Safety 

Installation of overhead power lines of different voltages. How to determine the voltage of an overhead power line using insulators

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 outside a power plant or substation and designed to transmit electrical energy.

Distinguish air And cable lines power transmission.

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 line 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 start 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.

- (VL) – a power line, the wires of which are supported above the ground with the help of supports and insulators. [GOST 24291 90] Term heading: Power equipment Encyclopedia headings: Abrasive equipment, Abrasives, Highways... Encyclopedia of terms, definitions and explanations of building materials

OVERHEAD POWER LINE- (power line, power transmission line, a structure designed to transmit electrical energy over a distance from power plants to consumers; located in the open air and usually made with bare wires, which are suspended using ... ... Big Polytechnic Encyclopedia

Overhead power line- (VL) a device for transmitting and distributing electricity through wires located in the open air and attached using insulators and fittings to supports or brackets, racks on engineering structures (bridges, overpasses, etc.) ... Official terminology

overhead power line- 51 overhead power lines; Overhead transmission line, the wires of which are supported above the ground by supports, insulators 601 03 04 de Freileitung en overhead line fr ligne aérienne

For an experienced electrician who has been working with overhead power lines for many years, it will not be difficult to visually determine the voltage of the overhead power line by
the type of insulators, supports, and the number of wires in the line without any devices. Although in most cases, to determine the voltage on an overhead line, you just need to look at the insulators. After reading this article, you will also be able to easily determine the voltage of overhead lines using insulators.

Photo 1. Pin insulators for voltage 0.4, 6-10, 35 kV.

Every person should know this! But why, why does a person far from the electric power industry need to be able to determine voltage? overhead line power transmission lines appearance insulators and the number of insulators in an overhead line garland? The answer is obvious, it's all about electrical safety. After all, for each voltage class of overhead lines, there are minimum permissible distances, closer than which approaching the overhead line wires is deadly.

In my practice, there were several accidents associated with the inability to determine the voltage class of overhead lines. Therefore, below is a table from the safety rules, which indicates the minimum permissible distances, the closer of which it is deadly to approach live parts that are energized.

Table 1. Permissible distances to live parts that are energized.

*D.C.

The first incident occurred at the construction site of a country house. For some unknown reason, there was no electricity at the construction site; a 10 kV overhead line ran near the unfinished house. Two workers decided to power an extension cord from this overhead line to connect power tools. After stripping two wires on the extension cord and making hooks, they decided to use a stick to hook them to the wires. On a 0.4 kV overhead line, this scheme would work. But since the voltage of the overhead line was 10 kV, one worker received serious electrical injuries, and miraculously survived.

The second incident occurred on the territory of the production base while unloading pipes. A working slinger was unloading metal pipes from a truck using a truck crane in the coverage area of ​​a 110 kV overhead line. During unloading, the pipes bent so that one end came dangerously close to the wires. And even despite the fact that there was no direct contact of the wires with the load, a breakdown occurred due to the high voltage and the worker died. After all, you can be killed by electric shock from a 110 kV overhead line even without touching the wires, you just need to get close to them. I think it’s now clear why it is so important to be able to determine the voltage of overhead lines by the type of insulators.

The main principle here is that the higher the power line voltage, the greater the number of insulators in the garland. By the way, the highest voltage power line in the world is located in Russia, its voltage is 1150 kV.

The first type of line whose voltage you need to know in person is a 0.4 kV overhead line. These overhead line insulators are the smallest, usually pin insulators made of porcelain or glass, mounted on steel hooks. The number of wires in such a line can be either two, if it is 220V, or 4 or more, if it is 380V.

Photo 2. wooden support of 0.4 kV overhead line.

The second type is VL-6 and 10 kV; outwardly they do not differ. 6 kV overhead lines are gradually becoming a thing of the past, giving way to 10 kV overhead lines. The insulators of these lines are usually pin-type, but are noticeably larger than 0.4 kV insulators. Suspension insulators, one or two in a garland, can be used on corner supports. They are also made of glass or porcelain, and are mounted on steel hooks. So: the main visual difference between the 0.4 kV overhead line and the 6, 10 kV overhead line is the larger insulators, as well as only three wires in the line.

