Transformers carry out direct transformation of electricity - changing the voltage value. Distribution devices are used to receive electricity from the supply side of transformers (receiving distribution devices) and to distribute electricity on the consumer side.

Subsequent chapters discuss the design of the main elements of power supply systems, provide the main types and diagrams of substations, and provide the basics of mechanical calculations of overhead power lines and busbar structures.

1. Designs of overhead power lines

1.1. General information

By air line(VL) is a device for transmitting electricity through wires located in the open air and attached to supports using insulators and fittings.

In Fig. Figure 1.1 shows a fragment of an overhead line. The distance l between adjacent supports is called span. The vertical distance between the straight line connecting the wire suspension points and the lowest point of its sagging is called wire sag f P . The distance from the lowest point of sagging wire to the surface of the earth is called overhead line size h G . A lightning protection cable is fixed at the top of the supports.

The size of the line size h g is regulated by the PUE depending on the voltage of the overhead line and the type of terrain (populated, unpopulated, difficult to access). The length of the garland of insulators λ and the distance between the wires of adjacent phases h p-p are determined by the rated voltage of the overhead line. The distance between the suspension points of the upper wire and the cable h p-t is regulated by the PUE based on the requirement of reliable protection of overhead line wires from direct lightning strikes.

To ensure economical and reliable transmission of electrical energy, conductor materials with high electrical conductivity (low resistance) and high mechanical strength are required. In the structural elements of power supply systems, copper, aluminum, alloys based on them, and steel are used as such materials.

Rice. 1.1. Fragment of an overhead power line

Copper has low resistance and fairly high strength. Its specific active resistance is ρ = 0.018 Ohm. mm2/m, and the ultimate tensile strength is 360 MPa. However, it is an expensive and scarce metal. Therefore, copper is used, as a rule, for transformer windings, less often for cable cores, and is practically not used for overhead line wires.

The resistivity of aluminum is 1.6 times greater, the ultimate tensile strength is 2.5 times less than that of copper. The high abundance of aluminum in nature and lower cost than copper have led to its widespread use for overhead line wires.

Steel has great resistance and high mechanical strength. Its specific active resistance is ρ = 0.13 Ohm. mm2/m, and the ultimate tensile strength is 540 MPa. Therefore, in power supply systems, steel is used, in particular, to increase the mechanical strength of aluminum wires, the manufacture of supports and lightning protection cables for overhead power lines.

1.2. Wires and cables of overhead lines

Overhead line wires serve directly to transmit electricity and differ in design and the conductor material used. Most economically feasible

The material for overhead line wires is aluminum and alloys based on it.

Copper wires for overhead lines are used extremely rarely and with an appropriate feasibility study. Copper wires are used in contact networks of mobile transport, in networks of special industries (mines, mines), sometimes when passing overhead lines near the seas and some chemical plants.

Steel wires are not used for overhead lines because they have high active resistance and are susceptible to corrosion. The use of steel wires is justified when performing particularly large spans of overhead lines, for example, when crossing overhead lines across wide navigable rivers.

Wire cross-sections correspond to GOST 839-74. The scale of nominal cross-sections of overhead line wires is the following row, mm2:

1,5; 2,5; 4; 6; 10; 16; 25; 35; 50; 70; 95; 120; 150; 185; 240; 300; 400; 500; 600; 700; 800; 1000.

According to their design, overhead line wires are divided into: single-wire;

multi-wire made of one metal (monometallic); stranded of two metals; self-supporting isolated.

Solid wires, as the name suggests, they are made from one wire (Fig. 1.2,a). Such wires are made of small sections up to 10 mm2 and are sometimes used for overhead lines with voltages up to 1 kV.

Stranded monometallic wires are made with a cross-section of more than 10 mm 2 . These wires are made twisted from individual wires. Around the central wire, a twist (row) of six wires of the same diameter is performed (Fig. 1.2,b). Each subsequent twist has six more wires than the previous one. Twisting of adjacent layers is done in different directions to prevent the wires from unwinding and to give the wire a more round shape.

The number of turns is determined by the cross-section of the wire. Wires with a cross-section of up to 95 mm2 are made with one layer, with a cross-section of 120...300 mm2 - with two layers, with a cross-section of 400 mm2 and more - with three or more layers. Compared to single-wire wires, stranded wires are more flexible, convenient for installation, and reliable in operation.

Rice. 1.2. Designs of non-insulated overhead line wires

To give the wire greater mechanical strength, stranded wires are made with a steel core 1 (Fig. 1.2, c, d, e). Such wires are called steel-aluminum. The core is made of galvanized steel wire and can be single-wire (Fig. 1.2, c) or multi-wire (Fig. 1.2, d). A general view of a large-section steel-aluminum wire with a stranded steel core is shown in Fig. 1.2, d.

Steel-aluminum wires are widely used for overhead lines with voltages above 1 kV. These wires are produced in various designs, differing in the ratio of sections of aluminum and steel parts. For ordinary steel-aluminum wires this ratio is approximately equal to six, for lightweight wires - eight, for reinforced wires - four. When choosing a particular steel-aluminum wire, external mechanical loads on the wire, such as ice and wind, are taken into account.

Wires, depending on the material used, are marked as follows:

M - copper, A - aluminum,

AN, AZh - made of aluminum alloys (have greater mechanical strength than grade A wire);

AC - steel-aluminum; ASO - steel-aluminum lightweight construction;

ACS - steel-aluminum reinforced structure.

The digital designation of the wire indicates its nominal cross-section. For example, A95 is an aluminum wire with a nominal cross-section of 95 mm2. The designation of steel-aluminum wires may additionally indicate the cross-section of the steel core. For example,

ACO240/32 is a lightweight aluminum-steel wire with a nominal cross-section of the aluminum part of 240 mm2 and a cross-section of the steel core of 32 mm2.

Corrosion resistant aluminum wires of the AKP brand and steel-aluminum wires of the ASKP, ASKS, ASK brands have an interwire space filled with a neutral lubricant of increased heat resistance that counteracts corrosion. For the automatic transmission and ASKP wires, the entire interwire space is filled with such a lubricant; for the ASKS wire, only the steel core is filled; for the ASK wire, the steel core is filled with neutral lubricant and isolated from the aluminum part with two polyethylene tapes. Wires AKP, ASKP, ASKS, ASK are used for overhead lines passing near seas, salt lakes and chemical plants.

