Section 2. Sewerage of electricity

Overhead power lines with voltage above 1 kV. Surge protection, grounding

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

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2.5.116. Overhead lines 110-750 kV with metal and reinforced concrete supports must be protected from direct lightning strikes by cables along the entire length.

The construction of 110-500 kV overhead lines or their sections without cables is allowed:

1) in areas with less than 20 thunderstorm hours per year and in mountainous areas with a ground discharge density of less than 1,5 per 1 km2 per year;

2) on sections of overhead lines in areas with poorly conductive soils (r> 103 Ohm m);

3) on sections of the route with an estimated ice wall thickness of more than 25 mm;

4) for overhead lines with reinforced wire insulation relative to grounded parts of the support, while providing the estimated number of lightning outages of the line corresponding to the estimated number of lightning outages of overhead lines of the same voltage with cable protection.

The number of lightning outages of the line for the cases given in paragraphs. 1-3, determined by calculation taking into account operating experience, should not exceed without strengthening the insulation three per year for 110-330 kV overhead lines and one per year for 500 kV overhead lines.

Overhead lines 110-220 kV, intended for power supply of oil and gas production and transportation facilities, must be protected from direct lightning strikes by cables along the entire length (regardless of the intensity of thunderstorm activity and specific equivalent earth resistance).

2.5.117. Protection of overhead lines to substations must be carried out in accordance with the requirements of Ch. 4.2.

2.5.118. For overhead lines up to 35 kV, the use of lightning protection cables is not required.

On VLZ 6-20 kV, it is recommended to install wire insulation protection devices in case of lightning strikes.

Overhead lines 110 kV on wooden poles in areas with up to 40 thunderstorm hours, as a rule, should not be protected by cables, and in areas with more than 40 thunderstorm hours, their protection with cables is mandatory.

On 6-20 kV overhead lines on wooden poles, according to the conditions of lightning protection, the use of metal traverses is not recommended.

2.5.119. Garlands of insulators of single metal and reinforced concrete supports, as well as extreme supports of sections with such supports and other places with weakened insulation on overhead lines with wooden supports should be protected by protective devices, which can be used as valve arresters (RV), non-linear surge arresters (OPN), tubular arresters (RT) and spark gaps (IP). Installed IP must comply with the requirements given in Ch. 4.2.

2.5.120. When protecting overhead lines from lightning surges with cables, the following should be followed:

1) single-column metal and reinforced concrete supports with one cable must have a protection angle of no more than 30º, and supports with two cables - no more than 20º;

2) on metal supports with a horizontal arrangement of wires and with two cables, the protection angle with respect to external wires for 110-330 kV overhead lines should be no more than 20º, for 500 kV overhead lines - no more than 25º, for 750 kV overhead lines - no more than 22º. In areas of ice IV or more and in areas with frequent and intense dancing of wires for 110-330 kV overhead lines, a protection angle of up to 30º is allowed;

3) on reinforced concrete and wooden supports of the portal type, the protection angle with respect to the outer wires is not more than 30º;

4) when protecting the overhead line with two cables, the distance between them on the support should be no more than 5 times the vertical distance from the cables to the wires, and if the cable suspension height on the support is more than 30 m, the distance between the cables should be no more than 5 times the vertical distance between the cable and the wire on the support, multiplied by a factor equal to 5,5 / √h, where h is the height of the cable suspension on the support.

2.5.121. The vertical distances between the cable and the wire of the overhead line in the middle of the span, without taking into account their deviation by the wind, according to the conditions of protection against lightning surges, must be at least those given in Table. 2.5.16 and not less than the vertical distance between the cable and the wire on the support.

For intermediate span lengths, the distances are determined by interpolation.

Table 2.5.16. The smallest distances between the cable and the wire in the middle of the span

2.5.122. The fastening of cables on all supports of 220-750 kV overhead lines must be carried out using insulators shunted by IP with a size of at least 40 mm.