Photo 3. Wooden support of 10 kV overhead line.

The third type is 35kV overhead line. Suspended insulators, or pin insulators, are already used here, but much bigger size. The number of pendant insulators in a garland can be from three to five, depending on the support and type of insulators. The supports can be either concrete or made of metal structures, as well as wood, but then it will also be a structure, and not just a pole.

Photo 4. Wooden support of 35 kV overhead line.

110 kV overhead line from 6 insulators in a garland. Each phase, single wire. The supports can be reinforced concrete, wooden (almost never used) or assembled from metal structures.

220 kV overhead line from 10 insulators in a garland. Each phase is carried out with a thick single wire. With voltages above 220 kV, supports are assembled from metal structures or reinforced concrete.

Photo 5. Reinforced concrete support of 110 kV overhead line.

330 kV overhead line from 14 insulators in a garland. There are two wires in each phase. The security zone of these overhead power lines is 30 meters on both sides of the outermost wires.

Photo 7. 330 kV power line support.

500 kV overhead line from 20 insulators in a garland, each phase is carried out with a triple wire arranged in a triangle. Security zone 40 meters.

Photo 8. 500 kV transmission line support.

750 kV overhead line from 20 insulators in a garland. Each phase has 4 or 5 wires arranged in a square or ring. Security zone 55 meters.

Photo 9. 750 kV transmission line support.

Table 2. Number of insulators in an overhead line garland.

What do the inscriptions on overhead line supports mean?

Surely many have seen inscriptions on power transmission line supports in the form of letters and numbers, but not everyone knows what they mean.

Photo 10. Designations on power line supports.

They mean the following: a capital letter indicates the voltage class, for example T-35 kV, S-110 kV, D-220 kV. The number after the letter indicates the line number, the second number indicates the serial number of the support.

T means 35 kV.
45 is the line number.
105 is the serial number of the support.
This method of determining power line voltage by the number of insulators in a garland is not accurate and does not provide a 100% guarantee. Russia is a huge country, therefore, for different operating conditions of power lines (cleanliness of the surrounding air, humidity, etc.), designers calculated different numbers of insulators and used different types supports But if you approach the issue comprehensively and determine the voltage according to all the criteria described in the article, then you can quite accurately determine the voltage class. If you are far from the electric power industry, then for a 100% determination of the power line voltage, it is still better for you to contact your local energy company.

Overhead lines are those intended for the transmission and distribution of energy through wires located in the open air and supported by supports and insulators. Overhead power lines are constructed and operated in a wide variety of climatic conditions and geographic areas and are exposed to atmospheric influences (wind, ice, rain, temperature changes).

In this regard, overhead lines must be constructed taking into account atmospheric phenomena, air pollution, laying conditions (sparsely populated areas, city areas, enterprises), etc. From the analysis of overhead line conditions, it follows that the materials and designs of the lines must satisfy 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 and chemical influences; lines must be electrically and environmentally safe and occupy a minimum area.

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

In terms of the design of supports, the most common are single- and double-circuit overhead lines. Up to four circuits can be constructed along the line route. The line route is the strip of land on which the line is being constructed. 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 overhead line span lengths l are chosen for economic reasons, since as the span length increases, the sag of the wires increases, it is necessary to increase the height of the supports H so as not to violate the permissible dimension of the line h (Fig. 3.1, b), this will reduce the number of supports and insulators on the line. Line size - the shortest distance from the bottom point of the wire to the ground (water, road surface) should be such as to ensure the safety of people and vehicles moving under the line.

This distance depends on the rated voltage of the line and terrain conditions (populated, unpopulated). 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 a phase is made of several wires, it is called split. The phases of high and ultra-high voltage overhead lines 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 line supports. Overhead line supports are structures designed to support wires at the required height above the ground, water, or some kind of engineering structure. In addition, if necessary, grounded steel cables are suspended from the supports to protect the wires from direct lightning strikes and associated overvoltages.

