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| Dimensions of overhead lines. | ||
| Suspension height line is the distance from the ground to the place where the wire is attached to the support insulator (see figure below). The shortest distance from the ground to the wire is in the middle of the span. Sag boom is the vertical distance from the lowest point of the wire in the span to the straight line between the wire attachment points on the supports. The sag of the wire depends on the air temperature, span length, external load on the wire (wind, ice), material and cross-section of the wire. The maximum sag for overhead lines with voltages up to 1000V with normal spans of 35 - 45 meters is up to 1.2 meters. The clearance of the wire above the ground is the distance from the wires to the surface of the earth at the greatest sag. The dimension of an overhead line at intersections is the smallest vertical distance from the line wires to the surface of highways, railways, rivers, and communication line wires when crossed by an overhead line. The dimension of an overhead line when approaching is the smallest permissible distance from overhead line wires to various objects when the line runs parallel to these objects (for example, buildings, structures, etc.). The dimensions of the wire above the ground , as well as the dimensions of overhead lines at intersections and approaches, are established by the Rules for the Construction of Electrical Installations (PUE) depending on the group of overhead lines and the terrain through which the line route passes. In populated areas, the PUE has the following dimensions of the wire above the ground:
When crossing an overhead line with railways, the size of the wire from the rail head, according to the PUE, must be 7.5 meters; when an overhead line with voltage up to 1000 V crosses tram and trolleybus lines - 8 and 9 meters, respectively, at a distance from the overhead line wires to the supporting cable or contact wire at least 1.5 meters. When an overhead line with a voltage of 6 - 10 kV crosses a tram and trolleybus lines - 9.5 and 11 meters, respectively, with a distance to the supporting cable or contact wire of 3 meters. The distance from overhead line wires with voltage up to 1000V at their greatest deviation from buildings and structures is allowed at least 1.5 meters to balconies and windows and 1 meter to blank walls. For an overhead line with a voltage of 6 - 10 kV - at least 2 meters. The passage of the overhead line over buildings is not allowed. In order to save money, it is possible to jointly hang overhead line wires with a voltage of no more than 380/220 V, radio network (RS) wires and street lighting wires on common supports , as well as jointly hang overhead line wires with a voltage of up to 10 kV and radio network wires. In this case, the wires of the overhead line with a voltage of 380/220 V are located above the RS wires and the vertical distance from the bottom wire of the overhead line to the top wire of the RS, regardless of their placement on the support, must be at least 1.5 meters, and between the wires of the branches from the overhead line and with PC wires at building inputs horizontally of at least 1.5 meters. PC wires are usually located on one side of the support. When jointly suspending overhead line wires with a voltage of 1 - 10 kV and radio network wires with a voltage between wires of more than 360V on common supports, the overhead line wires are also located above the PC wires. In this case, the vertical distance from the bottom wire of the overhead line to the top wire of the RS must be at least 1.2 meters and radio broadcast networks must meet special requirements. |
Overhead power line
Overhead power line (OTL) is a device designed for transmitting or distributing electrical energy through wires with a protective insulating sheath (OIL) or bare wires (OHL) located in the open air and attached using traverses (brackets), insulators and linear fittings to supports or other engineering structures (bridges, overpasses). The main elements of overhead lines are:
- wires;
- safety cables;
- support supporting wires and hummocks at a certain height above ground or water level;
- insulators that isolate wires from the support body;
- linear fittings.
The linear portals of the distribution devices are taken as the beginning and end of the overhead line. According to their design, overhead lines are divided into single-circuit and multi-circuit, usually 2-circuit.
Typically, an overhead line consists of three phases, so the supports of single-circuit overhead lines with voltages above 1 kV are designed to hang three phase wires (one circuit) (Fig. 1); six wires (two parallel circuits) are suspended on the supports of double-circuit overhead lines. If necessary, one or two lightning protection cables are suspended above the phase wires. From 5 to 12 wires are hung on the overhead line supports of a distribution network with voltages up to 1 kV to supply power to various consumers on one overhead line (external and internal lighting, power supply, household loads). An overhead line with a voltage of up to 1 kV with a solidly grounded neutral is equipped with a neutral wire in addition to the phase ones.
Rice. 1. Fragments of a 220 kV overhead line: a – single-circuit; b – double-chain
Wires of overhead power lines are mainly made of aluminum and its alloys, in some cases of copper and its alloys, and are made of cold-drawn wire with sufficient mechanical strength. However, the most widely used are stranded wires made of two metals with good mechanical characteristics and relatively low cost. Wires of this type include steel-aluminum wires with a ratio of the cross-sectional areas of the aluminum and steel parts from 4.0 to 8.0. Examples of the location of phase wires and lightning protection cables are shown in Fig. 2, and the design parameters of overhead lines of a standard voltage range are given in table. 1.
