Section 4. Switchgears and substations

Switchgears and substations with voltages above 1 kV. Lightning surge protection

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

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4.2.133. Protection against lightning overvoltage of switchgear and substation is carried out:

• from direct lightning strikes - rod and cable lightning rods;
• from incoming waves from outgoing lines - lightning rods from direct lightning strikes at a certain length of these lines by protective devices installed on the approaches and in the switchgear, which include valve arresters (RV), surge arresters (OPN), tubular arresters (shield spark gaps (SP ).

Surge arresters, the remaining voltages of which, at a rated discharge current, are not more than 10% lower than the remaining voltage PB or the average breakdown voltage RT or IP, are further called appropriate.

4.2.134. Open switchgears and substations 20-750 kV must be protected from direct lightning strikes. Protection against direct lightning strikes is not required for 20 and 35 kV substations with transformers with a unit capacity of 1,6 MVA or less, regardless of the number of such transformers and the number of lightning hours per year, for all outdoor switchgear of 20 and 35 kV substations in areas numbering thunderstorm hours per year is not more than 20, as well as for outdoor switchgear and substations of 220 kV and below on sites with equivalent earth resistivity in the thunderstorm season of more than 2000 Ohm m, with the number of thunderstorm hours per year not more than 20.

Buildings of closed switchgear and substations should be protected from direct lightning strikes in areas with more than 20 thunderstorm hours per year.

Buildings of closed switchgear and substations with metal roofing should be protected by grounding these coatings. In the presence of a reinforced concrete roof and continuous electrical connection of its individual elements, protection is carried out by grounding its fittings.

The protection of buildings of closed switchgear and substations, the roof of which does not have metal or reinforced concrete coatings with continuous electrical connection of its individual elements, should be carried out with lightning rods, or by laying a lightning protection mesh directly on the roof of buildings.

When installing rod lightning rods on the protected building, at least two down conductors must be laid from each lightning rod on opposite sides of the building.

The lightning protection mesh should be made of steel wire with a diameter of 6-8 mm and laid on the roof directly or under a layer of non-combustible insulation or waterproofing. The grid should have cells with an area of ​​no more than 150 m2 (for example, a cell of 12x12 m). Grid nodes must be connected by welding. Down conductors connecting the lightning protection mesh with the grounding device must be laid at least every 25 m along the perimeter of the building.

As down conductors, metal and reinforced concrete (in the presence of at least a part of non-stressed reinforcement) building structures should be used. In this case, a continuous electrical connection from the lightning rod to the ground electrode must be provided. The metal elements of the building (pipes, ventilation devices, etc.) should be connected to a metal roof or lightning protection mesh.

When calculating the number of reverse overlaps on a pole, one should take into account the increase in the inductance of the pole in proportion to the ratio of the distance along the down conductor from the pole to grounding to the distance from grounding to the top of the pole.

When entering into closed switchgears and substations of overhead lines through bushings located at a distance of less than 10 m from current conductors and other current-carrying parts associated with it, these inputs must be protected by RV or appropriate surge arresters. When connecting to the grounding lines of the substation at a distance of less than 15 m from power transformers, the conditions of 4.2.136 must be met.

For electrolysis buildings located on the territory of the substation, premises for storing hydrogen cylinders and installations with hydrogen receivers, the lightning protection mesh must have cells with an area of ​​​​not more than 36 m2 (for example, 6x6 m).

Protection of buildings and structures, including explosive and fire hazardous, as well as pipes located on the territory of power plants, is carried out in accordance with the technical documentation approved in the prescribed manner.

4.2.135. Protection of outdoor switchgear of 35 kV and above from direct lightning strikes must be performed by free-standing or installed on structures lightning rods. It is recommended to use the protective effect of high objects that are lightning rods (overhead line poles, searchlight masts, radio masts, etc.).

On outdoor switchgear structures of 110 kV and above, rod lightning rods can be installed with an equivalent earth resistivity in the thunderstorm season: up to 1000 Ohm m - regardless of the area of ​​the grounding device of the substation; more than 1000 to 2000 Ohm m - with the area of ​​the grounding device of the substation 10000 m2 or more.

The installation of lightning rods on the structures of 35 kV outdoor switchgear is allowed with an equivalent earth resistivity in the thunderstorm season: up to 500 Ohm m - regardless of the area of ​​the ground loop of the substation, more than 500 Ohm m - with the area of ​​the ground loop of the substation 10000 m2 or more.

From the racks of outdoor switchgear structures of 35 kV and above with lightning rods, the spreading of the lightning current along the grounding lines in at least two directions with an angle of at least 90º between adjacent ones should be ensured. In addition, at least one vertical electrode 3-5 m long must be installed in each direction, at a distance not less than the length of the electrode from the point of connection to the grounding line of the rack with a lightning rod.