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

Intermediate supports the simplest ones are used to support wires on 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 are attached to them using supporting (suspended) garlands of insulators or pin insulators. In normal mode, intermediate supports are loaded mainly from the own weight of wires, cables and insulators; hanging garlands of insulators hang vertically.

Anchor supports installed in places where wires are rigidly fastened; they are divided into end, corner, intermediate and special. Anchor supports designed for longitudinal and transverse components of tension of wires (tension garlands of insulators are located horizontally) experience the greatest loads, so they are much more complex 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 along the resultant of the angle of rotation; intermediate anchors installed on long straight sections are also designed for one-sided tension that may occur when part of the wires in the span adjacent to the support breaks.

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

Along with the purpose (type), the design of the support is determined by the number of overhead line circuits and the relative arrangement 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, reverse “Christmas tree” and hexagon or “barrel” (Fig. 3.2).

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

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

Wooden supports(Fig. 3.4) are made from pine or larch and are used on lines with voltages up to 110 kV in forest areas, currently less and less. The main elements of the supports are stepsons (attachments) 1, racks 2, traverses 3, braces 4, sub-traverse beams 6 and crossbars 5. The supports are easy to manufacture, cheap, and easy to transport. Their main drawback is their fragility due to wood rotting, despite its treatment with an antiseptic. The use of reinforced concrete stepsons (attachments) increases the service life of supports to 20-25 years.

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

Metal (steel) supports (Fig. 3.6) are used on lines with a voltage of 35 kV and higher. The main elements include racks 1, traverses 2, cable racks 3, guys 4 and a 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. protection against corrosion.

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

In Russia, unified metal and reinforced concrete supports of various types have been developed for overhead lines of all voltages, which allows them to be mass-produced, speeding up and reducing the cost of the construction of lines.

Overhead wires.

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

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

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

Steel-aluminum wires have strands of aluminum wires around a steel core. The cross-sectional area of ​​the steel part is usually 4-8 times smaller than the aluminum part, but steel absorbs 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 thicker ice wall).

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

Increasing the diameters of wires while maintaining the same consumption of conductor material can be done by using wires filled with dielectric and hollow wires (Fig. 3.7, d, e). This use reduces coronation losses (see clause 2.2). Hollow wires are used mainly for busbars distribution devices 220 kV and above.

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

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

The supporting 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 the supports, maximum use of the height of the support for hanging wires; there is no need to trim trees in the line area.

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 of ​​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 when using cables for high-frequency communication, steel-aluminum wires are used. The fastening of cables on all supports of overhead lines with a voltage of 220-750 kV must be done using an insulator bridged by a spark gap. On 35-110 kV lines, cables are fastened to metal and reinforced concrete intermediate supports without cable insulation.

Overhead line insulators. Insulators are designed for insulating and fastening wires. They are made of porcelain and tempered glass - materials with high mechanical and electrical strength and resistance to atmospheric influences. A significant advantage of glass insulators is that when damaged, tempered glass crumbles. This makes it easier to find damaged insulators on the line.

According to their design and method of fastening to the support, insulators are divided into pin and suspended. 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 using hooks or pins. Suspension insulators (Fig. 3.9, V) used on overhead lines with voltages 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.

Insulators are assembled into garlands (Fig. 3.9, G): supporting on intermediate supports and tensioning on anchor supports. The number of insulators in a garland depends on the voltage, type and material of supports, and atmospheric pollution. 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 the 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 using polymer materials have been developed and undergo experimental industrial testing. They are a core element made of fiberglass, protected by a coating with ribs made of fluoroplastic or silicone rubber. Rod insulators, compared to pendant insulators, have lower weight and cost, and higher mechanical strength than those made from tempered glass. The main problem is to ensure the possibility of their long-term (more than 30 years) operation.

Linear fittings designed for fastening 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 hanging and securing overhead line wires on intermediate supports with limited embedding 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 intended for hanging garlands on supports. The supporting garland (Fig. 3.10, d) is fixed on the traverse of the intermediate support using earring 1, the other side is inserted into the cap of the upper suspension insulator 2. Eyelet 3 is used to attach the supporting clamp 4 to the lower insulator of the garland.

