Overhead and cable power lines. Overhead power lines Power transmission lines: design, varieties, parameters High-voltage power transmission lines

What are the power lines

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

• by type of wire placement - air (located on outdoors) and cable (closed in insulation);
• by appointment - ultra-long, trunk, distribution.

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

Overhead power lines (VL)

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

Distinguish lines:

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

Alternating current

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

D.C

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

Since most consumers use alternating current, when arranging such lines, you have to spend an additional resource on energy conversion.

Installation of overhead power lines

The device of overhead power lines includes the following elements:

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

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

Cable power lines

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

Underground and underwater

The closing method allows you to place lines even in the most difficult conditions - underground and under the water surface. For their laying, special tunnels or other methods can be used. In this case, several cables can be used, as well as various fasteners.

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

Laying on structures

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

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

Insulation of cable power lines

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

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

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

Classification by purpose

Another characteristic according to which the classification of power lines takes place, taking into account voltage, is their purpose. Overhead lines are usually divided into: ultra-long, trunk, distribution. They differ depending on the power, type of recipient and sender of energy. These can be large stations or consumers - factories, settlements.

ultra-long

The main purpose of these lines is the connection between different energy systems. The voltage in these overhead lines starts from 500 kV.

Trunk

This power transmission line format assumes a voltage in the network of 220 and 330 kV. Trunk lines ensure the transmission of energy from power plants to distribution points. They can also be used to connect various power plants.

Distribution

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

Construction and repair of power lines

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

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

• Survey of the area.
• Line design, budgeting, technical documentation.
• Preparation of the territory, selection and purchase of materials.
• Assembly of supporting elements or preparation for cable installation.
• Installation or laying of wires, hanging devices, strengthening power lines.
• Improvement of the territory and preparation of the line for launch.
• Commissioning, official registration of documentation.

To provide effective work the line requires its competent maintenance, timely repair and, if necessary, reconstruction. All such activities must be carried out in accordance with the PUE (rules for technical installations).

Repair of electrical lines is divided into current and capital. During the first, the state of the system is monitored, work is carried out to replace various elements. Overhaul involves more serious work, which may include the replacement of supports, hauling lines, replacing entire sections. All types of work are determined depending on the state of the power transmission line.

power lines

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

According to MPTEEP (Intersectoral rules for the technical operation of consumer electrical installations) Power line- An electrical line extending outside the power plant or substation and intended for the transmission of electrical energy.

Distinguish air and cable power lines.

Information is also transmitted via power lines using high-frequency signals; according to estimates, about 60 thousand HF channels are used in Russia via power lines. They are used for supervisory control, transmission of telemetry data, relay protection signals and emergency automation.

Overhead power lines

Overhead power line(VL) - a device designed for the transmission or distribution of electrical energy through wires located in the open air and attached with the help of traverses (brackets), insulators and fittings to supports or other structures (bridges, overpasses).

Composition VL

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

Documents regulating overhead lines

VL classification

By type of current

• AC overhead line
• DC overhead line

Basically, overhead lines are used to transmit alternating current and only in some cases (for example, to connect power systems, power a contact network, etc.) use direct current lines.

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

By appointment

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

By voltage

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

These groups differ significantly mainly in the requirements in terms of design conditions and structures.

According to the mode of operation of neutrals in electrical installations

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

According to the mode of operation depending on the mechanical condition

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

The main elements of overhead lines

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

Cable power lines

Cable power line(KL) - is a line for the transmission of electricity or its individual impulses, consisting of one or more parallel cables with connecting, locking and end sleeves (terminals) and fasteners, and for oil-filled lines, in addition, with feeders and a pressure alarm system oils.

By classification cable lines are similar to overhead lines

Cable lines are divided according to the conditions of passage

• Underground
• By buildings
• Underwater

cable installations are

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

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

• cable shaft- vertical cable construction (usually rectangular section), whose height is several times greater than the side of the section, equipped with brackets or a ladder for people to move along it (walk-through shafts) or a completely or partially removable wall (non-walk-through shafts).

