Section 2. Sewerage of electricity

Overhead power lines with voltage above 1 kV. Supports and foundations

Encyclopedia of radio electronics and electrical engineering / Rules for the installation of electrical installations (PUE)

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2.5.135. VL supports are divided into two main types: anchor supports, which completely perceive the tension of wires and cables in spans adjacent to the support, and intermediate ones, which do not perceive the tension of wires or perceive it partially. On the basis of anchor supports, end and transposition supports can be made. Intermediate and anchor supports can be straight and angled.

Depending on the number of chains suspended on them, the supports are divided into single-chain, double-chain and multi-chain.

Supports can be free-standing or with braces.

Intermediate supports can be of flexible and rigid construction; anchor supports must be rigid. It is allowed to use anchor supports of a flexible design for overhead lines up to 35 kV.

Supports of a rigid structure include supports, the deviation of the top of which (without taking into account the rotation of the foundations) under the influence of design loads in the second group of limit states does not exceed 1/100 of the support height. When the deviation of the top of the support is more than 1/100 of the height of the support, they are classified as supports of a flexible design.

Anchor supports may be of normal or lightweight construction (see 2.5.145).

2.5.136. Anchor supports should be used in places determined by the working conditions on the overhead line during its construction and operation, as well as the operating conditions of the support structure.

Requirements for the use of anchor supports of normal design are established by this chapter.

On overhead lines of 35 kV and above, the distance between anchor supports should be no more than 10 km, and on overhead lines passing in hard-to-reach areas and in areas with especially difficult natural conditions, no more than 5 km.

On overhead lines of 20 kV and below with wires fixed on pin insulators, the distance between the anchor supports should not exceed 1,5 km in areas on ice I-III and 1 km in areas on ice IV and more.

On overhead lines of 20 kV and below with suspension insulators, the distance between the anchor supports should not exceed 3 km.

On overhead lines passing through mountainous or rugged terrain in areas with ice III or more, it is recommended to install anchor-type supports at passes and at other points that rise sharply above the surrounding terrain.

2.5.137. Limit states, according to which the calculation of supports, foundations and foundations of overhead lines, are divided into two groups.

The first group includes limit states that lead to the loss of the bearing capacity of the elements or to their complete unsuitability for operation, i.e., to their destruction of any nature. This group includes states at the highest external loads and at the lowest temperature, i.e. under conditions that can lead to the greatest bending or torque moments on supports, the greatest compressive or tensile forces on supports and foundations.

The second group includes limit states at which unacceptable deformations, displacements or deviations of elements occur that violate normal operation; this group includes states with the largest deflections of supports.

The method of calculation by limit states is intended to prevent, with a certain probability, the onset of limit states of the first and second groups during operation, as well as the first group during the construction of overhead lines.

2.5.138. The loads affecting the building structures of overhead lines, depending on the duration of action, are divided into permanent and temporary (long-term, short-term, special).

Permanent loads include:

• own weight of wires, cables, building structures, garlands of insulators, linear fittings;
• tension of wires and cables at average annual temperature and absence of wind and ice;
• the impact of prestressing structures, as well as the load from water pressure on foundations in riverbeds.

Long-term loads include:

• loads created by the impact of uneven deformations of the bases, not accompanied by a change in the structure of the soil, as well as by the effects of shrinkage and creep of concrete.

Short-term loads include:

• wind pressure on wires, cables and supports - free from ice and covered with ice;
• the weight of ice deposits on wires, cables, supports;
• tension of wires and cables in excess of their values ​​at an average annual temperature;
• loads from water pressure on supports and foundations in floodplains and from ice pressure;
• loads arising during the manufacture and transportation of structures, as well as during the installation of building structures, wires and cables.

Special loads include:

• loads arising from the breakage of wires and cables, as well as loads due to seismic effects.

2.5.139. Supports, foundations and foundations of overhead lines should be calculated for combinations of design loads of normal modes for the first and second groups of limit states and emergency and installation modes of overhead lines for the first group of limit states.

The calculation of supports, foundations and bases of foundations for strength and stability should be carried out for loads of the first group of limit states.

