Main overhead power lines. Overhead and cable lines

How can you indicate the meaning of power lines? Is there an exact definition of the wires through which electricity is transmitted? The inter-industry rules for the technical operation of consumer electrical installations have a precise definition. 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 rules of MPTEP, 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, this is quite an impressive list 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 high-frequency communication channels are carried along power line supports.

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 regulations and norms, 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 populated areas) 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 a 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 relating to 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. Usually cable power lines represent 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. There are distinctive features, but not many of them. Basically, these two categories differ from each other in the method of installation, 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 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.

Complex technical power lines (PTLs) are used to deliver electricity over long distances. On a national scale, they are strategically important objects 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 laying of which require mandatory compliance with 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 to which the wires are secured using special fittings (insulators and brackets). Most often these are SK racks.

The composition of overhead power lines includes:

supports for various voltages;
bare wires made of aluminum or copper;
traverses providing required distance, excluding the possibility of contact of wires with support elements;
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.

The following are used as high-voltage poles:

metal structures that are effectively used in any climatic zones and with different loads. They are characterized by sufficient strength, reliability and durability. They are a metal frame, 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 supports, which are the most cost-effective to produce and have excellent dielectric characteristics. The low weight of wooden structures allows them to be quickly delivered to the installation site and easily installed. The disadvantage of these power line supports is their low mechanical strength, which allows them to be installed only with a certain load, and their susceptibility to processes of biological destruction (rotting of the material).

The use of one design or another is determined by the voltage of the electrical network. It will be useful to have the skill of determining the voltage of power lines in appearance.

Overhead lines are classified:

by current - direct or alternating;
according to 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 installation of overhead lines is impossible - in cities and towns with dense buildings, in the territories of industrial enterprises.

Cable power lines are classified:

in terms of voltage - just like overhead lines;
by type of insulation - liquid and solid. The first type is petroleum oil, and the second is a cable braid consisting of polymers, rubber and oiled paper.

Their distinctive features are the laying method:

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 power lines, the “by construction” option involves the creation of:

cable tunnels, in which power cables are laid on special support structures that allow installation work and line maintenance;
cable channels, which are buried structures under the floor of buildings in which cable lines are laid in the ground;
cable shafts - vertical corridors with a rectangular cross-section that 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 trestles - for horizontal or inclined laying of cables;
chambers used for laying couplings of power transmission line sections;
galleries - the same overpasses, only closed.

Conclusion

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

Overhead power lines.

When constructing overhead power lines, the volume of excavation work is insignificant. In addition, they are easy to operate and repair. The cost of constructing an overhead line is approximately 25-30% less than the cost of a cable line of the same length. Overhead lines are divided into three classes:

class I - lines with a rated operating voltage of 35 kV for consumers of the 1st and 2nd categories and above 35 kV, regardless of consumer categories;

class II - lines with rated operating voltage from 1 to 20 kV for consumers of the 1st and 2nd categories, as well as 35 kV for consumers of the 3rd category;

class III - lines with a rated operating voltage of 1 kV and below. A characteristic feature of overhead lines with voltages up to 1000 V is the use of supports for simultaneously attaching wires of a radio network, outdoor lighting, remote control, and alarm systems to them.

The main elements of an overhead line are supports, insulators and wires.

For 1 kV lines, two types of supports are used: wooden with reinforced concrete attachments and reinforced concrete.
For wooden supports, logs impregnated with an antiseptic are used from grade II forest - pine, spruce, larch, fir. You can avoid soaking the logs when making supports from winter-cut hardwood trees. The diameter of the logs at the top should be at least 15 cm for single posts and at least 14 cm for double and A-frame supports. It is allowed to take the diameter of the logs in the upper cut at least 12 cm on the branches going to the entrances to buildings and structures. Depending on the purpose and design, there are intermediate, corner, branch, cross and end supports.

Intermediate supports on the line are the most numerous, since they serve to support the wires at a height and are not designed for the forces that are created along the line in the event of a wire break. To absorb this load, anchor intermediate supports are installed, placing their “legs” along the axis of the line. To absorb forces perpendicular to the line, intermediate anchor supports are installed, placing the “legs” of the support across the line.

Anchor supports have a more complex design and increased strength. They are also divided into intermediate, corner, branch and end, which increase the overall strength and stability of the line.

The distance between two anchor supports is called the anchor span, and the distance between intermediate supports is called the support spacing.
In places where the direction of the overhead line route changes, corner supports are installed.

To supply power to consumers located at some distance from the main overhead line, branch supports are used on which the wires connected to the overhead line and to the input of the electricity consumer are fixed.
End supports are installed at the beginning and end of the overhead line specifically to absorb unilateral axial forces.
The designs of various supports are shown in Fig. 10.
When designing an overhead line, the number and type of supports are determined depending on the configuration of the route, the cross-section of the wires, the climatic conditions of the area, the degree of population in the area, the topography of the route and other conditions.

For overhead line structures with voltages above 1 kV, predominantly reinforced concrete and wooden antiseptic supports on reinforced concrete attachments are used. The designs of these supports are unified.
Metal supports are used mainly as anchor supports on overhead lines with voltages above 1 kV.
On overhead line supports, the location of the wires can be any, only the neutral wire in lines up to 1 kV is placed below the phase wires. When hanging external lighting wires on supports, they are located below the neutral wire.
Overhead line wires with voltage up to 1 kV should be suspended at a height of at least 6 m from the ground, taking into account the sag.

The vertical distance from the ground to the point of greatest sag of the wire is called the dimension of the overhead line wire above the ground.
The wires of an overhead line can approach other lines along the route, intersect with them and pass at a distance from objects.
The approach gauge of overhead line wires is the permissible shortest distance from the line wires to objects (buildings, structures) located parallel to the overhead line route, and the intersection gauge is the shortest vertical distance from an object located under the line (intersected) to the overhead line wire.

Rice. 10. Designs of wooden supports for overhead power lines:
a - for voltages below 1000 V, b - for voltages of 6 and 10 kV; 1 - intermediate, 2 - corner with brace, 3 - corner with guy, 4 - anchor

Insulators.

For fastening overhead line wires with voltages above 1000 V, ShS, ShD, USHL, ShF6-A and ShF10-A insulators and suspension insulators are used.

All insulators, except for suspended ones, are tightly screwed onto hooks and pins, onto which tow soaked in lead or drying oil is first wound, or special plastic caps are put on.
For overhead lines with voltages up to 1000 V, KN-16 hooks are used, and above 1000 V, KV-22 hooks are used, made of round steel with a diameter of 16 and 22 mm 2, respectively. On the traverses of the supports of the same overhead lines with voltages up to 1000 V, when fastening the wires, ShT-D pins are used - for wooden traverses and ShT-S - for steel ones.

When the overhead line voltage is more than 1000 V, SHU-22 and SHU-24 pins are mounted on the support cross-arms.

According to the mechanical strength conditions for overhead lines with voltages up to 1000 V, single-wire and multi-wire wires are used with a cross-section of at least: aluminum - 16, steel-aluminum and bimetal - 10, multi-wire steel - 25, single-wire steel - 13 mm (diameter 4 mm).

The connection of wires to each other (Fig. 62) is performed by twisting, in a connecting clamp or in die clamps.

Fastening of overhead line wires and insulators is carried out using binding wire using one of the methods shown in Fig. 13.
Steel wires are tied with soft galvanized steel wire with a diameter of 1.5 - 2 mm, and aluminum and steel-aluminum wires with aluminum wire with a diameter of 2.5 - 3.5 mm (stranded wires can be used).

Aluminum and steel-aluminum wires at fastening points are pre-wrapped with aluminum tape to protect them from damage.

On intermediate supports, the wire is mounted mainly on the head of the insulator, and on corner supports - on the neck, placing it on the outside of the angle formed by the line wires. The wires on the insulator head are secured (Fig. 13, a) with two pieces of binding wire. The wire is twisted around the insulator head so that its ends of different lengths are on both sides of the insulator neck, and then two short ends are wrapped 4-5 times around the wire, and two long ends are transferred through the insulator head and also wrapped around the wire several times. When attaching the wire to the neck of the insulator (Fig. 13, b), the tying wire loops around the wire and the neck of the insulator, then one end of the tying wire is wound around the wire in one direction (top to bottom), and the other end in the opposite direction (bottom to top).

When assembling the supports, all wooden parts are tightly fitted to each other. The gap in the places of notches and joints should not exceed 4 mm.
Racks and attachments to overhead line supports are made in such a way that the wood at the junction has no knots or cracks, and the joint is completely tight, without gaps. The working surfaces of the cuts must be a continuous cut (without chiseling the wood).
Holes are drilled in the logs. It is prohibited to burn holes with heated rods.

Bandages for connecting attachments to the support are made of soft steel wire with a diameter of 4 - 5 mm. All turns of the bandage should be evenly tensioned and fit tightly to each other. If one turn breaks, the entire bandage should be replaced with a new one.

When connecting wires and cables of overhead lines with voltages above 1000 V in each span, no more than one connection is allowed for each wire or cable.

When using welding to connect wires, there should be no burnout of the outer wires or disruption of welding when the connected wires are bent.

Metal supports, protruding metal parts of reinforced concrete supports and all metal parts of wooden and reinforced concrete supports of overhead lines are protected with anti-corrosion coatings, i.e. paint. Places of assembly welding of metal supports are primed and painted to a width of 50 - 100 mm along weld immediately after welding work. Parts of structures that are subject to concreting are covered with cement laitance.

Rice. 14. Methods of attaching viscous wires to insulators:
a - head knitting, b - side knitting

Extraordinary inspections of overhead lines are carried out after accidents, hurricanes, during a fire near the line, during ice drifts, sleet, frost below -40 ° C, etc.

If a break in several wires is detected on a wire with a total cross-section of up to 17% of the wire cross-section, the break point is covered with a repair coupling or bandage. A repair coupling is installed on a steel-aluminum wire when up to 34% of the aluminum wires are broken. If more wires are broken, the wire must be cut and connected using a connecting clamp.

Insulators can suffer from punctures, glaze burns, melting of metal parts and even destruction of porcelain. This occurs in the event of breakdown of insulators by an electric arc, as well as in the deterioration of their electrical characteristics as a result of aging during operation. Often breakdowns of insulators occur due to severe contamination of their surface and at voltages exceeding the operating voltage. Data on defects discovered during inspections of insulators are entered into the defect log, and on the basis of these data plans for repair work of overhead lines are drawn up.

Cable power lines.

A cable line is a line for transmitting electrical energy or individual impulses, consisting of one or more parallel cables with connecting and end couplings (terminals) and fasteners.

Security zones are installed above underground cable lines, the size of which depends on the voltage of this line. Thus, for cable lines with voltages up to 1000 V, the security zone has an area of 1 m on each side of the outermost cables. In cities, under sidewalks, the line should run at a distance of 0.6 m from buildings and structures and 1 m from the roadway.
For cable lines with voltages above 1000 V, the security zone has a size of 1 m on each side of the outermost cables.

Submarine cable lines with voltages up to 1000 V and higher have a security zone defined by parallel straight lines at a distance of 100 m from the outermost cables.

The cable route is selected taking into account the lowest consumption and ensuring safety from mechanical damage, corrosion, vibration, overheating and the possibility of damage to adjacent cables if a short circuit occurs on one of them.

When laying cables, it is necessary to observe the maximum permissible bending radii, exceeding which leads to a violation of the integrity of the core insulation.

Laying cables in the ground under buildings, as well as through basements and warehouses is prohibited.

The distance between the cable and the foundations of buildings must be at least 0.6 m.

When laying a cable in a planted area, the distance between the cable and tree trunks must be at least 2 m, and in a green area with shrub plantings 0.75 m is allowed. In the case of laying the cable parallel to the heat pipe, the clear distance from the cable to the wall of the heat pipe channel must be at least 2 m, to the axis of the railway track - at least 3.25 m, and for an electrified road - at least 10, 75 m.

When laying the cable parallel to the tram tracks, the distance between the cable and the axis of the tram track must be at least 2.75 m.
At the intersection of railways and highways, as well as tram tracks, cables are laid in tunnels, blocks or pipes across the entire width of the exclusion zone at a depth of at least 1 m from the roadbed and at least 0.5 m from the bottom of drainage ditches, and in the absence of a zone Exclusion cables are laid directly at the intersection or at a distance of 2 m on both sides of the road surface.

The cables are laid in a “snake” pattern with a margin equal to 1 - 3% of its length in order to eliminate the possibility of dangerous mechanical stresses arising due to soil displacements and temperature deformations. Laying the end of the cable in the form of rings is prohibited.

For connections or cable terminations, the ends are cut, i.e., stepwise removal of protective and insulating materials. The dimensions of the groove are determined by the design of the coupling that will be used to connect the cable, the voltage of the cable and the cross-section of its conductors.
The finished cutting of the end of a three-core paper-insulated cable is shown in Fig. 15.

The connection of cable ends with voltages up to 1000 V is carried out in cast iron (Fig. 16) or epoxy couplings, and with voltages of 6 and 10 kV - in epoxy (Fig. 17) or lead couplings.

Rice. 16. Cast iron coupling:
1 - upper coupling, 2 - resin tape winding, 3 - porcelain spacer, 4 - cover, 5 - tightening bolt, 6 - ground wire, 7 - lower coupling half, 8 - connecting sleeve

The connection of current-carrying cable cores with voltages up to 1000 V is performed by crimping in a sleeve (Fig. 18). To do this, select a sleeve, punch and matrix according to the cross-section of the connected conductive cores, as well as a crimping mechanism (press tongs, hydraulic press, etc.), clean the inner surface of the sleeve to a metallic shine with a steel brush (Fig. 18, a), and the connected cores - with a brush - on card tapes (Fig. 18, b). Round the multi-wire sector cable cores with universal pliers. The cores are inserted into the sleeve (Fig. 18, c) so that their ends touch and are located in the middle of the sleeve.

