The device of overhead power lines of different voltages. Natural power and transmission capacity of power lines

The main elements of overhead lines are wires, insulators, linear fittings, supports and foundations. On overhead lines of three-phase alternating current, at least three wires are suspended that make up one circuit; on DC overhead lines - at least two wires.

By the number of circuits, overhead lines are divided into one, two and multi-circuit. The number of circuits is determined by the power supply scheme and the need for its redundancy. If two circuits are required according to the power supply scheme, then these circuits can be suspended on two separate single-circuit overhead lines with single-circuit supports or on one double-circuit overhead line with double-circuit supports. The distance / between adjacent supports is called the span, and the distance between the anchor type supports is called the anchor section.

Wires suspended on insulators (A, - the length of the garland) to the supports (Fig. 5.1, a) sag along the chain line. The distance from the suspension point to the lowest point of the wire is called the sag /. It determines the dimension of the approach of the wire to the ground A, which for a populated area is equal to: up to the surface of the earth up to 35 and PO kV - 7 m; 220 kV - 8 m; to buildings or structures up to 35 kV - 3 m; 110 kV - 4 m; 220 kV - 5 m. Span length / is determined by economic conditions. The span length up to 1 kV is usually 30 ... 75 m; PO kV - 150 ... 200 m; 220 kV - up to 400 m.

Types of power poles

Depending on the method of hanging the wires, the supports are:

1. intermediate, on which the wires are fixed in supporting clamps;
2. anchor type, used for tensioning wires; on these supports, the wires are fixed in tension clamps;
3. angular, which are installed at the angles of rotation of the overhead line with the suspension of wires in the supporting clamps; they can be intermediate, branch and corner, end, anchor corner.

Enlarged, however, the supports of overhead lines above 1 kV are divided into two types of anchors, which completely perceive the tension of wires and cables in adjacent spans; intermediate, not perceiving the tension of the wires or partially perceiving.

On overhead lines, wooden poles are used (Fig. 5L, b, c), new generation wooden poles (Fig. 5.1, d), steel (Fig. 5.1, e) and reinforced concrete poles.

Wooden supports VL

Wooden poles of overhead lines are still widespread in countries with forest reserves. The advantages of wood as a material for supports are: low specific gravity, high mechanical strength, good electrical insulating properties, natural round assortment. The disadvantage of wood is its decay, to reduce which antiseptics are used.

An effective method of combating decay is impregnation of wood with oily antiseptics. In the US, the transition to glued wood poles is underway.

For overhead lines with a voltage of 20 and 35 kV, on which pin insulators are used, it is advisable to use single-column candle-shaped supports with a triangular arrangement of wires. On overhead transmission lines 6-35 kV with pin insulators, for any arrangement of wires, the distance between them D, m, must be not less than the values ​​​​determined by the formula

where U - lines, kV; - the largest sag corresponding to the overall span, m; b - ice wall thickness, mm (not more than 20 mm).

For overhead lines of 35 kV and above with suspension insulators with a horizontal arrangement of wires, the minimum distance between the wires, m, is determined by the formula

The support stand is made of a composite: the upper part (the stand itself) is made of logs 6.5 ... or from logs 4.5 ... 6.5 m long. Composite supports with reinforced concrete stepson combine the advantages of reinforced concrete and wooden supports: lightning resistance and resistance to decay at the point of contact with the ground. The connection of the rack with the stepson is carried out with wire bandages made of steel wire with a diameter of 4 ... 6 mm, tensioned with a twist or a tension bolt.

Anchor and intermediate corner supports for 6-10 kV overhead lines are made in the form of an A-shaped structure with composite racks.

Steel transmission poles

Widely used on overhead lines with a voltage of 35 kV and above.

According to the design, steel supports can be of two types:

1. tower or single-column (see Fig. 5.1, e);
2. portal, which, according to the method of fixing, are divided into free-standing supports and supports on braces.

The advantage of steel supports is their high strength, the disadvantage is their susceptibility to corrosion, which requires periodic painting or application of an anti-corrosion coating during operation.

