Air lines are called lines intended for the transmission and distribution of EE through wires located on outdoors and supported by supports and insulators. Overhead power lines are constructed and operated in a wide variety of climatic conditions and geographical areas, subject to atmospheric influences (wind, ice, rain, temperature changes).

In this regard, overhead lines should be built taking into account atmospheric phenomena, air pollution, laying conditions (sparsely populated areas, urban areas, enterprises), etc. From the analysis of overhead lines conditions, it follows that the materials and designs of lines must meet a number of requirements: economically acceptable cost , good electrical conductivity and sufficient mechanical strength of the materials of wires and cables, their resistance to corrosion, chemical attack; lines must be electrically and environmentally safe, occupy a minimum area.

Structural design of overhead lines. The main structural elements of overhead lines are supports, wires, lightning protection cables, insulators and linear fittings.

According to the design of the supports, single- and double-circuit overhead lines are most common. Up to four circuits can be built on the line route. Line route - a strip of land on which a line is being built. One circuit of a high-voltage overhead line combines three wires (sets of wires) of a three-phase line, in a low-voltage line - from three to five wires. In general, the structural part of the overhead line (Fig. 3.1) is characterized by the type of supports, span lengths, overall dimensions, phase design, and the number of insulators.

The span lengths of overhead lines l are chosen for economic reasons, since with an increase in the span length, the sag of the wires increases, it is necessary to increase the height of the supports H so as not to violate the permissible size of the line h (Fig. 3.1, b), while the number of supports will decrease and line insulators. Line gauge - the smallest distance from the lowest point of the wire to the ground (water, roadbed) should be such as to ensure the safety of people and vehicles under the line.

This distance depends on the nominal voltage of the line and the local conditions (populated, uninhabited). The distance between adjacent phases of a line depends mainly on its rated voltage. The design of the overhead line phase is mainly determined by the number of wires in the phase. If the phase is made by several wires, it is called split. The phases of the overhead lines of high and ultra-high voltage are split. In this case, two wires are used in one phase at 330 (220) kV, three - at 500 kV, four or five - at 750 kV, eight, eleven - at 1150 kV.

Overhead lines. VL supports are structures designed to support wires at the required height above the ground, water, or some kind of engineering structure. In addition, grounded steel cables are suspended on supports, if necessary, to protect the wires from direct lightning strikes and related overvoltages.

The types and designs of supports are varied. Depending on the purpose and placement on the overhead line, they are divided into intermediate and anchor. The supports differ in material, design and method of fastening, tying wires. Depending on the material, they are wooden, reinforced concrete and metal.

intermediate supports the most simple, serve to support wires in straight sections of the line. They are the most common; their share on average is 80-90% of the total number of overhead line supports. The wires to them are fastened with the help of supporting (suspended) garlands of insulators or pin insulators. Intermediate supports in normal mode are loaded mainly from the own weight of wires, cables and insulators, hanging garlands of insulators hang vertically.

Anchor supports installed in places of rigid fastening of wires; they are divided into terminal, angular, intermediate and special. Anchor supports, designed for the longitudinal and transverse components of the tension of the wires (tension garlands of insulators are located horizontally), experience the greatest loads, therefore they are much more complicated and more expensive than intermediate ones; their number on each line should be minimal.

In particular, end and corner supports, installed at the end or at the turn of the line, experience constant tension of wires and cables: one-sided or by the resultant of the angle of rotation; intermediate anchors installed on long straight sections are also calculated for one-sided tension, which can occur when part of the wires break in the span adjacent to the support.

Special supports are of the following types: transitional - for large spans crossing rivers, gorges; branch lines - for making branches from the main line; transpositional - to change the order of the location of the wires on the support.

Along with the purpose (type), the design of the support is determined by the number of overhead lines and the relative position of the wires (phases). The supports (and lines) are made in a single- or double-circuit version, while the wires on the supports can be placed in a triangle, horizontally, a reverse Christmas tree and a hexagon or a barrel (Fig. 3.2).

The asymmetric arrangement of the phase wires with respect to each other (Fig. 3.2) causes the unequal inductances and capacitances of different phases. To ensure the symmetry of a three-phase system and phase alignment of reactive parameters on long lines (more than 100 km) with a voltage of 110 kV and above, the wires in the circuit are rearranged (transposed) using appropriate supports.

With a full cycle of transposition, each wire (phase) evenly along the length of the line occupies in series the position of all three phases on the support (Fig. 3.3).

wooden supports( fig. 3.4) are made of pine or larch and are used on lines with voltage up to 110 kV in forest areas, now less and less. The main elements of the supports are stepchildren (attachments) 1, racks 2, traverses 3, braces 4, under-traverse bars 6 and crossbars 5. Supports are easy to manufacture, cheap, and easy to transport. Their main drawback is their fragility due to the decay of wood, despite its treatment with an antiseptic. The use of reinforced concrete stepchildren (attachments) increases the service life of the supports up to 20-25 years.

Reinforced concrete supports (Fig. 3.5) are most widely used on lines with voltage up to 750 kV. They can be free-standing (intermediate) and with braces (anchor). Reinforced concrete supports are more durable than wooden ones, easy to operate, cheaper than metal ones.