Self-supporting insulated wires (SIP) used for overhead lines with voltage up to 20 kV. At voltages up to 1 kV (Fig. 1.3,a), such a wire consists of three phase stranded aluminum conductors 1. The fourth conductor 2 is carrier and at the same time neutral. The phase conductors are twisted around the carrier in such a way that the entire mechanical load is absorbed by the carrier conductor, made of durable aluminum alloy ABE.

Rice. 1.3. Self-supporting insulated wires

Phase 3 insulation is made from thermoplastic light-stabilized or cross-linked light-stabilized polyethylene. Due to its molecular structure, such insulation has very high thermomechanical properties and great resistance to solar radiation and the atmosphere. In some SIP designs, the zero load-bearing core is made with insulation.

The design of SIP for voltages above 1 kV is shown in Fig. 1.3, b. This wire is single-phase and consists of

current-carrying steel-aluminum core 1 and insulation 2 made of cross-linked light-stabilized polyethylene.

Overhead lines with SIP have the following advantages compared to traditional overhead lines:

lower voltage losses (improved power quality), thanks to approximately three times lower reactance of three-phase SIPs;

do not require insulators; There is practically no ice formation;

allow suspension of several lines of different voltages on one support;

lower operating costs due to a reduction of approximately 80% in the volume of emergency restoration work; possibility of using shorter supports thanks to

smaller permissible distance from the SIP to the ground; reduction of the security zone, permissible distances to buildings and

structures, clearing width in wooded areas; there is virtually no possibility of a fire occurring in

wooded areas when a wire falls to the ground; high reliability (5-fold reduction in the number of accidents according to

compared to traditional overhead lines); complete protection of the conductor from moisture and

corrosion.

The cost of overhead lines with self-supporting insulated wires is higher than traditional overhead lines.

Overhead line wires with voltages of 35 kV and above are protected from direct lightning strikes lightning protection cable, fixed in the upper part of the support (see Fig. 1.1). Lightning protection cables are elements of overhead lines, similar in design to stranded monometallic wires. The cables are made of galvanized steel wires. The nominal cross-sections of the cables correspond to the scale of the nominal cross-sections of the wires. The minimum cross-section of the lightning protection cable is 35 mm2.

When using lightning protection cables as high-frequency communication channels, instead of a steel cable, a steel-aluminum wire with a powerful steel core is used, the cross-section of which is comparable to or larger than the cross-section of the aluminum part.

1.3. Overhead line supports

The main purpose of supports is to support wires at the required height above the ground and above-ground structures. The supports consist of vertical posts, traverses and foundations. The main materials from which the supports are made are coniferous wood, reinforced concrete and metal.

Wood supports easy to manufacture, transport and operate, they are used for overhead lines with voltages up to 220 kV inclusive in logging areas or close to them. The main disadvantage of such supports is the susceptibility of wood to rotting. To increase the service life of the supports, the wood is dried and impregnated with antiseptics that prevent the development of the rotting process.

Due to the limited construction length of the wood, the supports are made as composite ones (Fig. 1.4a). The wooden stand 1 is connected by metal bands 2 to a reinforced concrete attachment 3. The lower part of the attachment is buried in the ground. Supports corresponding to Fig. 1.4a, are used for voltages up to 10 kV inclusive. For higher voltages, wooden supports are U-shaped (portal). Such a support is shown in Fig. 1.4, b.

It should be noted that in modern conditions of the need to preserve forests, it is advisable to reduce the use of wooden supports.

Reinforced concrete supports consist of a reinforced concrete rack 1 and a traverse 2 (Fig. 1.4, c). The stand is a hollow conical tube with a slight inclination of the cone's constituents. The lower part of the rack is buried in the ground. Traverses are made of galvanized steel. These supports are more durable than wood supports, are easier to maintain, and require less metal than steel supports.

The main disadvantages of supports made of reinforced concrete: heavy weight, which makes it difficult to transport supports to hard-to-reach places on the overhead line route, and the relatively low bending strength of concrete.

To increase the bending strength of supports in the manufacture of reinforced concrete racks, prestressed (tensioned) steel reinforcement is used.

To ensure high concrete density in the manufacture of support posts, they use vibration compaction and centrifugation concrete.

The racks of overhead line supports with voltages up to 35 kV are made of vibrated concrete, at higher voltages - from centrifuged concrete.

Rice. 1.4. Intermediate supports for overhead lines

Steel supports have high mechanical strength and a long service life. These supports are assembled from individual elements using welding and bolted connections, so it is possible to create supports of almost any design (Fig. 1.4d). Unlike supports made of wood and reinforced concrete, metal supports are installed on reinforced concrete foundations 1.

Steel supports are expensive. In addition, steel is susceptible to corrosion. To increase the service life of the supports, they are coated with anti-corrosion compounds and painted. Hot-dip galvanizing of steel supports is very effective against corrosion.

Aluminum alloy supports effective in the construction of overhead lines in conditions of hard-to-reach routes. Due to aluminum's resistance to corrosion, these supports do not require anti-corrosion coating. However, the high cost of aluminum significantly limits the possibilities of using such supports.

When passing through a certain territory, the air line can change direction and cross various engineering

structures and natural barriers, connect to the buses of substation switchgears. In Fig. Figure 1.5 shows a top view of a fragment of the overhead line route. From this figure it can be seen that different supports operate under different conditions and therefore must have a different design. Based on their design, the supports are divided into:

for intermediate(supports 2, 3, 7), installed on the straight section of the overhead line;

corner (support 4), installed at the turns of the overhead line route; end (supports 1 and 8), installed at the beginning and end of the overhead line; transitional (supports 5 and 6), installed in the span

the intersection of an overhead line with any engineering structure, such as a railway.

Rice. 1.5. Fragment of the overhead line route

Intermediate supports are designed to support wires on a straight section of an overhead line. The wires with these supports do not have a rigid connection, as they are secured using supporting garlands of insulators. These supports are subject to gravity forces of wires, cables, garlands of insulators, ice, as well as wind loads. Examples of intermediate supports are shown in Fig. 1.4.

The end supports are additionally affected by the gravitational force T of wires and cables directed along the line (Fig. 1.5). The corner supports are additionally affected by the gravitational force T of wires and cables, directed along the bisector of the angle of rotation of the overhead line.