The calculation of supports, foundations and their elements for endurance and deformation is carried out for loads of the second group of limit states.

Calculation of foundations by deformations is carried out for loads of the second group of limit states without taking into account the dynamic effect of wind gusts on the structure of the support.

Supports, foundations and bases must also be calculated for the loads and effects of the external environment in specific conditions (the impact of the eroding action of water, wave pressure, ice piles, soil pressure, etc.), which are taken in accordance with building codes and rules or other regulatory documents.

Additionally, the following is taken into account:

• the possibility of temporary reinforcement of individual structural elements in assembly modes;
• calculation of reinforced concrete supports and foundations for crack opening in normal conditions is carried out for loads of the second group of limit states, and short-term loads are reduced by 10%; when using supports and foundations in an aggressive environment, short-term loads are not reduced;
• deviation of the top of the support when exposed to design loads in the second group of limit states should not lead to violation of the minimum insulating distances established by these Rules from current-carrying parts (wires) to grounded support elements and to the ground surface and crossed engineering structures;
• calculation of supports of a flexible structure is carried out according to a deformed scheme (taking into account additional forces arising from weight loads during support deformations for the first and second groups of limit states);
• calculation of supports installed in areas with seismicity over 6 points for the impact of seismic loads must be carried out in accordance with building codes and rules for construction in seismic areas; in this case, the calculated loads from the weight of ice, from the tension of wires and cables in normal conditions are multiplied by the combination coefficient ψ = 0,8.

2.5.140. The supports must be calculated in the normal mode for the first and second groups of limit states for combinations of the conditions specified in paragraph 2.5.71. 4, 5, 6 and in 2.5.73 paragraphs. 1, 2, 3.

Anchor-type supports and intermediate corner supports must also be calculated for the conditions of 2.5.71, paragraph 2, if the tension of wires or cables in this mode is greater than in the mode of maximum loads.

Anchor supports must be designed for the difference in tension of wires and cables, which occurs due to the inequality of the values ​​of the given spans on both sides of the support. At the same time, the conditions for calculating the difference in tensions are established during the development of the design of the supports.

The end supports must also be designed for the one-sided tension of all wires and cables.

Double-chain supports in all modes must also be designed for conditions when only one chain is mounted.

2.5.141. Intermediate supports of overhead lines with supporting garlands of insulators and blind clamps should be calculated in emergency mode according to the first group of limit states for the calculated conditional horizontal static loads Tav.

The calculation is made under the following conditions:

1) the wire or wires of one phase of one span are broken (for any number of wires on the support), the cables are not broken;

2) one span cable is broken (for a split cable - all its components), the wires are not broken.

Conditional loads are applied at the attachment points of that phase or that cable, at the break of which the forces in the calculated elements are the greatest. In this case, combinations of the conditions specified in 2.5.72 p. 1 are accepted.

2.5.142. The calculated conditional horizontal static load Taw from the wires to the supports is taken equal to:

1) on overhead lines with non-split phases:

• for free-standing metal poles, poles of any material on braces, A-shaped and other types of rigid poles with wires with an aluminum section of up to 185 mm2 - 0,5Tmax, an aluminum section of 205 mm2 or more - 0,4Tmax;
• for reinforced concrete free-standing supports with wires with a cross-sectional area of ​​\u185b\u2bthe aluminum part up to 0,3 mm205 - 2Tmax; the cross-sectional area of ​​the aluminum part is 0,25 mmXNUMX or more - XNUMXTmax;
• for wooden free-standing poles with wires with a cross-sectional area of ​​\u185b\u2bthe aluminum part up to 0,25 mm205 - 2Tmax; sections of the aluminum part 0,2 mm2.5.70 and more XNUMXTmax, where Tmax is the maximum design load from wire tension (see XNUMX);
• for other types of supports (supports made of new materials, flexible metal supports, etc.) - depending on the flexibility of the calculated supports within the limits indicated above;

2) on overhead lines with voltage up to 330 kV with split phases by multiplying the values ​​\u1b\u0,8bspecified in clause 0,7 for non-split phases by additional coefficients: 0,6 - when splitting into two wires; XNUMX for three wires and XNUMX for four wires.