Supports are made of steel corner rolled products (basically, an isosceles corner is used); high transitional supports can be made of steel pipes. In the joints of the elements, a steel sheet of various thicknesses is used. Regardless of the design, steel supports are made in the form of spatial lattice structures.

Reinforced concrete power transmission poles

Compared to metal ones, they are more durable and economical in operation, as they require less maintenance and repair (if we take the life cycle, then reinforced concrete ones are more energy-intensive). The main advantage of reinforced concrete supports is a reduction in steel consumption by 40 ... 75%, the disadvantage is a large mass. According to the manufacturing method, reinforced concrete supports are divided into concreted at the installation site (for the most part, such supports are used abroad) and prefabricated.

Traverses are fastened to the trunk of a reinforced concrete support post using bolts passed through special holes in the post, or using steel clamps covering the trunk and having trunnions for attaching the ends of the traverse belts to them. Metal traverses are preliminarily hot-dip galvanized, so they do not require special care and supervision during operation for a long time.

The wires of overhead lines are made uninsulated, consisting of one or more twisted wires. Single-wire wires, called single-wire wires (they are made with a cross section of 1 to 10 mm2), have lower strength and are used only on overhead lines with voltages up to 1 kV. Multi-wire wires, twisted from several wires, are used on overhead lines of all voltages.

The materials of wires and cables must have high electrical conductivity, have sufficient strength, withstand atmospheric influences (in this respect, copper and bronze wires are the most resistant; aluminum wires are susceptible to corrosion, especially on sea coasts, where salts are contained in the air; steel wires are destroyed even under normal atmospheric conditions).

For overhead lines, single-wire steel wires with a diameter of 3.5 are used; 4 and 5 mm and copper wires up to 10 mm in diameter. The limitation of the lower limit is due to the fact that wires of smaller diameter have insufficient mechanical strength. The upper limit is limited due to the fact that bends of a single-wire wire of a larger diameter can cause permanent deformations in its outer layers that will reduce its mechanical strength.

Stranded wires, twisted from several wires, have great flexibility; such wires can be made with any section (they are made with a section from 1.0 to 500 mm2).

The diameters of the individual wires and their number are selected so that the sum of the cross sections of the individual wires gives the required total wire cross section.

As a rule, stranded wires are made from round wires, with one or more wires of the same diameter placed in the center. The length of the twisted wire is slightly longer than the length of the wire measured along its axis. This causes an increase in the actual mass of the wire by 1 ... 2% compared to the theoretical mass, which is obtained by multiplying the wire section by the length and density. All calculations assume the actual weight of the wire as specified in the relevant standards.

Grades of bare wires indicate:

• letters M, A, AC, PS - wire material;
• figures - section in square millimeters.

Aluminum wire A can be:

• Grade AT (hard not annealed)
• AM (annealed soft) alloys AN, AZh;
• AS, ASHS - from a steel core and aluminum wires;
• PS - from steel wires;
• PST - made of galvanized steel wire.

For example, A50 denotes an aluminum wire with a cross section of 50 mm2;

• AC50 / 8 - steel-aluminum wire with a section of the aluminum part of 50 mm2, a steel core of 8 mm2 (in electrical calculations, the conductivity of only the aluminum part of the wire is taken into account);
• PSTZ,5, PST4, PST5 - single-wire steel wires, where the numbers correspond to the diameter of the wire in millimeters.

Steel cables used on overhead lines as lightning protection are made of galvanized wire; their cross section must be at least 25 mm2. On overhead lines with a voltage of 35 kV, cables with a cross section of 35 mm2 are used; on PO kV lines - 50 mm2; on lines of 220 kV and above -70 mm2.

The cross section of stranded wires of various grades is determined for overhead lines with voltages up to 35 kV according to the conditions of mechanical strength, and for overhead lines with a voltage of 1 kV and higher - according to the conditions of corona losses. On overhead lines, when crossing various engineering structures (communication lines, railways and highways, etc.), it is necessary to ensure higher reliability, therefore, the minimum wire cross-sections in crossing spans should be increased (Table 5.2).