• cable floor- a part of the building bounded by the floor and the floor or cover, with a distance between the floor and the protruding parts of the floor or cover of at least 1.8 m.

• double floor- a cavity bounded by the walls of the room, interfloor overlapping and the floor of the room with removable plates (on the whole or part of the area).

• cable block- cable structure with pipes (channels) for laying cables in them with wells related to it.

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

• cable rack- above-ground or ground open horizontal or inclined extended cable structure. Cable overpass can be passable or non-passage.

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

By type of insulation

Cable line insulation is divided into two main types:

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

Gaseous insulation and some types of liquid and solid insulation are not indicated here due to their relatively rare use at the time of writing.

Losses in power lines

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

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

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

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

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

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

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

Power line

power lines

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

According to MPTEEP (Intersectoral rules for the technical operation of consumer electrical installations) Power line- An electrical line extending outside the power plant or substation and intended for the transmission of electrical energy.

Distinguish air and cable power lines.

Information is also transmitted via power lines using high-frequency signals; according to estimates, about 60 thousand HF channels are used in Russia via power lines. They are used for supervisory control, transmission of telemetry data, relay protection signals and emergency automation.

Overhead power lines

Overhead power line(VL) - a device designed for the transmission or distribution of electrical energy through wires located in the open air and attached with the help of traverses (brackets), insulators and fittings to supports or other structures (bridges, overpasses).

Composition VL

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

Documents regulating overhead lines

VL classification

By type of current

• AC overhead line
• DC overhead line

Basically, overhead lines are used to transmit alternating current and only in some cases (for example, to connect power systems, power a contact network, etc.) use direct current lines.

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

By appointment

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

By voltage

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

These groups differ significantly mainly in the requirements in terms of design conditions and structures.

According to the mode of operation of neutrals in electrical installations

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

According to the mode of operation depending on the mechanical condition

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

The main elements of overhead lines

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

Cable power lines

Cable power line(KL) - is a line for the transmission of electricity or its individual impulses, consisting of one or more parallel cables with connecting, locking and end sleeves (terminals) and fasteners, and for oil-filled lines, in addition, with feeders and a pressure alarm system oils.

By classification cable lines are similar to overhead lines

Cable lines are divided according to the conditions of passage

• Underground
• By buildings
• Underwater

cable installations are

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

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

• cable shaft- a vertical cable structure (usually of a rectangular section), whose height is several times greater than the side of the section, equipped with brackets or a ladder for people to move along it (passage shafts) or a completely or partially removable wall (non-passage mines).

• cable floor- a part of the building bounded by the floor and the floor or cover, with a distance between the floor and the protruding parts of the floor or cover of at least 1.8 m.

• double floor- a cavity bounded by the walls of the room, interfloor overlapping and the floor of the room with removable plates (on the whole or part of the area).

• cable block- cable structure with pipes (channels) for laying cables in them with wells related to it.

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

• cable rack- above-ground or ground open horizontal or inclined extended cable structure. Cable overpass can be passable or non-passage.

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

By type of insulation

Cable line insulation is divided into two main types:

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

Gaseous insulation and some types of liquid and solid insulation are not indicated here due to their relatively rare use at the time of writing.

Losses in power lines

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

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

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

Literature

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

Cable line (CL)- a line for the transmission of electricity, consisting of one or more parallel cables, made in some way by laying (Fig. 1.29). Cable lines are laid where the construction of overhead lines is impossible due to cramped territory, unacceptable in terms of safety regulations, impractical in terms of economic, architectural and planning indicators and other requirements. The greatest application of CL was found in the transmission and distribution of EE at industrial enterprises and in cities (internal power supply systems) when transmitting EE through large bodies of water

Advantages and advantages of cable lines in comparison with overhead lines: weatherproofness, secrecy of the route and inaccessibility to unauthorized persons, less damage, compactness of the line and the possibility of a wide 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), more difficult to construct and operate.

