Section 2. Sewerage of electricity

Overhead power lines with voltage above 1 kV. Big transitions

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

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2.5.150. The section of the large transition should be limited by end supports (terminal devices in the form of concrete anchors, etc.), separating the large transition into an independent part of the overhead line, the strength and stability of which do not depend on the influence of adjacent sections of the overhead line.

2.5.151. Depending on the type of wire fastening, the supports installed between the end (K) supports (devices) can be:

1) intermediate (P) - with fastening of all wires on a support using insulators supporting garlands;

2) anchor (A) - with fastening of all wires on a support using tension garlands of insulators;

3) combined (PA) - with mixed fastening of wires on a support using both supporting and tension garlands of insulators.

2.5.152. Transitional supports that limit the span of the intersection must be anchor end. It is allowed to use intermediate supports and light-weight anchor supports for transitions with steel-aluminum wires or wires made of heat-treated aluminum alloy with a steel core with an aluminum section for both types of wires of 120 mm2 or more or steel ropes of the TK type as wires with a ropes section of 50 mm2 and more . In this case, the number of intermediate supports between the end supports must comply with the requirements of 2.5.153.

2.5.153. Depending on the specific conditions, the following transition schemes can be applied:

1) single-span on end supports K-K;

2) two-span with supports K-P-K, K-PA-K;

3) three-span with supports K-P-P-K, K-PA-PA-K;

4) four-span with supports K-P-P-P-K, K-PA-PA-PA-K (only for standard ice wall thickness of 15 mm or less and lengths of transition spans no more than 1100 m);

5) multi-span with supports K-A...A-K;

6) when using supports P or PA, the transition must be divided by supports A into sections with the number of supports P or PA in each section no more than two, i.e. K-P-P-A ... A-P-P-K , K-PA-PA-A ... A-PA-PA-K (or no more than three according to clause 4).

2.5.154. Wind pressure on wires and cables of large passages through water spaces is determined in accordance with 2.5.44, but taking into account the following additional requirements.

1. For a transition consisting of one span, the height of the reduced center of gravity of wires or cables is determined by the formula

where hav1, hav2 - the height of the cables or the average height of the wires to the insulators on the crossing supports, measured from the low water level of the river, the normal horizon of the strait, canal, reservoir, and for crossing gorges, ravines and other obstacles - from the ground mark at the installation sites of the supports , m;

f - sag of the wire or cable at the highest temperature in the middle of the span, m

2. For a transition consisting of several spans, the wind pressure on the wires or cables is determined for the height hpr corresponding to the weighted average height of the reduced centers of gravity of the wires or cables in all spans and calculated by the formula

where hpr1, hpr2, ..., hprn are the heights of the reduced centers of gravity of wires or cables above the low water level of the river, the normal horizon of the strait, canal, reservoir in each of the spans, and for crossing gorges, ravines and other obstacles - above the arithmetic mean of the ground elevations in places installation of supports, m.

At the same time, if the intersected body of water has a high, flood-free shore, on which both transitional and adjacent supports are located, then the heights of the reduced centers of gravity in the span adjacent to the transitional span are counted from the ground level in this span;

l1, l2, …, ln are the lengths of the spans included in the passage, m.

Normative wind pressure on wires, cables and structures of supports of large crossings constructed in places protected from transverse winds is not allowed to be reduced.

2.5.155. Transitions can be performed single-stranded and double-stranded.

It is recommended to carry out double-circuit crossings in populated areas, in areas of industrial development, as well as if a second transition is needed in the future in uninhabited or hard-to-reach areas.

2.5.156. On single-circuit transitions for overhead lines of 330 kV and below, it is recommended to use a triangular arrangement of phases, a horizontal arrangement of phases is allowed; for 500-750 kV overhead lines, as a rule, a horizontal arrangement of phases should be used.

2.5.157. On double-circuit transitions of overhead lines up to 330 kV, the arrangement of wires in three tiers is recommended, the arrangement of wires in two tiers is also allowed. On double-circuit crossings of 500 kV overhead lines, it is recommended to use anchor-type supports with the arrangement of wires in one (horizontal) or two tiers.

2.5.158. The distances between wires, as well as between wires and cables from the working conditions in the span must be selected in accordance with 2.5.88 - 2.5.92, taking into account additional requirements:

1) the value of the coefficient Kg in the table. 2.5.13 it is necessary to increase by: 0,2 - with the ratio of loads Рg.p / PI in the range from 2 to 6,99; 0,4 - with a ratio of loads Рg.p / PI equal to 7 or more;

2) the distances between the nearest phases of single-circuit and double-circuit overhead lines must also meet the requirements of 2.5.159, 2.5.160.