When an air stream flows around the wires, directed across the axis of the overhead line or at a certain angle to this axis, turbulences appear on the leeward side of the wire. When the frequency of formation and movement of vortices coincides with one of the frequencies of natural oscillations, the wire begins to oscillate in a vertical plane.

Such oscillations of the wire with an amplitude of 2 ... 35 mm, a wavelength of 1 ... 20 m and a frequency of 5 ... 60 Hz are called vibration.

Usually vibration of wires is observed at a wind speed of 0.6 ... 12.0 m / s;

Steel wires are not allowed in spans over pipelines and railways.

Vibration typically occurs in spans longer than 120 m and in open areas. The danger of vibration lies in the breakage of individual wires of the wire in the areas of their exit from the clamps due to an increase in mechanical stress. Variables arise from periodic bending of the wires as a result of vibration and the main tensile stresses are stored in the suspended wire.

In spans up to 120 m, vibration protection is not required; sections of any overhead lines protected from transverse winds are not subject to protection; at large crossings of rivers and water spaces, protection is required regardless of the wires. On overhead lines with a voltage of 35 ... 220 kV and above, vibration protection is performed by installing vibration dampers suspended on a steel cable, absorbing the energy of vibrating wires with a decrease in vibration amplitude near the clamps.

When there is ice, the so-called dance of wires is observed, which, like vibration, is excited by the wind, but differs from vibration in a larger amplitude, reaching 12 ... 14 m, and a longer wavelength (with one and two half-waves in flight). In a plane perpendicular to the axis of the overhead line, the wire At a voltage of 35 - 220 kV, the wires are insulated from the supports with garlands of suspension insulators. Pin insulators are used for isolation of 6-35 kV overhead lines.

Passing through the wires of the overhead line, it releases heat and heats the wire. Under the influence of wire heating, the following occurs:

1. lengthening the wire, increasing the sag, changing the distance to the ground;
2. change in the tension of the wire and its ability to carry a mechanical load;
3. change in wire resistance, i.e. change in losses of electrical power and energy.

All conditions can change in the presence of constancy of environmental parameters or change together, affecting the operation of the overhead line wire. During the operation of the overhead line, it is considered that at the rated load current, the temperature of the wire is 60 ... 70 ″С. The temperature of the wire will be determined by the simultaneous effect of heat generation and cooling or heat sink. The heat removal of overhead lines increases with an increase in wind speed and a decrease in ambient air temperature.

With a decrease in air temperature from +40 to 40 °C and an increase in wind speed from 1 to 20 m/s, heat losses vary from 50 to 1000 W/m. At positive ambient temperatures (0...40 °C) and low wind speeds (1...5 m/s), heat losses are 75...200 W/m.

To determine the effect of overload on the increase in losses, first determine

where RQ - wire resistance at a temperature of 02, Ohm; R0] - wire resistance at a temperature corresponding to the design load under operating conditions, Ohm; A /.u.s - coefficient of temperature increase in resistance, Ohm / ° С.

An increase in the resistance of the wire compared to the resistance corresponding to the calculated load is possible with an overload of 30% by 12%, and with an overload of 50% - by 16%

An increase in AU loss during overload up to 30% can be expected:

1. when calculating the overhead line for AU = 5% A? / 30 = 5.6%;
2. when calculating the overhead line at A17 \u003d 10% D? / 30 \u003d 11.2%.

With an overload of overhead lines up to 50%, the increase in loss will be equal to 5.8 and 11.6%, respectively. Considering the load schedule, it can be noted that when the overhead line is overloaded up to 50%, the losses briefly exceed the permissible standard values ​​by 0.8 ... 1.6%, which does not significantly affect the quality of electricity.

Application of SIP wire

Since the beginning of the century, low-voltage overhead networks have become widespread, made as a self-supporting system of insulated wires (SIW).

SIP is used in cities as a mandatory laying, as a highway in rural areas with low population density, branches to consumers. Ways of laying SIP are different: pulling on supports; stretching on the facades of buildings; laying along the facades.

The design of SIP (unipolar armored and unarmored, tripolar with insulated or bare carrier neutral) generally consists of a copper or aluminum conductor stranded core, surrounded by an internal semiconductor extruded screen, then - insulation made of cross-linked polyethylene, polyethylene or PVC. The tightness is provided by powder and compounded tape, on top of which there is a metal screen made of copper or aluminum in the form of spirally laid threads or tape, using extruded lead.