Rice. 1.29. Ways of laying cables and cable structures: a - earthen trench; b-collector; c-tunnel; g-channel; d - flyover; e - block

AT CL composition includes: cable, equipment for connecting and sectioning cable sections and connecting cable ends to equipment and busbars of the switchgear (cable fittings - mainly various couplings), building structures, fastening elements, as well as oil or gas make-up equipment (for oil- and gas-filled cables ).

The classification of cable lines basically corresponds to the classification of the cables included in it. The main features are:

Type of current;

Rated voltage;

Number of current-carrying elements;

electrical insulating material;

The nature of the impregnation and the method of increasing the electrical strength of paper insulation;

Sheath material.

(These features only cover cables operating under free cooling conditions. There are cables with forced water or oil cooling, as well as cryogenic cables.)

Cable- a finished factory product, consisting of insulated current-conducting 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 - single-wire, over - multi-wire. According to the cross-sectional shape, the conductors are round, segmental or sector.

Cables with voltage up to 1 kV are made, as a rule, four-core, voltage 6-35 kV - three-core, and voltage 110-220 kV - single-core.

Protective shells are made of lead, aluminium, rubber and PVC. In 35 kV cables, each core is additionally enclosed in a lead sheath, which creates a more uniform electric field and improves heat dissipation. Equalization of the electric field in cables with plastic insulation and sheath is achieved by shielding each core with semi-conductive paper.

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

Cable armor made of steel tapes or galvanized steel wires is protected from corrosion by an outer cover of cable yarn impregnated with bitumen and coated with chalk.

In cables with a voltage of 110 kV and above, to increase the electrical strength of paper insulation, they are filled with gas or oil under pressure (gas-filled and oil-filled cables).

High voltage cable lines

Cable lines with viscous impregnation at voltages over 35 kV are not used. This is due to the fact that air inclusions always remain in the insulation of the finished cable. Their presence significantly reduces the dielectric strength of the insulation. Air inclusions, depending on their location, undergo ionization with all the ensuing consequences, or their negative role is manifested in connection with the occurrence of thermal processes. The cable is periodically subjected to heating and cooling due to changes in the transmitted power. An increase and decrease in the volume of the cable leads to an increase in air inclusions, their migration to the conductive core and subsequent breakdown.

You can eliminate these phenomena in two ways:

Exclude air inclusions;

Increase the pressure in the air (gas) inclusions.

The first method is used in low-pressure oil-filled cables (OLCs) with oil channels inside the core, the second - in OLS high pressure laid in steel pipelines.

Low pressure oil-filled cables .

Low-pressure MNCs (up to 0.05 MPa) are produced as single-core. They are mass-produced for voltages of 110, 150 and 220 kV and have copper conductors with a cross section of 120-800 in lead or aluminum sheaths.

Depending on the laying conditions - in the ground (in trenches), when the cable is not subjected to tensile conditions and is protected from mechanical damage; or under water, in swampy areas and where it is subjected to tensile forces, various types of oil-filled cable are used.

High pressure oil-filled cables .

High pressure oil-filled cables (OLC) are manufactured for voltages of 110, 220, 330, 380 and 500 kV.

The cores of such a cable are produced:

a) in a temporary lead sheath that protects the insulation from moisture and damage during transportation and is removed during installation;

b) without a shell. In this case, the cable cores are delivered to the track in a sealed container filled with oil.

During installation, insulated and shielded copper conductors with a cross section of 120-700 with semicircular sliding wires superimposed on them are pulled into steel pipes. At = 500 kV, the outer diameter of the pipe is 273 mm with a wall thickness of 10 mm.

For such cable lines, the oil pressure is 1.08 - 1.57 MPa. Due to the high pressure, the dielectric strength increases. Pipes are good protection against mechanical damage.

Pipelines are welded from segments 12 m long. Compensation for changes in oil volume with temperature changes and maintenance of oil pressure in the pipeline is carried out by an automatic feeding device, which is located at one end of the line (for short lengths) or at both ends (for long lengths).