Transition supports in normal operation of overhead lines act as intermediate supports. These supports take on the tension of wires and cables when they break in adjacent spans and eliminate unacceptable sagging of wires in the crossing span.

End, corner and transition supports must be sufficiently rigid and must not deviate from the vertical

position when exposed to the force of gravity of wires and cables. Such supports are made in the form of rigid spatial trusses or using special cable braces and are called anchor supports. Wires with anchor supports have a rigid connection, as they are fastened using tension garlands of insulators.

Rice. 1.6. Anchor corner supports for overhead lines

Anchor supports made of wood are made A-shaped at voltages up to 10 kV and AP-shaped at higher voltages. Reinforced concrete anchor supports have special cable braces (Fig. 1.6,a). Metal anchor supports have a wider base (lower part) than intermediate supports (Fig. 1.6b).

Based on the number of wires suspended on one support, they are distinguished single-chain and double-chain supports. Three wires (one three-phase circuit) are suspended on single-circuit supports, and six wires (two three-phase circuits) on double-circuit supports. Single-chain supports are shown in Fig. 1.4,a,b,d and fig. 1.6,a; double-chain - in Fig. 1.4,c and fig. 1.6, b.

A double-chain support is cheaper than two single-chain ones. The reliability of power transmission over a double-circuit line is slightly lower than over two single-circuit lines.

Double-chain wooden supports are not manufactured. Overhead line supports with voltages of 330 kV and higher are manufactured only in a single-circuit design with a horizontal arrangement of wires (Fig. 1.7). Such supports are made U-shaped (portal) or V-shaped with cable braces.

Rice. 1.7. Overhead line supports with voltage 330 kV and above

Among the overhead line supports, supports that have special design. These are branch, elevated and transposition supports. Branch supports are designed for intermediate power take-off from overhead lines. Raised supports are installed in large spans, for example when crossing wide navigable rivers. On transpositional the supports carry out the transposition of the wires.

The asymmetrical arrangement of wires on supports with a long overhead line leads to asymmetry of phase voltages. Balancing the phases by changing the relative position of the wires on the support is called transposition. Transposition is provided for overhead lines with a voltage of 110 kV and higher with a length of more than 100 km and is carried out on special transposition supports. The wire of each phase passes the first third of the length of the overhead line in one place, the second third in the other and the third in the third place. This movement of wires is called a complete transposition cycle

Overhead lines (OL) serve to transmit electricity through wires laid in the open air and secured to special supports or brackets of engineering structures using insulators and fittings. The main structural elements of overhead lines are wires, protective cables, supports, insulators and linear fittings. In urban environments, overhead lines are most widespread on the outskirts, as well as in areas with buildings up to five floors. Elements of overhead lines must have sufficient mechanical strength, therefore, when designing them, in addition to electrical ones, mechanical calculations are also made to determine not only the material and cross-section of the wires, but also the type of insulators and supports, the distance between wires and supports, etc.

Depending on the purpose and installation location, the following types of supports are distinguished:

intermediate, designed to support wires on straight sections of lines. The distance between supports (spans) is 35-45 m for voltages up to 1000 V and about 60 m for voltages of 6-10 kV. The wires are fastened here using pin insulators (not tightly);

anchor, having a more rigid and durable design in order to absorb longitudinal forces from the difference in tension along the wires and support (in the event of a break) all the wires remaining in the anchor span. These supports are also installed on straight sections of the route (with a span of about 250 m for a voltage of 6-10 kV) and at intersections with various structures. Wires are fastened to anchor supports tightly to pendant or pin insulators;

terminal, installed at the beginning and end of the line. They are a type of anchor supports and must withstand the constant one-way tension of the wires;

angular, installed in places where the direction of the route changes. These supports are strengthened with struts or metal braces;

special or transitional, installed at the intersections of overhead lines with structures or obstacles (rivers, railways, etc.). They differ from other supports of a given line in height or design.

Wood, metal or reinforced concrete are used to make supports.

Depending on the design, wooden supports can be:

single;

A-shaped, consisting of two posts, converging at the top and diverging at the base;

three-legged, consisting of three pillars converging at the top and diverging at the base;

U-shaped, consisting of two racks connected at the top by a horizontal crossbar;

AP-shaped, consisting of two A-shaped supports connected by a horizontal crossarm;

composite, consisting of a stand and an attachment (stepson), attached to it with a bandage made of steel wire.

To increase their service life, wooden supports are impregnated with antiseptics, which significantly slow down the process of wood decay. In operation, antiseptic treatment is carried out by applying an antiseptic bandage in places prone to rotting, with antiseptic paste applied to all cracks, joints and cuts.

Metal supports are made of pipes or profile steel, reinforced concrete - in the form of hollow round or rectangular posts with a decreasing cross-section towards the top of the support.

Insulators and hooks are used to fasten overhead line wires to supports, and insulators and pins are used to fasten them to a traverse. Insulators can be porcelain or glass, pin or suspended (in places of anchor fastening) (Fig. 1, a-c). They are firmly screwed onto hooks or pins using special polyethylene caps or tow impregnated with red lead or drying oil.

Picture 1. a - pin 6-10 kV; b - pin 35 kV; c - suspended; g, d - polymer rods

Overhead line insulators are made of porcelain or tempered glass - materials with high mechanical and electrical strength and resistance to weathering. A significant advantage of glass insulators is that if damaged, the tempered glass shatters. This makes it easier to locate damaged insulators on the line.

By design, insulators are divided into pin and pendant.

Pin insulators are used on lines with voltages up to 1 kV, 6-10 kV and, rarely, 35 kV (Fig. 1, a, b). They are attached to the supports using hooks or pins.

Suspended insulators (Fig. 1, c) are used on overhead lines with a voltage of 35 kV and higher. They consist of a porcelain or glass insulating part 1, a cap made of malleable cast iron 2, a metal rod 3 and a cement binder 4. Suspended insulators are assembled into garlands, which can be supporting (on intermediate supports) or tensioning (on anchor supports). The number of insulators in the garland is determined by the line voltage; 35 kV - 3-4 insulators, 110 kV - 6-8.