Distance spacers (Fig. 3.10, e), installed in the spans of lines 330 kV and above with split phases, prevent overlap, collision 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 technology for transmitting energy over long distances are various options for compact power lines, characterized by a smaller distance between phases and, as a consequence, smaller inductive reactances and line path width (Fig. 3.11). When using “female type” supports (Fig. 3.11, A) the reduction in distance is achieved due to the location of all phase split structures inside the “encompassing portal”, or on one side of the support column (Fig. 3.11, b). Phase proximity is ensured using interphase insulating spacers. Various options for compact lines with non-traditional layouts of split-phase wires have been proposed (Fig. 3.11, in and).

In addition to reducing the route width per unit of transmitted power, compact lines can be created to transmit increased powers (up to 8-10 GW); such lines cause a lower 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 split-phase configuration. They are double-circuit lines in which the like phases of different circuits are shifted in pairs. In this case, voltages are applied to the circuits, shifted by a certain angle. Due to the mode change using special devices The angle of the phase shift controls the parameters of the lines.

Transportation of electrical energy over medium and long distances is most often carried out via power lines located in the open air. Their design must always meet two basic requirements:

1. reliability of high power transmission;

2. ensuring safety for people, animals and equipment.

When operating under the influence of various natural phenomena associated with hurricane gusts of wind, ice, and frost, power lines are periodically subjected to increased mechanical loads.

To comprehensively solve the problems of safe transportation of electrical power, power engineers have to lift live wires to a great height, distribute them in space, isolate them from building elements and mount them with current conductors of increased cross-sections on high-strength supports.

General structure and layout of overhead power lines


Any power transmission line can be represented schematically:

    supports installed in the ground;

    wires through which current is passed;

    linear fittings mounted on supports;

    insulators attached to the fittings and holding the orientation of the wires in the air space.

In addition to the elements of overhead lines it is necessary to include:

    foundations for supports;

    lightning protection system;

    grounding devices.


The supports are:

1. anchor, designed to withstand the forces of tensioned wires and equipped with tensioning devices on the fittings;

2. intermediate, used to secure wires through supporting clamps.

The distance along the ground between two anchor supports is called the anchor section or span, and for intermediate supports between themselves or with the anchor - intermediate.

When an overhead power line passes over water barriers, engineering structures or other critical objects, supports with wire tensioning devices are installed at the ends of such a section, and the distance between them is called an intermediate anchor span.

The wires between the supports are never pulled like a string - in a straight line. They always sag a little, positioned in the air taking into account climatic conditions. But at the same time, the safety of their distance to ground objects must be taken into account:

    rail surfaces;

    contact wires;

    transport routes;

    wires of communication lines or other overhead lines;

    industrial and other facilities.

The sagging of the wire due to tension is called. She is being assessed different ways between the supports because the upper parts of them can be located at the same level or with excesses.

The sag relative to the highest point of support is always greater than that of the lower one.

The dimensions, length and design of each type of overhead power line depend on the type of current (alternating or direct) of the electrical energy transported through it and the magnitude of its voltage, which can be less than 0.4 kV or reach 1150 kV.

Arrangement of overhead line wires

Because the electricity passes only along a closed circuit, then the consumers are powered by at least two conductors. Using this principle, simple overhead power lines of single-phase alternating current with a voltage of 220 volts are created. More complex electrical circuits transmit energy using a three or four-wire circuit with a solidly insulated or grounded zero.

The diameter and metal of the wire are selected for the design load of each line. The most common materials are aluminum and steel. They can be made from a single monolithic core for low-voltage circuits or woven from multi-wire structures for high-voltage power lines.

The internal inter-wire space can be filled with a neutral lubricant, which increases resistance to heat, or without it.

Stranded structures made of aluminum wires that conduct current well are created with steel cores, which are designed to withstand mechanical tension loads and prevent breaks.


