Structures of all types of power transmission towers. Types of power transmission line supports by material

Construction of overhead power lines

Support structure

The structures of overhead power transmission line poles are very diverse and depend on the material from which the pole is made (metal, reinforced concrete, wood, fiberglass), the purpose of the pole (intermediate, angular, transpositional, transitional, etc.), on local conditions on the line route ( populated or uninhabited areas, mountainous conditions, areas with swampy or soft soils, etc.), line voltages, number of circuits (single circuit, double circuit, multi circuit), etc.

In the design of many types of supports, the following elements can be found:

1. Rack - is the main integral element of the support structure, unlike other elements that may be absent. The rack is designed to provide the required dimensions of the wires (wire gauge - the vertical distance from the wire in the span to the engineering structures intersected by the route, the surface of the earth or water). There can be one, two, three or more posts in the support structure.

a	b

Picture. VL supports: a - two-column 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 rods-braces and spacers, as well as additional connections.



Picture. Structural elements of a metal support: 1 - support post belt; 2 - rods-braces forming a rack lattice; 3 - diaphragm; 4 - traverse; 5 - cable rack.

2. 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 tension of the wire.



Picture. Corner support with two struts: 1 - rack; 2 - brace.

3. Attachment (stepson) - partially buried in the ground, the lower part of the structure of the combined support of overhead lines with a voltage of up to 35 kV, consisting of wooden racks and reinforced concrete attachments.
4. Braces are inclined support elements that serve to reinforce its structure and connect several support elements to each other, for example, a post with a traverse, or two support posts.



Picture. Structural elements of the combined support: 1 - wooden support post; 2 - reinforced concrete prefix (stepson); 3 - brace; 4 - traverse.

5. Traverse - provides fastening of the wires of the power line at a certain (permissible) distance from the support and from each other.

Picture. Support traverses: 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, but there are also wooden traverses and traverses made of composite materials.



Picture. 110 kV overhead line support traverse made of composite materials

In addition, so-called flexible traverses can be found on V-shaped supports of the "nabla" type and U-shaped supports.



Picture. VL support with a "flexible" traverse

In some pole designs, traverses may be absent, for example, for wooden or reinforced concrete poles of overhead lines with a voltage of up to 1 kV, for overhead lines with self-supporting insulated wires with a voltage of up to 1 kV, for anchor poles of overhead lines of any voltage, where each phase is mounted on a separate rack.



Picture. Support without traverse

6. Foundation - a structure embedded in the ground and transferring loads to it from the support, insulators, wires and external influences (ice, wind).



Picture. Mushroom reinforced concrete foundation

For single-rack supports, in which the lower end of the rack is embedded in the ground, the bottom of the rack 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.



Picture. Reinforced concrete piles used in single-pile and multi-pile foundations of overhead lines



Picture. Power transmission line support on a pile foundation

7. Crossbar - increases the side surface of the underground structure of reinforced concrete racks and footboards of metal supports. Crossbars increase the ability of the foundation to withstand horizontal loads acting on the support, preventing it from tipping over from the forces of tension of the wires when constructing supports in soft soil.



Picture. Mushroom reinforced concrete foundation (1) with three crossbars (2)

8. Guys - designed to increase the stability of the supports and perceive the forces from the tension of the wire.



Picture. Support secured with braces

The upper part of the guy is attached to the post or traverse of the support, and the lower part to the anchor or reinforced concrete slab. In addition, the design of the brace may include a tension coupling - a lanyard.

Picture. Lower part of the brace

9. Rope 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. On the support there can be one or two cable racks (on U-shaped supports), there are also supports without a cable rack.

Overhead power line towers

Overhead lines with a voltage of 0.4-35 kV

Overhead lines with voltage up to 1 kV are called low voltage lines (LV), 1 kV and more - high voltage (HV).

Low-voltage lines are the simplest structures in the form of single poles buried directly into the ground, with metal pins and insulators attached to them, to which wires are attached.

As supports, wooden, reinforced concrete and, less commonly, metal supports are used. The latter, as a rule, are used at critical intersections (electrified railways, highways, etc.). Wooden supports can be composite on wooden or reinforced concrete attachments or from solid logs of the appropriate length and diameter. Three wires are suspended on 6-35 kV lines, and on 0.4 kV lines, supports allow joint suspension of up to eight wires of brand A (Ap) with a cross section of 16-50 mm2.

HV lines 3-10 kV do not fundamentally differ from LV lines, however, due to the large distances between the phases and between the wires and the ground, the dimensions of the elements - poles, pins, insulators - are increased.

Reinforced concrete pylons for power transmission lines are designed and operated in areas with design air temperatures down to -55°C. The main element of such supports are centrifuged reinforced concrete racks. In addition to centrifuged racks, the structure of the reinforced concrete support of power transmission lines can include anchor plates, crossbars, anchors for guy wires, a lower concrete cover (thrust bearing) and metal structures in the form of traverses, extensions, cable racks, head restraints, clamps, braces, internal connections, attachment points. Fastening of metal structures to the support post is carried out using clamps or through bolts. Reinforced concrete supports are fixed in the ground by installing them in a cylindrical pit, followed by filling the sinuses with a sand and gravel mixture. To ensure the necessary strength of embedding in soft soils, crossbars are fixed on the underground part of the overhead line supports with the help of half-clamps. The main disadvantage of reinforced concrete supports is their low strength and weight characteristics, and as a result, high transportation costs due to the large dimensions and weight of the products. Dignity - high corrosion resistance to aggressive environments.