On a 500 kV overhead line with splitting into three or more wires in phase - 0,15Tmax, but not less than 18 kN.

On a 750 kV overhead line with splitting into four or more wires in phase - 27 kN.

In the calculations, it is allowed to take into account the supporting effect of unbroken wires and cables at an average annual temperature without ice and wind. In this case, the calculated conditional loads should be determined as in clause 1 of this paragraph, and the mechanical stresses arising in the supporting wires and cables should not exceed 70% of their breaking force.

When using means that limit the transfer of the longitudinal load to the intermediate support (multi-roller hangers, as well as other means), the calculation should be made for the loads that arise when using these means, but not more than the calculated conditional loads taken when hanging wires in blind clamps.

2.5.143. The calculated conditional horizontal static load on the intermediate supports Tav from the cables is taken equal to:

1) from a single cable - 0,5Tmax;

2) from a split cable (from two components) - 0,4 Tmax, but not less than 20 kN, where Tmax is the maximum design load from the tension of the cables (see 2.5.70).

2.5.144. Intermediate supports with pin insulators should be designed in emergency mode for a break in one wire, which gives the greatest effort in the elements of the support, taking into account the flexibility of the supports and the supporting action of unbroken wires. The calculated conditional horizontal static load Ta for racks and attachments is assumed to be 0,3Tmax, but not less than 3 kN; for other support elements - 0,15 Tmax, but not less than 1,5 kN, where Tmax is the same as in 2.5.142.

2.5.145. Anchor-type supports should be calculated in emergency mode according to the first group of limit states for the breakage of technical wires and cables, at the breakage of which the forces in the elements under consideration are the greatest.

The calculation is made on the following conditions:

1) for overhead lines with aluminum and steel wires of all sections, aluminum alloy wires of all sections, steel-aluminum wires and heat-treated aluminum alloy wires with a steel core with a cross-sectional area of ​​\u150b\u2bthe aluminum part for both types of wires up to XNUMX mmXNUMX:

a) the wires of two phases of one span are broken for any number of circuits on the support, the cables are not broken (anchor normal supports);

b) the wires of one phase of one span are broken with any number of chains on the support, the cables are not broken (lightweight anchor and end supports);

2) for overhead lines with steel-aluminum wires and wires made of heat-treated aluminum alloy with a steel core with a cross-sectional area of ​​\u185b\u2bthe aluminum part for both types of wires of XNUMX mmXNUMX or more, as well as with steel ropes of the TK type of all sections used as wires: the wires of one phase of one span with any number of chains on the support, the cables are not broken (anchor normal and end supports);

3) for overhead line supports, regardless of the brands and sections of the suspended wires: one cable of one span is broken (with a split cable - all components), the wires are not broken. Combinations of climatic conditions are accepted in accordance with paragraph 2.5.72. 2 and 3.

2.5.146. Anchor-type supports must be checked in the installation mode for the first group of limit states for the following conditions:

1) in one span all wires and cables are mounted, in the other span wires and cables are not mounted. The tension in the installed wires and cables is assumed to be 0,6Tmax, where Tmax is the maximum calculated horizontal tension of the wires and cables (see 2.5.70). In this case, combinations of climatic conditions are accepted according to 2.5.74.

In this mode, metal supports and their fastenings must have the strength required by the standards without installing temporary guys;

2) in one of the spans, with any number of wires on the support, the wires of one circuit are mounted sequentially and in any order, the cables are not mounted;

3) in one of the spans, with any number of cables on the support, the cables are mounted sequentially and in any order, the wires are not mounted.

When checking according to paragraphs. 2 and 3, it is allowed to provide for temporary reinforcement of individual elements of the supports and the installation of temporary braces.

2.5.147. The overhead line supports should be checked for design loads corresponding to the installation method adopted by the project, taking into account the components from the efforts of the traction cable, the weight of the mounted wires (cables), insulators, mounting fixtures and a fitter with tools.