Metal (steel) supports ( fig. 3.6) are used on lines with a voltage of 35 kV and above. The main elements include racks 1, traverses 2, cable racks 3, braces 4 and foundation 5. They are strong and reliable, but quite metal-intensive, occupy a large area, require special reinforced concrete foundations for installation and must be painted during operation for corrosion protection.

Metal poles are used in cases where it is technically difficult and uneconomical to build overhead lines on wooden and reinforced concrete poles (crossing rivers, gorges, making taps from overhead lines, etc.).

Russia has developed unified metal and reinforced concrete supports various types for overhead lines of all voltages, which allows them to be mass-produced, speed up and reduce the cost of line construction.

Overhead line wires.

Wires are designed to transmit electricity. Along with good electrical conductivity (possibly lower electrical resistance), sufficient mechanical strength and resistance to corrosion, they must satisfy the conditions of economy. For this purpose, wires are used from the cheapest metals - aluminum, steel, special aluminum alloys. Although copper has the highest conductivity, copper wires are not used in new lines due to significant cost and the need for other purposes.

Their use is allowed in contact networks, in networks of mining enterprises.

On overhead lines, predominantly uninsulated (bare) wires are used. According to the design, the wires can be single- and multi-wire, hollow (Fig. 3.7). Single-wire, mainly steel wires, are used to a limited extent in low-voltage networks. To give flexibility and greater mechanical strength, the wires are made of multi-wire from one metal (aluminum or steel) and from two metals (combined) - aluminum and steel. The steel in the wire increases the mechanical strength.

Based on the conditions of mechanical strength, aluminum wires of grades A and AKP (Fig. 3.7) are used on overhead lines with voltages up to 35 kV. Overhead lines 6-35 kV can also be made with steel-aluminum wires, and above 35 kV lines are mounted exclusively with steel-aluminum wires.

Steel-aluminum wires have layers of aluminum wires around the steel core. The cross-sectional area of ​​the steel part is usually 4-8 times less than aluminum, but the steel takes about 30-40% of the total mechanical load; such wires are used on lines with long spans and in areas with more severe climatic conditions (with a greater thickness of the ice wall).

The brand of steel-aluminum wires indicates the cross section of the aluminum and steel parts, for example, AC 70/11, as well as data on anti-corrosion protection, for example, AKS, ASKP - the same wires as AC, but with a core filler (C) or all wires (P) with anti-corrosion grease; ASC - the same wire as AC, but with a core covered with a polyethylene film. Wires with anti-corrosion protection are used in areas where the air is polluted with impurities that are destructive to aluminum and steel. The cross-sectional areas of wires are normalized by the State Standard.

An increase in the diameters of the wires with the same consumption of the conductor material can be carried out using wires with a dielectric filler and hollow wires (Fig. 3.7, d, e). This use reduces corona losses (see Section 2.2). Hollow wires are mainly used for busbars of switchgears 220 kV and above.

Wires made of aluminum alloys (AN - non-heat-treated, AJ - heat-treated) have greater mechanical strength compared to aluminum and almost the same electrical conductivity. They are used on overhead lines with a voltage above 1 kV in areas with an ice wall thickness of up to 20 mm.

Overhead lines with self-supporting insulated wires with a voltage of 0.38-10 kV are finding increasing use. In lines with a voltage of 380/220 V, the wires consist of a carrier bare wire, which is zero, three insulated phase wires, one insulated wire (any phase) for outdoor lighting. Phase insulated wires are wound around the carrier neutral wire (Fig. 3.8).

The carrier wire is steel-aluminum, and the phase 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 supports, the maximum use of the height of the support for hanging wires; there is no need to cut trees in the area where the line passes.

Lightning protection cables, along with spark gaps, arresters, voltage limiters and grounding devices, serve to protect the line from atmospheric overvoltages (lightning discharges). The cables are suspended above the phase wires ( fig. 3.5) on overhead lines with a voltage of 35 kV and higher, depending on the area for lightning activity and the material of the supports, which is regulated by the Electrical Installation Rules (PUE).

Galvanized steel ropes of grades C 35, C 50 and C 70 are usually used as lightning protection wires, and steel-aluminum wires are used when using cables for high-frequency communication. The fastening of cables on all supports of overhead lines with a voltage of 220-750 kV must be carried out using an insulator shunted with a spark gap. On 35-110 kV lines, cables are fastened to metal and reinforced concrete intermediate supports without cable insulation.

Air line insulators. Insulators are designed for insulation and fastening of wires. They are made of porcelain and tempered glass - materials with high mechanical and electrical strength and resistance to weathering. An essential advantage of glass insulators is that when damaged, the tempered glass shatters. This makes it easier to find damaged insulators on the line.

According to the design, the method of fixing on the support, the insulators are divided into pin and suspension insulators. Pin insulators (Fig. 3.9, a, b) are used for lines with voltages up to 10 kV and rarely (for small sections) 35 kV. They are attached to the supports with hooks or pins. Suspension insulators (Fig. 3.9, in) used on overhead lines with a voltage of 35 kV and above. They consist of a porcelain or glass insulating part 1, a ductile iron cap 2, a metal rod 3 and a cement binder 4.