Rice. 17. Epoxy coupling:
1 - wire bandage, 2 - coupling body, 3 - bandage made of solid threads, 4 - spacer, 5 - core winding, 6 - ground wire, 7 - core connection, 8 - sealing winding

Rice. 18. Connection of copper cable cores by crimping:

a - stripping inner surface sleeves with a steel wire brush, b - stripping the core with a brush made of carded tape, c - installation of the sleeve on the connected cores, d - crimping the sleeve in a press, e - finished connection; 1 - copper sleeve, 2 - brush, 3 - brush, 4 - core, 5 - press

The sleeve is installed flush in the matrix bed (Fig. 18, d), then the sleeve is pressed with two indentations, one for each core (Fig. 18, e). The indentation is carried out in such a way that the punch washer at the end of the process rests against the end (shoulders) of the matrix. The remaining cable thickness (mm) is checked using a special caliper or caliper (value H in Fig. 19):

4.5 ± 0.2 - with a cross-section of the connected conductors 16 - 50 mm 2

8.2 ± 0.2 - with a cross-section of the connected cores of 70 and 95 mm 2

12.5 ± 0.2 - with a cross-section of connected conductors of 120 and 150 mm 2

14.4 ± 0.2 - with a cross-section of connected cores of 185 and 240 mm 2

The quality of the pressed cable contacts is checked by external inspection. In this case, pay attention to the indentation holes, which should be located coaxially and symmetrically relative to the middle of the sleeve or the tubular part of the tip. There should be no tears or cracks in the places where the punch is pressed.

To ensure appropriate quality of cable crimping, the following work conditions must be met:
use lugs and sleeves whose cross-section corresponds to the design of the cable cores to be terminated or connected;
use dies and punches corresponding to the standard sizes of tips or sleeves used for crimping;
do not change the cross-section of the cable core to facilitate insertion of the core into the tip or sleeve by removing one of the wires;

After connecting the cable cores, the metal belt is removed between the first and second annular cuts of the sheath and a bandage of 5 - 6 turns of solid thread is applied to the edge of the belt insulation underneath it, after which spacer plates are installed between the cores so that the cable cores are held at a certain distance from each other friend and from the coupling body.
Lay the ends of the cable in the coupling, having previously wound 5 - 7 layers of resin tape around the cable at the points of entry and exit from the coupling, and then fasten both halves of the coupling with bolts. The grounding conductor, soldered to the armor and sheath of the cable, is inserted under the mounting bolts and thus firmly secured to the coupling.

The operations of cutting the ends of cables with voltages of 6 and 10 kV in a lead coupling are not much different from similar operations of connecting them in a cast iron coupling.

Cable lines can provide reliable and durable operation, but only if the installation technology and all the requirements of the technical operation rules are observed.

The quality and reliability of mounted cable couplings and terminations can be increased if during installation a set of necessary tools and devices is used for cutting the cable and connecting the cores, heating the cable mass, etc. The qualifications of the personnel are of great importance for improving the quality of the work performed.

For cable connections, sets of paper rolls, rolls and bobbins of cotton yarn are used, but they are not allowed to have folds, torn or wrinkled places, or be dirty.

Such kits are supplied in cans depending on the size of the couplings by numbers. Before use, the jar at the installation site must be opened and heated to a temperature of 70 - 80 °C. Heated rollers and rolls are checked for the absence of moisture by immersing paper strips in paraffin heated to a temperature of 150 °C. In this case, no cracking or foam should be observed. If moisture is detected, the set of rollers and rolls is rejected.
The reliability of cable lines during operation is supported by a set of measures, including monitoring cable heating, inspections, repairs, and preventive tests.

To ensure long-term operation of the cable line, it is necessary to monitor the temperature of the cable cores, since overheating of the insulation causes accelerated aging and a sharp reduction in the service life of the cable. The maximum permissible temperature of the cable conductors is determined by the cable design. Thus, for cables with a voltage of 10 kV with paper insulation and viscous non-drip impregnation, a temperature of no more than 60 ° C is allowed; for cables with voltage 0.66 - 6 kV with rubber insulation and viscous non-draining impregnation - 65 ° C; for cables with voltage up to 6 kV with plastic (polyethylene, self-extinguishing polyethylene and polyvinyl chloride plastic) insulation - 70 ° C; for cables with a voltage of 6 kV with paper insulation and depleted impregnation - 75 ° C; for cables with a voltage of 6 kV with plastic (vulcanized or self-extinguishing polyethylene or paper insulation and viscous or depleted impregnation - 80 ° C.

Long-term permissible current loads on cables with insulation made of impregnated paper, rubber and plastic are selected according to current GOSTs. Cable lines with a voltage of 6 - 10 kV, carrying less than rated loads, can be briefly overloaded by an amount that depends on the type of installation. So, for example, a cable laid in the ground and having a preload factor of 0.6 can be overloaded by 35% within half an hour, by 30% - 1 hour and by 15% - 3 hours, and with a preload factor of 0.8 - by 20% for half an hour, by 15% - 1 hour and by 10% - 3 hours.

For cable lines that have been in operation for more than 15 years, overload is reduced by 10%.

The reliability of a cable line largely depends on proper organization operational supervision of the condition of lines and their routes through periodic inspections. Routine inspections make it possible to identify various violations on cable routes (excavation work, storage of goods, planting trees, etc.), as well as cracks and chips in the insulators of the end couplings, loosening of their fastenings, the presence of bird nests, etc.

A great danger to the integrity of cables is posed by earth excavations carried out on or near the routes. The organization operating underground cables must provide an observer during excavations in order to avoid damage to the cable.

According to the degree of danger of cable damage, excavation sites are divided into two zones:

Zone I - a piece of land located on the cable route or at a distance of up to 1 m from the outermost cable with voltage above 1000 V;

Zone II - a piece of land located from the outermost cable at a distance of over 1 m.

When working in zone I, it is prohibited:

use of excavators and other earth-moving machines;
use of impact mechanisms (wedges, balls, etc.) at a distance closer than 5 m;

the use of mechanisms for excavating soil (jackhammers, electric hammers, etc.) to a depth above 0.4 m at a normal cable depth (0.7 - 1 m); carrying out excavation work in winter without preliminary heating of the soil;

performance of work without supervision by a representative of the organization operating the cable line.

In order to promptly identify defects in cable insulation, connecting and termination joints and prevent sudden cable failure or destruction by short circuit currents, preventive tests of cable lines with increased DC voltage are carried out.

Content:

One of the pillars of modern civilization is electricity supply. The key role in it is played by power transmission lines. Regardless of the distance of generating facilities from end consumers, extended conductors are needed to connect them. Next, we will talk in more detail about what these conductors, called power lines, are.

What types of overhead power lines are there?

The wires attached to the supports are overhead power lines. Today, two methods of transmitting electricity over long distances have been mastered. They are based on alternating and direct voltages. Transmission of electricity at constant voltage is still less common compared to alternating voltage. This is explained by the fact that direct current itself is not generated, but is obtained from alternating current.

For this reason, additional electric cars. And they began to appear relatively recently, since they are based on powerful semiconductor devices. Such semiconductors appeared only 20–30 years ago, that is, approximately in the 90s of the twentieth century. Consequently, before this time, a large number of AC power lines had already been built. The differences between power lines are shown below in the schematic diagram.

The greatest losses are caused by the active resistance of the wire material. It does not matter what current is direct or alternating. To overcome them, the voltage at the beginning of the transmission is increased as much as possible. The one million volt level has already been surpassed. Generator G supplies AC power lines through transformer T1. And at the end of the transmission the voltage decreases. The power line supplies load H through transformer T2. A transformer is the simplest and most reliable voltage conversion tool.

A reader with little knowledge of power supply will most likely have a question about the meaning of direct current power transmission. And the reasons are purely economic - direct current transmission of electricity in the power lines itself provides great savings:

The generator produces three-phase voltage. Therefore, three wires are always needed for AC power supply. And on direct current, all the power of the three phases can be transmitted through two wires. And when using the ground as a conductor, one wire at a time. Consequently, the savings on materials alone are threefold in favor of DC power lines.
AC electrical networks, when combined into one common system, must have the same phasing (synchronization). This means that the instantaneous voltage value in the connected electrical networks must be the same. Otherwise, there will be a potential difference between the connected phases of the electrical networks. As a consequence of a connection without phasing, an accident comparable to a short circuit occurs. This is not typical for DC power grids at all. For them, only the effective voltage at the time of connection matters.
For electrical circuits, operating on alternating current, is characterized by impedance, which is related to inductance and capacitance. AC power lines also have impedance. The longer the line, the greater the impedance and losses associated with it. For DC electrical circuits, the concept of impedance does not exist, as well as losses associated with changing the direction of movement of the electric current.
As already mentioned in paragraph 2, for stability in the power system, generators need to be synchronized. But the larger the system operating on alternating current, and, accordingly, the number of electric generators, the more difficult it is to synchronize them. And for DC power systems, any number of generators will work normally.

Due to the fact that today there are no powerful enough semiconductor or other systems to convert the voltage efficiently and reliably, most power lines still operate on alternating current. For this reason, we will further focus only on them.

Another point in the classification of power lines is their purpose. In this regard, the lines are divided into

ultra-long,
main lines,
distribution

Their design is fundamentally different due to different voltage values. Thus, in ultra-long-distance power lines, which are system-forming, the highest voltages that exist at the current stage of technology development are used. The value of 500 kV is the minimum for them. This is explained by the significant distance from each other of powerful power plants, each of which is the basis of a separate energy system.

It has its own distribution network, the task of which is to provide large groups of end consumers. They are connected to distribution substations with voltage of 220 or 330 kV on the high side. These substations are the end consumers for main power lines. Since the energy flow is already very close to the settlements, the tension must be reduced.

Electricity distribution is carried out by power lines with voltages of 20 and 35 kV for the residential sector, as well as 110 and 150 kV for powerful industrial facilities. The next point in classifying power lines is by voltage class. By this feature, power lines can be identified visually. Each voltage class has corresponding insulators. Their design is a kind of identification of the power line. Insulators are made by increasing the number of ceramic cups according to the increase in voltage. And its classes in kilovolts (including voltages between phases adopted for the CIS countries) are as follows:

1 (380 V);
35 (6, 10, 20);
110…220;
330…750 (500);
750 (1150).

In addition to insulators, distinctive features are wires. As the voltage increases, the effect of electrical corona discharge becomes more pronounced. This phenomenon wastes energy and reduces the efficiency of the power supply. Therefore, to attenuate the corona discharge with increasing voltage, starting from 220 kV, parallel wires are used - one for every approximately 100 kV. Some of the overhead lines (OHL) of different voltage classes are shown below in the images:

Power line supports and other visible elements

To ensure that the wire is securely held, supports are used. In the simplest case, these are wooden poles. But this design is applicable only to lines up to 35 kV. And with the increase in the value of wood, reinforced concrete supports are increasingly used in this stress class. As the voltage increases, the wires must be raised higher and the distance between phases greater. In comparison, the supports look like this:

In general, supports are a separate topic, which is quite extensive. For this reason, we will not delve into the details of the topic of power transmission line supports here. But in order to briefly and succinctly show the reader its basis, we will show the image:

To conclude the information about overhead power lines, let us mention those additional elements, which are found on supports and are clearly visible. This

lightning protection systems,
as well as reactors.

In addition to the listed elements, several more are used in power transmission lines. But let’s leave them outside the scope of the article and move on to cables.

Cable lines

Air is an insulator. Overhead lines are based on this property. But there are other more effective insulating materials. Their use makes it possible to significantly reduce the distances between phase conductors. But the price of such a cable is so high that there can be no question of using it instead of overhead power lines. For this reason, cables are laid where there are difficulties with overhead lines.

Electrical networks are designed for the transmission and distribution of electricity. They consist of a set of substations and lines of various voltages. At power plants, step-up transformer substations are built along power lines high voltage transmit electricity over long distances. Step-down transformer substations are built at places of consumption.

The basis of the electrical network is usually underground or overhead high voltage power lines. Lines running from the transformer substation to the input distribution devices and from them to power distribution points and to group panels is called the supply network. The power supply network, as a rule, consists of underground low-voltage cable lines.

According to the principle of construction, networks are divided into open and closed. An open network includes lines going to electrical receivers or their groups and receiving power from one side. An open network has some disadvantages, namely that in the event of an accident at any point in the network, the power to all consumers beyond the emergency section is interrupted.

A closed network can have one, two or more power sources. Despite a number of advantages, closed networks have not yet become widespread. Depending on the location where the network is laid, there are external and internal.
Each voltage has its own specific wiring method. This is because the higher the voltage, the more difficult it is to insulate the wires. For example, in apartments where the voltage is 220 V, wiring is done with rubber or plastic insulated wires. These wires are simple in design and cheap.
An underground cable designed for several kilovolts and laid underground between transformers is incomparably more complex. In addition to increased insulation requirements, it must also have increased mechanical strength and corrosion resistance.

For direct power supply to consumers, the following are used:

overhead or cable power lines with a voltage of 6 (10) kV for powering substations and high-voltage consumers;
cable power lines with a voltage of 380/220 V to power directly low-voltage electrical receivers.

To transmit voltages of tens and hundreds of kilovolts over distances, overhead power lines are created. The wires are raised high above the ground and air is used as insulation. The distances between the wires are calculated depending on the voltage that is planned to be transmitted. The dimensions increase and the designs become more complex as the operating voltage increases.