On top of the cable armor pad made of paper, PVC, polyethylene, aluminum armor is made in the form of a grid of strips and threads. The outer protection is made of PVC, gel-free polyethylene. The spans of the gasket, calculated taking into account its temperature and the cross-section of wires (at least 25 mm2 for mains and 16 mm2 for branches to consumer inputs, 10 mm2 for steel-aluminum wire) range from 40 to 90 m.

With a slight increase in costs (about 20%) compared to bare wires, the reliability and safety of a line equipped with SIP is increased to the level of reliability and safety of cable lines. One of the advantages of overhead lines with insulated VLI wires over conventional power lines is the reduction of losses and power by reducing reactance. Straight Line Sequence Options:

• ASB95 - R = 0.31 Ohm / km; X \u003d 0.078 Ohm / km;
• SIP495 - respectively 0.33 and 0.078 Ohm / km;
• SIP4120 - 0.26 and 0.078 Ohm / km;
• AC120 - 0.27 and 0.29 Ohm / km.

The effect of reducing losses when using SIP and the invariability of the load current can be from 9 to 47%, power losses - 18%.

Encyclopedic YouTube

1 / 5

✪ How power lines work. Transmission of energy over long distances. Animated training video. / Lesson 3

✪ Lesson 261 The condition for matching the current source with the load

✪ Installation methods for overhead power lines (lecture)

✪ ✅ How to charge a phone under a high-voltage power line with induced currents

✪ Dance of the wires of the overhead power line 110 kV

Subtitles

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

• Traverses
• 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 (equipment for high-frequency communication, capacitive power take-off, etc.)
• Elements for marking high-voltage wires and power transmission line poles to ensure the safety of aircraft flights. Supports are marked with a combination of paints of certain colors, wires - with aviation balloons for marking in the daytime. To indicate in the daytime and at night, the lights of the light fence are used.

Documents regulating overhead lines

VL classification

By type of current

Basically, overhead lines are used to transmit alternating current, and only in some cases (for example, for connecting power systems, powering a contact network, and others), direct current lines are used. DC lines have lower capacitive and inductive losses. In the USSR, several DC power lines were built:

• High-voltage direct current line Moscow-Kashira - Project "Elba",
• High voltage DC line Volgograd-Donbass,
• High-voltage direct current line Ekibastuz-Center, etc.

Such lines were not widely used.

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 in large areas - connect distribution points with consumers)
• VL 20 kV and below, supplying electricity to consumers.

By voltage

• VL up to 1000 V (VL of the lowest voltage class)
• VL above 1000 V
  • VL 1-35 kV (VL medium voltage class)
  • VL 35-330 kV (VL of high voltage class)
  • VL 500-750 kV (VL of extra-high voltage class)
  • Overhead lines above 750 kV (overhead lines of ultra-high voltage class)

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

In LPG networks of general purpose AC 50 Hz, according to GOST 721-77, the following nominal phase-to-phase voltages must be used: 380; (6) , 10, 20, 35, 110, 220, 330, 500, 750 and 1150 kV. There may also be networks built according to outdated standards with nominal phase-to-phase voltages: 220, 3 and 150 kV.

The highest voltage transmission line in the world is the Ekibastuz-Kokchetav line, with a nominal voltage of 1150 kV. However, at present the line is operated under half the voltage - 500 kV.

The rated voltage for DC lines is not regulated, the most commonly used voltages are: 150, 400 (Vyborgskaya  PS -  Finland) and 800 kV.

Other voltage classes can be used in special networks, mainly for railway traction networks (27.5 kV, 50 Hz AC and 3.3 kV DC), underground (825 V DC), trams and trolleybuses (600 in direct current).

