Overhead power lines are distinguished by a number of criteria. Let's give a general classification.
I. By the nature of the current
Drawing. 800 kV direct current overhead line
Currently, the transmission of electrical energy is carried out mainly on alternating current. This is due to the fact that the vast majority of electrical energy sources generate alternating voltage (with the exception of some non-traditional sources of electrical energy, such as solar power plants), and the main consumers are machines. alternating current.
In some cases, direct current transmission of electrical energy is preferable. The scheme for organizing DC transmission is shown in the figure below. To reduce the load losses in the line during the transmission of electricity at direct current, as well as at alternating current, with the help of transformers, the transmission voltage is increased. In addition, when organizing a transmission from a source to a consumer at direct current, it is necessary to convert electrical energy from alternating current to direct current (using a rectifier) and vice versa (using an inverter).
Drawing. Schemes for organizing the transmission of electrical energy on alternating (a) and direct (b) current: G - generator (energy source), T1 - step-up transformer, T2 - step-down transformer, V - rectifier, I - inverter, N - load (consumer).
The advantages of transmitting electricity through overhead lines at direct current are as follows:
The main disadvantage of DC power transmission is the need to use AC-to-DC converters (rectifiers) and vice versa, DC to AC (inverters), and the associated additional capital costs and additional losses for power conversion.
DC overhead lines are not currently widespread, so in the future we will consider the installation and operation of alternating current overhead lines.
II. By appointment
III. By voltage
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 built and operated in a wide variety of climatic conditions and geographic 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 length of the span, 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 (tension garlands of insulators are located horizontally), experience the greatest loads, therefore they are much more complicated and more expensive than intermediate ones; their number on each line should be minimal.
In particular, end and corner supports, installed at the end or at the turn of the line, experience constant tension of wires and cables: one-sided or by the resultant of the angle of rotation; intermediate anchors installed on long straight sections are also calculated for one-sided tension, which can occur when part of the wires break in the span adjacent to the support.
Special supports are of the following types: transitional - for large spans crossing rivers, gorges; branch lines - for making branches from the main line; transpositional - to change the order of the location of the wires on the support.
Along with the purpose (type), the design of the support is determined by the number of overhead lines and the relative position of the wires (phases). The supports (and lines) are made in a single- or double-circuit version, while the wires on the supports can be placed in a triangle, horizontally, a reverse Christmas tree and a hexagon or a barrel (Fig. 3.2).
The asymmetric arrangement of the phase wires with respect to each other (Fig. 3.2) causes the unequal inductances and capacitances of different phases. To ensure the symmetry of a three-phase system and phase alignment of reactive parameters on long lines (more than 100 km) with a voltage of 110 kV and above, the wires in the circuit are rearranged (transposed) using appropriate supports.
With a full cycle of transposition, each wire (phase) evenly along the length of the line occupies in series the position of all three phases on the support (Fig. 3.3).
wooden supports( fig. 3.4) are made of pine or larch and are used on lines with voltage up to 110 kV in forest areas, now less and less. The main elements of the supports are stepchildren (attachments) 1, racks 2, traverses 3, braces 4, under-traverse bars 6 and crossbars 5. Supports are easy to manufacture, cheap, and easy to transport. Their main drawback is their fragility due to the decay of wood, despite its treatment with an antiseptic. The use of reinforced concrete stepchildren (attachments) increases the service life of the supports up to 20-25 years.
Reinforced concrete supports (Fig. 3.5) are most widely used on lines with voltage up to 750 kV. They can be free-standing (intermediate) and with braces (anchor). Reinforced concrete supports are more durable than wooden ones, easy to operate, cheaper than metal ones.
Metal (steel) supports ( fig. 3.6) are used on lines with a voltage of 35 kV and above. The main elements include racks 1, traverses 2, cable racks 3, braces 4 and foundation 5. They are strong and reliable, but quite metal-intensive, occupy a large area, require special reinforced concrete foundations for installation and must be painted during operation for corrosion protection.
Metal poles are used in cases where it is technically difficult and uneconomical to build overhead lines on wooden and reinforced concrete poles (crossing rivers, gorges, making taps from overhead lines, etc.).
Russia has developed unified metal and reinforced concrete supports various types for overhead lines of all voltages, which allows them to be mass-produced, speed up and reduce the cost of line construction.
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 due to the significant cost and the need for other purposes, new lines are not used.
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 grade 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, V) 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 the earring 1, which is inserted with the other side into the cap of the upper suspension insulator 2. The 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 are 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.
What is the meaning of power lines? Is there a precise definition of the wires through which electricity is transmitted? There is an exact definition in the intersectoral rules for the technical operation of consumer electrical installations. So, a power line is, firstly, an electric line. Secondly, these are sections of wires that go beyond substations and power stations. Thirdly, the main purpose of power lines is the transmission of electric current at a distance.