GOST classifies open wires for overhead power lines and defines their markings: M, A, AC, PSO, PS, ACCC, ASKP, ASU, ACO, ASUS. In this case, single-wire wires are designated by their diameter. For example, the abbreviation PSO-5 reads “steel wire. made of one core with a diameter of 5 mm.” Multi-core wires for power lines use a different marking, including designation with two numbers written through a fraction:

    the first is the total cross-sectional area of ​​aluminum conductors in mm sq;

    the second is the cross-sectional area of ​​the steel insert (mm sq).

In addition to open metal conductors, wires are increasingly used in modern overhead lines:

    self-supporting isolated;

    protected by extruded polymer, which protects against the occurrence of short circuits when phases are overwhelmed by wind or when foreign objects are thrown from the ground.

Overhead lines are gradually replacing old non-insulated structures. They are increasingly used in internal networks, made of copper or aluminum conductors covered with rubber with a protective layer of dielectric fiber materials or polyvinyl chloride compounds without additional external protection.


To exclude the occurrence of a corona discharge over a long length of the 330 kV overhead line and high voltage split into additional streams.


On VL-330, two wires are mounted horizontally; for a 500 kV line they are increased to three and placed at the vertices of an equilateral triangle. For 750 and 1150 kV overhead lines, splitting into 4, 5 or 8 streams, respectively, is used, located at the corners of their own equilateral polygons.

The formation of a “corona” leads not only to energy losses, but also distorts the shape of the sinusoidal oscillation. Therefore, they fight it with constructive methods.

Support arrangement

Typically, supports are created to secure wires in one electrical circuit. But on parallel sections of two lines, one common support can be used, which is intended for their joint installation. Such designs are called double-chain.

Materials for making supports can be:

1. profiled corners made of various types of steel;

2. construction wood logs impregnated with anti-rotting compounds;

3. reinforced concrete structures with reinforced rods.

Support structures made of wood are the cheapest, but even with good impregnation and proper maintenance, they last no more than 50–60 years.


In terms of technical design, overhead line supports above 1 kV differ from low-voltage ones in their complexity and height of wire attachment.


They are made in the form of elongated prisms or cones with a wide base at the bottom.

Any support design is designed for mechanical strength and stability, and has a sufficient design margin for existing loads. But it should be taken into account that during operation, damage to its various elements is possible as a result of corrosion, impacts, and non-compliance with installation technology.

This leads to a weakening of the rigidity of the single structure, deformations, and sometimes falls of the supports. Often such cases occur when people work on supports, dismantling or tensioning wires, creating variable axial forces.

For this reason, the admission of a team of installers to work at height from the support structure is carried out after checking them technical condition with an assessment of the quality of its buried part in the ground.

Construction of insulators

On overhead power lines to separate live parts electrical diagram between each other and from the mechanical elements of the support structure, products made of materials with high dielectric properties with ÷ Ohm∙m are used. They are called insulators and are made from:

    porcelain (ceramics);

    glass;

    polymer materials.

The designs and dimensions of insulators depend on:

    on the magnitude of dynamic and static loads applied to them;

    values ​​of the effective voltage of the electrical installation;

    operating conditions.

The complex shape of the surface, operating under the influence of various atmospheric phenomena, creates an increased path for a possible electrical discharge to flow.

Insulators installed on overhead lines for fastening wires are divided into two groups:

1. pin;

2. suspended.

Ceramic models

Porcelain or ceramic pin single insulators have found greater use on overhead lines up to 1 kV, although they work on lines up to 35 kV inclusive. But they are used under the condition of fastening wires of low cross-sections, which create small traction forces.

Garlands of suspended porcelain insulators are installed on lines from 35 kV.


The single porcelain pendant insulator kit includes a dielectric body and a cap made of malleable cast iron. Both of these parts are held together with a special steel rod. The total number of such elements in the garland is determined by:

    the magnitude of the overhead line voltage;

    support structures;

    features of equipment operation.

As the line voltage increases, the number of insulators in the string is added. For example, for a 35 kV overhead line, it is enough to install 2 or 3 of them, and for 110 kV, 6 ÷ 7 will be required.