Classification of reinforced concrete supports of overhead lines

By appointment

intermediate supports are installed on straight sections of the overhead line route, are intended only for supporting wires and cables and are not designed for loads directed along the power line. As a rule, the total number of intermediate supports is 80 - 90% of all power transmission line supports.

Anchor supports are used on straight sections of the overhead line route at places of transition through engineering structures or natural barriers to limit the anchor span, as well as at places where the number, grades and cross sections of power line wires change. Anchor support perceives the load from the difference in tension of wires and cables, directed along the power line. The design of anchor reinforced concrete supports of overhead lines is characterized by increased strength. This is ensured, among other things, by the use of reinforced concrete pillars of increased strength in the support.

Angle supports designed for operation in places where the direction of the overhead line route changes, they perceive the resulting load from the tension of wires and cables of adjacent intersupport spans. At small angles of rotation (15 - 30 °), where the loads are small, angular intermediate supports are used. At angles of rotation of more than 30 °, angled anchor supports are used, which have a stronger structure and anchor fastening of wires.

end supports are a kind of anchor and are installed at the end and beginning of the power line, designed for the load from the one-sided tension of all wires and cables.

Special supports used for special tasks: transpositional- to change the order of the wires on the supports; transitional- to cross the power line through engineering structures or natural barriers; branch- for the device of branches from the main power line; antiwind- to enhance the mechanical strength of the power line section; cross- when crossing overhead power lines in two directions.

By design

Portal reinforced concrete supports of overhead lines with braces

Portal free-standing supports with internal connections

Single, double, triple and multi-column free-standing poles

One-, two-, three- and multi-stay guyed poles

By number of chains

single chain

double chain

Multi-chain

SUPPORTS OF AIR LINES.

Overhead line supports depending on the purpose and installation location on the track, they can be intermediate, anchor, corner, end and special. intermediate supports(see figure below) are used to support wires on straight sections of lines. On the intermediate supports, the wires are fixed with pin insulators. The spans between supports for lines with voltage up to 1000V are 35 - 45 meters, and for lines up to 10kV - 60 meters. Overhead line supports: a and 6 - intermediate, c - angular with a brace, g - angled with wire guy Anchor supports(see figure below) are also installed on straight sections of the route and on those crossed with various structures. They have a rigid and durable design, since under normal conditions they perceive the forces from the tension difference along the wires directed along the overhead line, and in the event of a wire break, they must withstand the tension of all remaining wires in the anchor span. Wires on anchor supports are fixed tightly to suspension or pin insulators. Anchor supports for overhead lines with a voltage of 10 kV are placed at a distance of about 250 meters. Overhead line anchor voltage 6 - 10kV end supports, which are a type of anchor, are installed at the beginning and end of the line. The end supports must withstand the permanent one-sided tension of the wires, and the corner supports (see the top figure c and d) - in places where the direction of the overhead line route changes. The special ones include transitional supports placed at the intersections of various structures or obstacles by power lines (for example, rivers, railways, etc.). These supports differ from others of this line in height or design. The supports are made of wood, metal, reinforced concrete, and are also made composite, matching the wooden support post with a wooden or reinforced concrete attachment. For overhead lines with voltage up to 10 kV For a long time, mainly wooden supports were used, which was due to the ease of processing wood and its cheapness compared to steel and reinforced concrete. The supports were made of pine, less often of larch, spruce or fir. The diameter in the upper cut of pine logs for supports and main parts must be at least 15 cm for lines with voltage up to 1000V and 16 cm for lines with voltage 1 - 10 kV. The main disadvantage of wooden untreated supports is their fragility. So, the service life of pine poles is on average 4-5 years, and poles made of spruce or fir 3-4 years. At present, reinforced concrete poles, due to their durability and in order to save the country's forest resources, are widely used in the construction of new overhead networks. By design wooden supports divide: on single; A-shaped of two racks diverging towards the base; three-legged of three stances converging to the top; U-shaped of two racks and a connecting horizontal traverse at the top (transverse beam); AP-shaped from two A-shaped supports and a connecting horizontal traverse. Composite supports are also used, consisting of a rack and a prefix (stepson). In these cases, the interface between the rack and the attachment must be at least 1300 mm (see figure below). Pairing a wooden support rack with an attachment: a - reinforced concrete, b - wooden; I and 4 - the lower part of the support and attachment, 2 and 3 - longitudinal and transverse reinforcement, 5 - prefix, 6 -. wire bandage Racks are connected to attachments with steel wire bandages. For intermediate supports, bandages are made of ten turns of wire with a diameter of 4 mm, for anchor, corner and end supports - of eight turns of wire with a diameter of 5 mm. Wire bandages are fixed with bolts, placing rectangular washers made of strip steel under the head of the bolts and under the nuts. Steel supports made of pipes or profile steel. Reinforced concrete supports are produced by factories in the form of hollow round-section racks with an outer diameter decreasing in steps and rectangular also with a decreasing section towards the top of the support. The factories also produce reinforced concrete prefixes of a round or rectangular profile. When using reinforced concrete attachments and wooden racks impregnated with an antiseptic, the service life of the supports is significantly extended. Overhead power line towers irrespective of their type, they can be performed with braces or braces (see the top figure wig). On all supports of overhead lines at a height of 2.5 - 3.0 meters from the ground, their serial number and year of installation are indicated.