Insulators are assembled into garlands (Fig. 3.9, G): supporting on intermediate supports and tension - on anchor. The number of insulators in a garland depends on the voltage, the type and material of the supports, and the pollution of the atmosphere. For example, in a 35 kV line - 3-4 insulators, 220 kV - 12-14; on lines with wooden supports, which have increased lightning resistance, the number of insulators in a garland is one less than on lines with metal supports; in tension garlands operating in the most difficult conditions, 1-2 more insulators are installed than in supporting ones.

Insulators have been developed and are undergoing experimental industrial testing using polymer materials. They are a fiberglass rod element protected by a coating with ribs made of fluoroplastic or silicone rubber. Rod insulators, in comparison with suspension insulators, have less weight and cost, higher mechanical strength than those made of tempered glass. The main problem is to ensure the possibility of their long-term (more than 30 years) work.

Linear reinforcement is designed to fasten wires to insulators and cables to supports and contains the following main elements: clamps, connectors, spacers, etc. (Fig. 3.10).

Supporting clamps are used for suspension and fastening of overhead lines on intermediate supports with limited termination rigidity (Fig. 3.10, a). On anchor supports for rigid fastening of wires, tension garlands and tension clamps are used - tension and wedge (Fig. 3.10, b, c). Coupling fittings (earrings, ears, brackets, rocker arms) are designed for hanging garlands on supports. The supporting garland (Fig. 3.10, d) is fixed on the traverse of the intermediate support with the help of an earring 1, inserted with the other side into the cap of the upper suspension insulator 2. Eyelet 3 is used to attach the supporting clip 4 to the lower insulator of the garland.

Distance spacers (Fig. 3.10, e), installed in spans of 330 kV and higher lines with split phases, prevent whipping, collisions and twisting of individual phase wires. Connectors are used to connect individual sections of wire using oval or pressing connectors (Fig. 3.10, e, g). In oval connectors, the wires are either twisted or crimped; in pressed connectors used to connect steel-aluminum wires of large cross-sections, the steel and aluminum parts are pressed separately.

The result of the development of EE transmission technology over long distances is various options compact transmission lines, characterized by a smaller distance between the phases and, as a result, smaller inductive resistances and the width of the line path (Fig. 3.11). When using supports of the "covering type" (Fig. 3.11, a) distance reduction is achieved due to the location of all phase split structures inside the “enveloping portal”, or on one side of the support rack (Fig. 3.11, b). The convergence of the phases is ensured with the help of interphase insulating spacers. Various options for compact lines with non-traditional wire layouts of split phases have been proposed (Fig. 3.11, in and).

In addition to reducing the width of the route per unit of transmitted power, compact lines can be created to transmit increased power (up to 8-10 GW); such lines cause less electric field strength at ground level and have a number of other technical advantages.

Compact lines also include controlled self-compensating lines and controlled lines with an unconventional configuration of split phases. They are double-circuit lines in which the phases of different circuits of the same name are shifted in pairs. In this case, voltages shifted by a certain angle are applied to the circuits. Due to the mode change using special devices angle of the phase shift, the line parameters are controlled.

Complex technical power lines (TL) are used to deliver electricity over long distances. On a national scale, they are strategically important facilities that are designed and built in accordance with SNiP and PUE.

These linear sections are classified into cable and overhead power lines, the installation and installation of which require mandatory compliance with the design conditions and the installation of special structures.

Overhead power lines

Fig.1 Overhead high-voltage power lines

The most common are overhead lines, which are laid outdoors using high-voltage poles, on which the wires are fixed using special fittings (insulators and brackets). Most often - these are racks SK.

The composition of overhead lines includes:

• supports for various voltages;
• bare wires made of aluminum or copper;
• traverses, providing the necessary distance, excluding the possibility of contact of the wires with the elements of the support;
• insulators;
• ground loop;
• arresters and lightning rod.

The minimum sag point of the overhead line is: 5÷7 meters in uninhabited areas and 6÷8 meters in populated areas.

As high-voltage poles are used:

• metal structures that are effectively used in any climatic zones and with different loads. They are distinguished by sufficient strength, reliability and durability. Represent metal carcass, the elements of which are connected using bolted connections, which facilitate the delivery and installation of supports at installation sites;
• reinforced concrete supports, which are the simplest type of structures that have good strength characteristics, are easy to install and install overhead lines on them. The disadvantages of installing concrete supports include - a certain influence on them of wind loads and soil characteristics;
• wooden poles, which are the most cost-effective to manufacture and have excellent dielectric characteristics. The light weight of wooden structures allows them to be quickly delivered to the installation site and easy to install. The disadvantage of these power transmission towers is their low mechanical strength, which allows them to be installed only with a certain load and susceptibility to biological destruction processes (material decay).

The use of a particular design is determined by the magnitude of the voltage of the electrical network. It will be useful to be able to determine the voltage of power lines in appearance.