There are also oil-filled medium pressure cables, cables with polymeric materials as insulation, etc.

The brand, designation of the cable indicates information about its design, rated voltage, number and cross-section of cores. For four-core cables with voltage up to 1 kV, the cross section of the fourth ("zero") core is smaller than the phase one. For example, cable VPG-1- 3x35 + 1x25 - a cable with three copper cores with a cross section of 35 mm 2 and a fourth with a cross section of 25 mm ", polyethylene (P) insulation for 1 kV with a PVC sheath (V), unarmored, without an outer cover (D) "_ for laying indoors, in channels, tunnels, in the absence of mechanical influences on the cable; cable AOSB-35-3x70 - a cable with three aluminum (A) cores of 70 mm 2, with 35 kV insulation, with separately leaded (O) cores, 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 fig. 1.30. On fig. 1.30, a, b power cables with voltage up to 10 kV are given.

A four-core cable with a voltage of 380 V (see Fig. 1.30, 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.

A three-core cable with paper insulation with a voltage of 10 kV (Fig. 1.30, b) contains the elements: 1 - current-carrying conductors; 2 - phase isolation; 3 - general belt insulation; 4 - protective shell; 5 - pillow under the armor; 6 - steel armor; 7 - protective cover; 8 - filler.

A three-core cable with a voltage of 35 kV is shown in fig. 1.30 a.m. It includes: 1 - round conductive wires; 2 - semi-conductive screens; 3 - phase isolation; 4 - lead sheath; 5 - pillow; 6 - cable yarn filler; 7 - steel armor; 8 - protective cover.

On fig. 1.30, d shows an oil-filled cable of medium and high pressure with a voltage of 110-220 kV. Oil pressure prevents air from entering and ionizing, eliminating one of the main causes of insulation breakdown. Three single-phase cables are placed in a steel pipe 4 filled with pressurized oil 2. The current-carrying core 6 consists of copper round wires and is covered with paper insulation 1 with viscous impregnation; screen 3 is superimposed over the insulation in the form of a perforated copper tape and bronze wires, which protect the insulation from mechanical damage when the cable is pulled through the pipe. Outside steel pipe protected by cover 5 .

Cables in PVC insulation, produced by three-, four- and five-core (1.30, e) or single-core (Fig. 1.30, e), are widespread. For more detailed information about the various types and brands of cables, their areas of application, see.

Cables are made in segments of limited length depending on the voltage and section. When laying, the segments are connected by means of couplings that seal the joints. In this case, the ends of the cable cores are released from insulation and sealed in the connecting clamps.

When laying 0.38-10 kV cables in the ground, to protect against corrosion and mechanical damage, the junction is enclosed in a protective cast-iron detachable casing. For 35 kV cables, steel or fiberglass casings are also used.

The reliability of the entire cable line is largely determined by the reliability of its fittings, i.e. couplings various types and appointments.

High voltage cable joints are classified according to three main features.

By appointment couplings are divided into three main groups - terminal, connecting and locking, moreover, among the terminal ones, open couplings and cable glands in transformers and high-voltage devices are distinguished, and among the connecting ones - the actual connecting, branching and connecting - branching couplings.

By type of electrical insulation couplings are divided into two groups: with layered and monolithic insulation. Laminated insulation is performed by winding tapes from cable paper, synthetic film or their compositions and filled with one or another medium (oil, gas) under or without excess pressure. Monolithic insulation formed by extrusion or sintering of insulating materials in heated molds.

By type of current distinguish between couplings for cables of alternating, direct and impulse current. Couplings of AC cables can be made single-phase and three-phase.

Coupling design power cables high voltage is primarily determined by the type of cable for which they are intended.

Use at the ends of the cables end sleeves or end fittings.