Polymer insulators are also used (Fig. 1, d). They are a rod element made of fiberglass, on which a protective coating with ribs made of fluoroplastic or silicone rubber is placed:

The overhead line wires are required to have sufficient mechanical strength. They can be single or multi-wire. Single-wire steel wires are used exclusively for lines with voltages up to 1000 V; stranded wires made of steel, bimetal, aluminum and its alloys have become prevalent due to their increased mechanical strength and flexibility. Most often, on overhead lines with voltages up to 6-10 kV, aluminum stranded wires of grade A and galvanized steel wires of grade PS are used.

Steel-aluminum wires (Fig. 2, c) are used on overhead lines with voltages above 1 kV. They are produced with different ratios of sections of aluminum and steel parts. The lower this ratio, the higher the mechanical strength of the wire and is therefore used in areas with more severe climatic conditions (with a thicker ice wall). The grade of steel-aluminum wires indicates the cross-sections of the aluminum and steel parts, for example, AC 95/16.

Figure 2. a - general view of a stranded wire; b - cross-section of aluminum wire; c - cross-section of steel-aluminum wire

Wires made of aluminum alloys (AN - not heat-treated, AZh - heat-treated) have greater mechanical strength and almost the same electrical conductivity compared to aluminum alloys. They are used on overhead lines with voltages above 1 kV in areas with ice wall thickness up to 20 mm.

Wires are arranged in different ways. On single-circuit lines they are usually arranged in a triangle.

Currently, so-called self-supporting insulated wires (SIP) with voltages up to 10 kV are widely used. In a 380 V line, the wires consist of a carrier uninsulated wire, which is neutral, three insulated linear wires, and one insulated outdoor lighting wire. Linear insulated wires are wound around the supporting neutral wire. The supporting wire is steel-aluminum, and the linear wires are aluminum. The latter are covered with light-resistant heat-stabilized (cross-linked) polyethylene (APV type wire). The advantages of overhead lines with insulated wires over lines with bare wires include the absence of insulators on the supports, maximum use of the height of the support for hanging wires; there is no need to trim trees in the line area.

For branches from lines with voltages up to 1000 V to inputs into buildings, insulated wires of the APR or AVT brand are used. They have a load-bearing steel cable and weather-resistant insulation.

Wires are fastened to supports in various ways, depending on their location on the insulator. On intermediate supports, the wires are attached to pin insulators with clamps or binding wire made of the same material as the wire, and the latter should not have bends at the point of attachment. The wires located on the head of the insulator are fastened with a head tie, and on the neck of the insulator with a side tie.

On anchor, corner and end supports, wires with voltages up to 1000 V are secured by twisting the wires with a so-called “plug”; wires with voltages of 6-10 kV are secured with a loop. At anchor and corner supports, at crossing points across railways, driveways, tram tracks and at intersections with various power and communication lines, double suspension of wires is used.

The wires are connected using die clamps, a crimped oval connector, an oval connector, or a twisted special device. In some cases, welding is used using thermite cartridges and a special apparatus. For solid steel wires, lap welding can be used using small transformers. In spans between supports it is not allowed to have more than two wire connections, and in spans where overhead lines intersect with various structures, wire connections are not allowed. On supports, the connection must be made in such a way that it does not experience mechanical stress.

Linear fittings are used for fastening wires to insulators and insulators to supports and are divided into the following main types: clamps, coupling fittings, connectors, etc.

Clamps are used to secure wires and cables and attach them to garlands of insulators and are divided into supporting, suspended on intermediate supports, and tension, used on anchor-type supports (Fig. 3, a, b, c).

Figure 3. a - supporting clamp; b - bolt tension clamp; c - pressed tension clamp; d - supporting garland of insulators; d - distance spacer; e - oval connector; g - pressed connector

Coupling fittings are designed for hanging garlands on supports and connecting multi-chain garlands with each other and includes brackets, earrings, ears, and rocker arms. The bracket is used to attach the garland to the support crossbeam. The supporting garland (Fig. 3, d) is fixed on the traverse of the intermediate support using earring 1, the other side of which is inserted into the cap of the upper suspension insulator 2. Eyelet 3 is used to attach the garland of supporting clamp 4 to the lower insulator.

Connectors are used to connect individual sections of wire. They are oval and pressed. In oval connectors, the wires are either crimped or twisted (Fig. 3, e). Pressed connectors (Fig. 3, g) are used to connect large cross-section wires. In steel-aluminum wires, the steel and aluminum parts are crimped separately.

Cables, along with spark gaps, arresters and grounding devices, serve to protect lines from lightning surges. They are suspended above the phase wires on overhead lines with a voltage of 35 kV and higher, depending on the area of ​​lightning activity and the material of the supports, which is regulated by the “Rules for the Construction of Electrical Installations”. Lightning protection cables are usually made of steel, but when used as high-frequency communication channels, they are made of steel and aluminum. On 35-110 kV lines, the cable is fastened to metal and reinforced concrete intermediate supports without cable insulation.

To protect against lightning overvoltages sections of overhead lines with a lower insulation level compared to the rest of the line, tubular arresters are used.

On the overhead line, all metal and reinforced concrete supports on which lightning protection cables are suspended or other lightning protection means (arresters, spark gaps) of 6-35 kV lines are installed are grounded. On lines up to 1 kV with a solidly grounded neutral, the hooks and pins of phase wires installed on reinforced concrete supports, as well as the fittings of these supports, must be connected to the neutral wire.

What kind of power lines are there?

A network of power lines is necessary for the movement and distribution of electrical energy: from its sources, between populated areas and final consumer objects. These lines are very diverse and are divided into:

• by type of wire placement - overhead (located in the open air) and cable (closed in insulation);
• by purpose - ultra-long-distance, trunk, distribution.

Overhead and cable power lines have a certain classification, which depends on the consumer, type of current, power, and materials used.

Overhead power lines (VL)

These include lines that are laid outdoors above the ground using various supports. The separation of power lines is important for their selection and maintenance.

There are lines:

• by the type of current being moved - alternating and direct;
• by voltage level - low-voltage (up to 1000 V) and high-voltage (more than 1000 V) power lines;
• on the neutral - a network with a solidly grounded, isolated, effectively grounded neutral.

Alternating current

Electric lines using alternating current for transmission are most often implemented by Russian companies. With their help, systems are powered and energy is transferred over various distances.

D.C

Overhead power lines providing direct current transmission are rarely used in Russia. The main reason for this is the high cost of installation. In addition to supports, wires and various elements, they require the purchase of additional equipment - rectifiers and inverters.