WIRES

Overhead line wires must have sufficient mechanical strength. By design, the wires can be single-wire or multi-wire. Single-wire wires consist of one copper or steel wire and are used exclusively for lines with voltage up to 1000V. Stranded wires made of copper, aluminum and its alloys, steel and bimetal, consist of several twisted wires. These wires are widely used due to their greater mechanical strength and flexibility compared to single-wire wires of the same cross section. Due to the scarcity and high cost of copper, copper wires are not used on overhead lines. Aluminum stranded wires of brand A are widely used on overhead lines. Steel wires are galvanized for protection from atmospheric influences. Single-core steel wires have the PSO brand, multi-wire - PS or PMS, if copper steel is used as the wire material. Steel-aluminum wires of grades AS and ASU (reinforced) consist of several twisted steel wires, on top of which aluminum wires are located, and have significantly greater mechanical strength compared to aluminum ones. Bare aluminum wires are made of the following sections: 6, 10, 16, 25, 35, 50, 70, 95, 120 mm 2. The cross-sections of the wires of overhead lines are determined by calculation depending on the transmitted power, permissible voltage drops, mechanical strength, span lengths, but they must not be less than those indicated in the following table. Minimum cross-sections of wires of overhead power lines For a branch line from a line with a voltage of up to 1000V to the inputs to the building, insulated wires APR or AVT are used, which have weather-resistant insulation and a supporting steel cable. Both on the support and on the building, the ABT wires are attached to a separate hook with an insulator using a cable. On intermediate supports, the wires are attached to the pin insulators with clamps or knitting wire of the same material as the wire, which should not have bends at the attachment point. Wire fastening methods depend on their location on the insulator - on the head (head knitting) or on the neck (side knitting). The main ways of attaching wires are shown in the following figure. Fastening wires on pin insulators: a - head viscous, b - lateral viscous, c - with clamps, d - plug, d - loop, e - double suspension On anchor, corner and end supports overhead line wires up to 1000V they are fixed by twisting the wires with a so-called plug (see figure, d), and above 1000V - with a loop (see figure, e). On anchor and corner supports, at the points of transition through railways, driveways, tram tracks and at intersections with various power lines and communication lines, a double suspension of wires is used (see figure, e). Wire connection produced by die clamps (see the figure below, a), a crimped oval connector (see the figure below, b), an oval connector twisted with a special device (in the figure, c), as well as welding using thermite cartridges and a special apparatus. Single-wire steel wires can be overlap welded using small transformers. In the span between the supports there should not be more than one connection, and in the spans of intersections of the overhead line with various structures, the connection of wires is not allowed. On the supports, the connections are made so that they are not subjected to mechanical stress. Wire connection: a - ram clamp, 6 - crimped oval connector, c - twisted oval connector

INSULATORS

When attaching the wires of overhead lines to the supports, apply insulators and hooks, and when attached to the traverse - insulators and pins. For overhead lines with voltages up to 1000V, pin porcelain insulators TF and ShN are used (figure below, a), for SHO branches (figure below, b) and glass TS. Insulators used for overhead lines, grades: a - TF and ShN, b - SHO, c - ShF-bA and ShF-10A, d - ShF-10B, e - P Hooks and pins for attaching insulators are shown in the figure below. For overhead lines with voltages up to 1000V, use KN hooks (see figure below, a), made of round steel with a diameter of 12 - 18 mm, or KV (see figure below, b), depending on the type of insulator, and pins SHN or SHU (see figure below , in). Details for fastening insulators: a - hook KN-16, b - hook KV-22, c - steel pin ShN or SHU On overhead lines with a voltage of 6 kV, pin insulators ShF-6(see the top figure, b) with KV-22 hooks and ShN-21 pins, on overhead lines with a voltage of 10 kV - ShF-10 pin insulators with KV-22 hooks and SHU-22 pins. ShF-10 insulators (see top figure, d) differ from ShF-6 in size and are produced each in three versions - A, B and C (see top figure, c and d). In places of anchor fastenings, suspension insulators P are used (upper figure, e). insulators firmly screwed onto hooks or pins using special polyethylene caps or tow impregnated with minium or drying oil. The location of the insulators on the support is different. So, for overhead lines with a voltage of up to 1000V with a four-wire line, insulators are placed two on each side of the support apart, observing the vertical distances between them of at least 400 mm, while the neutral wire is placed below the phase wires from the side of the pole facing the houses. With a three-wire line with a voltage of 6 - 10 kV, two insulators are located on one side of the support, the third on the other. Insulators must be clean, free of cracks, chips and damage to the glaze.