Rice. 2. Examples of the location of phase wires and lightning protection cables on supports : a – triangular; b – horizontal; c – hexagonal “barrel”; d – reverse “Christmas tree”
Table 1. Design parameters of overhead lines
Permissible distances from 6-10 kV overhead line wires to various objects
Permissible distances from 6-10 kV overhead line wires to various objects (PUE Seventh edition. Section 2. Chapter 2.5.)1. The shortest distances from overhead line wires to the surface of the earth, structures, roads and water surface (vertical)
No.
| Name of objects or sections of the route intersected | Minimum vertical distance, m | |
| 1 | To the surface of the earth, buildings and structures Populated area:
| 7 5,5 3 |
| 2 | Unpopulated area | 6 |
| 3 | Difficult terrain (swamps, swamps, etc.) | 5 |
| 4 | Inaccessible mountain slopes, rocks, cliffs, etc. | 3 |
| 5 | Regions of tundra, deserts, steppes with soils unsuitable for agriculture | 6 |
| 6 | To the wires of communication lines (LAN) and wire broadcasting lines (LBL) Normal mode:
| 2 4 1 |
| 7 | From VL wires to ground, underground pipelines, cable cars: - normal mode; - when a wire breaks in an adjacent span | 3 2 |
| No. | Name of objects or sections of the route intersected | Minimum vertical distance, m |
| 8 | From overhead power lines to various parts of dams and dams:
— up to the inclined surface of the slopes;
| 6 5 4 |
| 9 | To the roads Non-electrified broad gauge railways of general and non-public use and narrow gauge general use (up to the rail head):
| 7,5 6 |
| 10 | Non-electrified narrow gauge railways of non-public use (up to the rail head) | 6,5 |
| 11 | Electrified or subject to electrification railways up to the top wire or support cable:
| 3 1 |
| 12 | Highways: — up to covering the carriageway of roads of all categories; — to the road surface in case of a wire break in the adjacent span; | 7 5 |
| 13 | When crossing a trolleybus line in normal mode: a) to the highest mark of the roadway; b) to the overhead wire or support cables; c) to the overhead wires or supporting cables when a wire breaks in an adjacent span | 11 3 1 |
| 14 | Tram lines in normal overhead line mode: - up to the rail head;
| 9,5 3 1 |
| 15 | To the surface of the water of navigable rivers, canals, lakes and reservoirs - up to the size of ships or rafting at the highest level of high waters and the highest temperature; — to the highest ice level — to the high water level | 2 6 5,5 |
| 16 | Non-navigable rivers, canals, lakes, reservoirs: - up to the highest level of high waters at an air temperature of plus 15 | 5,5 |
| — to the ice level of rivers, canals, etc. at a temperature of minus 5 °C and in the presence of ice | 6 |
2. The shortest distances for approaching overhead lines to various objects and structures horizontally
| No. | Name of objects, structures | Minimum horizontal distance, m |
| 1 | Woodlands and green spaces:
| 3 2 2 When overhead lines pass through the territory of orchards, clearing of clearings is not necessary |
| 2 | Overhead lines when running in parallel and bringing overhead lines of one voltage closer to each other or overhead lines of other voltages: - a section of an unconstrained route; — a section of a cramped route, approaches to substations: between the outer wires in a non-deviated position | Height of the highest support 2.5 |
| 3 | To the nearest parts of production, warehouse, administrative, household and public buildings and structures | 2 The passage of overhead lines through the territories of stadiums, educational and children's institutions is not allowed |
| 4 | Railways: —non-electrified, in sections of cramped routes (from the deflected overhead line wire to the approach clearance of buildings); — electrified or subject to electrification, in sections of a cramped route (from the outermost wire of the overhead line to the outermost overhead contact line support suspended from the field side); — the same if there are no wires on the field side of the contact network support;
| 1.5 2.5 2 Support height + 3 m 3 |
| 5 | Car roads:
— the same at the intersection of VL with roads of categories 111.1 V, IC PS;
| Support height 5 1.5 Support height + 5 m 10 2 |
| № | Name of objects, structures | Least |
| P/ | distance along | |
| P | horizontal, m | |
| 6 | Trolleybus and tram lines: | |
| - distance when approaching non-deviated overhead line wires to supports | No less high | |
| contact network; | you are the support | |
| - the same, with their greatest deviation in sections of a cramped route; | 3 | |
| 7 | Ground, above-ground pipelines and cable cars: | Not less than height |
| — from the base of the support to any part of the pipeline or cableway | supports | |
| roads; | ||
| — the same, on sections of the route in cramped conditions; | 3 | |
| - from the outermost non-deviated wire to any part of the main | 50 m, but not | |
| oil pipeline and oil product pipeline; | less than height | |
| - the same, main gas pipeline (over 1.2 MPa) | supports | |
| - the same, non-trunk oil and product pipelines, gas pipelines | No less than doubled | |
| (less than 1.2 MPa), water supply, sewerage, drainage, heating network | given height | |
| supports, but no less | ||
| 50 m Not less | ||
| support height* | ||
| 8 | Antenna structures of transmitting radio centers | |
| - distance from overhead lines to medium-wave and long-wave transmitters | 100 | |
| antennas; | ||
| - the same, to short-wave transmitting antennas in the direction | 200 | |
| highest radiation; | ||
| - the same, up to shortwave transmitting antennas in the rest | 50 | |
| directions; | ||
| - the same, to short-wave transmitting weakly directed and | 150 | |
| omnidirectional antennas |
*If the height of an overhead structure exceeds the height of the overhead line support, the distance between this structure and the overhead line should be taken not less than the height of this structure.