The attachment point of each wire (eye, diaphragm, etc.) with separate fastening of the wires of the split phase should be calculated taking into account the redistribution of the load from the broken suspension chain to the remaining wires of the phase.

The support elements must withstand the vertical load from the weight of the installer with tools, the calculated value of which is 1,3 kN in combination with the loads of the normal mode from wires and cables free of ice at the average annual temperature, as well as with the loads of emergency and installation modes.

The calculated loads on the supports from the weight of the mounted wires (cables) under climatic conditions in accordance with 2.5.74 and insulator strings in flat terrain are recommended to be taken:

1) on intermediate supports - equal to twice the weight of the span of wires (cables) without ice and a garland of insulators, based on the possibility of lifting the mounted wires (cables) and a garland through one block;

2) on anchor supports and intermediate supports, when the installation area is limited by the latter, - taking into account the force in the traction cable, determined from the condition of the location of the traction mechanism at a distance of 2,5h from the support, where h is the height of the middle phase wire suspension on the support.

When installing the traction mechanism in rough terrain, it is necessary to additionally take into account the force from the inclination of the traction cable, taking into account the difference in elevation marks of the wire suspension point and the traction mechanism.

The calculated vertical load from the weight of the fitter and mounting fixtures applied at the point of attachment of the garlands of insulators, for supports of 500 - 750 kV overhead lines, is assumed to be 3,25 kN, for anchor-type supports of overhead lines up to 330 kV with suspension insulators - 2,6 kN, for intermediate supports of overhead lines up to 330 kV with suspension insulators - 1,95 kN, for supports with pin insulators - 1,3 kN.

2.5.148. The structures of the supports must provide on a disconnected overhead line, and on an overhead line of 110 kV and above and in the presence of voltage on it:

1) performance of their maintenance and repair work;

2) convenient and safe lifting of personnel to the support from the ground level to the top of the support and its movement along the elements of the support (racks, traverses, cable racks, struts, etc.). On the support and its elements, it should be possible to mount special devices and fixtures for performing maintenance and repair work.

2.5.149. To lift personnel to the support, the following measures should be provided:

1) on each rack of metal supports up to 20 m high to the top, with distances between the points of attachment of the lattice to the rack (trunk) belts of more than 0,6 m or when the lattice is tilted to the horizontal by more than 30º, and for supports with a height of more than 20 and less than 50 m independently from the distances between the attachment points of the grating and the angle of its inclination, special steps (step-bolts) should be made on one belt or stairs without a fence, reaching the mark of the upper traverse.

The design of the cable rack on these supports should provide a comfortable lift or have special steps (step bolts);

2) on each rack of metal supports with a height of more than 50 m to the top of the support, ladders with railings should be installed, reaching the top of the support. At the same time, platforms (ladders) with fences should be made every 15 m vertically. Ladders with railings must also be carried out on the traverses of these supports. On supports with trussed traverses, it should be possible to hold on to the rod when moving along the traverse;

3) on reinforced concrete supports of any height, it must be possible to climb to the lower traverse from telescopic towers, inventory ladders or using special inventory lifting devices. For climbing on a reinforced concrete centrifuged rack above the lower traverse on the supports of 35-750 kV overhead lines, stationary manholes (stairs without fences, etc.) must be provided.

To climb a reinforced concrete vibrating rack of an overhead line of 35 kV and below, on which power or instrument transformers, disconnectors, fuses or other devices are installed, it should be possible to mount inventory ladders or special inventory lifting devices. Reinforced concrete vibrated racks, on which the above electrical equipment is not installed, this requirement does not apply.

Convenient climbing to the cable racks and metal vertical parts of the racks of reinforced concrete supports of 35-750 kV overhead lines should be ensured by their design or special steps (step bolts);

4) reinforced concrete supports that do not allow climbing inventory stairs or with the help of special inventory lifting devices (supports with braces or internal connections fixed on a rack below the lower traverse, etc.) must be equipped with stationary stairs without railings, reaching the bottom traverses.

Above the lower traverse, the devices indicated in the first paragraph of clause 3 must be made.

See other articles Section Rules for the installation of electrical installations (PUE).

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