An overhead power line is a device for transmitting or distributing electricity through wires located in the open air and attached using traverses (brackets), insulators and fittings to supports or engineering structures. In accordance with the “Rules for Electrical Installations”, overhead lines are divided into two by voltage groups: voltage up to 1000 V and voltage over 1000 V. For each group of lines, the technical requirements for their design are established.

Power lines up to 1000 V

Overhead power lines 10 (6) kV are most widely used in rural areas and small towns. This is due to their lower cost compared to cable lines, lower building density, etc.
Various wires and cables are used to conduct overhead lines and networks. The main requirement for the material of overhead power line wires is low electrical resistance. In addition, the material used for the manufacture of wires must have sufficient mechanical strength and be resistant to moisture and airborne chemicals.

Currently, wires made of aluminum and steel are most often used, which saves scarce non-ferrous metals (copper) and reduces the cost of wires. Copper wires are used on special lines. Aluminum has low mechanical strength, which leads to an increase in sag and, accordingly, to an increase in the height of the supports or a decrease in the span length. When transmitting small amounts of electricity over short distances, steel wires are used.

To insulate wires and attach them to power line supports, linear insulators are used, which, along with electrical strength, must also have sufficient mechanical strength. Depending on the method of fastening to the support, there are pin insulators (they are attached to hooks or pins) and hanging insulators (they are assembled in a garland and attached to the support with special fittings).

Pin insulators are used on power lines with voltages up to 35 kV. They are marked with letters indicating the design and purpose of the insulator, and numbers indicating the operating voltage. On 400 V overhead lines, pin insulators TF, ShS, ShF are used. The letters in the symbols of insulators mean the following:

T - telegraph;
F - porcelain;
C - glass;
ShS - pin glass;
SHF - pin porcelain.

Pin insulators are used for hanging relatively light wires, and depending on the route conditions, they are used Various types fastening wires. The wire on intermediate supports is usually fixed on the head of the pin insulators, and on corner and anchor supports - on the neck of the insulators. The wire is placed on the corner supports with outside insulator in relation to the angle of rotation of the line.
Suspended insulators are used on overhead lines of 35 kV and above. They consist of a porcelain or glass plate (an insulating part), a ductile iron cap and a rod. The design of the cap socket and the rod head ensures a spherical hinge connection of the insulators when assembling garlands. The garlands are collected and suspended from supports and thereby provide the necessary insulation of the wires. The number of insulators in a garland depends on the line voltage and the type of insulators.

The material for tying an aluminum wire to an insulator is aluminum wire, and for steel wires it is soft steel. When knitting wires, a single fastening is usually performed, while double fastening is used in populated areas and under increased loads. Before knitting, prepare wire of the required length (at least 300 mm).

Head knitting is performed with two knitting wires of different lengths. These wires are secured to the neck of the insulator, twisting together. The ends of the shorter wire are wrapped around the wire and pulled tightly four to five times around the wire. The ends of another wire, longer ones, are placed on the insulator head crosswise through the wire four to five times.

To perform side knitting, take one wire, place it on the neck of the insulator and wrap it around the neck and the wire so that one end passes over the wire and bends from top to bottom, and the other from bottom to top. Both ends of the wire are brought forward and again wrapped around the neck of the insulator with the wire, changing places relative to the wire.

After this, the wire is tightly pulled to the neck of the insulator and the ends of the binding wire are wrapped around the wire on opposite sides of the insulator six to eight times. To avoid damage to aluminum wires, the binding area is sometimes wrapped with aluminum tape. It is not allowed to bend the wire on the insulator with strong tension on the binding wire.

The wiring is done manually using fitter's pliers. Particular attention is paid to the tightness of the tie wire to the wire and to the position of the ends of the tie wire (they should not stick out). Pin insulators are attached to supports on steel hooks or pins. The hooks are screwed directly into wooden supports, and the pins are installed on metal, reinforced concrete or wooden traverses. To attach insulators to hooks and pins, adapter polyethylene caps are used. The heated cap is tightly pushed onto the pin until it stops, after which the insulator is screwed onto it.

The wires are suspended on reinforced concrete or wooden supports using pendant or pin insulators.

The minimum permissible height of the lower hook on the support (from ground level) is:

in power lines with voltage up to 1000 V for intermediate supports from 7 m, for transition supports - 8.5 m;
in power lines with a voltage of more than 1000 V, the height of the lower hook for intermediate supports is 8.5 m, for corner (anchor) supports - 8.35 m.

The smallest permissible cross-sections of overhead power line wires with voltages of more than 1000 V are selected according to the conditions of mechanical strength, taking into account the possible thickness of their icing.

For overhead power lines with voltages up to 1000 V, according to the mechanical strength conditions, wires with cross-sections of at least:

aluminum - 16 mm²;
steel-aluminum -10 mm²;
single-wire steel - 4 mm².

Grounding devices are installed on overhead power lines with voltages up to 1000 V. The distance between them is determined by the number of thunderstorm hours per year:

up to 40 hours - no more than 200 m;
more than 40 hours - no more than 100 m.

The resistance of the grounding device must be no more than 30 Ohms.
Installation of overhead power lines.

Overhead power lines consist of supporting structures(supports and bases), traverses (or brackets), wires, insulators and fittings. In addition, the overhead line includes devices necessary to ensure uninterrupted power supply to consumers and normal operation of the line: lightning protection cables, arresters, grounding, as well as auxiliary equipment.

Overhead transmission towers support the wires at a given distance from each other and from the ground. And overhead line supports with voltages up to 1000 V can also be used to hang radio network wires, local telephone communications, and outdoor lighting on them.

Overhead lines are easy to operate and repair, and have a lower cost compared to cable lines of the same length.
Depending on the purpose, there are intermediate and anchor supports. Intermediate supports are installed on straight sections of the overhead line route, and they are intended only to support wires. Anchor supports are installed for the passage of overhead lines through engineering structures or natural barriers, at the beginning, at the end and at turns of power lines. Anchor supports perceive longitudinal load from the difference in tension of wires and cables in adjacent anchor spans. Tension is the force with which a wire or cable is pulled and secured to supports. The gravity changes depending on the strength of the wind, the ambient temperature, and the thickness of the ice on the wires.
The horizontal distance between the centers of the two supports on which the wires are suspended is called the span. The vertical distance between the lowest point of the wire in the span to the intersecting engineering structures or to the surface of the earth or water is called the wire gauge.

The wire sag is the vertical distance between the lowest point of the wire in the span and the horizontal straight line connecting the wire attachment points on the supports.

Power and lighting networks with voltages up to 1000 V, made with insulated wires of all appropriate sections or unarmored cables with rubber or plastic insulation with a cross-section of up to 16 mm2, are classified as electrical wiring. External wiring is considered to be electrical wiring laid along the outer walls of buildings and structures, between buildings, under canopies, as well as on supports (no more than 4 spans, each 25 m long) outside streets and roads.

Lay the wires at a height of at least 2.75 m from the ground surface. When crossing pedestrian paths, this distance is made at least 3.5 m, and when crossing driveways and paths for the transportation of goods - at least 6 m.

Power lines over 1000 V

Overhead power lines over 1 kV - a device for transmitting electricity through wires located in the open air and attached to supports using insulating structures and fittings, load-bearing structures, brackets and racks on engineering structures (bridges, overpasses, etc.).
Wires and protective cables through insulators or garlands of insulators are suspended on supports: intermediate, anchor, corner, end, transposition, reinforced (anti-wind and supports of large transitions). They are made free-standing or with guys - wooden, reinforced concrete or metal, single-chain, double-chain, etc.

For installation of overhead lines, uninsulated single- and multi-wire wires made of one and two metals (combined) are used.

Recently, self-supporting insulated wires (SIP) have begun to be used, which makes it possible to reduce the distance between overhead line wires. To isolate wires and cables from the ground and attach them to supports, insulators made of porcelain and glass are used.
On overhead lines of 110 kV and above, suspended insulators must be used; the use of rod and post-rod insulators is allowed.

On overhead lines 35 kV and below, suspended or rod insulators are used. The use of pin insulators is allowed.

Ha VL 20 kV and below should be used:

on intermediate supports - any kind of insulators;
on anchor-type supports - suspended insulators; It is allowed to use pin insulators in region I on ice and in uninhabited areas.

The choice of type and material (glass, porcelain, polymer materials) of insulators is made taking into account climatic conditions (temperature and humidity) and pollution conditions.

On overhead lines running in particularly difficult operating conditions (mountains, swamps, regions of the Far North, etc.), on overhead lines built on double-circuit and multi-circuit supports, on overhead lines feeding traction substations of electrified railways, and on large crossings independently against voltage, glass insulators or (if there is appropriate justification) polymer insulators should be used.

The overhead line route, i.e. the strip of terrain where it passes, after surveys and agreements with organizations whose interests are affected by the construction of the overhead line, is finally established by the project.

Before installation, documents are drawn up for the alienation and allotment of land plots, the demolition of structures, as well as the right to destroy crops and cut down forests. Production picketing is being carried out, i.e. breakdown of support installation centers at the installation site of overhead lines.

The complex of works for the construction of an overhead line includes preparatory, construction, installation and commissioning work, as well as commissioning of the line.
Work directly on the route begins with acceptance from the design organization and the customer of the production picket of the overhead line route. Then a clearing is cut (if the overhead line or its individual sections pass through a forested area). The width of the clearing between the crowns of trees in forests and green spaces is taken depending on the height of the trees, the voltage of the overhead line, and the terrain. The minimum width of the clearing is determined by the distance from the wires at their greatest deviation to the tree crown. This distance must be at least 2 m for overhead lines with voltages up to 20 kV and 3 m for overhead lines with voltages of 35-110 kV.

All trees located inside the clearing are cut down so that the height of the stump is no more than 1/3 of its diameter. To allow vehicles and machinery to pass through the middle of a clearing at a width of at least 2.5 m, trees are cut down flush with the ground. In winter, when cutting down trees, the snow around each tree is cleared to ground level. The wood obtained from cutting trees is sorted, cut and stacked along the clearing; The branches are piled up for removal.
Basic construction and installation works include the manufacture of wooden supports, distribution of supports or their parts along the route, laying out places for digging pits for supports, digging pits, assembly and installation of supports, distribution of wires and other materials along the route, installation of wires and protective grounding, phasing and numbering of supports .

For the anchor A-shaped support, two pits are laid out, the axes of which are placed from the center of the picket column of the support in both directions along the axis of the route. The pits for the corner A-shaped support are placed along the bisector of the angle of rotation of the line and the perpendicular to it (Fig. 4, b). Marking for supports with guys and struts, as well as for narrow-base and wide-base metal supports is done in the same way. If digging pits is carried out with drilling machines, then only the centers of the pits are broken down.

Digging pits manually is carried out in exceptional cases, if earthmoving machines cannot approach the picket due to terrain conditions. Digging pits should be mechanized as much as possible. For this purpose, drilling machines (hole drills), excavators, and bulldozers are used. Earthworks should be carried out with maximum compaction of the walls of the pit, which ensures in the future reliable fastening supports The depth of the pits for installing supports, depending on the soil and mechanical loads on the supports, is determined by the project.

Support elements are usually manufactured in special factories and transported partially assembled.
The final assembly of elements into supports is carried out at specialized sites (polygons) or directly at the pickets of the overhead line route. The assembly location of the supports is chosen depending on their type, transport capabilities, route characteristics, etc., it is determined in the PPR. The final (complete) assembly of complex supports, as a rule, is carried out at pickets of the overhead line route. Assembly is carried out on special sites, cleared of interfering objects. This provides convenience for laying out the support parts. In addition, for subsequent lifting of the supports, the path is cleared for the free passage of cranes and traction vehicles, anchors are securely fastened, and rigging cables are removed to the required distance from existing high-current overhead lines or communication lines.
As a rule, the supports are laid out and assembled in the direction of the line axis, near foundations or pits in such a way that the assembled supports do not need to be pulled up when lifting. The assembly of overhead line supports includes the installation of pin insulators mounted on hooks and pins using polyethylene caps.
The quality and serviceability of support parts is checked twice: first before assembly, then at the route picket, since there is a possibility of damage to the supports during transportation.
For each prefabricated support of overhead lines 35 kV and above, fill out a passport or make an entry in the support assembly log.
For lifting and installing supports the best remedy is a crawler crane that requires a minimum of rigging. The crane hook must grip the support slightly above its center of gravity, otherwise it may tip over.

If there is no crawler crane with the required lifting capacity or if the crane’s boom reach is insufficient, a truck crane with a lifting capacity of 5-7 tons can be used together with a tractor. The support is first lifted with a truck crane until it reaches an angle of 35-40° with respect to the horizontal surface of the earth. Further lifting of the support is carried out by a tractor pulling a cable attached to the support. To prevent the support from tipping towards the tractor, a brake cable is attached to the top of the support before lifting begins.
In the absence of cranes, the supports are installed using the falling boom method using a tractor. The falling boom is first raised manually or using a small crane. To prevent the support from passing through the vertical position, a brake cable is provided. There is also a method of installing supports by extension: the support is raised in separate sections, connecting them in a vertical position. This method is used when transporting high poles across rivers or when installing heavy poles.
After installing the supports in the pit or on the foundations, their position is verified in accordance with regulatory guidelines. For example, the deviation of reinforced concrete supports from the vertical axis along and across the line (the ratio of the deviation of the upper end of the support column to its height) should be 1:150. The vertical position of the 35-110 kV overhead line supports is checked with a theodolite.

The verified supports are firmly fixed: in the ground by careful layer-by-layer compaction; on foundations and reinforced concrete piles - by screwing nuts onto anchor bolts.
After alignment and fastening of the supports, permanent signs are applied to them - serial numbers, year of installation, symbol of the name of the overhead line, etc. The correct installation of the support is confirmed by a passport, which contains permission to carry out work on the installation of wires and cables.