VL supports are divided into anchor and intermediate. The supports of these two main groups differ in the way the wires are suspended. On the intermediate supports, the wires are suspended with the help of supporting garlands of insulators. Anchor-type supports are used to tension the wires, on these supports the wires are suspended using hanging garlands. The distance between the intermediate supports is called the intermediate span or simply the span, and the distance between the anchor supports is called the anchor span.

1. Anchor supports are designed for rigid fastening of wires at critical points of overhead lines: at the intersections of especially important engineering structures (for example, railways, 330-500 kV overhead lines, highways with a carriageway width of more than 15 m, etc.), at the ends of the overhead line and at the ends of its straight sections. Anchor supports on straight sections of the overhead line route when wires are suspended on both sides of the support with the same tensions in normal operating modes of the overhead line perform the same functions as the intermediate supports. But anchor supports are also calculated for the perception of significant tensions along wires and cables when some of them break in the adjacent span. Anchor supports are much more complicated and more expensive than intermediate ones, and therefore their number on each line should be minimal.

In the worst conditions are the end anchor supports installed at the exit of the line from the power plant or on the approaches to the substation. These supports experience one-sided tension of all wires from the side of the line, since the tension of wires from the side of the substation portal is insignificant.

2. Intermediate straight supports are installed on straight sections of overhead lines to maintain the wire in the anchor span. An intermediate support is cheaper and easier to manufacture than an anchor one, since, due to the equal tension of the wires on both sides, it does not experience forces along the line with unbroken wires, that is, in normal mode. Intermediate supports make up at least 80-90% of the total number of overhead line supports.

3. Angle supports set at the turning points of the line.

In addition to the loads perceived by the intermediate straight supports, the loads from the transverse components of the tension of the wires and cables also act on the corner supports. Most often, at angles of rotation of lines up to 20 °, angled anchor-type supports are used (see Fig. 1.). At angles of rotation of the power line of more than 20 °, the weight of the intermediate corner supports increases significantly.

Rice. 1. Scheme of the anchor span of the overhead line and the span of the intersection with the railway.

4. Wooden poles are widely used on overhead lines up to 110 kV inclusive. Wooden poles have also been developed for 220 kV overhead lines, but they are not widely used. The advantages of these supports are low cost (in areas with forest resources) and ease of manufacture. The disadvantage is the susceptibility of wood to decay, especially at the point of contact with the soil. An effective anti-rotting agent is impregnation with special antiseptics.

Supports are made in most cases composite. The leg of the support consists of two parts of a long (rack ) and short (stepson). The stepson is connected to the rack with two bandages made of steel wire. Anchor and intermediate corner supports for 6-10 kV overhead lines are made in the form of an A-shaped structure.

The intermediate support is a portal having two racks with wind connections and a horizontal traverse. Anchor corner supports for V L 35-110 kV are made in the form of spatial A-P-shaped structures.

5. Metal poles (steel) used on power lines with a voltage of 35 kV and above, rather metal-intensive and require painting during operation to protect against corrosion. Install metal supports on reinforced concrete foundations. The most common design supports 500 kV - guyed portal (Fig. 2). For the 750 kV line, both portal poles on guys and V-shaped poles of the Nabla type with split guys are used. For use on 1150 kV lines under specific conditions, a number of tower designs have been developed - portal, V-shaped, with a cable-stayed traverse. The main type of intermediate supports for 1150 kV lines are V-shaped supports on guys with a horizontal arrangement of wires (Fig. 2). A DC line with a voltage of 1500 (±750) kV Ekibastuz-Center is designed on metal supports (Fig. 2) .

Fig.2. Metal supports:

a - intermediate single-circuit on braces 500 kV;b - intermediate V-shaped 1150 kV;in - intermediate support of 1500 kV direct current overhead line;G - elements of spatial lattice structures

6. Reinforced concrete poles are more durable than wooden poles, require less metal than metal poles, are easy to maintain and therefore are widely used on overhead lines up to 500 kV inclusive. The unification of the structures of metal and reinforced concrete supports for 35-500 kV overhead lines was carried out. As a result, the number of types and designs of supports and their parts has been reduced. This made it possible to mass-produce supports at factories, which accelerated and cheapened the construction of lines.

Support types

Overhead power lines. Support structures.

Supports and foundations for overhead power lines with a voltage of 35-110 kV have a significant share both in terms of material consumption and in terms of cost. Suffice it to say that the cost of the mounted support structures on these overhead lines is, as a rule, 60-70% of the total cost of the construction of overhead power lines. For lines located at industrial enterprises and areas immediately adjacent to them, this percentage can be even higher.

Overhead line supports are designed to support line wires at a certain distance from the ground, ensuring the safety of people and reliable operation of the line.

Overhead power line towers are divided into anchor and intermediate. The supports of these two groups differ in the way the wires are suspended.

Anchor supports completely perceive the tension of wires and cables in spans adjacent to the support, i.e. serve to stretch the wires. On these supports, the wires are suspended with the help of hanging garlands. Anchor type supports can be of normal and lightweight construction. Anchor supports are much more complicated and more expensive than intermediate ones, and therefore their number on each line should be minimal.

Intermediate supports do not perceive the tension of the wires or perceive it partially. On the intermediate supports, the wires are suspended with the help of insulators supporting garlands, fig. one.