Rice. 1.30. Power cables: a - four-core voltage 380 V;

b- wire-core with paper insulation with a voltage of 10 kV; c - three-core voltage 35 kV; g - oil-filled high pressure; d - single-core with plastic insulation

On fig. 1.31a, the connection of a three-core low-voltage cable 2 in a cast-iron sleeve 1 is shown. The ends of the cable are fixed with a porcelain spacer 3 and connected with a clamp 4. Cable sleeves up to 10 kV with paper insulation are filled with bituminous compounds, cables 20-35 kV are oil-filled. For cables with plastic insulation, couplings are used from heat-shrinkable insulating tubes, the number of which corresponds to the number of phases, and one heat-shrinkable tube for a zero core, seated in a sealed sleeve (Fig. 1.31, b).

Rice. 1.31. Couplings for three- and four-core cables with voltage up to 1 kV: a - cast iron; b- from heat-shrinkable insulating tubes

On fig. 1.32, and shows a mastic-filled three-phase coupling for outdoor installation with porcelain insulators for cables with a voltage of 10 kV. For three-core plastic insulated cables, the termination shown in fig. 1.32b. It consists of a heat-shrinkable glove 1 resistant to environment, and semi-conductive 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 put on separate cores. The required number of heat-shrinkable insulators 4 is mounted on them.

Rice. 1.32. Terminations for three-core cables with a voltage of 10 kV: a - outdoor installation with porcelain insulators; b - outdoor installation with plastic insulation; c - indoor installation with dry cutting

For cables of 10 kV and below with plastic insulation in the interior, dry cutting is used (Fig. 1.32, e). The cut ends of the cable with insulation 3 are wrapped with adhesive PVC tape 5 and varnished; the ends of the cable are sealed with cable mass 7 and an insulating glove 1 that overlaps the sheath of the cable 2, the ends of the glove and the core are additionally sealed and wrapped with PVC tape 4, 5, the latter is fixed with twine bandages 6 to prevent lagging and unwinding.

Cable laying method 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 along the floors of buildings (Fig. 1.29).

Most often in cities, industrial enterprises, cables are laid in earthen trenches . To prevent damage due to deflections at the bottom of the trench, a soft cushion is created 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 against mechanical damage. After that, the cable trench is covered with earth. In places of crossing roads and at the entrances to buildings, the cable is laid in asbestos-cement or other pipes. This protects the cable from vibrations and allows repair without opening the roadbed. Laying in trenches is the least expensive way of EE cable ducting.

In places of laying a large number cables, aggressive soil and stray currents limit the possibility of their laying in the ground. Therefore, along with other underground communications, special structures are used: collectors, tunnels, channels, blocks and overpasses .

Collector(Fig. 1.29, b) serves for the joint placement of various underground communications in it: cable power lines and communications, water supply along city highways and on the territory of large enterprises.

At large numbers cables laid in parallel, for example, from the building of a powerful power plant, laying is used in tunnels

(Fig. 1.29, c). This improves operating conditions, reduces the surface area of ​​the earth required for laying cables. However, the cost of tunnels is very high. Tunnel It is intended only for laying cable lines. It is built underground from precast concrete or large diameter sewer pipes, the capacity of the tunnel is from 20 to 50 cables.

With fewer cables, use cable channels (Fig. 1.29, d), closed by the ground or reaching the level of the ground surface.

Cable racks and galleries(Fig. 1.29, e) are used for above-ground cable laying. This type of cable structures is widely used where the direct laying of power cables in the ground is dangerous due to landslides, landslides, permafrost, etc. In cable ducts, tunnels, collectors and overpasses, cables are laid along cable brackets.

In large cities and large enterprises, cables are sometimes laid in blocks (Fig. 1.29, 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 flows of cables are laid in metal trays and boxes. Single cables can be laid openly along walls and ceilings or hidden: in pipes, in hollow slabs and other building parts buildings.

Overhead power lines.

An overhead electric line is a device that serves to transmit electrical energy through wires located in the open air and attached to supports with the help of insulators and fittings. Overhead power lines are divided into overhead lines with voltage up to 1000 V and above 1000 V.