During installation work on overhead lines, the following basic operations are performed:

rolling out wires and cables, including their connection, and lifting supporting garlands onto supports. The installation of pin insulators on supports is carried out, as a rule, during the assembly of supports, i.e. before the start of installation work;
tensioning of wires and cables, including sighting, and adjustment of sag, fastening of wires and cables to anchor-type supports;
fastening (transfer from unrolling rollers to clamps) of wires and cables on intermediate supports.

Long-term practice of constructing overhead lines has revealed the most appropriate organization of work, called the flow method. Each type of work is assigned to a specialized team. So, if in the first anchor span, where the installation begins, wires are fastened to intermediate supports, then in the second they are tensioned with wires and cables, in the third they are rolled out, etc.

After completing all the preparatory work and inspecting the route prepared for installation, they begin directly rolling out the wires. As a rule, rolling is carried out in two ways: from stationary rolling devices installed at the beginning of the mounted section, or using movable rolling devices (carts, sleds, cable conveyors, etc.) moved along the route by a traction mechanism.
The first method does not require the manufacture of special mobile unrolling devices (trolleys), but when moving on the ground, damage to the cable and the upper layers of aluminum wires is possible. Drums with wire are installed 15-20 m from the first anchor support in the direction of rolling out. A wire or cable unwound from each drum to a length of 15-20 m with a mounting clamp installed at the end is attached to the traction mechanism. It moves along the route and after approaching the first intermediate support at 30-40 m it stops. The wires are unhooked and laid out in the starting position for lifting onto the support.

After making sure that the garland of insulators is assembled correctly, they are lifted onto the support.
This method is used when installing short lines, as well as in areas where, when rolling out wires, the possibility of their damage is unlikely (with good snow or grass cover).
In the second rolling method, the wires and cables are first anchored on the first anchor support. Then the traction mechanism together with the unrolling trolley is moved to the first intermediate support. Before moving to the second intermediate support, 5-10 turns of wire or cable are unwinded from the drum and laid out in its original position. Subsequent operations are carried out in the same way as with the first method. Rolling out of wires and cables is carried out only on rolling rollers suspended on supports. When rolling out, measures are taken to protect the wires from damage due to friction with the ground, especially hard soils.

The connection of steel-aluminum wires with a cross-section of up to 185 mm2 in spans of overhead lines above 1000 V is made with oval connectors mounted by twisting, and with a cross-section of up to 240 mm2 - with connecting clamps mounted by continuous crimping. In the loops of anchor and node supports, the connection is made by thermite welding for steel-aluminum wires with a cross-section of up to 240 mm2. Wires with a cross-section of 300 mm2 are connected with press-fit connectors, and when connecting wires of different brands, bolt clamps are used.

When installing a tension clamp mounted with cutting the wire, wire bands are applied to the end of the wire forming a loop (loop) and the wire extending into the span. The ends of the wires are cut and cleaned of dirt with a napkin soaked in gasoline. The inner surface of the aluminum housing 1 is cleaned with a steel brush, the aluminum wires of the wire are filed down and the steel core of the wire is released. After wiping the core with gasoline and lubricating it with a thin layer of technical petroleum jelly, push it into the hole of anchor 2 until it stops. The tension clamp is crimped in the direction from the eyelet to the wire, and the aluminum body is crimped from the middle of the clamp to its end.

If a detachable connection is required in the loops, bolt and die clamps are used, but such a connection does not provide a completely stable and reliable electrical contact.
The standards establish requirements for the mechanical strength of connections in spans, which must be at least 90% of the strength of the whole wire. In loops (loops) a smaller safety margin is allowed (30-50% of the strength of the whole wire). The instructions for installing overhead power lines provide data on the loads that welded joints must withstand for each type of wire.
Welding wires with a propane-oxygen flame requires oxygen, propane and a special torch; this welding gives a good quality joint.

The reliability of the electrical contact of a welded joint is determined by a coefficient expressing the ratio of the ohmic resistance of a section of wires with a welded joint to the resistance of the same section of a whole wire. This coefficient should not exceed 1.2. The ohmic resistance of short sections of wire is measured with a microohmmeter.

The need to connect wires made of heterogeneous materials or wires of different sections arises during critical crossings across rivers, lakes and railways. This kind of connection is made with special transition loop clamps PP, which are two sleeves with paws connected with bolts.

The tension of the wires is carried out, as a rule, in the spans between anchor or anchor-corner supports, to which the rolled and connected wires are attached using tension clamps and tension insulating garlands. The tension garland and tension clamp are lifted onto the support with a block having a cable and a mounting clamp. To lift the garland, use a car, tractor or winch.

When lifting a garland with a wire by tension onto the first anchor support during installation, this support does not experience tensile forces. But when stretching and securing the garland on the second anchor support, both anchor supports experience tensile forces, and therefore during this period they are strengthened with guy wires.

Before stringing of wires begins, all work on rolling out and connecting wires and cables must be completed.
Tractors, cars, and winches are used as traction mechanisms. The choice of mechanism depends on the actual installation conditions (traction forces, route, etc.). When tensioning, observe the lifting of wires and cables in the spans and the removal of caught objects and dirt from them; for the passage of repair couplings and connecting clamps through the unrolling rollers; behind roadways and other obstacles in the work area.
The tension of wires on metal supports is performed in the same way.

When tensioning wires and cables, use the data of the overhead line design, the tables of which indicate the sag values depending on the distance between the supports and the air temperature during installation. It must be borne in mind that in spring and autumn the air temperature in the mornings can significantly exceed the temperature of the wire lying on the ground. In this case, the wire is lifted from the ground by a car or tractor and held in this position until it reaches the ambient temperature.

Typically, the sag values are given in the design installation tables or in the curves for the intermediate span of the anchor section. When the anchor section has uneven spans, the sag is given for the so-called reduced span, the length of which is indicated in the tables or curves of the overhead line design.
Before stringing the wires, you should prepare a reliable connection (alarm) between all the people involved in this work: the fitter who sights the sag, the observer in the intermediate span, and the driver of the car or tractor with which the wires are pulled.

Reception of the sag during direct sighting begins with the middle wire when the wires are horizontal and from the top wire when the wires are vertical.

When sighting, the wire (or cable) is brought to the line of sight from above, for which the wire is first slightly pulled (by 0.3-0.5 m), and then released to the specified sag. For long anchor spans (more than 3 km), sighting is carried out in two spans located in each third of the anchor section. When the length of the anchor span is less than 3 km, sighting is carried out in two spans: the one furthest from the traction mechanism (in the first place) and closer (in the second place) to it.

When tensioning and sighting wires and cables, the specified sag value is strictly maintained at the appropriate air temperature. The actual sag should not differ from the design one by more than ±5%, subject to mandatory compliance with the standardized distances to the ground and engineering structures. The amount of misalignment of a wire or cable in relation to another should not be more than 10% of the design sag.
After sighting is completed, a mark is applied to the wire at the anchor support located on the side opposite the traction mechanism (with a bandage or indelible paint). Then, if the tension clamp is mounted on the ground, the wire is lowered to the ground.

Fastening of wires and cables to anchor-type supports on overhead lines 35-100 kV with suspended insulators is carried out using tension clamps: wedge type “wedge-throat”, bolted and pressed.
On overhead lines up to 10 kV, where pin insulators are mainly used, anchorage carried out using cone clamps. The type of fastening of wires on pin insulators (single or double) depends on the characteristics of the overhead line (route conditions, brand of wires, etc.) and is determined by the project.

Before installation, the ends of the wires and the contact surfaces of the tension clamps are thoroughly wiped with a rag soaked in a solvent (gasoline, acetone, etc.), and then cleaned with a card brush or a steel brush under a layer of neutral technical petroleum jelly.

To expose the steel core of the steel-aluminum wire, the aluminum conductors of the lower layer are filed only to half their diameter to avoid damage to the core. The exposed ends of the core are washed in a solvent, wiped dry with a rag and lubricated with Vaseline. The process of crimping tension and connecting clamps is similar.

Installation of wires and cables should be carried out, as a rule, without breaking them in loops (loops). Cutting loops (stubs) is allowed only in exceptional cases, for example, to avoid installing a connecting clamp in the span or on supports that limit the span of the intersection with engineering structures. Installation of wedge and bolt clamps with uncut loops is carried out simultaneously in the direction of the mounted anchor span and in the direction of the span as the wires are rolled out.

Fastening of wires and cables on intermediate supports on overhead lines up to 35 kV on pin insulators and in the supporting clamps of garlands of insulators on overhead lines 35-110 kV is carried out only after the final fastening of the wires to the anchor supports limiting the mounted section of the overhead line.

The transfer of overhead line wires from unrolling rollers and their fastening is carried out without lowering them to the ground. On 35-110 kV overhead lines, wires are transferred from telescopic towers, and in the absence of mechanisms, suspended ladders (cradles) are used.
On overhead lines up to 35 kV using pin insulators, the relaying and fastening of wires is carried out directly from the support.
On 6-35 kV overhead lines, aluminum and steel-aluminum wires are secured with a lateral viscous sheath of the wire with aluminum wire in the area of its contact with the neck of the insulator. Wire knitting begins from point 0, where the middle of the knitting wire is placed. The right end of the wire follows line i, it is secured with three turns on the wire, then directed along line a. The left end of the wire follows line b, it is also secured with three turns on the wire and directed along line b, after which both ends of the wire are secured to the wire. Aluminum wire for winding and tying is taken of the same diameter as the wire of the mounted wire, but not less than 2.5 and not more than 4 mm. The length of the knitting wire for one fastening is 1.4 m, the length of the wire for winding is about 0.8 m.

Installation of wires and cables on transitions is carried out in the same sequence and order as when installing them between anchor supports. Upon completion of the installation of wires and cables, the crossing is handed over to the owner organization according to the act. If the installation was carried out with deviations from the project, the act provides a list of these deviations and indicates who authorized them.

The insulation of overhead electrical networks is exposed to various types of overvoltages. These overvoltages (especially atmospheric) can cause flashovers of external insulation, interruptions in internal insulation, electric arc short circuits, emergency shutdowns and disrupt the continuity of power supply.

110 kV overhead lines on metal reinforced concrete supports are usually protected from direct lightning strikes by cables along their entire length. Overhead lines with a voltage of 110 kV on wooden supports and overhead lines with a voltage up to 35 kV do not require such protection. Single metal and reinforced concrete supports and other places with weakened insulation on overhead lines with a voltage of 35 kV with wooden supports are protected with tubular arresters or, if there are autorecloser protection gaps, and on overhead lines with a voltage of 110-220 kV with tubular arresters.

Experience in operating tubular arresters has shown that their use to increase the lightning resistance of overhead lines does not give the desired effect. The fact is that the probability of damage to tubular arresters during the thunderstorm season is of the order of 0.001, which, with a large number of them, reduces the lightning resistance index. In addition, tubular arresters have upper and lower limits on short-circuit current, and this requires systematic revisions and delays the extinguishing of the electric arc during multiple lightning discharges and parallel operation of several tubular arresters. Therefore, at present, tubular arresters are installed only to protect points with weakened insulation. These include: the intersection of power lines, as well as the intersection of an overhead line with a communication line. On lines with wooden supports, tubular arresters are installed on the first cable support of the approach to the substation and on separate corner metal supports. On high transition supports, due to increased induced overvoltage components during a direct lightning strike into the support, it is recommended to install tubular or valve arresters or a lightning protection cable.
Before installation on the support, tubular arresters are inspected, without removing the paper wrapper until installation is completed.

The arresters are installed at transitions in such a way that if the arrester is damaged and the wire burns out, the latter falls not in the transition, but in the adjacent span. The installation of the spark gap should ensure the stability of the external spark gap and exclude the possibility of blocking it with a stream of water that can flow from the upper electrode. The arrester is securely fixed to the support and grounded. The dimensions of the external spark gap should not differ from the design ones by more than ± 10%.

The installation of arresters on the supports of 35-110 kV overhead lines is carried out in such a way as to ensure the possibility of installing and dismantling the arresters without disconnecting the line. The gas exhaust zones of arresters of adjacent phases should not intersect, and there should be no structural elements of supports, wires, etc. in them.

Supports with lightning protection cable or other devices, lightning protection, reinforced concrete and metal supports with a voltage of 3-35 kV, supports on which power or instrument transformers, disconnectors, fuses or other devices are installed, as well as metal and reinforced concrete supports of overhead lines with a voltage of 110-500 kV without cables and other lightning protection devices, if this is necessary to ensure reliable operation of relay protection and automation, they must be grounded. In this case, the resistance value of grounding devices is taken in accordance with the PUE.
Installation of tubular arresters on 35 kV overhead lines

To ground reinforced concrete supports, elements of the longitudinal reinforcement of the racks are used as grounding conductors, which are metallic connected to each other and can be connected to grounding.
Artificial grounding conductors in lightning protection devices are used in cases where the resistance of natural grounding conductors exceeds the standardized value. They are laid in the ground during the construction and installation process.
The cables and parts for fastening the insulators to the traverse of reinforced concrete supports are metallic connected to a grounding descent or grounded equipment. The cross-section of each of the grounding slopes on the overhead line support is taken to be at least 35 mm2, and for single-wire ones, the diameter is at least 10 mm. It is allowed to use galvanized steel single-wire descents with a diameter of at least 6 mm.

On overhead lines with wooden supports, a bolted connection of grounding descents is recommended; on metal and reinforced concrete supports, the connection of grounding slopes can be either welded or bolted.
Overhead line grounding conductors, as a rule, are buried to the depth specified in the design.