2.5.159. To ensure the normal operation of wires in a span in any area along the dance of wires, when they are located in different tiers, the distance between adjacent tiers of intermediate transitional supports with a height of more than 50 m and the horizontal displacement should be:

2.5.160. On double-circuit supports, the distance between the axes of the phases of different circuits must be at least as follows:

2.5.161. At crossings with spans exceeding the spans of the main line by no more than 1,5 times, it is recommended to check the feasibility of using wire of the same brand as on the main line. At overhead lines up to 110 kV, it is recommended to check the feasibility of using steel ropes as wires, if the electrical calculation of the wires allows it.

On transitions with split phases, it is recommended to consider phases with a smaller number of wires of large cross sections with checking the wires for heating.

2.5.162. As lightning protection cables, steel ropes and steel-aluminum wires according to 2.5.79 should be used.

In the case of using lightning protection cables for organizing high-frequency communication channels, it is recommended to use heat-treated aluminum alloy wires with a steel core and steel-aluminum wires as cables, as well as cables with built-in optical cables.

2.5.163. Single and split wires and cables must be protected from vibration by installing on each side of the transition span up to 500 m long - one vibration damper on each wire and cable and from 500 to 1500 m long - at least two different types of vibration dampers on each wire and cable.

Protection against vibration of wires and cables in spans with a length of more than 1500 m, as well as regardless of the span length for wires with a diameter of more than 38 mm and wires with tension at an average annual temperature of more than 180 kN, must be carried out according to a special project.

2.5.164. As a rule, glass insulators should be used at overhead line transitions.

2.5.165. The number of insulators in the garlands of transitional supports is determined in accordance with Ch. 1.9.

2.5.166. Supporting and tension garlands of insulators should be provided with at least two chains with separate fastening to the support. Multi-chain tension garlands must be attached to the support at least at two points.

2.5.167. The design of the garlands of split phase insulators and their fastening to the support should, if possible, ensure separate installation and dismantling of each of the wires included in the split phase.

2.5.168. To fasten wires and cables to insulator strings on transitional supports, it is recommended to use blind support clamps or support devices of a special design (roller hangers).

2.5.169. When performing protection of transitions of 110-750 kV overhead lines from lightning surges, it is necessary to be guided by the following:

1) all crossings should be protected from direct lightning strikes by cables;

2) the number of cables must be at least two with a protection angle in relation to the outermost wires of not more than 20º.

When the transition is located outside the length of the protected approach of the overhead line to the switchgear and substations with an increased protective level in areas on ice III and more, as well as in areas with frequent and intense dancing of wires, a protection angle of up to 30º is allowed;

3) it is recommended to install protective devices (2.5.119) at crossings with spans longer than 1000 m or with tower heights higher than 100 m;

4) the horizontal displacement of the cable from the center of the extreme phase must be at least: 1,5 m - for 110 kV overhead lines; 2 m - for 150 kV overhead lines; 2,5 m - for 220 kV overhead lines; 3,5 m - for 330 kV overhead lines and 4 m - for 500-750 kV overhead lines;

5) the choice of the distance between the cables is made in accordance with 2.5.93 and 2.5.120 p. 4.

2.5.170. The fastening of the cables on all the supports of the transition must be carried out using insulators with a destructive mechanical load of at least 120 kN.

In order to reduce power losses in the insulating cable fastening, there must be at least two insulators. Their number is determined taking into account the accessibility of the terrain and the height of the supports.

When using cables for arranging high-frequency communication channels or for ice melting, the number of insulators determined by the conditions for ensuring the reliability of communication channels or for the conditions for ensuring ice melting should be increased by two.

The insulators on which the cable is suspended shall be shunted with a spark gap, the size of which is selected in accordance with 2.5.122, without taking into account the installation of additional insulators.

2.5.171. Suspension of lightning protection cables to protect transitions of overhead lines of 35 kV and below is not required. Protective devices must be installed on the transitional supports. The size of the IP when using them as protective devices is recommended to be taken in accordance with Ch. 4.2. With an increase in the number of insulators due to the height of the support, the electrical strength of the IP must be coordinated with the electrical strength of the garlands.

2.5.172. To ensure the safe movement of service personnel along the traverses of transition towers with a height of more than 50 m with phases in different tiers, the smallest permissible insulating distance in air from current-carrying to grounded parts of the towers must be at least: 3,3 m - for overhead lines up to 110 kV; 3,8 m - for 150 kV overhead lines; 4,3 m - for 220 kV overhead lines; 5,3 m - for 330 kV overhead lines; 6,3 m - for 500 kV overhead lines; 7,6 m - for 750 kV overhead lines.