Tags: | help | norms | 6 kV | 10 kV |
Cable power line
A cable power line (CL) consists of one or more cables and cable fittings for connecting cables and for connecting cables to electrical devices or distribution device buses.
Unlike overhead lines, cables are laid not only outdoors, but also indoors (Fig. 8), in ground and water. Therefore, CLs are susceptible to moisture, chemical aggressiveness of water and soil, mechanical damage during excavation work and soil displacement during heavy rains and floods. The design of the cable and cable laying structures must provide protection from the specified influences.
Rice. 8. Laying power cables indoors and outdoors
According to the rated voltage, cables are divided into three groups: low voltage cables (up to 1 kV), medium voltage cables (6...35 kV), high voltage cables (110 kV and above). According to the type of current, AC and DC cables are distinguished.
Power cables are made as single-core, two-core, three-core, four-core and five-core. High voltage cables are made of single cores; two-core – DC cables; three-core – medium voltage cables.
Low voltage cables are made with up to five cores. Such cables can have one, two or three phase conductors, as well as a neutral working conductor N and a neutral protective conductor PE or a combined neutral working and protective conductor PEN .
Based on the material of the current-carrying conductors, cables with aluminum and copper conductors are distinguished. Due to the scarcity of copper, cables with aluminum conductors are most widely used. Cable paper impregnated with oil rosin, plastic and rubber are used as insulating materials. There are cables with normal impregnation, depleted impregnation and impregnation with a non-drip composition. Cables with depleted or non-draining impregnation are laid along a route with a large difference in heights or along vertical sections of the route.
High voltage cables are made oil-filled or gas-filled. In these cables, the paper insulation is filled with oil or gas under pressure.
Protection of the insulation from drying out and the ingress of air and moisture is ensured by applying a sealed shell to the insulation. The cable is protected from possible mechanical damage by armor. To protect against the aggressiveness of the external environment, an external protective cover is used.
When studying cable lines, it is advisable to note superconducting cables for power transmission lines, the design of which is based on the phenomenon of superconductivity. In a simplified form, the phenomenon of superconductivity in metals can be represented as follows. Coulomb repulsive forces act between electrons as between similarly charged particles. However, at ultra-low temperatures for superconducting materials (which includes 27 pure metals and a large number of special alloys and compounds), the nature of the interaction of electrons with each other and with the atomic lattice changes significantly. As a result, it becomes possible to attract electrons and form so-called electron (Cooper) pairs. The appearance of these pairs, their increase, and the formation of a “condensate” of electron pairs explains the appearance of superconductivity. With increasing temperature, some electrons become thermally excited and go into a single state. At a certain so-called critical temperature, all electrons become normal and the state of superconductivity disappears. The same thing happens when the magnetic field strength increases. The critical temperatures of superconducting alloys and compounds used in technology are 10 - 18 K, i.e. from –263 to –255°С.
The first projects, experimental models and prototypes of such cables in flexible corrugated cryostatic sheaths were implemented only in the 70-80s of the 20th century. As a superconductor, tapes based on an intermetallic compound of niobium with tin, cooled with liquid helium, were used.
In 1986, the phenomenon of high-temperature superconductivity was discovered, and already at the beginning of 1987, conductors of this kind were obtained, which are ceramic materials, the critical temperature of which was increased to 90 K. The approximate composition of the first high-temperature superconductor is YBa2Cu3O7–d (d 2, from them with a cross section of up to 16 mm 2 - single-wire, above - multi-wire.
Wire - one uninsulated or one or more insulated conductors, on top of which, depending on the installation and operating conditions, there may be a non-metallic sheath, winding and (or) braiding with fibrous materials or wire.
Cord - two or more insulated or especially flexible conductors with a cross-section of up to 1.5 mm 2, twisted or laid in parallel, on top of which, depending on the installation and operating conditions, a non-metallic sheath and protective coatings can be applied.