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 the CIS, 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 earth via an inductance). In the CIS, 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, in which transformers are used (autotransformers require obligatory deaf neutral grounding).
• Networks with deaf-earthed neutral (the neutral of the transformer or generator is connected to the grounding device directly or through a small 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 lines of emergency operation (with a complete or partial breakage of wires and cables).
• VL 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 mark on the route of the overhead line under construction, it indicates the center of the support location.
• 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 the load to it from the support, insulators, wires (cables) and from external influences (ice, wind).
• foundation foundation- soil of the lower part of the pit, which takes the load.
• span(span length) - the distance between the centers of the two supports on which the wires are suspended. Distinguish intermediate span (between two adjacent intermediate supports) and anchor span (between anchor supports). 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 wire in the span to the engineering structures intersected by the route, 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.

Installation of overhead power lines

The installation of power transmission lines is carried out by the "Mounting" "pull-up" method. This is especially true in the case of complex terrain. When selecting equipment for the installation of power transmission lines, it is necessary to take into account the number of wires in the phase, their diameter and the maximum distance between the power transmission line supports.

Cable power lines

Cable power line(KL) - 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 an oil pressure alarm system .

Classification

Cable lines are classified similarly to overhead lines. In addition, cable lines share:

• according to the conditions of passage:
  • underground;
  • by buildings;
  • underwater.
• type of insulation:
  • liquid (impregnated with cable oil oil);
  • solid:
    • paper-oil;
    • polyvinyl chloride (PVC);
    • rubber-paper (RIP);
    • 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 [ when?] .

cable structures

Cable structures include:

• 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, which allows cable laying, repair and inspection of cable lines.
• cable channel- an impassable structure, closed and partially or completely buried in the ground, floor, ceiling, etc., and intended for placing cables in it, laying, inspecting and repairing 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 wall that is fully or partially removable (impassable 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, the interfloor overlap 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 deaf removable concrete slab, designed for laying cable boxes or for pulling cables into blocks. A chamber having a hatch to enter it is called 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 (in whole or in part, for example, without side walls) horizontal or inclined extended cable structure.

Fire safety

The temperature inside the cable channels (tunnels) in summer should be no more than 10 °C higher than the outside air temperature.

In case of fires in cable rooms, in the initial period, combustion develops slowly and only after some time does the combustion spread rate increase significantly. Practice shows that during real fires in cable tunnels, temperatures up to 600 ° C and above are observed. This is explained by the fact that in real conditions, cables burn, which are under current load for a long time and the insulation of which warms up from the inside to a temperature of 80 ° C and above. Simultaneous ignition of cables in several places and over a considerable length can occur. This is due to the fact that the cable is under load and its insulation is heated to a temperature close to the self-ignition temperature.

The cable consists of many structural elements, for the manufacture of which a wide range of combustible materials are used, including materials with a low ignition temperature, materials prone to smoldering. Also, the design of the cable and cable structures includes metal elements. In the event of a fire or current overload, these elements are heated to a temperature of about 500-600 ˚C, which exceeds the ignition temperature (250-350 ˚C) of many polymeric materials included in the cable structure, and therefore they can be re-ignited from heated metal elements after stopping the supply of fire extinguishing agent. In this regard, it is necessary to choose the normative indicators for the supply of fire extinguishing agents in order to ensure the elimination of fiery combustion, as well as to exclude the possibility of re-ignition.

For a long time, foam extinguishing installations were used in cable rooms. However, operating experience revealed a number of shortcomings:

• limited shelf life of the foaming agent and the inadmissibility of storing their aqueous solutions;
• instability in work;
• complexity of setup;
• the need for special care for the foam concentrate dosing device;
• rapid destruction of the foam at high (about 800 ° C) ambient temperature during a fire.

Studies have shown that sprayed water has a greater fire extinguishing ability compared to air-mechanical foam, as it wets and cools burning cables and building structures well.

The linear speed of flame propagation for cable structures (cable burning) is 1.1 m/min.

High temperature superconductors

HTS wire

Losses in power lines

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

In ultra-high voltage overhead lines, there are active power losses to the corona (corona discharge). A corona discharge occurs when the electric field strength E (\displaystyle E) at the surface of the wire will exceed the threshold value E k (\displaystyle E_(k)), which can be calculated using Pick's empirical formula:
E k = 30 , 3 β (1 + 0.298 r β) (\displaystyle E_(k)=30(,)3\beta \left((1+(\frac (0(,)298)(\sqrt (r \beta))))\right)) kV/cm,
where r (\displaystyle r)- radius of the wire in meters, β (\displaystyle \beta )- the ratio of air density to normal.