VL are classified:

1. by current - direct or alternating;
2. by voltage ratings - for direct current with a voltage of 400 kilovolts and alternating current - 0.4 ÷ 1150 kilovolts.

Cable power lines

Fig. 2 Underground cable lines

Unlike overhead lines, cable lines are insulated and therefore more expensive and reliable. This type of wire is used in places where the installation of overhead lines is not possible - in cities and towns with dense buildings, in the territories of industrial enterprises.

Cable power lines are classified:

1. by voltage - just like overhead lines;
2. according to the type of insulation - liquid and solid. The first type is petroleum oil, and the second is the cable sheath, which consists of polymers, rubber and oiled paper.

Their distinctive features are the method of laying:

• underground;
• underwater;
• for structures that protect cables from atmospheric influences and provide a high degree of safety during operation.

Fig.3 Laying an underwater power line

Unlike the first two methods of laying cable transmission lines, the “by construction” option provides for the creation of:

• cable tunnels, in which power cables are laid on special support structures that allow installation work and maintenance of lines;
• cable channels, which are buried structures under the floor of buildings in which cable lines are laid in the ground;
• cable shafts - vertical corridors having a rectangular section, which provide access to power lines;
• cable floors, which are a dry, technical space with a height of about 1.8 m;
• cable blocks, consisting of pipes and wells;
• open type flyovers - for horizontal or inclined cable laying;
• chambers used for laying couplings of power transmission line sections;
• galleries - the same flyovers, only closed.

Conclusion

Despite the fact that cable and overhead power lines are used everywhere, both options have their own characteristics, which should be taken into account in the design documentation that defines

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

• wires;
• protective cables;
• a support that supports wires and hummocks at a certain height above ground or water level;
• insulators that isolate the wires from the body of the support;
• linear armature.

Linear portals of distribution devices are taken as the beginning and end of the overhead line. By constructive device VL are divided into single-circuit and multi-valued, usually 2-chain.

Usually, an overhead line consists of three phases, so the supports of single-circuit overhead lines with a voltage above 1 kV are designed for hanging three phase wires (one circuit) (Fig. 1), six wires are suspended on the supports of double-circuit overhead lines (two parallel circuits). If necessary, one or two lightning protection cables are suspended above the phase wires. From 5 to 12 wires are suspended on the supports of the overhead line of the distribution network with a voltage of up to 1 kV to supply various consumers with one overhead line (outdoor and indoor lighting, electric power, household loads). An overhead line with a voltage of up to 1 kV with a dead-earthed neutral, in addition to the phase ones, is equipped with a neutral wire.

Rice. one. Fragments of 220 kV overhead lines:a - single-chain; b - double-chain

The wires of overhead power lines are mainly made of aluminum and its alloys, in some cases of copper and its alloys, they are made of cold-drawn wire with sufficient mechanical strength. However, the most widespread are multi-wire wires made of two metals with good mechanical characteristics and relatively low cost. Wires of this type include steel-aluminum wires with a cross-sectional area ratio of 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 the overhead line of a standard range of voltages are given in table. one.

Rice. 2. : a - triangular; b - horizontal; in - hexagonal "barrel"; d - reverse "Christmas tree"

Table 1. Structural parameters of overhead lines

Rated VL voltage, kV	The distance between phase wires, m	Length span, m	Height	Dimension
Less than 1	0,5	40 – 50	8 – 9	6 – 7
6 – 10	1,0	50 – 80	10	6 – 7
35	3	150 – 200	12	6 – 7
110	4 – 5	170 – 250	13 – 14	6 – 7
150	5,5	200 – 280	15 – 16	7 – 8
220	7	250 – 350	25 – 30	7 – 8
330	9	300 – 400	25 – 30	7,5 – 8
500	10 – 12	350 – 450	25 – 30	8
750	14 – 16	450 – 750	30 – 41	10 – 12
1150	12 – 19	–	33 – 54	14,5 – 17,5

For all the above options for the location of phase wires on supports, an asymmetric arrangement of wires in relation to each other is characteristic. Accordingly, this leads to unequal reactance and conductivity of different phases, due to the mutual inductance between the wires of the line and, as a result, to phase voltage unbalance and voltage drop.

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

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

The transposition of the phase wires of an overhead power line with bare wires is used for a voltage of 110 kV and above and with a line length of 100 km or more. One of the options for mounting wires on a transposition support is shown in fig. 4. It should be noted that the transposition of conductive wires is sometimes used in cable lines, in addition modern technologies design and construction of overhead lines make it possible to technically implement the control of line parameters (controlled self-compensating lines and compact overhead lines of extra-high voltage).

Rice. four.

