminum wires. PSO and PS are wires made of steel, single-wire and multi-wire, respectively. The brand of the wire also indicates its nominal cross-section. For example, A-50 means aluminum wire 50 mm². For single-wire steel wires, the brand indicates the diameter of the wire. So, PSO-5 means single-wire steel wire with a diameter of 5 mm
– AC - a wire consisting of a steel core and aluminum wires (the most widespread). – ASKS - AC grade wire, but the interwire space of the steel core, including its outer surface, is filled with a neutral lubricant of increased heat resistance. – ASKP - AC grade wire, but the interwire space of the entire wire, with the exception of outer surface, filled with neutral lubricant with increased heat resistance. – ACS - steel-aluminum wires with a reinforced steel core. – ASO - steel-aluminum wires with a lightweight steel core.
Insulated wires Self-supporting insulated wire (SIP) - stranded wire, containing insulated conductors and a supporting element intended for fastening or hanging the wire. Current-carrying conductors made of copper or aluminum wire. Insulating shell made of rubber or PVC plastic. Protective covers of wires with rubber insulation in the form of a braid made of fibrous materials, impregnated with an anti-rotten composition. PVC-insulated wires are usually made without protective covers. Metallic ones are also used protective shells to protect against mechanical damage. Protected wire - a wire with extruded polymer protective insulation over the current-carrying core (excludes short circuit between the wires when they overlap and the likelihood of a ground fault is reduced).
Wooden anchor-corner support for overhead line 10 kV on wooden stepsons
Design of overhead power transmission line supports
Support design
The designs of overhead power transmission line supports are very diverse and depend on the material from which the support is made (metal, reinforced concrete, wood, fiberglass), the purpose of the support (intermediate, corner, transposition, transition, etc.), and on local conditions on the line route ( populated area or unpopulated area, mountain conditions, areas with marshy or soft soils, etc.), line voltage, number of circuits (single-circuit, double-circuit, multi-circuit), etc.
The following elements can be found in the design of many types of supports:
- The stand is the main integral element of the support structure, in contrast to other elements that may be missing. The stand is designed to provide the required dimensions of the wires (wire size is the vertical distance from the wire in the span to the engineering structures crossed by the route, the surface of the earth or water). The support structure can have one, two, three or more posts.
- Struts – used for corner, end, anchor and branch supports of overhead lines with voltage up to 10 kV. They take on part of the load of the support from the one-sided pull of the wire.
- Attachment (stepson) - partially buried in the ground, the lower part of the structure of a combined overhead line support with voltage up to 35 kV, consisting of wooden racks and reinforced concrete attachments.
- Braces are inclined elements of a support that serve to strengthen its structure and connect several support elements to each other, for example, a post with a traverse, or two support posts.
- Crossbar – provides fastening of power line wires at a certain (permissible) distance from the support and from each other.
- Foundation - a structure embedded in the ground and transferring loads from supports, insulators, wires and external influences(ice, wind).
- Crossbar - increases lateral surface underground structure of reinforced concrete pillars and metal support footboards. Crossbars increase the ability of the foundation to withstand horizontal loads acting on the support, preventing it from tipping over from the gravitational forces of the wires when constructing supports in soft soil.
- Guys - designed to increase the stability of supports and absorb the forces from the tension of the wire.
- Cable stand - the upper part of the support, designed to support the lightning protection cable. Usually it is a trapezoidal spire at the top of the support. The support may have one or two cable supports (on U-shaped supports); there are also supports without cable supports.
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Drawing. Overhead line supports: a – two-post support; b – three-post support.
A rack of lattice-type metal supports is called a trunk. The barrel is usually a tetrahedral truncated lattice pyramid made of rolled steel profiles (angle, strip, sheet), and consists of a belt, a lattice and a diaphragm. The lattice, in turn, has bracing rods and struts, as well as additional connections.
Drawing. Structural elements of a metal support: 1 – belt of the support post; 2 – brace rods forming the rack lattice; 3 – diaphragm; 4 – traverse; 5 – cable support.
Drawing. Corner support with two struts: 1 – stand; 2 – strut.
Drawing. Structural elements of the combined support: 1 – wooden stand supports; 2 – reinforced concrete attachment (stepson); 3 – brace; 4 – traverse.
Drawing. Crossbars of supports: a - for reinforced concrete supports 10 kV; b - for reinforced concrete supports 110 kV.
Most often you can find traverses in the form of a rigid metal structure, however, there are also wooden traverses and traverses made of composite materials.
Drawing. Cross beam of 110 kV overhead line support made of composite materials
In addition, on V-shaped supports of the “nabla” type and U-shaped supports, you can find so-called flexible traverses.
Drawing. Overhead line support with a “flexible” crossarm
In some support designs, crossarms may be absent, for example, wooden or reinforced concrete overhead line supports with voltages up to 1 kV, overhead line supports with self-supporting insulated wires with voltages up to 1 kV, and anchor supports of overhead lines of any voltage, where each phase is mounted on a separate stand.
Drawing. Support without traverse
Drawing. Mushroom reinforced concrete foundation
For single-post supports, in which the lower end of the post is embedded in the ground, the bottom of the post serves as the foundation; for metal supports, pile or prefabricated mushroom-shaped reinforced concrete ones are used, and when installing transitional supports and supports in swamps, monolithic concrete foundations are used.
Drawing. Reinforced concrete piles used in single-pile and multi-pile foundations for overhead line supports
Drawing. Power transmission line support on a pile foundation
Drawing. Mushroom-shaped reinforced concrete foundation (1) with three crossbars (2)
Drawing. Support secured with guy wires
The upper part of the guy rope is attached to the post or traverse of the support, and the lower part is attached to the anchor or reinforced concrete slab. In addition, the guy structure may include a tension coupling - a lanyard.
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Drawing. Lower part of the guy