At each anchor section up to 10 km long, the cables must be grounded at one point by installing special jumpers on the anchor support. With a longer anchor span, the number of grounding points in the span is chosen so that at the highest value of the longitudinal electromotive force induced in the cable during a short circuit (SC) on the overhead line, there is no breakdown of the IP.

Insulated cable fastening is recommended to be carried out with glass suspension insulators.

At the approaches of 220-330 kV overhead lines to substations at a length of 1-3 km and at the approaches of 500-750 kV overhead lines at a length of 3-5 km, if the cables are not used for capacitive selection, ice melting or communication, they should be grounded at each support ( see also 2.5.192).

On overhead lines of 150 kV and below, if ice melting or the organization of high-frequency communication channels on a cable is not provided, the cable should be insulated fastened only on metal and reinforced concrete anchor supports.

In sections of overhead lines with non-insulated fastening of the cable and a short-circuit current to earth exceeding 15 kA, as well as at approaches to substations, the cable must be grounded with the installation of a jumper that shunts the clamp.

When using cables for the device of high-frequency communication channels, they are isolated from the supports along the entire length of the high-frequency communication channels and grounded at substations and amplifying points through high-frequency barriers.

The number of insulators in the supporting cable fastening should be at least two and be determined by the conditions for ensuring the required reliability of high-frequency communication channels. The number of insulators in the tension cable fastening should be taken twice as compared to the number of insulators in the supporting cable fastening.

The insulators on which the cable is suspended must be shunted with a spark gap. The size of the IP is chosen as minimally possible according to the following conditions:

1) the discharge voltage of the power supply must be lower than the discharge voltage of the insulating cable fastening by at least 20%;

2) The power supply should not overlap with a single-phase short circuit to ground on other supports;

3) when switching off the power supply from lightning discharges, self-extinguishing of the arc of the accompanying current of industrial frequency should occur.

On 500-750 kV overhead lines, in order to improve the conditions for self-extinguishing of the arc of the accompanying current of industrial frequency and reduce power losses, it is recommended to use cable crossing.

If ice melting is provided on the overhead lines, then the insulated fastening of the cables is carried out throughout the entire melting area. At one point of the melting section, the cables are grounded using special jumpers. Rope insulators are shunted by IP, which must be minimal, withstand the melting voltage and have a discharge voltage less than the discharge voltage of the rope garland. The size of the MT should ensure self-extinguishing of the arc of the accompanying current of industrial frequency when it overlaps during a short circuit or lightning discharges.

2.5.123. On overhead lines with portal-type wooden supports, the distance between the phases along the tree must be at least: 3 m - for 35 kV overhead lines; 4 m - for 110 kV overhead lines; 4,8 m - for 150 kV overhead lines; 5 m - for 220 kV overhead lines.

In some cases, for 110-220 kV overhead lines, if there are justifications (small short-circuit currents, areas with weak thunderstorm activity, etc.), it is allowed to reduce the indicated distances to the value recommended for overhead lines with a voltage one step lower.

On single-column wooden supports, the following distances between phases along the tree are allowed: 0,75 m - for 3-20 kV overhead lines; 2,5 m - for 35 kV overhead lines, subject to the span distances in accordance with 2.5.94.

2.5.124. Cable inserts in overhead lines must be protected at both ends of the cable from lightning surges by protective devices. The grounding clamp of protective devices, the metal sheaths of the cable, the body of the cable box must be connected to each other along the shortest path. The grounding clamp of the protective device must be connected to the grounding conductor by a separate conductor.

Do not require lightning surge protection:

1) cable inserts 35-220 kV with a length of 1,5 km or more in overhead lines, protected by cables;

2) cable inserts in overhead lines with a voltage of up to 20 kV, made with cables with plastic insulation and sheath, 2,5 km or more in length and cables of other designs 1,5 km or more in length.