For the installation of overhead lines with voltages up to 1000 V, wooden, mainly with reinforced concrete attachments (stepchildren) and reinforced concrete supports are used. For the manufacture of wooden supports, antiseptic-impregnated logs from grade III forest (pine, spruce, fir) are used, and for traverses - only pine or larch. Impregnating wood with an antiseptic significantly extends the service life of wooden supports.

Vertical and horizontal distances from overhead line wires to trees and bushes must be at least 1 m. Cutting clearings through forests and green spaces where the overhead line runs is not mandatory.
In populated areas with one- and two-story buildings, overhead lines must have grounding devices designed to protect against atmospheric surges. The resistance of these grounding devices must be at least 30 Ohms, and the distance between them must be at least 200 m for areas with the number of thunderstorm hours per year up to 40,100 m - for areas with the number of thunderstorm hours per year more than 40.

In addition, grounding devices must be made:

on supports with branches to entrances to buildings in which a large number of people can be concentrated (schools, nurseries, hospitals) or which represent a large material value(livestock and poultry premises, warehouses);
on the end supports of lines with branches.

Pits for single-post intermediate supports, as a rule,
are developed using hole drills with markings exactly along the axis of the route to avoid the support leaving the line alignment. In places where underground communications (for example, cables) pass, soil excavation is carried out manually.
The connection of wires in overhead line spans should be made using connecting clamps that provide mechanical strength of at least 90% of the breaking force of the wire.

In one span of an overhead line, no more than one connection per wire is allowed.
In the spans of intersection of overhead lines with engineering structures, the connection of overhead line wires is not allowed.
The connection of wires in the loops of anchor supports must be made using clamps or welding.
Wires of different brands or sections should only be connected in the loops of anchor supports.
It is recommended to fasten bare wires to insulators and insulating cross-arms on overhead line supports, with the exception of supports for intersections, in a single manner.

On overhead lines above 1,000 V, double fastening of wires is performed on anchor supports, intersection supports and in populated areas.

The location of the phase wires on the support can be any, and the neutral wire, as a rule, is located below the phase wires.

Safety during construction and installation work is ensured by continuous supervision of the work of the team, which is carried out by the foreman, who is responsible for monitoring compliance by workers with safety rules for work, the serviceability of tools and protective devices, and the correct placement of people.

In addition to general safety rules, the following rules must be observed when installing overhead lines:

When a thunderstorm approaches, all work on overhead lines must be stopped, and people must be removed from the route. When installing long-distance overhead lines to remove individual lightning strikes, mandatory grounding of all installed wires is required in sections 3-5 km long.
Protection of personnel from the effects of electrical potentials induced in wires and cables (especially in the hot season and during thunderstorms) should be carried out by installing protective grounding and short-circuiting the leads and cables on all anchor supports of the mounted area.
The supports are lifted using lifting and traction mechanisms and devices. To prevent the support from deflecting and falling to the side, proper adjustment of its position must be ensured using guys and braces.
When lifting the support, it is not allowed to stand or walk under the cables and booms of the mechanisms, as well as near them and in the area of possible fall of the support or mounting boom. All persons not directly involved in lifting the support must be removed from the work area. When lifting a support using the mounting boom method, it should first be lifted from the ground by 0.5 m and all mechanisms and fastenings should be checked, and then lifting should continue. When lifting a support at crossings through utility structures or in difficult conditions (for example, in a corridor between two energized lines), the presence of a work supervisor is required. When lifting a support near an active overhead line, when wires may touch, they must be turned off.
When installing wires, it is prohibited:
climb onto anchor, corner, or poorly secured or swinging supports;
work without a safety belt;
be under the wires during their installation.

Transmission lines are the central element of the EE transmission and distribution system. The lines are carried out mainly by overhead and cable. Energy-intensive enterprises also use conductors. on the generator voltage of power plants - busbars; in industrial and residential buildings - internal wiring.

The choice of the type of power transmission line and its design is determined by the purpose of the line, location (laying) and, accordingly, its rated voltage, transmitted power, power transmission range, area and cost of the occupied (alienated) territory, climatic conditions, electrical safety and technical aesthetics requirements, and a number of others factors and, ultimately, the economic feasibility of transmitting electrical energy. This choice is made at the stages of making design decisions.

This section formulates the requirements that power transmission lines must satisfy, the conditions for their implementation, and on their basis, some principles and design options for power lines are presented.

Overhead lines are the most common at all stages of the power supply system due to their relatively low cost. For this reason, the use of VL should be considered first.

Overhead power lines

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 geographical areas, 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, urban areas, enterprises), etc. From the analysis of overhead line conditions it follows that the materials and designs of lines must satisfy a number of requirements: economically acceptable cost, good electrical conductivity and sufficient mechanical strength of wire and cable materials, 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. 1) is characterized by the type of supports, span lengths, overall dimensions, phase design, and the number of insulators.

The lengths of overhead line spans 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. 1. b), this will reduce the number of supports and insulators on the line. The line dimension - the shortest distance from the bottom point of the wire to the ground (water, road surface) - should have been. in such a way as to ensure the safety of the movement of people and vehicles under the line. This the distance depends on the rated voltage of the line and terrain conditions (populated, uninhabited). The distance between adjacent phases of a line depends mainly on its rated voltage. The main design dimensions of the overhead line are given in table. 1. The design of an 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 to five at 750 kV, eight to twelve at 1150 kV.

Overhead line supports. Overhead line supports are structures designed to support wires at the required height above ground, water and any engineering structure. In addition, in necessary cases, the necessary steel grounded cables are suspended from the supports to protect the wires from direct lightning strikes and the associated overvoltage.

Table No. 1

Design dimensions of overhead lines

Rated voltage, kV	Phase distance D, m	Span length l, m	Support height N, m	Line size h, m
	0,5	40-50	8-9	6-7
6-10	1	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

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 averages 80-90% total number 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; suspended 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 wire tension (tension garlands of insulators are located horizontally), experience the greatest loads, so they are much more expensive and more complex 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 on the 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.

There are special supports following types: transitional - for large spans of crossing rivers and gorges; branch - for making branches from the main line; transposition - 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. 2).

The asymmetrical arrangement of phase wires in relation to each other (Fig. 2) causes the dissimilarity of 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. At full cycle transposition, each wire (phase) occupies a sequential position evenly along the length of the line all three phases on the support (Fig. 3).

Wooden supports(Fig. 4) are made from pine or larch and are used on lines with voltages up to 110 kV in forest areas, but less and less often. 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. Application of reinforced concrete stepsons (attachments) increases the service life of supports to 20-25 years.

Reinforced concrete supports(Fig. No. 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. 6) are used on lines with voltages of 35 kV and higher. The main elements include racks 1, traverses 2, cable racks 3, guys 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 to protect them from 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.)

Overhead wires. Wires are designed to transmit electricity. Along with good electrical conductivity (possibly less electrical resistance), sufficient mechanical strength and resistance to corrosion, they must satisfy the conditions of efficiency. For this purpose, wires made from the cheapest metals, aluminum, steel, and special aluminum alloys, are used. Although copper is the most conductive, copper wires are not used in new lines due to their high cost and need for other purposes. 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. 7). Single-wire, predominantly steel wires are used to a limited extent in low-voltage networks. To give them flexibility and greater mechanical strength, the 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. 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 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 a core filler (C) or the entire wire ( P) 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.

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. 7, d, e). This use reduces coronation losses. Hollow wires are used mainly for busbars of switchgears 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 a wall thickness of 20 mm.

Overhead lines with self-supporting insulated wires of 0.38-10 kV are increasingly used. In 380/220 V lines, the wires consist of a carrier insulated or non-insulated wire, which is neutral, three insulated phase wires, one insulated wire (of any phase) for external lighting. Phase insulated wires are wound around the supporting neutral wire (Fig. 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, they serve to protect the line from atmospheric overvoltages (lightning discharges). The cables are suspended above the phase wires (Fig. 2) 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. 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 from porcelain and tempered glass- materials with high mechanical and electrical strength and resistance to atmospheric influences. A significant advantage of glass insulators is that if damaged, tempered glass crumbles. This makes it easier to locate 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. 9, a, b) 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. Suspended insulators (Fig. 9, c) are used on overhead lines with a voltage of 35 kV and higher. They consist of a porcelain or glass insulating part 1, a cap made of malleable cast iron 2, a metal rod 3 and a cement binder 4. The insulators are assembled into garlands (Fig. 10, G): supporting on intermediate supports and tension on anchor ones. 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 load capacity, 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 are undergoing experimental industrial testing (Fig. 9, d, e). They are a core element made of fiberglass, protected by a coating with ribs made of fluoroplastic or organosilicon 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. 10). Supporting clamps are used for hanging and securing overhead line wires on intermediate supports with limited embedding rigidity (Fig. 10, A). On anchor supports for rigid fastening of wires, tension garlands and clamps are used - tension and wedge (Fig. 10, b, V). Coupling fittings (earrings, ears, brackets, rocker arms) are designed for hanging garlands on supports. Supporting garland (Fig. 10, G) is fixed on the traverse of the intermediate support using earring 1, inserted on the other side into the cap of the upper suspension insulator 2. Eyelet 3 is used to attach the garland of supporting clamp 4 to the lower insulator. Distance spacers (Fig. 10, d), 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. 10, e, and). 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 is various variants of compact power lines, characterized by a smaller distance between phases and, as a consequence, smaller inductive reactances and line path width (Fig. 11). When using “female type” supports (Fig. 11, A) reducing the distance is achieved by locating all phase split structures inside the “encompassing portal” or on one side of the support column (Fig. 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. 11, V-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 phases of the same name of different values are shifted in pairs. In this case, voltages are applied to the circuits, shifted by a certain angle. Due to the regime change using special phase shift angle devices, the line parameters are controlled.

Cable power lines

Cable line (CL) is a line for transmitting electricity, consisting of one or more parallel cables, made by some method of installation (Fig. 11). Cable lines are laid where the construction of overhead lines is impossible due to cramped territory, is unacceptable due to safety conditions, is impractical due to economic, architectural and planning indicators and other requirements. CLs are most widely used in the transmission and distribution of electrical energy at industrial enterprises and in cities (internal power supply systems) when transmitting electrical energy through large bodies of water, etc. The advantages and disadvantages of cable lines compared to overhead lines: immunity to atmospheric influences, concealment of the route and inaccessibility for unauthorized persons, less damage, compactness of the line and the possibility of widespread development of power supply to consumers in urban and industrial areas. However, cable lines are much more expensive than air lines of the same voltage (on average 2-3 times for lines of 6-35 kV and 5-6 times for lines of 110 kV and above), and are more difficult to construct and operate.

The cable line includes: cable, connecting and end couplings, building structures, fastening elements, etc.

A cable is a finished factory product consisting of insulated conductive cores enclosed in a protective hermetic sheath and armor, protecting them from moisture, acids and mechanical damage. Power cables have from one to four aluminum or copper conductors with a cross-section of 1.5-2000 mm 2. Cores with a cross section of up to 16 mm 2 are single-wire, above - multi-wire. The cross-sectional shape of the cores is round, segment or sector.

Cables with voltages up to 1 kV are usually made with four-core cables, with voltages of 6-35 kV - with three-core cables, and with voltages of 110-220 kV - with single-core cables.

Protective shells are made from lead, aluminum, rubber and polyvinyl chloride. In cables with a voltage of 35 kV, each core is additionally enclosed in a lead sheath, which will create a more uniform electric field and improves heat dissipation. The equalization of the electrical zero in cables with plastic insulation and sheath is achieved by shielding each core with semiconducting paper.

In cables for voltages of 1-35 kV, to increase the electrical strength, a layer of belt insulation is laid between the insulated cores and the sheath.

The cable armor, made of steel tapes or galvanized steel wires, is protected from corrosion by an outer cover of cable traction, impregnated with bitumen and coated with a chalk composition.

In cables with voltages of 110 kV and above, increasing the electrical strength of paper insulation, they are filled with gas or oil under overpressure(gas-filled and oil-filled cables).

The cable mark indicates information about its design, rated voltage, number and cross-section of cores. For four-core cables with voltages up to 1 kV, the cross-section of the fourth (“zero”) conductor is smaller than the phase conductor. For example, cable VPG-1-3X35+1X25 is a cable with three copper conductors with a cross-section of 35 mm 2 and a fourth with a cross-section of 25 mm 2 , polyethylene (P) insulation at 1 kV, polyvinyl chloride sheath (B), unarmored, without outer cover (D) - for laying indoors, in channels, tunnels, in the absence of mechanical stress on the cable; cable AOSB-35-3Х70 - cable with three aluminum (A) conductors of 70 mm 2 each, with 35 kV insulation, with separately leaded (O) conductors, in a lead (C) sheath, armored (B) with steel tapes, with an outer protective cover - for laying in an earthen trench; OSB-35-3X70 - the same cable, but with copper conductors.

The designs of some cables are shown in Figure 13. In Figure 13 , a, b Power cables with voltages up to 10 kV are provided.

Four-core cable voltage 380 V (see Fig. 13, A) contains the elements: 1 - conductive phase conductors; 2 - paper phase and belt insulation; 3 - protective shell; 4 - steel armor; 5 - protective cover; 6 - paper filler; 7 - zero core.

Three-core cable with paper insulation voltage 10 kV (Fig. 13, b) contains the elements: 1 - current-carrying conductors; 2 - phase insulation; 3 - general waist insulation; 4 - protective shell; 5 - pillow under armor; 6 - steel armor; 7 - protective cover; 8 - placeholder.

Three-core cable voltage 35 kV is shown in Fig. 1.3, V. It includes: 1 - round conductive cores; 2 - floor with conductive screens; 3 - phase insulation; 4 - lead sheath; 5 - pillow; 6 - cable yarn filler; 7 - steel armor; 8 - protective cover.