The electric field strength is directly proportional to the voltage on the wire and inversely proportional to its radius, so corona losses can be combated by increasing the radius of the wires, and also (to a lesser extent) by using phase splitting, that is, using several wires in each phase held by special spacers at a distance of 40-50 cm. The corona loss is approximately proportional to the product U (U − U cr) (\displaystyle U(U-U_(\text(cr)))).

Losses in AC power lines

An important value that affects the efficiency of AC transmission lines is the value that characterizes the ratio between active and reactive power in the line - cos φ. Active power - part of the total power that passed through the wires and transferred to the load; Reactive power is the power that is generated by the line, its charging power (capacitance between the line and ground), as well as the generator itself, and is consumed by a reactive load (inductive load). Active power losses in the line also depend on the transmitted reactive power. The greater the flow of reactive power, the greater the loss of active.

With a length of AC power lines of more than several thousand kilometers, another type of loss is observed - radio emission. Since such a length is already comparable with the length of an electromagnetic wave with a frequency of 50 Hz ( λ = c / ν = (\displaystyle \lambda =c/\nu =) 6000 km, quarter wave vibrator length λ / 4 = (\displaystyle \lambda /4=) 1500 km), the wire works as a radiating antenna.

Natural power and transmission capacity of power lines

natural power

Power lines have inductance and capacitance. Capacitive power is proportional to the square of the voltage, and does not depend on the power transmitted over the line. The inductive power of the line is proportional to the square of the current, and hence the power of the line. At a certain load, the inductive and capacitive powers of the line become equal, and they cancel each other out. The line becomes "ideal", consuming as much reactive power as it produces. This power is called natural power. It is determined only by the linear inductance and capacitance, and does not depend on the length of the line. By the value of natural power, one can roughly judge the transmission capacity of the power line. When transmitting such power on the line, there is minimal power loss, the mode of its operation is optimal. When splitting the phases, by reducing the inductive resistance and increasing the capacitance of the line, the natural power increases. With an increase in the distance between the wires, the natural power decreases, and vice versa, to increase the natural power, it is necessary to reduce the distance between the wires. Cable lines with high capacitive conductivity and low inductance have the highest natural power.

Bandwidth

Power transmission capacity is understood as the maximum active power of the three phases of power transmission, which can be transmitted in a long-term steady state, taking into account operational and technical limitations. The highest transmitted active power of power transmission is limited by the conditions of static stability of generators of power plants, the transmitting and receiving parts of the electric power system, and the allowable power for heating line wires with allowable current. From the practice of operating electric power systems, it follows that the transmission capacity of power transmission lines of 500 kV and above is usually determined by the static stability factor, for power transmission lines of 220-330 kV, restrictions can occur both in terms of stability and in permissible heating, 110 kV and below - only in heating.

Characteristics of the throughput capacity of overhead power lines

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 mark 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 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 wall that is completely or partially removable (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

The loss of electricity in the wires depends on the strength of the current, therefore, when transmitting it over long distances, the voltage is increased many times (reducing the strength of the current 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 transmission 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

Overhead lines are called lines intended for the transmission and distribution of EE 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, subject to atmospheric influences (wind, ice, rain, temperature changes).

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

In Russia, unified metal and reinforced concrete supports of various types have been developed for overhead lines of all voltages, which makes it possible to mass-produce them, speed up and reduce the cost of line construction.

Overhead line wires.

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

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

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

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

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

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

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

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

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

The carrier wire is steel-aluminum, and the phase wires are aluminum. The latter are covered with light-resistant heat-stabilized (cross-linked) polyethylene (APV-type wire). The advantages of overhead lines with insulated wires over lines with bare wires include the absence of insulators on supports, the maximum use of the height of the support for hanging wires; there is no need to cut trees in the area where the line passes.

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

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

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

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

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

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

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

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

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

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

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

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