Rice. one. Scheme of the anchor span of the overhead line and the span of the intersection with the railway

On the basis of anchor supports can be performed end and transposition supports. Intermediate and anchor supports can be straight and angled.

End anchor supports installed at the exit of the line from the power plant or at the approaches to the substation are in the worst conditions. These supports experience one-sided tension of all wires from the side of the line, since tension from the side of the substation portal is insignificant.

Intermediate lines supports are installed on straight sections of overhead power lines to support wires. An intermediate support is cheaper and easier to manufacture than an anchor one, since in normal mode it does not experience forces along the line. Intermediate supports make up at least 80-90% of the total number of overhead line supports.

Angle supports are set at the turning points of the line. At angles of rotation of the line up to 20 °, angled anchor-type supports are used. At angles of rotation of the power line more than 20 ° - intermediate corner supports.

Depending on the method of suspension of wires, the supports of overhead lines (VL) are divided into two main groups:

a) intermediate supports, on which the wires are fixed in supporting clamps,

b) anchor type supports used to tension the wires. On these supports, the wires are fixed in tension clamps.

The distance between the supports (power lines) is called the span, and the distance between the anchor type supports is anchored section(Fig. 1).

In accordance with the intersection of some engineering structures, such as public railways, it is necessary to perform on anchor-type supports. At the corners of the line, corner supports are installed, on which the wires can be suspended in support or tension clamps. Thus, the two main groups of supports - intermediate and anchor - are divided into types that have a special purpose.

Rice. 1. Scheme of the anchored section of the overhead line

Intermediate straight supports are installed on straight sections of the line. On intermediate supports with suspension insulators, the wires are fixed in supporting garlands hanging vertically; on intermediate supports with pin insulators, the wires are fixed by wire knitting. In both cases, intermediate supports perceive horizontal loads from wind pressure on the wires and on the support, and vertical - from the weight of wires, insulators and the own weight of the support.

With unbroken wires and cables, intermediate supports, as a rule, do not perceive the horizontal load from the tension of wires and cables in the direction of the line and therefore can be made of a lighter design than other types of supports, for example, end supports that perceive the tension of wires and cables. However, to ensure reliable operation of the line, intermediate supports must withstand some loads in the direction of the line.

Intermediate corner supports installed at the corners of the line with a suspension of wires in supporting garlands. In addition to the loads acting on the intermediate straight supports, the intermediate and anchor angle supports also perceive loads from the transverse components of the tension of the wires and cables.

At angles of rotation of the power line of more than 20 °, the weight of the intermediate corner supports increases significantly. Therefore, intermediate corner supports are used for angles up to 10 - 20°. At large angles of rotation, anchor angle supports.

Rice. 2. Intermediate supports VL

Anchor supports. On lines with suspension insulators, the wires are fixed in the clamps of the tension garlands. These garlands are, as it were, a continuation of the wire and transfer its tension to the support. On lines with pin insulators, the wires are fixed on anchor supports with reinforced viscous or special clamps that ensure the transfer of the full tension of the wire to the support through the pin insulators.

When installing anchor supports on straight sections of the route and suspending wires on both sides of the support with the same tensions, the horizontal longitudinal loads from the wires are balanced and the anchor support works in the same way as the intermediate one, i.e. it perceives only horizontal transverse and vertical loads.

Rice. 3. Anchor-type overhead line supports

If necessary, the wires on one and the other side of the anchor support can be pulled with different tension, then the anchor support will perceive the difference in tension of the wires. In this case, in addition to horizontal transverse and vertical loads, the horizontal longitudinal load will also act on the support. When installing anchor supports at the corners (at the turning points of the line), the anchor corner supports also perceive the load from the transverse components of the tension of the wires and cables.

End supports are installed at the ends of the line. From these supports depart wires suspended on the portals of substations. When hanging wires on the line until the end of the construction of the substation, the end supports perceive full one-sided tension.

In addition to the listed types of supports, special supports are also used on the lines: transpositional, serving to change the order of the wires on the supports, branch - to carry out branches from the main line, support for large crossings over rivers and water spaces, etc.

The main type of supports on overhead lines are intermediate ones, the number of which usually makes up 85-90% of the total number of supports.

According to the design of the support can be divided into free-standing and braced supports. Guys are usually made of steel cables. On overhead lines, wooden, steel and reinforced concrete supports are used. Designs of supports made of aluminum alloys have also been developed.
Structures of overhead lines

1. Wooden support LOP 6 kV (Fig. 4) - single-column, intermediate. It is made of pine, sometimes larch. The stepson is made of impregnated pine. For 35-110 kV lines, wooden U-shaped two-column supports are used. Additional elements of the support structure: hanging garland with a hanging clip, traverse, braces.
2. Reinforced concrete supports are made as single-column free-standing, without braces or with braces to the ground. The support consists of a post (trunk) made of centrifuged reinforced concrete, a traverse, a lightning protection cable with a ground electrode on each support (for lightning protection of the line). With the help of a grounding pin, the cable is connected to a grounding conductor (a conductor in the form of a pipe hammered into the ground next to the support). The cable serves to protect the lines from direct lightning strikes. Other elements: rack (trunk), traction, traverse, cable rack.
3. Metal (steel) supports (Fig. 5) are used at a voltage of 220 kV or more.