If the protection zones of lightning rods do not cover the entire territory of the outdoor switchgear, lightning rods located above the busbar are additionally used.

Garlands of suspended insulation on the portals of 20 and 35 kV outdoor switchgear with catenary or rod lightning rods, as well as on the end supports of overhead lines, must have the following number of insulators:

1) on the portals of outdoor switchgear with lightning rods:

• at least six insulators with the location of valve arresters or the corresponding level of the remaining voltages of the surge arrester not further than 15 m along the mains of the grounding device from the place of connection to it;
• at least seven insulators in other cases;

2) on end supports:

• at least seven insulators when connected to the portals of the PS cable;
• at least eight insulators, if the cable does not enter the structure of the substation and when installing a rod lightning rod on the end support.

The number of insulators for 20 and 35 kV outdoor switchgear and end supports should be increased if required by the conditions of Ch. 1.9.

When installing lightning rods on the end supports of 110 kV overhead lines and above, there are no special requirements for the implementation of insulator strings. Installation of lightning rods on the end supports of 3-20 kV overhead lines is not allowed.

The air distance from the structures of the outdoor switchgear, on which lightning rods are installed, to the current-carrying parts must be at least the length of the garland.

The place of connection of a structure with a rod or cable lightning rod to the grounding device of the substation should be located at a distance of at least 15 m along the ground lines from the place of connection of transformers (reactors) and KRUN structures 6-10 kV to it.

The distance in the ground between the grounding point of the lightning rod and the grounding point of the neutral or transformer tank must be at least 3 m.

4.2.136. On transformer portals, portals of shunt reactors and outdoor switchgear structures remote from transformers or reactors along grounding lines at a distance of less than 15 m, lightning rods can be installed with an equivalent earth resistivity in the thunderstorm season of not more than 350 Ohm m and subject to the following conditions:

1) directly on all terminals of the windings of 3-35 kV transformers or at a distance of not more than 5 m from them along the busbar, including branches to protective devices, the corresponding surge arresters 3-35 kV or RV must be installed;

2) the spreading of the lightning current from the post structure with a lightning rod in three or four directions with an angle of at least 90º between them must be ensured;

3) in each direction, at a distance of 3-5 m from the post with a lightning rod, one vertical electrode 5 m long should be installed;

4) at a substation with a higher voltage of 20 and 35 kV, when installing a lightning rod on a transformer portal, the resistance of the grounding device should not exceed 4 ohms, excluding grounding conductors located outside the ground loop of the outdoor switchgear;

5) it is recommended to connect the grounding conductors of the RT or OPD and power transformers to the grounding device of the SS nearby one from the other or make them so that the place of connection of the RT or OPD to the grounding device is between the points of connection of the grounding conductors of the portal with a lightning rod and the transformer. Grounding conductors of measuring current transformers must be connected to the grounding device of the switchgear in the places farthest from the grounding of the RT or surge arrester.

4.2.137. Protection against direct lightning strikes of outdoor switchgear, on the structures of which the installation of lightning rods is not allowed or impractical for structural reasons, should be carried out by separate lightning rods with separate ground electrodes with a resistance of not more than 80 ohms at a pulsed current of 60 kA.

The distance Sz, m, between the isolated lightning rod ground electrode and the grounding device of the outdoor switchgear (PS) must be equal (but not less than 3 m):

Sz > 0,2 Ri

where Ri is the impulse resistance of grounding, Ohm, of a separate lightning rod.

The air distance Sv.o, m, from a separate lightning rod with a separate ground electrode to current-carrying parts, grounded structures and equipment of the switchgear (SS) must be equal (but not less than 5 m):

Sv.o > 0,12 R and + 0,1 H

where H is the height of the considered point on the current-carrying part or equipment above ground level, m.

Grounding conductors of separate lightning rods in the outdoor switchgear can be connected to the grounding device of the outdoor switchgear (PS) subject to the conditions specified in 4.2.135 for installing lightning rods on the outdoor switchgear structures. The place of connection of the grounding conductor of a separate lightning rod to the grounding device of the substation must be removed along the grounding lines at a distance of at least 15 m from the place of connection of the transformer (reactor) to it. At the point of connection of the grounding conductor of a free-standing lightning rod to the grounding device of the 35-150 kV outdoor switchgear, the grounding lines must be made in two or three directions with an angle of at least 90º between them.