Glass insulators

These designs have a number of advantages over porcelain ones:

    the absence of internal defects in the insulating material that affect the formation of leakage currents;

    increased strength to torsional forces;

    transparency of the design, allowing you to visually assess the condition and control the polarization angle of the light flux;

    absence of signs of aging;

    automation of production and smelting.

The disadvantages of glass insulators are:

    weak anti-vandal resistance;

    low resistance to impact loads;

    possibility of damage during transportation and installation from mechanical forces.

Polymer insulators

They have increased mechanical strength and a weight reduction of up to 90% compared to ceramic and glass counterparts. Additional benefits include:

    ease of installation;

    greater resistance to atmospheric pollution, which, however, does not exclude the need for periodic cleaning of their surface;

    hydrophobicity;

    good susceptibility to overvoltage;

    increased vandal resistance.

The durability of polymer materials also depends on operating conditions. In an air environment with increased pollution from industrial enterprises, polymers may exhibit “brittle fracture” phenomena, which consist in a gradual change in the properties of the internal structure under the influence of chemical reactions from pollutants and atmospheric moisture, occurring in combination with electrical processes.

When vandals shoot at polymer insulators with shot or bullets, the material usually does not completely collapse, like glass. Most often, a pellet or bullet flies through or gets stuck in the body of the skirt. But the dielectric properties are still underestimated and damaged elements in the garland require replacement.

Therefore, such equipment must be periodically inspected using visual inspection methods. And it is almost impossible to detect such damage without optical instruments.

Overhead line fittings

To attach insulators to an overhead line support, assemble them into garlands and install current-carrying wires to them, special fastening elements are produced, which are commonly called line fittings.


According to the tasks performed, fittings are classified into the following groups:

    coupling designed for connecting suspended elements different ways;

    tension, used for attaching tension clamps to wires and garlands of anchor supports;

    supporting, holding fastenings of wires, cables and screen mounting units;

    protective, designed to preserve the operability of overhead line equipment when exposed to atmospheric discharges and mechanical vibrations;

    connecting, consisting of oval connectors and thermite cartridges;

    contact;

    spiral;

    installation of pin insulators;

    installation of SIP wires.

Each of the listed groups has a wide range of parts and requires closer study. For example, only protective fittings include:

    protective horns;

    rings and screens;

    arresters;

    vibration dampers.

Protective horns create a spark gap, divert the emerging electric arc when an insulation flashover occurs, and in this way protect overhead line equipment.

Rings and screens divert the arc from the surface of the insulator and improve voltage distribution over the entire area of ​​the garland.

Arresters protect equipment from surge voltage waves caused by lightning strikes. They can be used on the basis of tubular structures made of vinyl plastic or fiber bakelite tubes with electrodes, or they can be manufactured as valve elements.

Vibration dampers work on cables and wires to prevent damage from fatigue stresses created by vibrations and oscillations.

Grounding devices for overhead lines

The need for re-grounding of overhead line supports is caused by the requirements for safe operation in the event of emergency conditions and lightning overvoltages. The resistance of the grounding device circuit should not exceed 30 Ohms.

For metal supports, all fasteners and reinforcement must be connected to the PEN conductor, and for reinforced concrete supports, the combined zero connects all the struts and reinforcement of the racks.

On supports made of wood, metal and reinforced concrete, pins and hooks when installing self-supporting insulated wires with a supporting insulated conductor are not grounded, except in cases where it is necessary to perform repeated grounding for surge protection.


Hooks and pins mounted on the support are connected to the ground loop by welding, using steel wire or rod no thinner than 6 mm in diameter with the obligatory presence of an anti-corrosion coating.

On reinforced concrete supports, metal reinforcement is used for grounding. All contact connections of grounding conductors are welded or clamped in a special bolted fastening.

The supports of overhead power lines with voltages of 330 kV and higher are not grounded due to the complexity of implementing technical solutions to ensure safe values ​​of touch and step voltages. The protective functions of grounding in this case are assigned to high-speed line protection.