During the construction of overhead power lines, the volume earthworks insignificant. In addition, they are easy to operate and repair. The cost of building an overhead line is approximately 25-30% less than the cost of a cable line of the same length. Air 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 the categories of consumers;

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. characteristic feature overhead line with a voltage of up to 1000 V is the use of supports for the simultaneous fastening of radio network wires, outdoor lighting, telecontrol, and signaling on them.

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

For lines with a voltage of 1 kV, 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 forests - pines, spruces, larches, fir. It is possible not to impregnate logs in the manufacture of supports from hardwood winter felling. The diameter of the logs in the top cut must be at least 15 cm for single poles and at least 14 cm for double and A-shaped poles. It is allowed to take the diameter of the logs in the upper cut at least 12 cm on the branches leading to the inputs to buildings and structures. Depending on the purpose and design, intermediate, angular, branch, cross and end supports are distinguished.

Intermediate supports on the line are the most numerous, as they serve to maintain 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 perceive this load, anchor intermediate supports are installed, placing their "legs" along the axis of the line. To absorb forces perpendicular to the line, anchor intermediate supports are installed, placing the "legs" of the support across the line.

Anchor supports have more complex structure 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 the intermediate supports is called the support pitch.
In places where the direction of the overhead line route changes, corner supports are installed.

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

For overhead lines with voltages above 1 kV, reinforced concrete and wooden antiseptic supports on reinforced concrete attachments are mainly used. The structures of these supports are unified.
Metal supports are mainly used as anchor supports on overhead lines with voltages above 1 kV.
On the VL supports, the arrangement of wires can be any, only the neutral wire in lines up to 1 kV is placed below the phase ones. When suspended on outdoor lighting wire poles, they are placed below neutral wire.
Wires of overhead lines with voltage up to 1 kV should be hung 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 sagging of the wire is called the gauge of the overhead line wire above the ground.
Overhead line wires can come close to other lines along the route, intersect with them and pass at a distance from objects.
The approach dimension of the overhead line wires is the permissible smallest 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 the object located under the line (intersected) to the overhead line wire.

Rice. 10. Structures of wooden poles for overhead power lines:
a - for voltages below 1000 V, b - for voltages of 6 and 10 kV; 1 - intermediate, 2 - angled with a brace, 3 - angled with a brace, 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 SHO-16 with a wire cross section of up to 16 mm 2; TF-2, AIK-2, SHO-70 and ShN-1 with a wire cross section of up to 50 mm 2; TF-1 and AIK-1 with a wire cross section of up to 95 mm 2.

Insulators ShS, ShD, USHL, ShF6-A and ShF10-A and suspension insulators are used to fasten wires of overhead lines with voltages above 1000 V.

All insulators, except for suspension ones, are tightly screwed onto hooks and pins, on which tow is preliminarily wound, soaked in minium or drying oil, 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 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 a voltage of up to 1000 V, when attaching wires, pins ШТ-Д are used - for wooden traverses and ШТ-С - for steel ones.

When the voltage of overhead lines is more than 1000 V, the pins SHU-22 and SHU-24 are mounted on the traverses of the supports.

According to the conditions of mechanical strength for overhead lines with a voltage of up to 1000 V, single-wire and multi-wire wires are used with a cross section of at least: aluminum - 16 steel-aluminum and bimetallic -10, steel stranded - 25, steel single-wire - 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 an ice layer formed on the surface of the wire (ice wall) up to 10 mm, in spans without intersections with structures, the use of single-wire steel wires is allowed if there is a special instruction.
In spans that cross pipelines not intended for flammable liquids and gases, it is allowed to use steel wires with a cross section of 25 mm 2 or more. 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 carried out by twisting, in a connecting clamp or in die clamps.

The fastening of wires of overhead lines and insulators is carried out with a knitting wire in one of the ways 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 (multi-wire wires can be used).

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

On intermediate supports, the wire is fixed mainly on the head of the insulator, and on the corner supports - on the neck, placing it on the outside of the angle formed by the line wires. The wires on the head of the insulator are fixed (Fig. 13, a) with two pieces of knitting 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 ones 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 knitting wire loops around the wire and the neck of the insulator, then one end of the knitting wire is wrapped around the wire in one direction (from top to bottom), and the other end - in the opposite direction (from bottom to top).