VL supports are designed to provide the required distances between the phases and the ground. The horizontal distance between the centers of two adjacent supports of the same line is called the span. There are transitional, intermediate and anchor spans. The anchor span usually consists of several intermediate spans.

Support types

According to the number of chains, the supports are classified into single-chain and double-chain. An overhead line with two circuits, made on double-circuit supports, is cheaper than two parallel lines, made on single-circuit supports, and can be built in a shorter time.

VL supports are divided into two main groups: intermediate and anchor. In addition, corner, end and special supports are distinguished.

Intermediate supports are installed on straight sections of the route. In normal mode, they perceive vertical loads from the mass of wires, insulators, fittings and horizontal loads from wind pressure on wires and supports. When one or more wires break, the intermediate supports take on an additional load directed along the line and are subjected to torsion and bending. Therefore, they are made with a certain margin of safety. The number of intermediate supports on overhead lines is up to 80%.

Anchor supports are installed on straight sections of the route for the passage of overhead lines through engineering structures or natural obstacles. Their design is stiffer and stronger, as they perceive the longitudinal load from the difference in tension of wires and cables in adjacent anchor spans, and during installation - from the tension of wires suspended from one side.

Corner supports are installed at the corners of the overhead line. The angle of rotation of the line is the angle in the plan of the line (Fig. 2.1), which complements the internal angle of the line to 180 0. If the angle of rotation of the route is less than 20 0, angular intermediate supports are installed, if more than 20 0 - angular anchors (Fig. 2.1).

Rice. 2.1. Plan and profile of the VL section:

A - anchor support, P - intermediate support, UP - angular intermediate support, UA - corner anchor support, KA - end anchor support

End supports are a type of anchor and are installed at the end and beginning of the line. Under normal operating conditions, they perceive the load from the one-sided pull of the wires.

Specialized ones include transposition supports, the design of which allows you to change the order of the wires on the support; branch lines - for branching off the main line, etc.

Support material

According to the technological design standards for overhead power lines with a voltage of 35 kV and above, the following areas of use of various materials for the manufacture of supports are recommended.

wooden supports(pine, winter larch, for non-critical parts - spruce, fir) impregnated with an antiseptic are used for single-circuit overhead lines 35 - 150 kV where the use of wood is economically beneficial. The advantage of wooden poles is due to their low cost, sufficiently high mechanical strength, high electrical insulating properties, and low cost. The main disadvantage is fragility.

Reinforced concrete supports are used in flat terrain for single-circuit lines 35 - 220 kV, on all double-circuit lines - 35 - 110 kV, on overhead lines - 500 kV, passing in a flat area where metal supports are not economically feasible. Reinforced concrete supports are not allowed to be used on overhead lines passing in mountainous or rugged terrain. Reinforced concrete supports have high mechanical strength, are durable, cheap to operate, manufacture and assemble compared to metal ones. Their disadvantage is their large mass, which increases transport costs. In reinforced concrete supports, the main tensile forces are taken up by steel reinforcement, since concrete does not work well in tension, but in compression, the main loads are perceived by concrete.

The joint work of concrete and steel is due to the following properties. Concrete during hardening is firmly bonded to reinforcement due to gluing and friction caused by shrinkage of concrete during hardening, resulting in compression of reinforcement bars by concrete. As a result, when exposed to external forces, both materials work together, adjacent sections of concrete and steel receive the same deformations. Steel and concrete have approximately the same coefficients of linear expansion, which eliminates the appearance of internal stresses in reinforced concrete when the outside temperature changes. Concrete reliably protects reinforcement from corrosion and perceives compressive stress during temperature fluctuations. The disadvantage of reinforced concrete is the formation of cracks in it, especially at the points of contact with the ground. To increase crack resistance, prestressing of reinforcement is used, which creates additional compression of concrete. The main elements of reinforced concrete supports are racks, traverses, cable racks and crossbars. At reinforced concrete plants, racks are made either on centrifuges that perform concrete shaping and compaction, or by vibrating, compacting the concrete mixture with vibrators. By centrifugation, round hollow conical and cylindrical racks are made, by vibration - rectangular (GOST 22387.0-85). For double-circuit overhead lines with a voltage of more than 35 kV and above, centrifuged racks are used, labeled SK (conical racks) and STs (cylindrical racks). SK racks are used on 35-750 kV overhead lines of two types: 22.6 m and 26 m long with upper and lower diameters of 440/650 mm and 416/650 mm, respectively, made in one unified formwork. STs racks are made with a length of 20 m and a diameter of 800 mm. For 35 kV overhead lines, vibration-resistant CBs with a length of 16.4 m are used.

Metal supports are used on double-circuit overhead lines 35-500 kV, on single-circuit overhead lines 110, 220, 330 kV, where it is impossible or impractical to use reinforced concrete supports, on overhead lines 750 kV. The main structures of metal supports are made of St3 steel, the most stressed support units are made of low-alloy steels. Parts of the supports are factory hot-dip galvanized. The assembly of supports is carried out using bolted connections. Their advantage over reinforced concrete is that they allow you to create structures designed for heavy loads and any climatic conditions, have high mechanical strength with a relatively small mass. However, they are quite expensive and subject to corrosion. Steel supports can be single-column (tower) and portal in design, and free-standing or with braces according to the method of fixing on foundations.