How can you indicate the meaning of power lines? Is there an exact definition of the wires through which electricity is transmitted? There is a precise definition in the inter-industry rules for the technical operation of consumer electrical installations. So, a power line is, firstly, an electric line. Secondly, these are sections of wires that extend beyond the boundaries of substations and power stations. Thirdly, the main purpose of power lines is to transmit electric current over a distance.

According to the same MPTEP rules, power lines are divided into overhead and cable. But it should be noted that power lines also transmit high-frequency signals, which are used to transmit telemetric data, for dispatch control of various industries, for emergency automation signals and relay protection. According to statistics, 60,000 high-frequency channels today pass through power lines. Let's face it, the figure is significant.

Overhead power lines

Overhead power lines, usually designated by the letters “VL”, are devices that are located in the open air. That is, the wires themselves are laid through the air and fixed to special fittings (brackets, insulators). Moreover, their installation can be carried out on poles, bridges, and overpasses. It is not necessary to consider “overhead lines” those lines that are laid only along high-voltage poles.

What is included in overhead power lines:

  • The main thing is the wires.
  • Crossbars, with the help of which conditions are created to prevent the wires from coming into contact with other elements of the supports.
  • Insulators.
  • The supports themselves.
  • Ground loop.
  • Lightning rods.
  • Arresters.

That is, a power line is not just wires and supports; as you can see, it is a fairly impressive list of various elements, each of which carries its own specific loads. You can also add fiber optic cables and auxiliary equipment to them. Of course, if power line supports are carried out high frequency channels communications.

The construction of a power transmission line, as well as its design, plus the design features of the supports are determined by the rules for the design of electrical installations, that is, the PUE, as well as various building rules and regulations, that is, SNiP. In general, the construction of power lines is not an easy and very responsible task. Therefore, their construction is carried out by specialized organizations and companies with highly qualified specialists on staff.

Classification of overhead power lines

The overhead high-voltage power lines themselves are divided into several classes.

By type of current:

  • Variable
  • Permanent.

Basically, overhead overhead lines serve to transmit alternating current. It's rare to see the second option. It is usually used to power a contact or communication network to provide communications to several power systems; there are other types.

By voltage, overhead power lines are divided according to the nominal value of this indicator. For information, we list them:

  • for alternating current: 0.4; 6; 10; 35; 110; 150; 220; 330; 400; 500; 750; 1150 kilovolts (kV);
  • For constant voltage, only one type of voltage is used - 400 kV.

In this case, power lines with voltages up to 1.0 kV are considered low class, from 1.0 to 35 kV - medium, from 110 to 220 kV - high, from 330 to 500 kV - ultra-high, above 750 kV - ultra-high. It should be noted that all these groups differ from each other only in the requirements for design conditions and design features. In all other respects, these are ordinary high-voltage power lines.


The voltage of the power lines corresponds to their purpose.

  • High-voltage lines with voltages over 500 kV are considered ultra-long-distance; they are intended to connect individual power systems.
  • High-voltage lines with voltages of 220 and 330 kV are considered main lines. Their main purpose is to connect powerful power plants, individual power systems, as well as power plants within these systems.
  • Overhead power lines with a voltage of 35-150 kV are installed between consumers (large enterprises or settlements) and distribution points.
  • Overhead lines up to 20 kV are used as power lines that directly supply electric current to the consumer.

Classification of power lines by neutral

  • Three-phase networks in which the neutral is not grounded. Typically, this scheme is used in networks with a voltage of 3-35 kV, where low currents flow.
  • Three-phase networks in which the neutral is grounded through inductance. This is the so-called resonant grounded type. Such overhead lines use a voltage of 3-35 kV, in which large currents flow.
  • Three-phase networks in which the neutral bus is completely grounded (effectively grounded). This mode of neutral operation is used in overhead lines with medium and ultra-high voltage. Please note that in such networks it is necessary to use transformers, and not autotransformers, in which the neutral is tightly grounded.
  • And, of course, networks with solidly grounded neutral. In this mode, overhead lines with voltages below 1.0 kV and above 220 kV operate.