The wires and protective cables of the overhead line in certain places must be rigidly fixed on 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 stretched to a predetermined tension. Intermediate supports are installed between the anchor supports , necessary to support wires and cables, with the help of supporting garlands of insulators with supporting clamps, at a given height (supports 2, 3, 6), installed on a straight section of overhead lines; angular (supports 4 and 5), installed at turns of the overhead line route; transitional (supports 2 and 3) installed in the span of the 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 transitional 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 at its greatest sag is called the line gauge to the ground - h . The line size must be maintained for all rated voltages, taking into account the risk of closing 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 largest deviation of the phase wire f n or ground wire f t from the horizontal under the action of a uniformly distributed load from its own mass, the mass of ice and wind pressure is called the sag. To prevent wires from lashing, the cable sag boom is less than the wire sag boom by 0.5 - 1.5 m.

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 tensile forces on the wire from the weight of the wire, the weight of the tension garlands of insulators and ice formations are directed downwards along the normal, and the forces due to the wind pressure are directed along the normal away from the wind flow vector, as shown in Fig. 7.

Rice. 7.

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

2. Cable power line

Cable power line (KL) consists of one or more cables and cable fittings for connecting cables and for connecting cables to electrical apparatus or switchgear busbars.

Unlike overhead lines, cables are laid not only outdoors, but also indoors (Fig. 8), in the ground and in water. Therefore, CL are exposed to moisture, chemical aggressiveness of water and soil, mechanical damage during earthworks and soil displacement during heavy rains and floods. The design of the cable and structures for laying the cable must provide protection against the specified impacts.

Rice. eight.

According to the value of the rated voltage, the 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 performed single-wire, two-wire, three-wire, four-wire and five-wire. High voltage cables are made as single-core; 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 cores, as well as a zero working core. N and zero protective conductor RE or combined zero working and protective core PEN .

According to the material of the conductive 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 oil rosin, 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 height difference or along vertical sections of the route.

High voltage cables are made oil-filled or gas-filled. In these cables, the paper insulation is filled with pressurized oil or gas.

Protection of the insulation from drying out and ingress of air and moisture is ensured by the imposition of a hermetic shell on the insulation. Protection of the cable from possible mechanical damage is provided 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 whose design is based on the phenomenon of superconductivity. In a simplistic way, the phenomenon superconductivity in metals can be represented as follows. Coulomb repulsive forces act between electrons as between similarly charged particles. However, at ultralow temperatures for superconducting materials (and these are 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, the attraction of electrons and the formation of so-called electron (Cooper) pairs becomes possible. The appearance of these pairs, their increase, the formation of a "condensate" of electron pairs and explains the appearance of superconductivity. As the temperature rises, some of the electrons are thermally excited and go into a single state. At a certain so-called critical temperature, all electrons become normal and the superconductivity state disappears. The same thing happens when tension increases. magneticla. The critical temperatures of superconducting alloys and compounds used in engineering 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 XX century. Ribbons based on an intermetallic compound of niobium with tin, cooled with liquid helium, were used as a superconductor.

In 1986, the phenomenon was discovered high temperature superconductivity, and already at the beginning of 1987, conductors of this kind were obtained, which are ceramic materials, the critical temperature of which was increased to 90 K. The approximate composition of the first high-temperature superconductor 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 already at 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 inputs to megacities and large energy-intensive complexes. At the same time, it is necessary to realistically assess the economic aspects and the full range of work to ensure the reliability of such cables in operation.

However, it should be noted that during the construction of new and reconstruction of old cable lines, it is necessary to be guided by the provisions of PJSC Rosseti, according to which it is forbidden 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 the silanol crosslinking technology (silanol crosslinkable compositions contain grafted organofunctional silane groups, and the crosslinking of the polyethylene (PE) molecular chain, leading to the formation of a spatial structure, in this case occurs due to the silicon-oxygen-silicon (Si-O-Si) bond , and not carbon-carbon (C-C), as is the case with peroxide crosslinking).

Cable products, depending on the designs, are divided into cables , wires and cords .

Cable- a completely ready-to-use factory electrical product, consisting of one or more insulated conductive cores (conductors), enclosed, as a rule, in a metal or non-metallic sheath, over which, depending on the conditions of installation and operation, there may be an appropriate protective cover, which includes may include armor. Power cables, depending on the voltage class, have from one to five aluminum or copper conductors 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, more - multi-wire.

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

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

Transformers carry out a direct conversion of electricity - a change in the magnitude of the voltage. Distribution boards are used to receive electricity from the supply side of transformers (receiving distribution boards) and to distribute electricity on the consumer side.

In the following chapters, the design implementation of the main elements of power supply systems is considered, the main types and schemes of substations are given, and the basics of mechanical calculation of overhead power lines and busbar structures are given.

1. Structures 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 with insulators and fittings to supports.

On fig. 1.1 shows a fragment of the overhead line. The distance l between adjacent supports is called the span. The vertical distance between the straight line connecting the suspension points of the wire and the lowest point of its sag is called wire sag f P . Distance from lowest point sagging wire to the ground is called overhead line size h G . A lightning protection cable is fixed in the upper part 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, uninhabited, hard to reach). 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 reliable protection overhead lines from direct lightning strikes.

To ensure economical and reliable power transmission, 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 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, to make windings of transformers, less often - for cable cores and is practically not used for wires of overhead lines.