Unification of supports

Based on the results of many years of practice in the construction and operation of overhead lines, the most appropriate and economical types and designs of supports are determined and their unification is systematically carried out, which allows the use of a single convenient system of designations and classifications. Unification makes it possible to reduce the total number of types of supports, the number of standard sizes of support parts, to select, if necessary, a rational replacement for supports or their parts, and to organize their mass production at specialized plants. According to the unification, for each type of support, the conditions for use are established: voltage of overhead lines, number of circuits, ice area, maximum wind speed, ranges of wire brands, cable brands. The last unification for steel poles was carried out in 1995-96, according to it, the range of applied wire cross-sections was expanded, which allows for optimal current density, the lengths of insulator strings were unified, recommendations were developed to take into account the degree of atmospheric pollution when choosing insulators, changes were made to the design of poles , the names of support types have been changed. According to these conditions, the appropriate type of support is selected in the reference books, the name of which reflects the following features:

1) type of support: P - intermediate, U - angular (intermediate or anchor), C - specialized;

2) support material: D - wood, B - reinforced concrete, there is no letter designation for metal supports;

3) rated voltage of overhead lines;

4) standard size - this is a figure that reflects the strength properties of the support: an even number is assigned to a double-chain support, an odd number is assigned to a single-circuit one.

For example, PB35-3 is an intermediate reinforced concrete single-circuit support for 35 kV overhead lines (intended for the construction of overhead lines in III-IV regions on ice, wind speeds up to 30 m / s, with AS95 / 16-AC150 / 24 wires and TK-35 cable ).

The most important characteristics of overhead lines, depending on the type of support, are the concepts of overall and overall span. Dimension G is the smallest allowable PUE, the vertical distance between the lowest point of sagging of the wire to the crossed engineering structures or the surface of the earth or water. The dimensions are determined for reasons of safe operation of overhead lines (Table 2.1).

Table 2.1

The overall span is a span determined by the condition of the permissible distance from the wires to the ground, provided that the supports are installed on a perfectly flat surface. The values ​​of the overall spans are indicated in the technical characteristics of the supports.

Most often, we imagine a power transmission line support in the form of a lattice structure. About 30 years ago it was the only option, and today they continue to be built. A set of metal corners is brought to the construction site and a support is screwed step by step from these typical elements. Then a crane arrives and puts the structure upright. Such a process takes quite a lot of time, which affects the timing of laying the lines, and these supports themselves with dull lattice silhouettes are very short-lived. The reason is poor corrosion protection. The technological imperfection of such a support is complemented by a simple concrete foundation. If it is done in bad faith, for example, using a solution of inadequate quality, then after some time the concrete will crack, water will get into the cracks. Several freeze-thaw cycles, and the foundation needs to be redone or seriously repaired.

Tubes instead of corners

We asked representatives of Rosseti PJSC what kind of alternative is replacing traditional ferrous metal supports. “In our company, which is the largest electric grid operator in Russia,” says a specialist from this organization, “we have long tried to find a solution to the problems associated with lattice supports, and in the late 1990s we began to switch to faceted supports. These are cylindrical racks made of a bent profile, actually pipes, in cross section having the form of a polyhedron. In addition, we began to apply new methods of anti-corrosion protection, mainly hot-dip galvanizing. This is an electrochemical method of applying a protective coating to metal. In an aggressive environment, the zinc layer becomes thinner, but the supporting part of the support remains intact.”

In addition to greater durability, the new supports are also easy to install. There is no need to screw any more corners: the tubular elements of the future support are simply inserted into each other, then the connection is fixed. It is possible to mount such a structure eight to ten times faster than to assemble a lattice one. The foundations have also undergone corresponding transformations. Instead of the usual concrete, so-called shell piles began to be used. The structure is lowered into the ground, a counter flange is attached to it, and the support itself is already placed on it. The estimated service life of such supports is up to 70 years, that is, approximately twice as long as that of lattice ones.

We usually imagine the supports of electric overhead lines in this way. However, the classic lattice structure is gradually giving way to more advanced options - multifaceted supports and supports made of composite materials.

Why are the wires buzzing

And the wires? They hang high above the ground and from a distance look like thick monolithic cables. In fact, high-voltage wires are made of wire. A common and widely used wire has a steel core, which provides structural strength and is surrounded by aluminum wire, the so-called outer layers, through which the current load is transmitted. Grease is laid between steel and aluminum. It is needed in order to reduce friction between steel and aluminum - materials that have different coefficients of thermal expansion. But since the aluminum wire has a circular cross section, the turns do not fit tightly to each other, the surface of the wire has a pronounced relief. This shortcoming has two consequences. Firstly, moisture penetrates into the gaps between the turns and flushes out the lubricant. Friction increases and conditions for corrosion are created. As a result, the service life of such a wire is no more than 12 years. To extend the service life, repair cuffs are sometimes put on the wire, which can also cause problems (more on that below). In addition, this wire design contributes to the creation of a well-defined hum near the overhead line. It occurs due to the fact that an alternating voltage of 50 Hz gives rise to an alternating magnetic field, which causes the individual strands in the wire to vibrate, which causes them to collide with each other, and we hear a characteristic buzz. In the EU countries, such noise is considered acoustic pollution and is being combated. Now such a struggle has begun with us.