On anchor and end supports, the wire is fixed 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.

All wooden details when assembling the supports, they are tightly adjusted to each other. The gap in the places of cuts 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 does not have knots and cracks, and the joint is completely tight, without gaps. The working surfaces of the cuts must be continuous cut (without grooving wood).
Holes are drilled in logs. It is forbidden to burn holes with heated rods.

Bandages for pairing attachments with a support are made of soft steel wire with a diameter of 4 - 5 mm. All turns of the bandage must be evenly stretched and fit snugly to each other. In the event of a break in one turn, the entire bandage should be replaced with a new one.

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

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

Metal poles, protruding metal parts of reinforced concrete poles and all metal parts of wooden and reinforced concrete poles 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. Ways of fastening wires with viscous to insulators:
a - head knit, b - side knit

During operation, overhead power lines are periodically inspected, as well as preventive measurements and checks are made. The value of wood decay is measured at a depth of 0.3 - 0.5 m. The 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, in case of fire near the line, during ice drifts, ice, frost below -40 ° C, etc.

If a break is found on the wire of several wires with a total cross section of up to 17% of the wire cross section, the break is blocked by a repair sleeve or bandage. A repair sleeve on a steel-aluminum wire is installed when up to 34% of aluminum wires break. If more strands are broken, the wire must be cut and connected with a connecting clamp.

Insulators can suffer punctures, glaze burns, melting of metal parts, and even destruction of porcelain. This happens in case of breakdown of insulators by an electric arc, as well as when their deterioration 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 found during inspections of insulators are entered in the defect log, and plans are made based on these data. repair work air lines.

Cable power lines.

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

Protective zones are installed above underground cable lines, the size of which depends on the voltage of this line. So, for cable lines with voltage up to 1000 V, the security zone has a platform size of 1 m on each side of the extreme 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 carriageway.
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 voltage up to 1000 V and above have a security zone defined by parallel straight lines at a distance of 100 m from the outermost cables.

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

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

Cable laying in the ground under buildings, as well as through basements and storage facilities is prohibited.

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

When laying the cable in the plantation zone, the distance between the cable and tree trunks must be at least 2 m, and in the green zone with shrub plantings, 0.75 m is allowed. 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 railway 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 an exclusion zone, cables are laid directly at the intersection or at a distance of 2 m on both sides of the roadbed.

Cables are laid in a "snake" with a margin equal to 1 - 3% of its length in order to exclude the possibility of dangerous mechanical stresses arising from soil displacements and temperature deformations. It is forbidden to lay the end of the cable in the form of rings.

The number of couplings on the cable should be the smallest, so the cable is laid in full construction lengths. For 1 km of cable lines, there can be no more than four couplings for three-core cables with voltage 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 sleeves per 1 km of cable lines are allowed.

For connections or cable terminations, the ends are cut, that is, the stepwise removal of protective and insulating materials. The dimensions of the cut 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 conductive cores.
The finished cutting of the end of a three-core cable with paper insulation is shown in fig. fifteen.

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


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

The connection of the conductors of the cable with voltage up to 1000 V is carried out by crimping in the sleeve (Fig. 18). To do this, a sleeve, a punch and a matrix, as well as a crimping mechanism (press tongs, hydraulic press, etc.), are selected according to the cross section of the connected conductive wires, the inner surface of the sleeve is cleaned to a metallic sheen with a steel brush (Fig. 18, a), and the connected wires - with a brush - on carded tapes (Fig. 18, b). Round 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 of harsh threads, 4 - spacer, 5 - core winding, 6 - ground wire, 7 - core connection, 8 - sealing winding


Rice. 18. Connection of copper conductors of the cable by crimping:

a - cleaning the inner surface of the sleeve with a steel wire brush, b - stripping the core with a brush made of cardolent tape, c - installing the sleeve on the connected cores, d - crimping the sleeve in a press, e - finished connection; 1 - copper sleeve, 2 - ruff, 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 made in such a way that the punch washer at the end of the process abuts against the end (shoulders) of the matrix. The residual cable thickness (mm) is checked using a special caliper or caliper (H value in Fig. 19):

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

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

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

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

The quality of the pressed cable contacts is checked by external inspection. At the same time, attention is paid to the indentation holes, which should be located coaxially and symmetrically with respect to the middle of the sleeve or the tubular part of the tip. There should be no tears or cracks at the points of indentation of the punch.