2.5.173. The resistance of the grounding devices of the supports should be selected in accordance with Table. 2.5.19 and 2.5.129.

The resistance of the grounding device of supports with protective devices should be no more than 10 ohms with an earth resistivity not higher than 1000 ohm m and no more than 15 ohms with a higher specific resistance.

2.5.174. When designing crossings through water spaces, it is necessary to carry out the following calculations for the hydrology of the river floodplain:

1) a hydrological calculation that establishes the estimated water level, the level of ice drift, the distribution of water discharge between the channel and floodplains and the speed of water flow in the channels and floodplains;

2) channel calculation, which establishes the size of the opening of the transition and the depth after erosion at the transition supports;

3) hydraulic calculation, which sets the water level before the crossing, jet-directing dams and embankments, the height of the waves on the floodplains;

4) calculation of loads on foundations located in the channel and floodplain of the river, taking into account the impact of ice pressure and bulk ships.

The height of the foundations of supports located in the channel and floodplain of the river should exceed the level of ice drift by 0,5 m.

The deepening of the foundations of the supports of shallow and deep crossings with the possibility of soil erosion should be at least 2,5 m (counting from the soil mark after erosion). The depth of immersion of piles into the ground with a pile foundation should be at least 4 m from the level of erosion.

2.5.175. Intermediate and combined supports (P and PA) with fastening of wires using insulators supporting garlands should be calculated in emergency mode according to the first group of limit states for the following conditions:

1) a single wire or all wires of one phase of one span are broken, the cables are not broken (single-chain supports);

2) the wires of two phases of one span are broken, the cables are not broken (double-circuit supports, as well as single-circuit supports with steel-aluminum wires and wires made of heat-treated aluminum alloy with a steel core with an aluminum section for both types of wires up to 150 mm2);

3) one cable of one span is broken (when the cable is split, all its components are broken), the wires, regardless of grades and sections, are not broken.

In the calculations of supports, the calculated horizontal static load from wires is taken equal to:

a) with an unsplit phase and its fastening in a blind clamp - reduced tension that occurs when a phase breaks. In this case, combinations of conditions are accepted in accordance with 2.5.72 p.3.

With a split phase and its fastening in blind clamps, the values ​​​​for non-split phases are multiplied by additional coefficients: 0,8 - when splitting into 2 wires; 0,7 - for three wires; 0,6 - for four wires and 0,5 - for five or more;

b) with non-split and split phases of the wire and their fastening in a supporting device of a special design - a conditional load equal to 25 kN with one wire in the phase; 40 kN with two wires in phase; 60 kN with three or more wires in phase.

The design load from a rope fixed in a blind clamp is assumed to be equal to the maximum design horizontal tension of the rope under the combination of the conditions specified in 2.5.72, paragraph 3.

In this case, for cables split into two components, the tension should be multiplied by 0,8.

The design load from the cable, fixed in the supporting device of a special design, is assumed to be 40 kN. Loads are applied at the points of attachment of the wires of those phases or that cable, at the break of which the forces in the calculated elements are the greatest.

2.5.176. Anchor-type supports should be calculated in emergency mode according to the first group of limit states for the breakage of those phases or that cable, at the breakage of which the forces in the elements under consideration are the largest. The calculation is made on the following conditions:

1) the wire or wires of one phase of one span are broken, the cables are not broken (single-circuit supports with steel-aluminum wires and wires made of heat-treated aluminum alloy with a steel core with an aluminum part section for both types of wires of 185 mm2 and more, as well as with steel ropes of the TK type of all sections used as wires);

2) the wires of two phases of one span are broken, the cables are not broken (double-circuit supports, as well as single-circuit supports with steel-aluminum wires and wires from heat-treated aluminum alloy with a steel core with an aluminum section for both types of wires up to 150 mm2);

3) one cable of one span is broken (when the cable is split, all its components are broken), the wires, regardless of grades and sections, are not broken.

The design loads from wires and cables are taken equal to the maximum calculated horizontal tension of the wire or cable under a combination of conditions in accordance with 2.5.72 paragraphs. 2 and 3.

When determining the forces in the support elements, conditional loads or unbalanced tensions that occur when those wires or cables break, at which these forces have the greatest values, are taken into account.

2.5.177. Supports of a large crossing shall have day marking (painting) and signal lighting in accordance with 2.5.292.

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

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