Since most consumers use alternating current, when installing such lines, it is necessary to spend additional resources on energy conversion.

Installation of overhead power lines

The installation of overhead power lines includes the following elements:

• Support systems or electric poles. They are placed on the ground or other surfaces and can be anchor (take the main load), intermediate (usually used to support wires in spans), corner (placed in places where wire lines change direction).
• Wires. They have their own varieties and can be made of aluminum or copper.
• Traverses. They are mounted on line supports and serve as the basis for installing wires.
• Insulators. With their help, wires are mounted and insulated from each other.
• Grounding systems. The presence of such protection is necessary in accordance with the PUE standards (electrical installation rules).
• Lightning protection. Its use protects overhead power lines from voltage that may arise when a discharge hits.

Each element of the electrical network plays an important role, taking on a certain load. In some cases, it may use additional equipment.

Cable power lines

Cable power lines, unlike overhead ones, do not require a large free area for placement. Due to the presence of insulating protection, they can be laid: on the territory of various enterprises, in populated areas with dense buildings. The only drawback in comparison with overhead lines is the higher installation cost.

Underground and underwater

The closure method allows you to place lines even in the most difficult conditions - underground and under the water surface. Special tunnels or other methods can be used to lay them. In this case, you can use several cables, as well as various fasteners.

Special security zones are established near electrical networks. According to the rules of the PUE, they must ensure safety and normal operating conditions.

Laying on structures

Laying high-voltage power lines with different voltages is possible inside buildings. The most commonly used designs include:

• Tunnels. They are separate rooms, inside which the cables are located along the walls or on special structures. Such spaces are well protected and provide easy access to installation and maintenance of lines.
• Channels. These are ready-made structures made of plastic, reinforced concrete slabs and other materials, inside of which wires are located.
• Floor or shaft. Premises specially adapted for the placement of power lines and the possibility of a person being there.
• Overpass. They are open structures that are laid on the ground, foundation, support structures with wires attached inside. Closed overpasses are called galleries.
• Placement in the free space of buildings - gaps, space under the floor.
• Cable block. Cables are laid underground in special pipes and brought to the surface using special plastic or concrete wells.

Insulation of cable power lines

The main condition when choosing materials for insulating power lines is that they should not conduct current. Typically, the following materials are used in the construction of cable power lines:

• rubber of synthetic or natural origin (it has good flexibility, so lines made of such material are easy to lay even in hard-to-reach places);
• polyethylene (sufficiently resistant to chemical or other aggressive environments);
• PVC (the main advantage of such insulation is accessibility, although the material is inferior to others in terms of durability and various protective properties);
• fluoroplastic (highly resistant to various influences);
• paper-based materials (low resistance to chemical and natural influences, even if impregnated with a protective composition).

In addition to traditional solid materials, liquid insulators and special gases can be used for such lines.

Classification by purpose

Another characteristic by which power lines are classified taking into account voltage is their purpose. Overhead lines are usually divided into: ultra-long-distance, trunk, distribution. They vary depending on the power, type of energy receiver and energy sender. These can be large stations or consumers - factories, settlements.

Ultra-long

The main purpose of these lines is communication between various energy systems. The voltage in these overhead lines starts from 500 kV.

Trunk

This transmission line format assumes a network voltage of 220 and 330 kV. Trunk lines transport energy from power plants to distribution points. They can also be used to communicate between different power plants.

Distribution

The type of distribution lines includes networks under voltage of 35, 110 and 150 kV. With their help, electrical energy moves from distribution networks to populated areas, as well as large enterprises. Lines with a voltage of less than 20 kV are used to ensure the supply of energy to end consumers, including for connecting electricity to the site.

Construction and repair of power lines

Laying networks of high-voltage cable power lines and overhead lines is a necessary way to provide energy to any objects. With their help, electricity is transmitted over any distance.

The construction of networks for any purpose is a complex process that includes several stages:

• Survey of the area.
• Design of lines, preparation of estimates, technical documentation.
• Preparation of the territory, selection and purchase of materials.
• Assembling support elements or preparing for cable installation.
• Installation or laying of wires, hanging devices, strengthening power lines.
• Landscaping and preparation of the line for launch.
• Commissioning, official documentation.

To ensure efficient operation of the line, it requires competent maintenance, timely repairs and, if necessary, reconstruction. All such activities must be carried out in accordance with the PUE (technical installation rules).

Repair of electrical lines is divided into current and major. During the first, the state of operation of the system is monitored, and work is carried out to replace various elements. Major repairs involve more serious work, which may include replacing supports, re-tensioning lines, and replacing entire sections. All types of work are determined depending on the condition of the power lines.

Overhead power line(VL) - a device intended for transmitting or distributing electrical energy through wires with a protective insulating sheath (VLZ) or bare wires (VL), located in the open air and attached using traverses (brackets), insulators and linear fittings to supports or other engineering structures (bridges, overpasses). The main elements of overhead lines are:

• wires;
• safety cables;
• support supporting wires and hummocks at a certain height above ground or water level;
• insulators that isolate wires from the support body;
• linear fittings.

The linear portals of the distribution devices are taken as the beginning and end of the overhead line. According to their design, overhead lines are divided into single-circuit and multi-circuit, usually 2-circuit.

Typically, an overhead line consists of three phases, so the supports of single-circuit overhead lines with voltages above 1 kV are designed to hang three phase wires (one circuit) (Fig. 1); six wires (two parallel circuits) are suspended on the supports of double-circuit overhead lines. If necessary, one or two lightning protection cables are suspended above the phase wires. From 5 to 12 wires are hung on the overhead line supports of a distribution network with voltages up to 1 kV to supply power to various consumers on one overhead line (external and internal lighting, power supply, household loads). An overhead line with a voltage of up to 1 kV with a solidly grounded neutral is equipped with a neutral wire in addition to the phase ones.

Rice. 1. Fragments of 220 kV overhead line:a – single-chain; b – double-chain

Wires of overhead power lines are mainly made of aluminum and its alloys, in some cases of copper and its alloys, and are made of cold-drawn wire with sufficient mechanical strength. However, the most widely used are stranded wires made of two metals with good mechanical characteristics and relatively low cost. Wires of this type include steel-aluminum wires with a ratio of the cross-sectional areas of the aluminum and steel parts from 4.0 to 8.0. Examples of the location of phase wires and lightning protection cables are shown in Fig. 2, and the design parameters of overhead lines of a standard voltage range are given in table. 1.