2.5.125. For overhead lines passing at an altitude of up to 1000 m above sea level, the insulating air distances from live wires and fittings to the grounded parts of the supports must be at least those given in Table. 2.5.17. It is allowed to reduce the insulation distances for lightning overvoltages indicated in Table. 2.5.17, subject to a decrease in the overall level of lightning resistance of overhead lines by no more than 20%. For 750 kV overhead lines passing at an altitude of up to 500 m above sea level, the distances indicated in Table. 2.5.17, can be reduced by 10% for the gap "loop wire - anchor-angle support post", "wire-guy" and by 5% for other gaps. The smallest insulation distances for internal overvoltages are given for the following values ​​of the calculated multiplicity: 4,5 - for 6-10 kV overhead lines; 3,5 - for 20-35 kV overhead lines; 3,0 - for 110-220 kV overhead lines; 2,7 - for 330 kV overhead lines; 2,5 - for 500 kV overhead lines and 2,1 - for 750 kV overhead lines.

For other, lower values ​​of the calculated multiplicity of internal overvoltages, the permissible insulation distances for them are recalculated proportionally.

Insulating air distances between current-carrying parts and a wooden support that does not have grounding slopes can be reduced by 10%, with the exception of distances selected according to the condition of safe climbing to the support.

When passing overhead lines in mountainous areas, the smallest insulating distances for operating voltage and for internal overvoltages should be increased compared to those given in Table. 2.5.17 by 1% for every 100 m above 1000 m above sea level.

Table 2.5.17. The smallest insulating distance in air (in the light) from current-carrying to grounded parts of the support

* In the denominator - the gap "loop wire - anchor-angle support post", in the numerator - all gaps, except for the gap "wire - support" for the middle phase, which should be at least 480 cm.

2.5.126. The smallest distances on the support between the wires of the overhead line at the place of their intersection with each other during transposition, branches, transition from one location of the wires to another must be at least those given in table. 2.5.18.

Table 2.5.18. The smallest distance between the phases on the support

* For calculated internal overvoltage ratios less than 2,1, the allowable insulation distances are recalculated proportionally.

2.5.127. Additional requirements for protection against lightning overvoltages of overhead lines when they intersect with each other and when they intersect various structures are given in 2.5.229, 2.5.238, 2.5.267.

2.5.128. On double-circuit overhead lines of 110 kV and above, protected by a cable, in order to reduce the number of double-circuit lightning surges, it is allowed to increase the insulation of one of the circuits by 20-30% compared to the insulation of the other circuit.

2.5.129. On the overhead line must be grounded:

1) supports with a lightning protection cable or other lightning protection devices;

2) reinforced concrete and metal supports of 3-35 kV overhead lines;

3) supports on which power or instrument transformers, disconnectors, fuses and other devices are installed;

4) metal and reinforced concrete poles of 110-500 kV overhead lines without cables and other lightning protection devices, if necessary for the conditions of ensuring the operation of relay protection and automation.

Wooden poles and wooden poles with metal traverses of overhead lines without lightning protection cables or other lightning protection devices are not grounded.

The resistance of the grounding devices of the supports given in clause 1, with their height up to 50 m, should be no more than those given in table. 2.5.19; with a support height of more than 50 m - 2 times lower than those given in Table. 2.5.19. On double-circuit and multi-circuit poles of overhead lines, regardless of the line voltage and the height of the poles, it is recommended to reduce the resistance of grounding devices by 2 times compared to those given in Table. 2.5.19.

It is allowed to exceed the grounding resistance of a part of the towers in comparison with the normalized values, if there are towers with low grounding resistance values, and the expected number of lightning outages does not exceed the values ​​​​obtained when meeting the requirements of Table. 2.5.19 for all overhead lines.

For supports of mountain overhead lines located at altitudes of more than 700 m above sea level, indicated in Table. 2.5.19 ground resistance values ​​can be doubled. The resistance of the grounding devices of the supports specified in clause 2 for 2-3 kV overhead lines passing in populated areas, as well as all 20 kV overhead lines, should be no more than those given in table. 35: for 2.5.19-3 kV overhead lines in uninhabited areas in soils with resistivity ρ up to 20 Ohm m - no more than 100 Ohm, and in soils with ρ above 30 Ohm m - no more than 100 ρ Ohm.