According to the same rules of the MPTEEP, power transmission lines are divided into overhead and cable ones. But it should be noted that high-frequency signals are also transmitted through power lines, which are used to transmit telemetry data, for supervisory control of various industries, for emergency control signals and relay protection. According to statistics, 60,000 high-frequency channels today pass through power lines. To put it bluntly, the figure is significant.
Overhead power lines, they are usually denoted by the letters "VL" - these are devices that are located in the open air. That is, the wires themselves are laid through the air and fixed on special fittings (brackets, insulators). At the same time, their installation can be carried out along poles, and along bridges, and along overpasses. It is not necessary to consider "VL" those lines that are laid only along high-voltage poles.
What is included in the composition of overhead power lines:
That is, a power line is not just wires and supports, as you can see, it is a rather impressive list of various elements, each of which carries its own specific loads. Here you can also add fiber optic cables, and their ancillary equipment. Of course, if there are high frequency channels connections.
The construction of a power transmission line, as well as its design, plus the design features of the supports, are determined by the rules for the installation of electrical installations, that is, the PUE, as well as various building rules and regulations, that is, SNiP. In general, the construction of power lines is a difficult and very responsible business. Therefore, their construction is carried out by specialized organizations and companies, where there are highly qualified specialists in the state.
The overhead high-voltage power lines themselves are divided into several classes.
By type of current:
Basically, overhead lines are used to transmit alternating current. It is rare to find the second option. It is usually used to power a contact or communication network to provide communication to several power systems, there are other types.
By voltage, overhead power lines are divided according to the nominal value of this indicator. For information, we list them:
At the same time, power lines with voltage up to 1.0 kV are considered to be of the lowest class, from 1.0 to 35 kV - medium, from 110 to 220 kV - high, from 330 to 500 kV - ultra-high, above 750 kV ultra-high. It should be noted that all these groups differ from each other only in the requirements for design conditions and design features. In all other respects, these are ordinary high-voltage power lines.
The voltage of power lines corresponds to their purpose.
Unfortunately, there is also such a separation of power lines, which takes into account the operational state of all elements of the power transmission line. This is a transmission line in good condition, where wires, poles and other components are in good condition. Basically, the emphasis is on the quality of wires and cables, they should not be broken. Emergency condition, where the quality of wires and cables leaves much to be desired. And the installation condition, when repairing or replacing wires, insulators, brackets and other components of power lines.
There are always conversations between specialists in which special terms are used regarding power lines. For the uninitiated in the subtleties of slang, it is quite difficult to understand this conversation. Therefore, we offer a decoding of these terms.
So, we turn to the consideration of such a thing as cable power lines. Let's start with the fact that these are not bare wires that are used in overhead power lines, these are cables enclosed in insulation. Typically, cable transmission lines are several lines installed next to each other in a parallel direction. The length of the cable is not enough for this, so couplings are installed between the sections. By the way, you can often find oil-filled cable power lines, so such networks are often equipped with special low-fill equipment and an alarm system that responds to oil pressure inside the cable.
If we talk about the classification of cable lines, they are identical to the classification of overhead lines. Distinctive features are, but they are not so many. Basically, these two categories differ from each other in the way they are laid, as well as design features. For example, according to the type of laying, cable power lines are divided into underground, underwater and by structures.
The first two positions are clear, but what about the position “on structures”?
And the last classification in cable transmission lines is the type of insulation. In principle, there are two main types: solid insulation and liquid insulation. The first includes insulating braids made of polymers (polyvinyl chloride, cross-linked polyethylene, ethylene-propylene rubber), as well as other types, for example, oiled paper, rubber-paper braid. Liquid insulators include petroleum oil. There are other types of insulation, for example, with special gases or other types of solid materials. But they are rarely used today.
The variety of power lines is reduced to the classification of two main types: overhead and cable. Both options are used everywhere today, so you should not separate one from the other and give preference to one over the other. Of course, the construction of overhead lines is associated with large capital investments, because the laying of the route is the installation of supports, mainly metal, which have a rather complex structure. This takes into account which network, under what voltage will be laid.
power lines
Power line(power line) - one of the components electrical network, a power equipment system 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 line(VL) - a device designed for transmission or distribution electrical energy along wires located in the open air and attached with the help of traverses (brackets), insulators and fittings to supports or other structures bridges , viaducts).
Basically, overhead lines serve to transmit alternating current and only in individual cases(for example, to connect power systems, power contact networks, etc.) use DC 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.
These groups differ significantly mainly in the requirements in terms of design conditions and structures.
Cable power line(CL) - is a line for the transmission of electricity or its individual pulses, consisting of one or more parallel cables with connecting, locking and end sleeves (terminals) and fasteners, and for oil-filled lines, in addition, with feed devices and an oil pressure alarm system.
By classification cable lines are similar to overhead lines
Cable line insulation is divided into two main types:
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.
Electricity losses in wires depend on the strength current, therefore, when transmitting it over long distances, voltage repeatedly increase (by the same number of times reducing the current strength) with the help of 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 extra-high voltage overhead lines, there are active power losses 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 materialsOVERHEAD 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