Rice. 2. : a – triangular; b – horizontal; c – hexagonal “barrel”; d – reverse “Christmas tree”

Table 1. Design parameters of overhead lines

All of the above options for the arrangement of phase wires on supports are characterized by an asymmetrical arrangement of the wires in relation to each other. Accordingly, this leads to unequal reactance and conductivity of different phases, caused by mutual inductance between the wires of the line and, as a consequence, to asymmetry of phase voltages and voltage drop.

In order to make the capacitance and inductance of all three phases of the circuit the same, transposition of wires is used on the power line, i.e. mutually change their location relative to each other, with each phase wire traveling one third of the way (Fig. 3). One such triple movement is called a transposition cycle.

Rice. 3. Scheme of the full cycle of transposition of overhead power line sections: 1, 2, 3 – phase wires

Transposition of phase wires of overhead power lines with bare wires is used for voltages of 110 kV and higher and for line lengths of 100 km and more. One of the options for installing wires on a transposition support is shown in Fig. 4. It should be noted that the transposition of current-carrying cores is sometimes used in overhead lines; in addition, modern technologies for the design and construction of overhead lines make it possible to technically implement control of line parameters (controlled self-compensating lines and compact overhead lines of ultra-high voltage).

Rice. 4.

Wires and protective cables of the overhead line in certain places must be rigidly fixed to the tension insulators of the anchor supports (end supports 1 and 7, installed at the beginning and end of the overhead line, as shown in Fig. 5 and tensioned to a given tension. Intermediate supports are installed between the anchor supports , necessary to support wires and cables, using supporting garlands of insulators with supporting clamps, at a given height (supports 2, 3, 6), installed on a straight section of the overhead line; corner (supports 4 and 5), installed at turns of the overhead line route; transitional (supports 2 and 3), installed in the span of an overhead line crossing any natural obstacle or engineering structure, for example, a railway or highway.

Rice. 5.

The distance between the anchor supports is called the anchor span of the overhead power line (Fig. 6). The horizontal distance between the wire attachment points on adjacent supports is called the span length L . A sketch of the overhead line span is shown in Fig. 7. The span length is chosen mainly for economic reasons, except for transition spans, taking into account both the height of the supports and the sagging of wires and cables, as well as the number of supports and insulators along the entire length of the overhead line.

Rice. 6. : 1 – supporting garland of insulators; 2 – tension garland; 3 – intermediate support; 4 – anchor support

The smallest vertical distance from the ground to the wire with its greatest sag is called the line dimension to the ground - h . The line dimensions must be maintained for all rated voltages, taking into account the risk of blocking the air gap between the phase conductors and the highest point of the terrain. It is also necessary to take into account the environmental aspects of the impact of high electromagnetic field strengths on living organisms and plants.

The greatest deviation of the phase wire f p or lightning protection cable f t from the horizontal under the influence of a uniformly distributed load from its own mass, ice mass and wind pressure is called a sag arrow. To prevent wires from tangling, the cable sag is 0.5 - 1.5 m less than the wire sag.

Structural elements of overhead lines, such as phase wires, cables, garlands of insulators, have a significant mass, so the forces acting on one support reach hundreds of thousands of Newtons (N). The gravitational forces on the wire from the weight of the wire, the weight of the tension strings of insulators and ice formations are directed normally downward, and the forces caused by wind pressure are directed normally away from the wind flow vector, as shown in Fig. 7.

Rice. 7.

In order to reduce the inductive reactance and increase the capacity of long-distance overhead lines, various variants of compact power lines are used, a characteristic feature of which is a reduced distance between phase wires. Compact power lines have a narrower spatial corridor, a lower level of electric field strength at ground level and allow technical implementation of control of line parameters (controlled self-compensating lines and lines with an unconventional configuration of split phases).

2. Cable power line

Cable power line (CL) consists of one or more cables and cable fittings for connecting cables and for connecting cables to electrical devices or distribution device buses.

Unlike overhead lines, cables are laid not only outdoors, but also indoors (Fig. 8), in ground and water. Therefore, CLs are susceptible to moisture, chemical aggressiveness of water and soil, mechanical damage during excavation work and soil displacement during heavy rains and floods. The design of the cable and cable laying structures must provide protection from the specified influences.

Rice. 8.

According to the rated voltage, cables are divided into three groups: cables low voltage(up to 1 kV), cables medium voltage(6…35 kV), cables high voltage(110 kV and above). According to the type of current they distinguish AC and DC cables.

Power cables are carried out single-core, two-core, three-core, four-core and five-core. High voltage cables are made of single cores; two-core – DC cables; three-core – medium voltage cables.

Low voltage cables are made with up to five cores. Such cables can have one, two or three phase conductors, as well as a zero working conductor N and zero protective core RE or combined zero working and protective core PEN .

Based on the material of the current-carrying cores, cables with aluminum and copper conductors. Due to the scarcity of copper, cables with aluminum conductors are most widely used. Used as an insulating material cable paper impregnated with rosin oil, plastic and rubber. There are cables with normal impregnation, depleted impregnation and impregnation with a non-drip composition. Cables with depleted or non-draining impregnation are laid along a route with a large difference in heights or along vertical sections of the route.

High voltage cables are carried out oil-filled or gas-filled. In these cables, paper insulation is filled with oil or gas under pressure.

Protection of the insulation from drying out and the ingress of air and moisture is ensured by applying a sealed shell to the insulation. The cable is protected from possible mechanical damage by armor. To protect against the aggressiveness of the external environment, an external protective cover is used.

When studying cable lines, it is advisable to note superconducting cables for power lines The design of which is based on the phenomenon of superconductivity. In a simplified form, the phenomenon superconductivity in metals can be represented as follows. Coulomb repulsive forces act between electrons as between similarly charged particles. However, at ultra-low temperatures for superconducting materials (which includes 27 pure metals and a large number of special alloys and compounds), the nature of the interaction of electrons with each other and with the atomic lattice changes significantly. As a result, it becomes possible to attract electrons and form so-called electron (Cooper) pairs. The appearance of these pairs, their increase, and the formation of a “condensate” of electron pairs explains the appearance of superconductivity. With increasing temperature, some electrons become thermally excited and go into a single state. At a certain so-called critical temperature, all electrons become normal and the state of superconductivity disappears. The same thing happens when tension increases. magnetic accordingla. The critical temperatures of superconducting alloys and compounds used in technology are 10 - 18 K, i.e. from –263 to –255°С.