In Fig. 1.3, G presented oil-filled cable medium and high pressure voltage 110-220 kV. Oil pressure prevents air from ionizing it, eliminating one of the main causes of insulation breakdown. Three single-phase cables are placed in a steel pipe 4 filled with oil 2 under excess pressure. The current-carrying core 6 consists of copper round wires and is covered with paper insulation 1 with viscous impregnation; A screen 3 in the form of a copper perforated mite and bronze wires is placed on top of the insulation, protecting the insulation from mechanical damage when pulling the cable through the pipe. The outside of the steel pipe is protected by a cover 5.

Cables in PVC insulation are widely used, produced in three-, four- and five-core (1.3, e) or single-core (Fig. 1.3, d).

Cables are manufactured in pieces of limited length depending on the conjugations and sections. When laying, the sections are connected using couplings that seal the joints. In this case, the ends of the cable cores are freed from insulation and sealed into connecting clamps.

When laying 0.38-10 kV cables in the ground, to protect them from corrosion and mechanical damage, the connection point is enclosed in a protective cast-iron detachable casing. For 35 kV cables, steel or fiberglass casings are also used. In Fig. 14, A shows the connection of a three-core low-voltage cable 2 in a cast iron coupling 1. The ends of the cable are fixed with a porcelain spacer 3 and connected with a bond 4. The couplings of cables up to 10 kV with paper insulation are filled with bituminous compounds, cables 20-35 kV are filled with oil-filled compounds. For cables with plastic insulation, connecting sleeves are used from heat-shrinkable insulating tubes, the number of which corresponds to the number of phases, and one heat-shrinkable tube for the neutral core, seated in a heat-shrinkable sleeve (Fig. 14, b) . Other designs of couplings are also used.

End sleeves or terminations are used at the ends of cables. In Fig. 15, A a mastic-filled three-phase coupling for outdoor installation with porcelain insulators for cables with a voltage of 10 kV is shown. For three-core cables with plastic insulation, an end sleeve is used, shown in Fig. 15, 6. It consists of a heat-shrinkable glove 1, resistant to environment, and semi-conducting heat-shrinkable tubes 2, with the help of which three single-core cables are created at the end of a three-core cable. Insulating heat-shrinkable tubes 3 are placed on individual cores. The required number of heat-shrinkable insulators 4 is mounted on them.

For cables of 10 kV and below with plastic insulation, dry cutting is used in interior spaces (Fig. 15, c). The cut ends of the cable with insulation 3 are wrapped with adhesive polyvinyl chloride tape 5 and varnished; the ends of the cable are sealed with cable mass 7 and an insulating glove 1 covering the cable sheath 2, the ends of the glove and the cores are additionally sealed and wrapped with polyvinyl chloride tape 4, 5, the latter is fixed with twine bands 6 to prevent lag and unwinding.

The method of laying cables is determined by the conditions of the line route. Cables are laid in earthen trenches, blocks, tunnels, cable tunnels, collectors, along cable overpasses, as well as over the floors of buildings (Fig. 12).

Most often, in cities and industrial enterprises, cables are laid in earthen trenches (Fig. 12, A). To prevent damage due to deflections at the bottom of the trench, create soft pillow from a layer of sifted earth or sand. When laying several cables up to 10 kV in one trench, the horizontal distance between them must be at least 0.1 m, between cables 20-35 kV - 0.25 m. The cable is covered with a small layer of the same soil and covered with brick or concrete slabs for protection from mechanical damage. After this, the cable trench is covered with earth. At road crossings and at entrances to buildings, the cable is laid in asbestos-cement or other pipes. This protects the cable from vibrations and makes it possible to repair without opening the road surface. Laying in trenches is the least expensive method of EE cable ducting.

In places where a large number of cables are laid, aggressive soil and wandering cables limit the possibility of laying them in the ground. Therefore, along with other underground communications, special structures are used: collectors, tunnels ropes, blocks and overpasses. The collector (Fig. 12, b) serves for the joint placement of various underground communications: cable power lines and communications, water supply along city highways and on the territory of large enterprises. When there are a large number of cables laid in parallel, for example, from the building of a powerful power plant, installation in tunnels is used (Fig. 12, c). At the same time, operating conditions are improved and the surface area of the earth required for laying cables is reduced. However, the cost of tunnels is very high. The tunnel is intended only for laying cable lines. It is constructed underground from precast concrete or sewer pipes large diameter, tunnel capacity - from 20 to 50 cables.

With a smaller number of cables, cable channels are used (Fig. 12, d), covered with earth or extending to the level of the ground surface. Cable racks and galleries (Fig. 12, d) used for overhead cable laying. This kind cable structures widely used where the direct laying of power cables in the ground is dangerous due to landslides, landslides, permafrost, etc. cable channels, tunnels, collectors and overpasses, cables are laid on cable brackets.

In large cities and large enterprises, cables are sometimes laid in blocks (Fig. 12, e), representing asbestos-cement pipes, joints that are sealed with concrete. However, the cables are poorly cooled in them, which reduces their throughput. Therefore, cables should be laid in blocks only if it is impossible to lay them in trenches.

In buildings, along walls and ceilings, large streams of cables are laid in metal trays and boxes. Single cables can be laid openly along walls and ceilings or hidden: in pipes, hollow slabs and other building parts of buildings.

Conductors, busbars and internal wiring

A current conductor is a power transmission line, the current-carrying parts of which are made of one or more rigidly fixed aluminum or copper wires or busbars and related supporting and supporting structures and insulators, protective shells (boxes). Busbars are protected and enclosed busbars made of rigid busbars. Busbars up to 1 kV are used in workshop networks of industrial enterprises, more than 1 kV - in generator voltage circuits for transmitting energy to step-up transformers of power plants. 6-35 kV conductors are used for main supply of energy-intensive enterprises at currents of 1.5-6.0 kA. Busbars up to 1 kV of industrial enterprises (complete busbars) are mounted from standard sections of factory production. Separate sections 1 of such a conductor (Fig. 15, A) consist of boxes with conductor elements placed in them, branch 3 and input 2 boxes, connected through branch section 4 to main line 5. Complete busbar, produced in three- and four-pass (Fig. 15, b) consists of sections in the form of sections of busbars 1, mounted on gaskets 3 in a box 2 with clamps 4 for connecting electrical consumers. According to transportation conditions, the length of such sections does not exceed 6 m. Busbar trunking boxes are necessary for protection from external influences; sometimes they are used as a neutral conductor.

Rigid symmetrical current conductor 6-10 kV is made of box-section busbars, rigidly fixed to support insulators attached to the general steel structure along the vertices of an equilateral triangle. The conductor can be laid openly - on supports or overpasses, or hidden - in tunnels (Fig. 17) and galleries.

A flexible unified symmetrical current conductor 6-10 kV with external filling is essentially a double-circuit overhead line with split phases (Fig. 18, A). Each phase consists of 4, 6, 8 or 10 wires of grade A 600, located on supporting clamps around a circle with a diameter of 600 mm. Using a special suspension system on insulators, all three phases are placed at the vertices of the triangle and attached to the supports. To prevent the phases from clashing with each other, interphase insulating spacers are installed in the spans.

For a flexible 35 kV current conductor (Fig. 18), the phases consist of three wires, grade A 600, fixed in rings and suspended on insulators to a support by means of a supporting steel cable. Supports for flexible conductors, constructed of reinforced concrete or steel, are installed every 50-100 m. Branches from conductors to electrical consumers are made with busbars or bare wires.

Internal wiring are wires and cables with electrical installation and electrical installation products intended for the implementation of internal networks in buildings. They are performed open and hidden, in most cases with insulated wires laid on insulators or in pipes. Cables are laid in ducts, floors or walls. Sometimes internal electrical wiring also includes busbars (busbars) of workshop networks of industrial enterprises.

To My World

3) overhead line wires should be located, as a rule, above the overhead cable of the LAN and LPV (see also 1.76, clause 4);
4) connection of overhead line wires in the intersection span with overhead cable LS and LPV is not allowed. The cross-section of the supporting conductor of the SIP must be at least 35 sq. mm. Overhead line wires must be multi-wire with a cross-section of at least: aluminum - 35 sq. mm, steel-aluminum - 25 sq. mm; cross-section of the SIP core with all load-bearing conductors of the bundle - at least 25 sq. mm;
5) the metal sheath of the overhead cable and the cable on which the cable is suspended must be grounded on the supports limiting the span of the intersection;
6) the horizontal distance from the base of the LS and LPV cable support to the projection of the nearest overhead line wire onto the horizontal plane must be no less than the greatest height of the intersection span support.

1.78. When crossing VLI with bare wires of LS and LPV, the following requirements must be met:
1) the intersection of VLI with LS and LPV can be carried out in the span and on a support;
2) VLI supports, limiting the span of the intersection with the LAN of backbone and intra-zonal communication networks and with connecting lines STS must be of the anchor type. When crossing all other LS and LPV on the overhead line, the use of intermediate supports reinforced with an additional attachment or strut is allowed;
3) the supporting core of the SIP or bundle with all supporting conductors at the intersection must have a tensile safety factor at the highest design loads of at least 2.5;
4) the VLI wires should be located above the LAN and LPV wires. On the supports that limit the span of the intersection, the supporting wires of self-supporting insulated wires must be secured with tension clamps. VLI wires may be placed under the LPV wires. In this case, the LPV wires on the supports limiting the span of the intersection must have double fastening;
5) connection of the load-bearing core and load-bearing conductors of the SIP harness, as well as LS and LPV wires in intersection spans is not allowed.

1.79. When crossing insulated and non-insulated overhead line wires with non-insulated LAN and LPV wires, the following requirements must be met:
1) the intersection of overhead line wires with LAN wires, as well as LPV wires with voltages above 360 V, should only be carried out in the span.
The intersection of overhead line wires with subscriber and feeder lines of overhead power lines with voltages up to 360 V can be carried out on overhead line supports;
2) overhead line supports limiting the span of the intersection must be of the anchor type;
3) LS wires, both steel and non-ferrous metal, must have a tensile safety factor at the highest design loads of at least 2.2;
4) overhead line wires should be located above the LAN and LPV wires. On the supports that limit the span of the intersection, the overhead line wires must have double fastening. Overhead line wires with voltages of 380/220 V and below may be placed under the wires of LPV and GTS lines. In this case, the wires of LPV and GTS lines on the supports limiting the span of the intersection must have double fastening;
5) connection of overhead line wires, as well as LAN and LPV wires in intersection spans is not allowed. Overhead line wires must be stranded with cross-sections of at least: aluminum - 35 sq. mm, steel-aluminum - 25 sq. mm.

1.80. When crossing an underground cable insert in an overhead line with bare and insulated LAN and LPV wires, the following requirements must be met:
1) the distance from the underground cable insert in the overhead line to the support of the LAN and LPV and its grounding conductor must be at least 1 m, and when laying the cable in an insulating pipe - at least 0.5 m;
2) the horizontal distance from the base of the overhead line cable support to the projection of the nearest LAN and LPV wire onto the horizontal plane must be no less than the greatest height of the intersection span support.

1.81. The horizontal distance between the VLI wires and the LS and LPV wires when passing parallel or approaching must be at least 1 m.
When approaching overhead lines with overhead lines and overhead lines, the horizontal distance between the insulated and non-insulated wires of the overhead line and the wires of the line and line lines must be at least 2 m. In cramped conditions, this distance can be reduced to 1.5 m. In all other cases, the distance between the lines must be no less than the height of the highest support of overhead lines, LS and LPV.
When approaching overhead lines with underground or overhead cables of LAN and LPV, the distances between them must be taken in accordance with 1.77 paragraphs. 1 and 5.

1.82. The proximity of overhead lines to antenna structures of transmitting radio centers, receiving radio centers, designated receiving points for wired broadcasting and local radio centers is not standardized.

1.83. The wires from the overhead line support to the entrance to the building should not intersect with the wires of branches from the LAN and LPV, and they should be located at the same level or above the LAN and LPV. The horizontal distance between overhead line wires and LAN and LPV wires, television cables and descents from radio antennas at the inputs must be at least 0.5 m for self-supporting insulated wires and 1.5 m for uninsulated overhead line wires.

1.84. Joint suspension of rural telephone overhead cable and overhead lines is allowed if the following requirements are met:
1) the zero core of the SIP must be insulated;
2) the distance from the SIP to the overhead cable of the STS in the span and on the VLI support must be at least 0.5 m;
3) each VLI support must have a grounding device, and the grounding resistance must be no more than 10 Ohms;
4) at each VLI support, the PEN conductor must be re-grounded;
5) the supporting rope of the telephone cable, together with the metal mesh outer cover of the cable, must be connected to the ground electrode of each support by a separate independent conductor (descent).

1.85. Joint suspension on common supports of non-insulated wires of overhead lines, LANs and LPVs is not allowed.
On common supports, joint suspension of non-insulated overhead line wires and insulated LPV wires is allowed. In this case, the following conditions must be met:
1) the rated voltage of the overhead line must be no more than 380 V;
3) the distance from the lower wires of the LPV to the ground, between the LPV circuits and their wires must comply with the requirements of the current rules of the Russian Ministry of Communications;
4) uninsulated overhead line wires should be located above the LPV wires; in this case, the vertical distance from the bottom wire of the overhead line to the top wire of the LPV must be at least 1.5 m on the support, and at least 1.25 m in the span; when the LPV wires are located on brackets, this distance is taken from the bottom wire of the overhead line, located on the same side as the LPV wires.