Grounding conductors of lightning rods installed on searchlight masts must be connected to the grounding device of the substation. In case of non-compliance with the conditions specified in 4.2.135, in addition to the general requirements for connecting grounding conductors of separate lightning rods, the following requirements must be met:

1) within a radius of 5 m from the lightning rod, three vertical electrodes 3-5 m long should be installed;

2) if the distance along the grounding line from the place of connection of the grounding conductor of the lightning rod to the grounding device to the place of connection of the transformer (reactor) to it exceeds 15 m, but less than 40 m, then at the terminals of the windings with a voltage of up to 35 kV of the transformer, RV or surge arresters must be installed.

The air distance Sv.s from a separate lightning rod, the ground electrode of which is connected to the grounding device of the outdoor switchgear (PS), to the current-carrying parts should be:

Sv.s > 0,1 H + m

where H is the height of current-carrying parts above ground level, m; m - the length of the garland of insulators, m.

4.2.138. Rope lightning rods of overhead lines of 110 kV and above, as a rule, should be connected to grounded structures of outdoor switchgear (PS).

From the racks of 110-220 kV outdoor switchgear structures, to which catenary wire lightning rods are connected, grounding lines must be made in at least two or three directions with an angle of at least 90º between them.

Cable lightning rods protecting the approaches of 35 kV overhead lines are allowed to be connected to grounded outdoor switchgear structures with equivalent earth resistivity in the thunderstorm season: up to 750 Ohm m - regardless of the area of ​​the ground loop of the substation; more than 750 Ohm m - with the area of ​​the ground loop of the substation 10000 m2 or more.

From the racks of 35 kV outdoor switchgear structures, to which catenary wire lightning rods are connected, grounding lines must be made in at least two or three directions with an angle of at least 90º between them. In addition, one vertical electrode 3-5 m long should be installed in each direction at a distance of at least 5 m.

The resistance of the ground electrodes closest to the switchgear of the overhead lines with a voltage of 35 kV should not exceed 10 ohms.

Rope lightning rods at the approaches of 35 kV overhead lines to those outdoor switchgears to which they are not allowed to be connected should end at the support closest to the outdoor switchgear. The cableless span of these overhead lines, the first from the outdoor switchgear, must be protected by rod lightning rods installed on the substation, overhead line supports or near the overhead line.

Garlands of insulators on the portals of the 35 kV outdoor switchgear and on the end supports of the 35 kV overhead line should be selected in accordance with 4.2.135.

4.2.139. The device and protection of overhead lines approaches to outdoor switchgear and substations must meet the requirements given in 4.2.138, 4.2.142 - 4.2.146, 4.2.153 - 4.2.157.

4.2.140. It is not allowed to install lightning rods on structures:

• transformers to which rotating machines are connected by open conductors;
• supports of open conductors, if rotating machines are attached to them.

Portals of transformers and supports of open conductors connected with rotating machines must be included in the protection zones of lightning rods that stand alone or installed on other structures.

These requirements also apply to cases of connecting open conductors to the busbars of switchgear to which rotating machines are connected.

4.2.141. When using floodlight masts as lightning rods, electrical wiring to them in the area from the point of exit from the cable structure to the mast and further along it should be carried out with cables with a metal sheath or cables without a metal sheath in pipes. Near a structure with a lightning rod, these cables must be laid directly in the ground for a distance of at least 10 m.

At the place where the cables enter the cable structure, the metal sheath of the cables, the armor and the metal pipe must be connected to the grounding device of the substation.

4.2.142. Protection of overhead lines of 35 kV and above from direct lightning strikes at the approaches to the switchgear (SS) must be performed by lightning rods in accordance with Table. 4.2.8.

At each approach tower, except for the cases provided for in 2.5.122, the cable must be connected to the tower's earth electrode.

An increase is allowed compared to those given in table. 4.2.8 resistance of grounding devices of supports at the approaches of overhead lines of 35 kV and above to the substation with the number of thunderstorm hours per year not less than 20 - 1,5 times; less than 10 - 3 times.

If it is not possible to make earth electrodes with the required ground resistances, horizontal earth electrodes should be used, laid along the axis of the overhead line from support to support (ground electrodes-counterweights) and connected to the support earth electrodes.

In especially icy areas and in areas with an equivalent earth resistivity of more than 1000 Ohm m, it is allowed to protect the approaches of overhead lines to the switchgear (SS) with separate lightning rods, the resistance of the ground electrodes of which is not standardized.

Table 4.2.8. Protection of overhead lines from direct lightning strikes at the approaches to switchgear and substations

* The choice of the length of the protected approach is made taking into account the table. 4.2.10 - 4.2.13.