“We now want to replace the old wires with wires of a new design that we are developing,” says a representative of PJSC Rosseti. - These are also steel-aluminum wires, but the wire is used there not with a round section, but rather with a trapezoidal one. The twist turns out to be dense, and the surface of the wire is smooth, without cracks. Moisture almost cannot get inside, the lubricant is not washed out, the core does not rust, and the service life of such a wire approaches thirty years. Wires of a similar design are already in use in countries such as Finland and Austria. There are also lines with new wires in Russia - in the Kaluga region. This is the Orbit-Sputnik line, 37 km long. Moreover, there the wires have not only a smooth surface, but also a different core. It is not made of steel, but fiberglass. Such a wire is lighter, but more tensile than ordinary steel-aluminum.

However, the latest design achievement in this area can be considered a wire created by the American concern 3M. In these wires, the carrying capacity is provided only by conductive layers. There is no core, but the layers themselves are reinforced with aluminum oxide, which achieves high strength. This wire has an excellent bearing capacity, and with standard supports, due to its strength and low weight, it can withstand spans up to 700 m long (standard 250-300 m). In addition, the wire is very resistant to thermal stress, which leads to its use in the southern states of the United States and, for example, in Italy. However, the wire from 3M has one significant drawback - the price is too high.

The original "designer" supports serve as an undoubted decoration of the landscape, but they are unlikely to be widely used. The priority for power grid companies is the reliability of energy transmission, and not expensive "sculptures".

Ice and strings

Overhead power lines have their natural enemies. One of them is icing of wires. This disaster is especially typical for the southern regions of Russia. At temperatures around zero, drops of drizzle fall on the wire and freeze on it. A crystal cap is formed on the top of the wire. But this is only the beginning. The hat, under its weight, gradually turns the wire, exposing the other side to the freezing moisture. Sooner or later, an ice sleeve will form around the wire, and if the weight of the sleeve exceeds 200 kg per meter, the wire will break and someone will be left without light. Rosseti has its own know-how to deal with ice. The section of the line with iced wires is disconnected from the line, but connected to a direct current source. When using direct current, the ohmic resistance of the wire can be practically ignored and pass currents, say, twice as strong as the calculated value for alternating current. The wire heats up and the ice melts. Wires shed unnecessary cargo. But if there are repair sleeves on the wires, then additional resistance arises, and then the wire may burn out.

Another enemy is high and low frequency vibrations. A stretched wire of an overhead line is a string that, under the influence of the wind, begins to vibrate at a high frequency. If this frequency coincides with the natural frequency of the wire and the amplitudes coincide, the wire may break. To cope with this problem, special devices are installed on the lines - vibration dampers, which look like a cable with two weights. This design, which has its own oscillation frequency, detunes the amplitudes and dampens the vibration.

Such a harmful effect as "dance of wires" is associated with low-frequency vibrations. When a break occurs on the line (for example, due to the formation of ice), vibrations of the wires occur, which go further in a wave, through several spans. As a result, five to seven supports that make up the anchor span (the distance between two supports with a rigid wire fastening) can bend or even fall. A well-known means of combating "dance" is the establishment of interphase spacers between adjacent wires. If there is a spacer, the wires will mutually dampen their vibrations. Another option is to use on the line supports made of composite materials, in particular fiberglass. Unlike metal supports, the composite one has the property of elastic deformation and will easily “play out” the vibrations of the wires by bending down and then restoring the vertical position. Such a support can prevent the cascading fall of an entire section of the line.

The photo clearly shows the difference between the traditional high voltage wire and the new design wire. Instead of a round wire, a pre-deformed wire was used, and a composite core took the place of a steel core.

Unique supports

Of course, there are all sorts of unique cases associated with the laying of overhead lines. For example, when installing supports in flooded soil or in permafrost conditions, conventional pile-shells for the foundation will not work. Then screw piles are used, which are screwed into the ground like a screw in order to achieve the most solid foundation. A special case is the passage of power lines of wide water barriers. They use special high-altitude supports that weigh ten times more than usual and have a height of 250-270 m. Since the span can be more than two kilometers, a special wire with a reinforced core is used, which is additionally supported by a load cable. This is how, for example, the transition of a power transmission line across the Kama with a span of 2250 m is arranged.

A separate group of supports is represented by structures designed not only to hold wires, but also to carry a certain aesthetic value, for example, sculpture supports. In 2006, the Rosseti company initiated a project to develop poles with an original design. There were interesting works, but their authors, designers, often could not appreciate the possibility and manufacturability of the engineering implementation of these structures. In general, it must be said that poles in which an artistic concept is invested, such as, for example, figure poles in Sochi, are usually installed not at the initiative of network companies, but by order of some third-party commercial or government organizations. For example, in the USA, a support in the form of the letter M, stylized as the logo of the McDonald's fast food chain, is popular.