The specific resistance of aluminum is 1.6 times greater, the ultimate tensile strength is 2.5 times less than that of copper. The high prevalence of aluminum in nature and the lower cost than that of copper led to its widespread use for overhead lines.

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

1.2. Wires and cables of overhead lines

VL wires serve directly for the transmission of electricity and differ in design and the conductor material used. Most cost-effective

the material for wires of overhead lines 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 industries.

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 especially large spans of overhead lines, for example, when crossing overhead lines through wide navigable rivers.

Wire cross-sections comply with GOST 839-74. The scale of the nominal cross-sections of the wires of the overhead line is the following series, 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 the design, the wires of the overhead lines are divided into: single-wire;

stranded from one metal (monometallic); stranded of two metals; self-supporting isolated.

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

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

The number of layers is determined by the cross section of the wire. Wires with a cross section of up to 95 mm2 are made with one strand, a cross section of 120 ... 300 mm2 - with two strands, a cross section of 400 mm2 or more - with three or more layers. Stranded wires are more flexible, easy to install, and reliable in operation compared to single-wire ones.

Rice. 1.2. Designs of uninsulated wires VL

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) and multi-wire (Fig. 1.2, d). A general view of a steel-aluminum wire of large cross section 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 six, for light-weight wires - eight, for reinforced wires - four. When choosing one or another 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 - from aluminum alloys (they have greater mechanical strength than grade A wire);

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

ACS - steel-aluminum reinforced design.

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

АСО240/32 - steel-aluminum wire of lightweight design with a nominal section of the aluminum part of 240 mm2 and a steel core section of 32 mm2.

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

Self-supporting insulated wires (SIP) are 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 a carrier and at the same time zero. The phase conductors are twisted around the carrier in such a way that the entire mechanical load is taken up by the carrier conductor, made of durable ABE aluminum alloy.

Rice. 1.3. Self-supporting insulated wires

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

The design of SIP for voltages above 1 kV is shown in fig. 1.3b. Such a wire is made 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 compared to traditional overhead lines have the following advantages:

lower voltage losses (improvement in power quality), due to approximately three times lower reactance of three-phase SIPs;

do not require insulators; practically no icing;

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

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

smaller allowable distance from SIP to the ground; decrease security zone, allowable distances to buildings and

structures, the width of the clearing in a wooded area; the practical absence of the possibility of a fire in

wooded area when the wire falls to the ground; high reliability (5-fold reduction in the number of accidents due to

compared with 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.

Wires of overhead lines with a voltage of 35 kV and above are protected from a direct lightning strike ground wire, fixed in the upper part of the support (see Fig. 1.1). Lightning cables are elements of overhead lines, similar in design to multi-wire monometallic wires. Cables are made of galvanized steel wires. Nominal sections of cables correspond to the scale of nominal sections of wires. The minimum 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 commensurate with or greater than the cross section of the aluminum part.

1.3. Overhead line supports

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

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

Due to the limited building length of wood, the supports are made of composite (Fig. 1.4, a). Wooden rack 1 is articulated with metal bands 2 with reinforced concrete prefix 3. The lower part of the prefix is ​​buried in the ground. Supports corresponding to fig. 1.4, a, apply to voltages up to 10 kV inclusive. For higher voltages, wood supports are U-shaped (portal). Such a support is shown in Fig. 1.4b.

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 reinforced concrete rack 1 and traverse 2 (Fig. 1.4, c). The rack is a hollow conical pipe with a small inclination of the cone generatrices. The lower part of the rack is buried in the ground. Traverses are made of galvanized steel. These poles are more durable than wood poles, are easy to maintain and require less metal than steel poles.

The main disadvantages of reinforced concrete poles: high weight, which makes it difficult to transport the poles to hard-to-reach places overhead lines, and relatively low bending strength of concrete.

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

To ensure a high density of concrete in the manufacture of pillars, supports are used vibrocompaction and centrifugation concrete.

Racks of supports of overhead lines with voltage up to 35 kV are made of vibrated concrete, at higher voltages - from centrifuged concrete.

Rice. 1.4. Intermediate supports VL

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

Steel poles 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 poles is very effective against corrosion.

Supports made of aluminum alloys effective in the construction of overhead lines in hard-to-reach routes. Due to the resistance of aluminum to corrosion, these supports do not need an anti-corrosion coating. However, the high cost of aluminum significantly limits the use of such supports.

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

structures and natural barriers, to be connected to the substation switchgear busbars. On fig. 1.5 shows a top view of a fragment of the overhead line route. It can be seen from this figure that different supports work in different conditions and, therefore, must have a different design. By design, the supports are divided into:

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

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

crossing an overhead line of any engineering structure, such as a railway.

Rice. 1.5. Fragment of the VL route

Intermediate supports are designed to support wires in a straight section of overhead lines. The wires with these supports do not have a rigid connection, as they are attached using insulators supporting garlands. Gravity forces of wires, cables, garlands of insulators, ice, as well as wind loads act on these supports. Examples of intermediate supports are shown in fig. 1.4.

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

Transitional supports in the normal mode of overhead lines act as intermediate supports. These supports take on the tension of wires and cables in case of their breakage in adjacent spans and exclude unacceptable sagging of wires in the crossing span.