The first projects, experimental models and prototypes of such cables in flexible corrugated cryostatic sheaths were implemented only in the 70-80s of the 20th century. As a superconductor, tapes based on an intermetallic compound of niobium with tin, cooled with liquid helium, were used.

In 1986, the phenomenon was discovered high temperature superconductivity, and already at the beginning of 1987, conductors of this kind were obtained, which were ceramic materials, the critical temperature of which was increased to 90 K. The approximate composition of the first high-temperature superconductor is YBa 2 Cu 3 O 7–d (d< 0,2). Такой сверхпроводник представляет собой неупорядоченную систему мелких кристаллов, имеющих размер от 1 до 10 мкм, находящихся в слабом электрическом контакте друг с другом. К концу XX века были начаты и к этому времени достаточно продвинуты работы по созданию сверхпроводящих кабелей на основе высокотемпературных сверхпроводников. Такие кабели принципиально отличаются от своих предшественников. Жидкий азот, применяемый для охлаждения, на несколько порядков дешевле гелия, а его запасы практически безграничны. Очень важным является то, что жидкий азот при рабочих давлениях 0,8 - 1 МПа является прекрасным диэлектриком, превосходящим по своим свойствам пропиточные составы, используемые в традиционных кабелях.

Feasibility studies show that high-temperature superconducting cables will be more efficient compared to other types of power transmission even with a transmitted power of more than 0.4 - 0.6 GVA, depending on the actual application. High-temperature superconducting cables are expected to be used in the future in the energy sector as current conductors at power plants with a capacity of over 0.5 GW, as well as deep leads into megacities and large energy-intensive complexes. At the same time, it is necessary to realistically evaluate the economic aspects and the full range of work to ensure the reliability of such cables in operation.

However, it should be noted that when constructing new and reconstructing old cable lines, it is necessary to be guided by the provisions of PJSC Rosseti, according to which it is prohibited to use :

• power cables that do not meet current fire safety requirements and emit large concentrations of toxic products during combustion;
• cables with paper-oil insulation and oil-filled;
• cables made using silanol cross-linking technology (silanol cross-linking compositions contain grafted organofunctional silane groups, and cross-linking of the molecular chain of polyethylene (PE), leading to the formation of a spatial structure, in this case occurs due to the silicon-oxygen-silicon (Si-O-Si) bond , rather than carbon-carbon (C-C), as is the case with peroxide cross-linking).

Depending on the design, cable products are divided into cables , wires And cords .

Cable– a fully ready-to-use factory-made electrical product, consisting of one or more insulated current-carrying cores (conductors), usually enclosed in a metal or non-metallic shell, on top of which, depending on the conditions of installation and operation, there may be an appropriate protective cover, which includes armor may be included. Power cables, depending on the voltage class, have from one to five aluminum or copper cores with a cross-section from 1.5 to 2000 mm 2, of which with a cross-section of up to 16 mm 2 - single-wire, above - multi-wire.

The wire– one uninsulated or one or more insulated conductors, on top of which, depending on the installation and operating conditions, there may be a non-metallic sheath, winding and (or) braiding with fibrous materials or wire.

Cord– two or more insulated or especially flexible conductors with a cross-section of up to 1.5 mm 2, twisted or laid in parallel, on top of which, depending on the installation and operating conditions, a non-metallic sheath and protective coatings can be applied.

Power line

Power lines

Power line(power line) - one of the components of the electrical network, a system of energy equipment designed to transmit electricity.

According to MPTEP (Inter-industry rules for the technical operation of consumer electrical installations) Power line- An electrical line extending beyond a power plant or substation and designed to transmit electrical energy.

Distinguish air And cable power lines.

Power lines also transmit information using high-frequency signals; according to estimates, about 60 thousand HF channels are used in Russia over power lines. They are used for dispatch control, transmission of telemetric data, relay protection signals and emergency automation.

Overhead power lines

Overhead power line(VL) - a device intended for transmitting or distributing electrical energy through wires located in the open air and attached using traverses (brackets), insulators and fittings to supports or other structures (bridges, overpasses).

Composition of VL

• Sectioning devices
• Fiber-optic communication lines (in the form of separate self-supporting cables, or built into a lightning protection cable or power wire)
• Auxiliary equipment for operational needs (high-frequency communication equipment, capacitive power take-off, etc.)

Documents regulating overhead lines

Classification of overhead lines

By type of current

• AC overhead line
• DC overhead line

Basically, overhead lines are used to transmit alternating current and only in some cases (for example, for connecting power systems, powering contact networks, etc.) do they use direct current lines.

For AC overhead lines, the following scale of voltage classes has been adopted: alternating - 0.4, 6, 10, (20), 35, 110, 150, 220, 330, 400 (Vyborg substation - Finland), 500, 750 and 1150 kV; constant - 400 kV.

By purpose

• ultra-long-distance overhead lines with a voltage of 500 kV and higher (designed to connect individual power systems)
• main overhead lines with voltages of 220 and 330 kV (designed to transmit energy from powerful power plants, as well as to connect power systems and combine power plants within power systems - for example, they connect power stations with distribution points)
• distribution overhead lines with voltages of 35, 110 and 150 kV (designed for power supply to enterprises and settlements of large areas - connecting distribution points with consumers)
• Overhead lines 20 kV and below, supplying electricity to consumers

By voltage

• Overhead lines up to 1 kV (overhead lines of the lowest voltage class)
• Overhead lines above 1 kV
  • Overhead lines 1-35 kV (overhead lines of medium voltage class)
  • Overhead lines 110-220 kV (overhead lines of high voltage class)
  • 330-500 kV overhead lines (overhead lines of ultra-high voltage class)
  • Overhead lines 750 kV and higher (overhead lines of ultra-high voltage class)

These groups differ significantly mainly in requirements regarding design conditions and structures.