Unfortunately, there is also a division of power lines where the operational condition of all elements of the power line is taken into account. This is a power line in good condition, where the wires, supports and other components are in good condition. The main emphasis is on the quality of wires and cables; they should not be broken. Emergency condition, where the quality of wires and cables leaves much to be desired. And the installation condition when repairs or replacement of wires, insulators, brackets and other components of power lines are carried out.


Elements of overhead power lines

There are always conversations between specialists in which special terms regarding power lines are used. For the uninitiated in the subtleties of slang, it is quite difficult to understand this conversation. Therefore, we offer a definition of these terms.

  • The route is the axis of the power transmission line, which runs along the surface of the earth.
  • PC – pickets. Essentially, these are sections of the power line route. Their length depends on the terrain and the rated voltage of the route. Zero picket is the beginning of the route.
  • The construction of a support is indicated by a center sign. This is the center of the support installation.
  • Picketing is essentially easy installation pickets.
  • The span is the distance between the supports, or more precisely, between their centers.
  • The sag is the delta between the lowest point of the wire sag and the strictly tensioned line between the supports.
  • The wire size is again the distance between the lowest point of the sag and the highest point of the engineering structures running under the wires.
  • Loop or train. This is the part of the wire that connects the wires of adjacent spans on the anchor support.

Cable power lines

So, let's move on to considering such a concept as cable power lines. Let's start with the fact that these are not bare wires that are used in overhead power lines, these are cables enclosed in insulation. Typically, cable power lines are several lines installed next to each other in a parallel direction. The cable length is not enough for this, so couplings are installed between sections. By the way, you can often find oil-filled cable power lines, so such networks are often equipped with special low-fill equipment and an alarm system that responds to oil pressure inside the cable.

If we talk about the classification of cable lines, they are identical to the classification of overhead lines. Distinctive features there are, but there are not many of them. Basically, these two categories differ from each other in the method of laying, as well as design features. For example, according to the type of installation, cable power lines are divided into underground, underwater and by structure.


The first two positions are clear, but what applies to the “structures” position?

  • Cable tunnels. These are special closed corridors in which cables are laid along installed support structures. You can walk freely in such tunnels while installing, repairing and maintaining power lines.
  • Cable channels. Most often they are buried or partially buried channels. They can be laid in the ground, under the floor base, or under ceilings. These are small canals in which it is impossible to walk. To check or install the cable, you will have to dismantle the ceiling.
  • Cable mine. This is a vertical corridor with a rectangular cross-section. The shaft can be walk-through, that is, with the ability for a person to fit into it, for which it is equipped with a ladder. Or impassable. In this case, you can get to the cable line only by removing one of the walls of the structure.
  • Cable floor. This is a technical space, usually 1.8 m high, equipped with floor slabs at the bottom and top.
  • Cable power lines can also be laid in the gap between the floor slabs and the floor of the room.
  • A cable block is a complex structure consisting of laying pipes and several wells.
  • A chamber is an underground structure covered on top with reinforced concrete or a slab. In such a chamber, sections of cable power lines are connected with couplings.
  • An overpass is a horizontal or inclined open structure. It can be above-ground or above-ground, walk-through or impassable.
  • A gallery is practically the same as an overpass, only closed.

And the last classification in cable power lines is the type of insulation. In principle, there are two main types: solid insulation and liquid. The first includes insulating braids made of polymers (polyvinyl chloride, cross-linked polyethylene, ethylene-propylene rubber), as well as other types, for example, oiled paper, rubber-paper braid. Liquid insulators include petroleum oil. There are other types of insulation, for example, special gases or other types of solid materials. But they are used very rarely today.

Conclusion on the topic

The variety of power lines comes down to the classification of two main types: overhead and cable. Both options are used everywhere today, so there is no need to separate one from the other and give preference to one over the other. Of course, the construction of overhead lines involves large capital investments, because laying a route involves installing mostly metal supports, which have a rather complex design. In this case, it is taken into account which network will be laid under what voltage.