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

position when exposed to the tensile force 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 attached using tension garlands of insulators.

Rice. 1.6. Anchor corner supports VL

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

By the number of wires suspended on one support, they distinguish single and double chain supports. Three wires (one three-phase circuit) are suspended on single-circuit supports, six wires (two three-phase circuits) are suspended 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, in and fig. 1.6b.

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

Supports made of wood in double-circuit design are not manufactured. Supports of overhead lines with a voltage of 330 kV and above are made only in a single-circuit version with a horizontal arrangement of wires (Fig. 1.7). Such supports are made U-shaped (portal) or V-shaped with cable extensions.

Rice. 1.7. Supports of overhead lines with a voltage of 330 kV and above

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

The asymmetric arrangement of wires on supports with a large length of the overhead line leads to asymmetry in the phase voltages. Phase balancing 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 above, more than 100 km long 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 cycle of transposition.

The movement of electricity is carried out using power lines. Such installations should be hopeful, as well as safe for people and the environment. This article talks about what an overhead power line is, and also presents some simple diagrams.

The abbreviation stands for power lines. This installation is necessary for the transmission of electrical energy through cables located in open areas (air) and installed with insulators and fittings to racks or supports. The line inputs or line outputs of the switchgear are taken as the point of beginning and end of power lines, and for branching - a special support and a line input.

What does a power station look like?

Supports can be divided into:

• intermediate ones that are located on straight sections of the installation route, they are used only to hold cables;
• anchors are mainly mounted on the straight boundaries of overhead lines;
• end posts are a subspecies of anchor posts, they are placed at the beginning and end of the overhead line. Under standard operating conditions of the installation, they take the load from the cables;
• special racks are used to change the position of cables on power lines;
• decorated racks, in addition to support, they play the role of aesthetic beauty.

Power lines can be divided into overhead and underground. The latter are increasingly gaining popularity due to ease of installation, high reliability and reduced voltage losses.

Note! These lines differ in the laying method, design feature. Each has its pros and cons.

When working with power lines, it is necessary to follow all safety rules, because during installation you can not only get injured, but also die.

Types of supports used

Technical characteristics of power lines

The main parameters of the power line:

• l - gaps between racks or supports of power lines;
• dd - space between adjacent cable lines;
• λλ - can be deciphered as the length of the power line garland;
• HH - rack height;
• hh is the shortest distance allowed from the low cable mark to the ground.

Not everyone can decipher all the characteristics of the installations. Therefore, you can turn to a professional for help.

Below is a table of transmission lines updated in 2010. More Full description can be found on the forums of electricians.

	Rated voltage, kV
	40	115	220	380	500	700
Gap l, m	160-210	170-240	240-360	300-440	330-440	350-550
Space d, m	3,0	4,5	7,5	9,0	11,0	18,5
Garland length X, m	0,8-1,0	1,4-1,7	2,3-2,8	3,0-3,4	4,6-5,0	6,8-7,8
Rack height H, m	11-22	14-32	23-42	26-44	28-33	39-42
Line parameter h, m	6-7	7-8	7-8	8-11	8-14	12-24
Number of cables per phase*	1	1	2	2	3	4-6
Volume of sections wires, mm2	60-185	70-240	250-400	250-400	300-500	250-700

To reduce the number of emergency shutdowns that occur during bad weather conditions, power plant lines are equipped with lightning protection ropes that are installed on racks above the cables and are used to suppress direct lightning strikes into power lines. They are similar to metal galvanized multi-wire cables or special small section reinforced aluminum cables.

Such lightning protection devices are produced and used with optical fiber cores built into their tubular rod, which provide multi-channel communication. In areas with constantly recurring and severe frosts, ice is deposited on wires and accidents are formed due to breaking through overhead lines when sagging ropes and cables approach.

The operating temperature of power lines is from 150 to 200 degrees. The wires are not insulated inside. They must have a high degree of conductivity, as well as resistance to mechanical damage.

The following describes which power lines are used to transmit electricity.

Kinds

Power lines are used to move and distribute electricity. Line types can be divided:

• by type of cable arrangement - air (located in the open air) and closed (in cable channels);
• by function - ultra-long, for highways, distribution.

Overhead power lines can also be divided into subspecies, which depend on conductors, type of current, power, raw materials used. These classifications are detailed below.

Alternating current

According to the type of current, power lines can be divided into two groups. The first of these is DC power lines. Such installations help to minimize losses when moving energy, therefore they are used to transmit current over long distances. This type of power transmission line is quite popular in European countries, but in Russia such power lines can be counted on the fingers. Many railroads run on alternating current.

Power transmission scheme

Direct current

The second group is DC power lines, in which the energy is always the same regardless of direction and resistance. Almost all installations in Russia are powered by direct current. They are easier to produce and operate, but the losses during the movement of current very often reach 10 kW / km for six months on a power line with a voltage of 450 kV.

Power line classification

Such installations can be classified by purpose, voltage, mode of operation, and so on. Each item is described in detail below.