1.86. On common supports, joint suspension of SIP VLI with non-insulated or insulated LS and LPV wires is allowed. In this case, the following conditions must be met:
1) the rated voltage of the VLI must be no more than 380 V;
2) the rated voltage of the LPV should be no more than 360 V;
3) the rated voltage of the LAN, the calculated mechanical stress in the wires of the LAN, the distances from the lower wires of the LAN and LPV to the ground, between the circuits and their wires must comply with the requirements of the current rules of the Ministry of Communications of Russia;
4) VLI wires up to 1 kV should be located above the LAN and LPV wires; in this case, the vertical distance from the self-supporting insulated wire to the upper wire of the LS and LPV, regardless of their relative position, must be at least 0.5 m on the support and in the span. It is recommended to place the VLI and LS and LPV wires on different sides of the support.

1.87. Joint suspension of uninsulated overhead line wires and LAN cables on common supports is not allowed. Joint suspension of overhead line wires with a voltage of no more than 380 V and LPV cables on common supports is permitted if the conditions are met.
OCNN optical fibers must meet the requirements.

1.88. Joint suspension of overhead line wires with a voltage of no more than 380 V and telemechanics wires on common supports is permitted subject to the requirements given in 1.85 and 1.86, and also if the remote control circuits are not used as wired telephone communication channels.

1.89. Suspension of fiber-optic communication cables (OK) is allowed on overhead line (VLI) supports:
non-metallic self-supporting (OSSN);
non-metallic, wound onto a phase wire or SIP harness (OKNN).
Mechanical calculations of overhead line (VLI) supports with OKSN and OKNN must be carried out for the initial conditions specified in 1.11 and 1.12.
The overhead line supports on which the OC is suspended and their fastenings in the ground must be designed taking into account the additional loads arising in this case.
The distance from the OKSN to the surface of the earth in populated and uninhabited areas must be at least 5 m.
The distances between the wires of overhead lines up to 1 kV and the OCSN on the support and in the span must be at least 0.4 m.

Page 5 of 14

§ 2. Overhead and cable power lines

Overhead power lines.

An overhead electric line is a device used to transmit electrical energy through wires located in the open air and attached to supports using insulators and fittings. Overhead power lines are divided into overhead lines with voltages up to 1000 V and above 1000 V.
When constructing overhead power lines, the volume of excavation work is insignificant. In addition, they are easy to operate and repair. The cost of constructing an overhead line is approximately 25-30% less than the cost of a cable line of the same length. Overhead lines are divided into three classes:
class I - lines with a rated operating voltage of 35 kV for consumers of the 1st and 2nd categories and above 35 kV, regardless of consumer categories;
class II - lines with rated operating voltage from 1 to 20 kV for consumers of the 1st and 2nd categories, as well as 35 kV for consumers of the 3rd category;
class III - lines with a rated operating voltage of 1 kV and below. A characteristic feature of overhead lines with voltages up to 1000 V is the use of supports for simultaneously attaching wires of a radio network, outdoor lighting, remote control, and alarm systems to them. The main elements of an overhead line are supports, insulators and wires.
For 1 kV lines, two types of supports are used: wooden with reinforced concrete attachments and reinforced concrete.
For wooden supports, logs impregnated with an antiseptic are used from grade II forest - pine, spruce, larch, fir. You can avoid soaking the logs when making supports from winter-cut hardwood trees. The diameter of the logs at the top should be at least 15 cm for single posts and at least 14 cm for double and A-frame supports. It is allowed to take the diameter of the logs in the upper cut at least 12 cm on the branches going to the entrances to buildings and structures. Depending on the purpose and design, there are intermediate, corner, branch, cross and end supports.
Intermediate supports on the line are the most numerous, since they serve to support the wires at a height and are not designed for the forces that are created along the line in the event of a wire break. To absorb this load, anchor intermediate supports are installed, placing their “legs” along the axis of the line. To absorb forces perpendicular to the line, intermediate anchor supports are installed, placing the “legs” of the support across the line.
Anchor supports have a more complex design and increased strength. They are also divided into intermediate, corner, branch and end, which increase the overall strength and stability of the line.
The distance between two anchor supports is called the anchor span, and the distance between intermediate supports is called the support spacing.
In places where the direction of the overhead line route changes, corner supports are installed.
To supply power to consumers located at some distance from the main overhead line, branch supports are used on which the wires connected to the overhead line and to the input of the electricity consumer are fixed.
End supports are installed at the beginning and end of the overhead line specifically to absorb unilateral axial forces.
The designs of various supports are shown in Fig. 10.
When designing an overhead line, the number and type of supports are determined depending on the configuration of the route, the cross-section of the wires, the climatic conditions of the area, the degree of population in the area, the topography of the route and other conditions.
For overhead line structures with voltages above 1 kV, predominantly reinforced concrete and wooden antiseptic supports on reinforced concrete attachments are used. The designs of these supports are unified.
Metal supports are used mainly as anchor supports on overhead lines with voltages above 1 kV.
On overhead line supports, the location of the wires can be any, only the neutral wire in lines up to 1 kV is placed below the phase wires. When hanging external lighting wires on supports, they are located below the neutral wire.
Overhead line wires with voltage up to 1 kV should be suspended at a height of at least 6 m from the ground, taking into account the sag.
The vertical distance from the ground to the point of greatest sag of the wire is called the dimension of the overhead line wire above the ground.
The wires of an overhead line can approach other lines along the route, intersect with them and pass at a distance from objects.
The approach gauge of overhead line wires is the permissible shortest distance from the line wires to objects (buildings, structures) located parallel to the overhead line route, and the intersection gauge is the shortest vertical distance from an object located under the line (intersected) to the overhead line wire.

Rice. 10. Designs of wooden supports for overhead power lines:
A- for voltage below 1000 V, b- for voltage 6 and 10 kV; 1 - intermediate, 2 - corner with brace, 3 - corner with guy, 4 - anchor

Insulators.

The overhead line wires are fastened to the supports using insulators (Fig. 11) mounted on hooks and pins (Fig. 12).
For overhead lines with a voltage of 1000 V and below, insulators TF-4, TF-16, TF-20, NS-16, NS-18, AIK-4 are used, and for branches - SHO-12 with a wire cross-section of up to 4 mm 2; TF-3, AIK-3 and ШО-16 with wire cross-section up to 16 mm 2; TF-2, AIK-2, ШО-70 and ШН-1 with wire cross-section up to 50 mm 2; TF-1 and AIK-1 with wire cross-section up to 95 mm 2.
For fastening overhead line wires with voltages above 1000 V, ShS, ShD, USHL, ShF6-A and ShF10-A insulators and suspension insulators are used.
All insulators, except for suspended ones, are tightly screwed onto hooks and pins, onto which tow soaked in lead or drying oil is first wound, or special plastic caps are put on.
For overhead lines with voltages up to 1000 V, KN-16 hooks are used, and above 1000 V, KV-22 hooks are used, made of round steel with a diameter of 16 and 22 mm 2, respectively. On the traverses of the supports of the same overhead lines with voltages up to 1000 V, when fastening the wires, ShT-D pins are used - for wooden traverses and ShT-S - for steel ones.
When the overhead line voltage is more than 1000 V, SHU-22 and SHU-24 pins are mounted on the support cross-arms.
According to the mechanical strength conditions for overhead lines with voltages up to 1000 V, single-wire and multi-wire wires are used with a cross-section of at least: aluminum - 16, steel-aluminum and bimetal - 10, multi-wire steel - 25, single-wire steel - 13 mm (diameter 4 mm).

On an overhead line with a voltage of 10 kV and below, passing in an uninhabited area, with an estimated thickness of the layer of ice formed on the surface of the wire (ice wall) of up to 10 mm, in spans without intersections with structures, the use of single-wire steel wires is allowed, subject to special instructions.
In spans that cross pipelines not intended for flammable liquids and gases, the use of steel wires with a cross-section of 25 mm 2 or more is allowed. For overhead lines with voltages above 1000 V, only stranded copper wires with a cross-section of at least 10 mm 2 and aluminum wires with a cross-section of at least 16 mm 2 are used.
The connection of wires to each other (Fig. 62) is performed by twisting, in a connecting clamp or in die clamps.
Fastening of overhead line wires and insulators is carried out using binding wire using one of the methods shown in Fig. 13.
Steel wires are tied with soft galvanized steel wire with a diameter of 1.5 - 2 mm, and aluminum and steel-aluminum wires with aluminum wire with a diameter of 2.5 - 3.5 mm (stranded wires can be used).
Aluminum and steel-aluminum wires at fastening points are pre-wrapped with aluminum tape to protect them from damage.
On intermediate supports, the wire is mounted mainly on the head of the insulator, and on corner supports - on the neck, placing it on the outside of the angle formed by the line wires. The wires on the insulator head are secured (Fig. 13, a) with two pieces of binding wire. The wire is twisted around the insulator head so that its ends of different lengths are on both sides of the insulator neck, and then two short ends are wrapped 4-5 times around the wire, and two long ends are transferred through the insulator head and also wrapped around the wire several times. When attaching the wire to the neck of the insulator (Fig. 13, b), the tying wire loops around the wire and the neck of the insulator, then one end of the tying wire is wound around the wire in one direction (top to bottom), and the other end in the opposite direction (bottom to top).

On anchor and end supports, the wire is secured with a plug on the neck of the insulator. In places where overhead lines cross railways and tram tracks, as well as at intersections with other power lines and communication lines, double fastening of wires is used.
When assembling the supports, all wooden parts are tightly fitted to each other. The gap in the places of notches and joints should not exceed 4 mm.
Racks and attachments to overhead line supports are made in such a way that the wood at the junction has no knots or cracks, and the joint is completely tight, without gaps. The working surfaces of the cuts must be a continuous cut (without chiseling the wood).
Holes are drilled in the logs. It is prohibited to burn holes with heated rods.
Bandages for connecting attachments to the support are made of soft steel wire with a diameter of 4 - 5 mm. All turns of the bandage should be evenly tensioned and fit tightly to each other. If one turn breaks, the entire bandage should be replaced with a new one.
When connecting wires and cables of overhead lines with voltages above 1000 V in each span, no more than one connection is allowed for each wire or cable.
When using welding to connect wires, there should be no burnout of the outer wires or disruption of welding when the connected wires are bent.
Metal supports, protruding metal parts of reinforced concrete supports and all metal parts of wooden and reinforced concrete supports of overhead lines are protected with anti-corrosion coatings, i.e. paint. Places of assembly welding of metal supports are primed and painted to a width of 50 - 100 mm along the weld immediately after welding. Parts of structures that are subject to concreting are covered with cement laitance.

Rice. 14. Methods of attaching viscous wires to insulators:
A- head knitting, b- side knitting

During operation, overhead power lines are periodically inspected, and preventive measurements and checks are also carried out. The amount of wood decay is measured at a depth of 0.3 - 0.5 m. A support or attachment is considered unsuitable for further use if the depth of decay along the radius of the log is more than 3 cm with a log diameter of more than 25 cm.
Extraordinary inspections of overhead lines are carried out after accidents, hurricanes, during a fire near the line, during ice drifts, sleet, frost below -40 ° C, etc.
If a break in several wires is detected on a wire with a total cross-section of up to 17% of the wire cross-section, the break point is covered with a repair coupling or bandage. A repair coupling is installed on a steel-aluminum wire when up to 34% of the aluminum wires are broken. If more wires are broken, the wire must be cut and connected using a connecting clamp.
Insulators can suffer from punctures, glaze burns, melting of metal parts and even destruction of porcelain. This occurs in the event of breakdown of insulators by an electric arc, as well as in the deterioration of their electrical characteristics as a result of aging during operation. Often breakdowns of insulators occur due to severe contamination of their surface and at voltages exceeding the operating voltage. Data on defects discovered during inspections of insulators are entered into the defect log, and on the basis of these data plans for repair work of overhead lines are drawn up.

Cable power lines.

A cable line is a line for transmitting electrical energy or individual impulses, consisting of one or more parallel cables with connecting and end couplings (terminals) and fasteners.
Security zones are installed above underground cable lines, the size of which depends on the voltage of this line. Thus, for cable lines with voltages up to 1000 V, the security zone has an area of 1 m on each side of the outermost cables. In cities, under sidewalks, the line should run at a distance of 0.6 m from buildings and structures and 1 m from the roadway.
For cable lines with voltages above 1000 V, the security zone has a size of 1 m on each side of the outermost cables.
Submarine cable lines with voltages up to 1000 V and higher have a security zone defined by parallel straight lines at a distance of 100 m from the outermost cables.
The cable route is selected taking into account the lowest consumption and ensuring safety from mechanical damage, corrosion, vibration, overheating and the possibility of damage to adjacent cables if a short circuit occurs on one of them.
When laying cables, it is necessary to observe the maximum permissible bending radii, exceeding which leads to a violation of the integrity of the core insulation.
Laying cables in the ground under buildings, as well as through basements and warehouses is prohibited.
The distance between the cable and the foundations of buildings must be at least 0.6 m.
When laying a cable in a planted area, the distance between the cable and tree trunks must be at least 2 m, and in a green area with shrub plantings, 0.75 m is allowed. If the cable is laid parallel to the heat pipe, the clear distance from the cable to the wall of the heat pipe channel should not be less than 2 m, to the axis of the railway track - at least 3.25 m, and for an electrified road - at least 10.75 m.
When laying the cable parallel to the tram tracks, the distance between the cable and the axis of the tram track must be at least 2.75 m.
At the intersection of railways and highways, as well as tram tracks, cables are laid in tunnels, blocks or pipes across the entire width of the exclusion zone at a depth of at least 1 m from the roadbed and at least 0.5 m from the bottom of drainage ditches, and in the absence of a zone Exclusion cables are laid directly at the intersection or at a distance of 2 m on both sides of the road surface.
The cables are laid in a “snake” pattern with a margin equal to 1 - 3% of its length in order to eliminate the possibility of dangerous mechanical stresses arising due to soil displacements and temperature deformations. Laying the end of the cable in the form of rings is prohibited.