To ensure the appropriate quality of cable crimping, the following work conditions must be met:
use lugs and sleeves, the cross section of which 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 in crimping;
do not change the cross section of the cable core to facilitate the insertion of the core into the tip or sleeve by removing one of the wires;

do not pressurize without preliminary cleaning and lubrication with quartz-vaseline paste of the contact surfaces of the tips and sleeves on aluminum conductors; finish crimping not earlier than the punch washer comes close to the end of the die.

After connecting the cable cores, a metal belt is removed between the first and second annular notches of the sheath and a bandage of 5-6 turns of harsh threads is applied to the edge of the belt insulation under 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 clutch housing.
The ends of the cable are laid in the sleeve, having previously wound I onto the cable at the points of its entry and exit from the sleeve 5-7 layers of resin tape, and then fasten both halves of the sleeve with bolts. The grounding conductor, soldered to the armor and cable sheath, is led under the fixing bolts and thus firmly fixed to the sleeve.

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

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

The quality and reliability of the mounted cable glands and terminations can be improved if the installation kit is used. necessary tool and devices for cutting the cable and connecting the cores, heating the cable mass, etc. Great importance to improve the quality of the work performed, has the qualifications of personnel.

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

Such kits are supplied in cans depending on the size of the couplings by numbers. The jar at the installation site must be opened and heated to a temperature of 70 - 80 °C before use. Heated rollers and rolls are checked for the absence of moisture by immersing paper tapes in paraffin heated to a temperature of 150 ° C. In this case, crackling and foaming should not be observed. If moisture is detected, the set of rollers and rolls is rejected.
The reliability of cable lines during operation is supported by the implementation of a set of measures, including cable heating control, inspections, repairs, 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 allowable temperature of the conductors of the cable is determined by the design of the cable. So, for cables with a voltage of 10 kV with paper insulation and viscous non-flowing impregnation, a temperature of not more than 60 ° C is allowed; for cables with a voltage of 0.66 - 6 kV with rubber insulation and viscous non-flowing impregnation - 65 ° C; for cables with voltage up to 6 kV with plastic (made of polyethylene, self-extinguishing polyethylene and polyvinyl chloride plastic compound) 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 (from 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 the current GOSTs. Cable lines with a voltage of 6 - 10 kV, carrying loads less than the nominal ones, can be temporarily overloaded by an amount that depends on the type of laying. So, for example, a cable laid in the ground and having a preload factor of 0.6 can be overloaded by 35% for half an hour, 30% for 1 hour and 15% for 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, the overload is reduced by 10%.

The reliability of the cable line depends to a large extent on proper organization operational supervision of the condition of lines and their routes through periodic inspections. Scheduled inspections make it possible to identify various violations on cable routes (excavation work, warehousing, planting trees, etc.), as well as cracks and chips on the insulators of the end sleeves, weakening of their fastenings, the presence of bird nests, etc.

A great danger to the integrity of the cables is the excavation of the earth, carried out on the routes or near them. The organization operating underground cables, should distinguish the observer during the excavation in order to avoid damage to the cable.

According to the degree of danger of damage to cables, earthworks are divided into two zones:

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

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

When working in zone I, it is prohibited:

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

the use of mechanisms for excavating soil (jackhammers, electric hammers, etc.) to a depth of more than 0.4 m at a normal cable laying depth (0.7 - 1 m); earthworks in winter time without preliminary heating of the soil;

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

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