By type of current

In recent years, electricity transmission has been carried out mainly on alternating current. This method is popular because more power sources produce AC voltage (with the exception of individual sources, for example solar panels), and the main consumers are the installations alternating current.

Wiring diagram for overhead lines

Very often DC power transmission is more favorable. To reduce losses in power lines, during the transmission of electrical energy on any type of current, with the help of transformers (TT) raise the voltage.

Also, when performing a transfer from the installation to the consumer at direct current, it is necessary to convert electrical energy from alternating current to direct current, for this there are special rectifiers.

By destination

According to the purpose of the power lines can be divided into several types. According to the distance, the lines are divided into:

• ultra-long. On such power lines, the voltage will be over 500 kilovolts. They are used to move energy over long distances. Basically, they are necessary in order to combine different power systems or their elements;

• trunk. Such lines come with a voltage of 220 or 380 kV. They combine with each other large energy centers or different installations;
• distribution. This type includes systems with a voltage of 35, 110 and 150 kV. They are used to unite districts and small feeding centers;
• supplying electricity to people. Voltage - no higher than 20 kV, the most popular types are 6 and 10 kV. These power lines bring energy to distribution points, and then to people in the house.

By voltage

According to the base voltage, such power lines are mainly divided into two main groups. With low voltage up to 1 kV. GOSTs indicate four main voltages, 40, 220, 380 and 660 V.

With voltage above 1 kV. GOST describes 12 parameters here, average indicators - from 3 to 35 kV, high - from 100 to 220 kV, the highest - 330, 500 and 700 kV and ultra-high - more than 1 MV. It is also called high voltage.

According to the system of functioning of neutrals in electrical installations

Such installations can be divided into four networks:

• three-phase, in which there is no grounding. Basically, this scheme is used in networks with voltages up to 35 kV, where small currents move;
• three-phase, in which there is grounding using inductance. This installation is also called the resonant-grounded type. In such overhead lines, a voltage of 3-35 kV is used, where large currents move;
• three-phase, in which there is a full ground. This mode of operation of the neutral is used in overhead lines with medium and high voltages. Here you need to use current transformers;
• grounded neutral. Overhead lines with a voltage of less than 1.0 kV or more than 220 kV operate here.

Mounting process

According to the mode of operation depending on the mechanical condition

There is also such a separation of power lines, which provides for the external state of all parts of the installation. These are power lines in good condition, where cables, racks and other items are almost new. The main emphasis is on the quality of cables and ropes, they should not be mechanically damaged.

There is also an emergency situation, where the quality of cables and ropes is quite low. Such installations require immediate repair.

• power lines good regimen works - all components are new and not damaged;
• emergency lines - with obvious visible damage to the wires;
• installation lines - during the installation of racks, cables and ropes.

It is only necessary for an experienced electrician to determine the condition of power lines.

If the installation is emergency, then this can lead to a number of consequences. For example, energy will not be supplied constantly, a short circuit is possible, bare wires can cause a fire when they come into contact. If the power line was not installed on time and irreparable consequences occurred, then this can lead to huge fines.

Underground cable lines power lines

Purpose of overhead lines

Such overhead lines are called installations that are used to move and distribute electrical energy through cables located in the open air and held with the help of special racks. Overhead lines are installed and used in a wide variety of weather conditions and geographic areas, are prone to atmospheric influence(precipitation, temperature changes, winds).

Therefore, overhead lines must be installed taking into account weather factors, atmospheric pollution, laying requirements (for a city, field, village), and so on. The installation must comply with a number of rules and regulations:

• cost-effective cost;
• high electrical conductivity, strength of the ropes and racks used;
• resistance to mechanical damage, corrosion;
• be safe for nature and man, do not occupy a lot of free territory.

What do insulators look like?

What is the voltage of the power line

According to certain characteristics, you can find out the voltage of power lines by appearance. The first thing you should pay attention to is the insulator. The more of them are on the installation, the more powerful it will be.

The most popular insulators for overhead lines 0.4kV. They are usually made from durable glass. By their number can be determined in power.

VL-6 and VL-10 are similar in shape, but much larger. In addition to pin fixing, such insulators are sometimes used in the same way as garlands in one / two samples.

Note! On a 35 kV overhead line, hanging insulators are most often installed, although sometimes you can see a pin type. The garland consists of three to five types.

The number of rollers in a garland can be as follows:

• VL-110kV - 6 rollers;
• VL-220kV - 10 rollers;
• VL-330kV - 12 rollers;
• VL-500kV - 22 rollers;
• VL-750kV - from 20 and above.

How to find out the power of power lines

You can also find out the voltage by the number of cables:

• VL-0.4 kV number of wires from 2 to 4 and more;
• VL-6, 10 kV - only three cables per unit;
• VL-35 kV, 110 kV - each insulator has its own wire;
• VL-220 kV - for each insulator one large wire;
• VL-330 kV - in phases of two cables;
• VL-750 kV - from 3 to 5 wires.

In conclusion, it should be noted that in modern world it is impossible to do without power lines. They supply the whole country with electricity. Currently, air and cable power lines are used everywhere.