The number of couplings on the cable should be minimal, so the cable is laid in full construction lengths. Per 1 km of cable lines there can be no more than four couplings for three-core cables with voltages up to 10 kV with a cross-section of up to 3x95 mm 2 and five couplings for sections from 3x120 to 3x240 mm 2. For single-core cables, no more than two couplings are allowed per 1 km of cable lines.
For connections or cable terminations, the ends are cut, i.e., stepwise removal of protective and insulating materials. The dimensions of the groove are determined by the design of the coupling that will be used to connect the cable, the voltage of the cable and the cross-section of its conductors.
The finished cutting of the end of a three-core paper-insulated cable is shown in Fig. 15.
The connection of cable ends with voltages up to 1000 V is carried out in cast iron (Fig. 16) or epoxy couplings, and with voltages of 6 and 10 kV - in epoxy (Fig. 17) or lead couplings.

Rice. 16. Cast iron coupling:
1 - upper coupling, 2 - winding made of resin tape, 3 - porcelain spacer, 4 - lid, 5 - tightening bolt, 6 - grounding wire, 7 - lower coupling half, 8 - connecting sleeve

Rice. 17. Epoxy coupling:
1 - wire bandage, 2 - coupling body, 3 - a bandage made of coarse threads, 4 - spacer, 5 - winding the core, 6 - ground wire, 7 - connection of cores, 8 - sealing winding

Rice. 18. Connection of copper cable cores by crimping:

A- cleaning the inner surface of the liner with a steel wire brush, b- stripping the core with a carded brush, V- installation of the sleeve on the connected cores, G- crimping the sleeve in a press, d- ready connection; 1 - copper sleeve, 2 - ruff, 3 - brush, 4 - lived, 5 - press
The sleeve is installed flush in the matrix bed (Fig. 18, d), then the sleeve is pressed with two indentations, one for each core (Fig. 18, e). The indentation is carried out in such a way that the punch washer at the end of the process rests against the end (shoulders) of the matrix. The remaining cable thickness (mm) is checked using a special caliper or caliper (value N in Fig. 19):
4.5 ± 0.2 - with a cross-section of the connected conductors 16 - 50 mm 2
8.2 ± 0.2 - with a cross-section of the connected cores of 70 and 95 mm 2
12.5 ± 0.2 - with a cross-section of connected conductors of 120 and 150 mm 2
14.4 ± 0.2 - with a cross-section of connected cores of 185 and 240 mm 2
The quality of the pressed cable contacts is checked by external inspection. In this case, pay attention to the indentation holes, which should be located coaxially and symmetrically relative to the middle of the sleeve or the tubular part of the tip. There should be no tears or cracks in the places where the punch is pressed.
To ensure appropriate quality of cable crimping, the following work conditions must be met:
use lugs and sleeves whose cross-section corresponds to the design of the cable cores to be terminated or connected;
use dies and punches corresponding to the standard sizes of tips or sleeves used for crimping;
do not change the cross-section of the cable core to facilitate insertion of the core into the tip or sleeve by removing one of the wires;

do not perform crimping without first cleaning and lubricating the contact surfaces of the tips and sleeves on aluminum conductors with quartz-vaseline paste; Complete crimping no earlier than the punch washer comes close to the end of the matrix.
After connecting the cable cores, the metal belt is removed between the first and second annular cuts of the sheath and a bandage of 5 - 6 turns of solid thread is applied to the edge of the belt insulation underneath it, after which spacer plates are installed between the cores so that the cable cores are held at a certain distance from each other friend and from the coupling body.
Lay the ends of the cable in the coupling, having previously wound 5 - 7 layers of resin tape around the cable at the points of entry and exit from the coupling, and then fasten both halves of the coupling with bolts. The grounding conductor, soldered to the armor and sheath of the cable, is inserted under the mounting bolts and thus firmly secured to the coupling.
The operations of cutting the ends of cables with voltages of 6 and 10 kV in a lead coupling are not much different from similar operations of connecting them in a cast iron coupling.
Cable lines can provide reliable and durable operation, but only if the installation technology and all the requirements of the technical operation rules are observed.
The quality and reliability of mounted cable couplings and terminations can be increased if during installation a set of necessary tools and devices is used for cutting the cable and connecting the cores, heating the cable mass, etc. The qualifications of the personnel are of great importance for improving the quality of the work performed.
For cable connections, sets of paper rolls, rolls and bobbins of cotton yarn are used, but they are not allowed to have folds, torn or wrinkled places, or be dirty.
Such kits are supplied in cans depending on the size of the couplings by numbers. Before use, the jar at the installation site must be opened and heated to a temperature of 70 - 80 °C. Heated rollers and rolls are checked for the absence of moisture by immersing paper strips in paraffin heated to a temperature of 150 °C. In this case, no cracking or foam should be observed. If moisture is detected, the set of rollers and rolls is rejected.
The reliability of cable lines during operation is supported by a set of measures, including monitoring cable heating, inspections, repairs, and preventive tests.
To ensure long-term operation of the cable line, it is necessary to monitor the temperature of the cable cores, since overheating of the insulation causes accelerated aging and a sharp reduction in the service life of the cable. The maximum permissible temperature of the cable conductors is determined by the cable design. Thus, for cables with a voltage of 10 kV with paper insulation and viscous non-drip impregnation, a temperature of no more than 60 ° C is allowed; for cables with voltage 0.66 - 6 kV with rubber insulation and viscous non-draining impregnation - 65 ° C; for cables with voltage up to 6 kV with plastic (polyethylene, self-extinguishing polyethylene and polyvinyl chloride plastic) insulation - 70 ° C; for cables with a voltage of 6 kV with paper insulation and depleted impregnation - 75 ° C; for cables with a voltage of 6 kV with plastic (vulcanized or self-extinguishing polyethylene or paper insulation and viscous or depleted impregnation - 80 ° C.
Long-term permissible current loads on cables with insulation made of impregnated paper, rubber and plastic are selected according to current GOSTs. Cable lines with a voltage of 6 - 10 kV, carrying less than rated loads, can be briefly overloaded by an amount that depends on the type of installation. So, for example, a cable laid in the ground and having a preload factor of 0.6 can be overloaded by 35% within half an hour, by 30% - 1 hour and by 15% - 3 hours, and with a preload factor of 0.8 - by 20% for half an hour, by 15% - 1 hour and by 10% - 3 hours.
For cable lines that have been in operation for more than 15 years, overload is reduced by 10%.
The reliability of a cable line largely depends on the proper organization of operational supervision of the condition of the lines and their routes through periodic inspections. Routine inspections make it possible to identify various violations on cable routes (excavation work, storage of goods, planting trees, etc.), as well as cracks and chips in the insulators of the end couplings, loosening of their fastenings, the presence of bird nests, etc.
A great danger to the integrity of cables is posed by earth excavations carried out on or near the routes. The organization operating underground cables must provide an observer during excavations in order to avoid damage to the cable.
According to the degree of danger of cable damage, excavation sites are divided into two zones:
Zone I - a piece of land located on the cable route or at a distance of up to 1 m from the outermost cable with voltage above 1000 V;
Zone II - a piece of land located from the outermost cable at a distance of over 1 m.
When working in zone I, it is prohibited:
use of excavators and other earth-moving machines;
use of impact mechanisms (wedges, balls, etc.) at a distance closer than 5 m;
the use of mechanisms for excavating soil (jackhammers, electric hammers, etc.) to a depth above 0.4 m at a normal cable depth (0.7 - 1 m); carrying out excavation work in winter without preliminary heating of the soil;
performance of work without supervision by a representative of the organization operating the cable line.
In order to promptly identify defects in cable insulation, connecting and termination joints and prevent sudden cable failure or destruction by short circuit currents, preventive tests of cable lines with increased DC voltage are carried out.

An overhead power line (OTL) is a device for transmitting and distributing electricity through wires located in the open air, attached using insulators and fittings to the supports or brackets of engineering structures (bridges, overpasses, etc.). The installation of an overhead line, its design and construction must comply with the “Rules for the Construction of Electrical Installations” (RUE), which are mandatory for all power lines, except special ones (for example, contact networks of a tram, trolleybus, railway, etc.)

Classification and operating modes of overhead lines. Overhead power lines, as a rule, are designed to transmit three-phase alternating current and, according to their purpose, are divided into:

– ultra-long-range voltages of 500 kV and higher, serving mainly for communication between individual power systems;
– main lines with voltages of 220 and 330 kV, used to transmit energy from powerful power plants, as well as for communication between power systems and the integration of power plants within power systems (usually connecting power plants with distribution points);
– distribution voltages of 35, PO and 150 kV, serving for power supply to enterprises and settlements of large areas (connect distribution points with consumers and represent branched networks with transformer substations);
– power transmission lines of 20 kV and below, used to supply electricity to consumers.
Electricity consumers are divided into three categories based on the reliability of power supply:
– the first category includes consumers whose power supply disruption can lead to danger to human life, damage to equipment, massive defective products, disruption important elements urban economy;
– the second - consumers, whose power supply interruption leads to massive under-supply of products, downtime of equipment and workers, and disruption of the normal activities of a significant part of the urban population;
- to the third - the remaining consumers.

Based on voltage, overhead power lines are divided into two groups by the Electrical Installation Rules: overhead lines with voltages up to 1000 V (low-voltage) and overhead lines with voltages above 1000 V (high-voltage). For each group of lines, the technical requirements for their design are established. The rated linear voltage of three-phase current lines is regulated by GOST 721-62 and can have the following values: 750, 500, 330, 220, 150, 110, 35, 20, 10, 6 and 3 kV, as well as 660, 380 and 220 V.

According to the electrical mode of operation, the lines are divided into: lines with an isolated neutral, when the common point of the windings (neutral) is not connected to the grounding device or is connected to it through devices having high resistance, and with a solidly grounded neutral, when the neutral of the generator or transformer is tightly connected to the ground.

In networks with an isolated neutral, the line insulation must be no less than the value of the line voltage, since when one phase is short-circuited to ground, the voltage of the other two phases relative to the ground becomes equal to the linear voltage. In networks with a solidly grounded neutral, if one phase is damaged, a short circuit occurs through the ground and line protection disconnects the damaged section. In this case, phase overvoltage does not occur and the line insulation is selected according to the phase voltage. The disadvantage of these networks is the large magnitude of the ground fault current and the disconnection of the line in the event of a single-phase ground fault. In our country, networks with a solidly grounded neutral are used in systems with voltages up to 1000 V and from 110 kV and above.

Depending on the mechanical condition, they are distinguished following modes overhead line work:
– normal - wires and cables are not broken;
– emergency - wires and cables are broken completely or partially;
– installation - in the conditions of installation of supports, wires and cables.

Mechanical loads on overhead line elements largely depend on the climatic conditions of the area and the nature of the terrain through which the line runs. When designing overhead lines, the highest value of wind speed and wall thickness of ice formed on the wires, observed in the given area once every 15 years for overhead lines with a voltage of 500 kV and once every 10 years for overhead lines with a voltage of 6-330 kV, is taken as a basis.

The terrain through which the overhead line passes, depending on accessibility for people, transport and agricultural machinery, is divided according to the PUE into three categories:

– populated areas include the territory of cities, towns, villages, industrial and agricultural enterprises, ports, marinas, railway stations, parks, boulevards, beaches, taking into account the boundaries of their development for the next 10 years;

– to uninhabited - an undeveloped territory, partially visited by people and accessible to transport and agricultural machinery (uninhabited areas are also considered to be vegetable gardens, orchards and areas with separate, sparsely standing buildings and temporary structures);

– hard-to-reach - territory inaccessible to transport and agricultural machinery.
Design and main elements of overhead lines. Overhead power lines consist of supporting structures (supports and bases), wires, insulators and line fittings. In addition, the overhead line includes devices necessary to ensure uninterrupted power supply to consumers and normal operation of the line: lightning protection cables, arresters, grounding, as well as auxiliary equipment for operational needs (high-frequency communication devices, capacitive power take-off, etc.)

Overhead transmission line supports support wires at a given distance between each other and from the surface of the earth. The horizontal distances between the centers of two supports on which the wires are suspended are called span, or span length. There are transition, intermediate and anchor spans. An anchor span usually consists of several intermediate spans.

The angle of rotation of the line is the angle between the directions of the line in adjacent spans.
The vertical distance hg (Figure 1, a) between the lowest point of the wire in the span to the intersecting engineering structures or to the surface of the earth or water is called the wire gauge.

Figure 1 – Dimensions (a) and sag (b) of wires:
F, f - wire sag; hg-dimension of the wire from the ground, A, B - wire suspension points

The sag f of a wire is the vertical distance between the lowest point of the wire in the span and the horizontal straight line connecting the points where the wire is suspended from the supports. If the height of the attachment points is different, the sag arrow is considered relative to the highest and lowest points of wire attachment (F and f in Figure 1,b).
Tension is the force with which a wire or cable is pulled and secured to supports. The tension varies depending on the strength of the wind, the ambient temperature, the thickness of the ice on the wires and can be normal or weakened.

The safety factor, or safety factor of overhead power line elements, is the ratio of the minimum design load that destroys a given element to the actual load in the most severe conditions.

Mechanical stress of a material is the load on overhead line elements per unit area of their working section. For example, the tension of a wire relative to its cross-section determines the mechanical stress of the wire material.

Temporary resistance is the maximum permissible mechanical stress of a material, after exceeding which the destruction of the product begins.

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