According to the operating mode of neutrals in electrical installations

• Three-phase networks with ungrounded (isolated) neutrals (the neutral is not connected to the grounding device or is connected to it through devices with high resistance). In Russia, this neutral mode is used in networks with a voltage of 3-35 kV with low currents of single-phase ground faults.
• Three-phase networks with resonantly grounded (compensated) neutrals (the neutral bus is connected to grounding through inductance). In Russia it is used in networks with a voltage of 3-35 kV with high currents of single-phase ground faults.
• Three-phase networks with effectively grounded neutrals (high and ultra-high voltage networks, the neutrals of which are connected to the ground directly or through a small active resistance). In Russia, these are networks with voltages of 110, 150 and partially 220 kV, i.e. networks in which transformers are used, rather than autotransformers, which require mandatory solid grounding of the neutral according to the operating mode.
• Networks with a solidly grounded neutral (the neutral of a transformer or generator is connected to a grounding device directly or through low resistance). These include networks with voltages less than 1 kV, as well as networks with voltages of 220 kV and higher.

According to the operating mode depending on the mechanical condition

• Overhead line of normal operation (wires and cables are not broken)
• Overhead lines of emergency operation (in case of complete or partial breakage of wires and cables)
• Overhead lines of installation mode (during installation of supports, wires and cables)

Main elements of overhead lines

• Route- position of the overhead line axis on the earth's surface.
• Pickets(PC) - segments into which the route is divided, the length of the PC depends on the rated voltage of the overhead line and the type of terrain.
• Zero picket sign marks the beginning of the route.
• Center sign indicates the center location of the support in situ on the route of the overhead line under construction.
• Production picketing- installation of picket and center signs on the route in accordance with the list of support placement.
• Support foundation- a structure embedded in the ground or resting on it and transferring loads to it from supports, insulators, wires (cables) and from external influences (ice, wind).
• Foundation base- the soil of the lower part of the pit, which absorbs the load.
• Span(span length) - the distance between the centers of two supports on which the wires are suspended. Distinguish intermediate(between two adjacent intermediate supports) and anchor(between anchor supports) spans. Transition span- a span crossing any structure or natural obstacle (river, ravine).
• Line rotation angle- angle α between the directions of the overhead line route in adjacent spans (before and after the turn).
• Sag- vertical distance between the lowest point of the wire in the span and the straight line connecting the points of its attachment to the supports.
• Wire size- vertical distance from the lowest point of the wire in the span to the intersecting engineering structures, the surface of the earth or water.
• Plume (a loop) - a piece of wire connecting the tensioned wires of adjacent anchor spans on an anchor support.

Cable power lines

Cable power line(CL) - called a line for transmitting electricity or individual pulses of it, consisting of one or more parallel cables with connecting, locking and end couplings (terminals) and fasteners, and for oil-filled lines, in addition, with feeding devices and a pressure alarm system oils

By classification cable lines are similar to overhead lines

Cable lines are divided according to the conditions of passage

• Underground
• By buildings
• Underwater

cable structures include

• Cable tunnel- a closed structure (corridor) with supporting structures located in it for placing cables and cable couplings on them, with free passage along the entire length, allowing cable laying, repairs and inspections of cable lines.

• cable channel- a closed and buried (partially or completely) in the ground, floor, ceiling, etc., a non-passable structure designed to accommodate cables, the installation, inspection and repair of which can only be done with the ceiling removed.

• Cable mine- a vertical cable structure (usually rectangular in cross-section), the height of which is several times greater than the side of the section, equipped with brackets or a ladder for people to move along it (through shafts) or a completely or partially removable wall (non-through shafts).

• Cable floor- part of the building limited by the floor and the ceiling or covering, with a distance between the floor and the protruding parts of the ceiling or covering of at least 1.8 m.

• Double floor- a cavity limited by the walls of the room, the interfloor ceiling and the floor of the room with removable slabs (over the entire or part of the area).

• Cable block- a cable structure with pipes (channels) for laying cables in them with associated wells.

• Cable camera- an underground cable structure, covered with a blind removable concrete slab, intended for laying cable couplings or for pulling cables into blocks. A chamber that has a hatch to enter it is called a cable well.

• Cable rack- above-ground or above-ground open horizontal or inclined extended cable structure. The cable rack can be pass-through or non-pass-through.

• Cable gallery- above-ground or above-ground, fully or partially closed (for example, without side walls), horizontal or inclined extended cable passage structure.

By type of insulation

Cable line insulation is divided into two main types:

• liquid
  • cable oil
• hard
  • paper-oil
  • polyvinyl chloride (PVC)
  • rubber-paper (RIP)
  • cross-linked polyethylene (XLPE)
  • ethylene propylene rubber (EPR)

Insulation with gaseous substances and some types of liquid and solid insulation are not listed here due to their relatively rare use at the time of writing.

Losses in power lines

Electricity losses in wires depend on the current strength, therefore, when transmitting it over long distances, the voltage is increased many times (reducing the current strength by the same amount) using a transformer, which, when transmitting the same power, can significantly reduce losses. However, as the voltage increases, various types of discharge phenomena begin to occur.

Another important quantity that affects the efficiency of power transmission lines is cos(f) - a quantity characterizing the ratio of active and reactive power.

In ultra-high voltage overhead lines there are active power losses due to corona (corona discharge). These losses depend largely on weather conditions (in dry weather the losses are smaller, respectively, in rain, drizzle, snow these losses increase) and the splitting of the wire in the phases of the line. Corona losses for lines of different voltages have their own values ​​(for a 500 kV overhead line, the average annual corona losses are about ΔР = 9.0 -11.0 kW/km). Since corona discharge depends on the tension on the surface of the wire, phase splitting is used to reduce this tension in ultra-high voltage overhead lines. That is, instead of one wire, three or more wires in phase are used. These wires are located at an equal distance from each other. An equivalent radius of the split phase is obtained, this reduces the voltage on a separate wire, which in turn reduces corona losses.

Literature

• Electric installation work. In 11 books. Book 8. Part 1. Overhead power lines: Textbook. allowance for vocational schools. / Magidin F. A.; Ed. A. N. Trifonova. - M.: Higher School, 1991. - 208 with ISBN 5-06-001074-0
• Rozhkova L. D., Kozulin V. S. Electrical equipment of stations and substations: Textbook for technical schools. - 3rd ed., revised. and additional - M.: Energoatomizdat, 1987. - 648 p.: ill. BBK 31.277.1 R63
• Design of the electrical part of stations and substations: Textbook. allowance / Petrova S.S.; Ed. S.A. Martynov. - L.: LPI im. M.I. Kalashnikov, 1980. - 76 p. UDC 621.311.2(0.75.8)