The resistance of the grounding devices of the supports of overhead lines of 110 kV and above, specified in clause 3, should be no more than those given in table. 2.5.19, and for 3-35 kV overhead lines should not exceed 30 ohms.

The resistances of the grounding devices of the supports specified in clause 4 are determined during the design of the overhead line.

For overhead lines protected by cables, the resistance of grounding devices, made according to the conditions of lightning protection, must be provided with the cable disconnected, and for other conditions - with the cable not disconnected.

The resistance of the grounding devices of the overhead line supports must be provided and measured at industrial frequency currents during their highest values ​​in the summer. It is allowed to make measurements in other periods with the correction of the results by introducing a seasonal coefficient, however, measurements should not be made during the period when the resistance value of grounding devices is significantly affected by soil freezing.

The place where the grounding device is connected to the reinforced concrete support must be accessible for measurements.

Table 2.5.19. The greatest resistance of grounding devices of overhead lines

2.5.130. Reinforced concrete foundations of poles of 110 kV and higher overhead lines can be used as natural grounding conductors (exception 2.5.131 and 2.5.253) when there is a metal connection between the anchor bolts and foundation reinforcement and there is no waterproofing of reinforced concrete with polymeric materials.

Bituminous coating on reinforced concrete supports and foundations does not affect their use as natural ground electrodes.

2.5.131. When passing overhead lines of 110 kV and higher in areas with clay, loamy, sandy and similar soils with a resistivity of ρ≤1000 Ohm m, reinforcement of reinforced concrete foundations, supports and stepchildren should be used as natural ground electrodes without additional laying or in combination with laying artificial ground electrodes. In soils with higher resistivity, the natural conductivity of reinforced concrete foundations should not be taken into account, and the required resistance value of the grounding device should be provided only by the use of artificial ground electrodes.

The required resistance of the grounding devices of the 35 kV overhead line supports should be ensured by the use of artificial ground electrodes, and the natural conductivity of the foundations, underground parts of the supports and stepchildren (attachments) should not be taken into account in the calculations.

2.5.132. For grounding reinforced concrete supports, as grounding conductors, it is necessary to use those elements of stressed and non-stressed longitudinal reinforcement of racks, the metal elements of which are interconnected and can be connected to the ground electrode.

A special conductor can be laid as a ground conductor outside the rack or inside, if necessary. Armature elements used for grounding must satisfy thermal resistance when short-circuit currents flow. During the short circuit, the rods should be heated by no more than 60 ºС.

Guys of reinforced concrete supports should be used as grounding conductors in addition to fittings.

Cables, grounded in accordance with 2.5.122, and fastening parts of insulator strings to the traverse of reinforced concrete supports shall be metal-coupled to a grounding descent or grounded armature.

2.5.133. The cross section of each of the grounding slopes on the overhead line support must be at least 35 mm2, and for single-wire slopes, the diameter must be at least 10 mm (section 78,5 mm2). The number of descents must be at least two.

For areas with an average annual relative humidity of 60% or more, as well as for medium and highly aggressive degrees of environmental impact, grounding slopes at the place of their entry into the ground must be protected from corrosion in accordance with the requirements of building codes and regulations.

In case of danger of corrosion of grounding conductors, their cross section should be increased or galvanized grounding conductors should be used.

On overhead lines with wooden supports, a bolted connection of grounding slopes is recommended; on metal and reinforced concrete supports, the connection of grounding slopes can be made both bolted and welded.

2.5.134. Ground electrodes of overhead line supports, as a rule, should be located at a depth of at least 0,5 m, and in arable land - 1 m. .0,1 m. With a smaller thickness of this layer or its absence, it is recommended to lay ground electrodes on the rock surface with filling them with cement mortar.

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

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