** On the approaches of 110-330 kV overhead lines with double-circuit poles, it is recommended to carry out the grounding devices of the poles with a resistance half that indicated in Table. 4.2.8.

*** On reinforced concrete supports, a protection angle of up to 30º is allowed.

**** For towers with a horizontal arrangement of wires installed in the ground with an equivalent resistivity of more than 1000 Ohm m, the resistance of the grounding device is 30 Ohm.

4.2.143. In areas with no more than 60 thunderstorm hours per year, it is allowed not to carry out protection with a cable for the approach of a 35 kV overhead line to a 35 kV substation with two transformers with a capacity of up to 1,6 MVA each or with one transformer with a capacity of up to 1,6 MVA and availability of backup power.

At the same time, the supports for the approach of the overhead line to the substation over a length of at least 0,5 km must have ground electrodes with the resistance indicated in Table. 4.2.8. When performing overhead lines on wooden supports, in addition, it is required to attach the fastenings of insulators to the earthing of the supports on the approach 0,5 km long and install a set of tubular arresters on the first support of the approach from the side of the overhead line. The distance between the RV or the corresponding surge arresters and the transformer must be no more than 10 m.

In the absence of backup power at a substation with one transformer with a power of up to 1,6 MB A, the approaches of the 35 kV overhead line to the substation must be protected by a cable for a length of at least 0,5 km.

4.2.144. On the first tower of the 35-220 kV overhead line approach to the substation, counting from the side of the line, a set of tubular arresters (RT1) or appropriate protective devices should be installed in the following cases:

1) the line along its entire length, including the approach, is built on wooden supports;

2) the line is built on wooden supports, the approach of the line is on metal or reinforced concrete supports;

3) on the approaches of 35 kV overhead lines on wooden supports to the 35 kV substation, protection is carried out in accordance with 4.2.155.

Installation of RT1 at the beginning of overhead line approaches built along the entire length on metal or reinforced concrete supports is not required.

The resistance of the grounding device of supports with tubular dischargers 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. On wooden poles, grounding descents from these devices should be laid along two racks or on both sides of one rack.

On 35-110 kV overhead lines that are not protected by a cable along the entire length and can be disconnected for a long time on one side during the thunderstorm season, as a rule, a set of tubular arresters (RT2) or appropriate protective devices should be installed at the entrance portals or on the first from the substation the support of the end of the overhead line that can be turned off. If there are voltage transformers at the disconnected end of the overhead line, instead of RT2, RV or the corresponding surge arresters should be installed.

The distance from RT2 to the disconnected end of the line (device) should be no more than 60 m for 110 kV overhead lines and no more than 40 m for 35 kV overhead lines.

4.2.145. On overhead lines operating at a voltage reduced relative to the insulation class, on the first pillar of its protected approach to the substation, counting from the side of the line, i.e. at a distance from the substation, determined by the table. 4.2.10 - 4.2.12, depending on the removal of the RV or surge arrester from the protected equipment, RT or IP of the voltage class corresponding to the operating voltage of the line must be installed.

It is allowed to install protective gaps or shunt some insulators in garlands on several adjacent supports with jumpers (in the absence of insulation pollution by industrial, saline, marine and other entrainments). The number of insulators in the strings that are not shunted must correspond to the operating voltage.

On overhead lines with insulation reinforced according to the condition of atmospheric pollution, if the beginning of a protected approach to the substation in accordance with Table. 4.2.10 - 4.2.12 is located in the zone of reinforced insulation, a set of protective devices corresponding to the operating voltage of the overhead line must be installed on the first pillar of the protected approach.

4.2.146. Tubular arresters must be selected for short-circuit current in accordance with the following requirements:

1) for networks up to 35 kV, the upper limit of the current switched off by the tubular arrester must be at least the highest effective value of the three-phase short-circuit current at a given point in the network (taking into account the aperiodic component), and the lower limit - no more than the smallest possible value of the steady-state value at a given point in the network (excluding the aperiodic component) of the two-phase short circuit current;

2) for networks of 110 kV and above, the upper limit of the current switched off by the tubular arrester must be not less than the largest possible effective value of the current of a single-phase or three-phase short circuit at a given point in the network (taking into account the aperiodic component), and the lower limit must not be more than the smallest possible value in a given point of the network of the value of the steady-state (without taking into account the aperiodic component) current of a single-phase or two-phase short circuit. In the absence of a tubular arrester for the required values ​​of short-circuit currents, it is allowed to use SP instead of them.

On 220 kV overhead lines with wooden poles, in the absence of tubular arresters, they must be grounded on one or two garland suspension poles, while the number of insulators should be the same as for metal poles.

4.2.147. On overhead lines with wooden poles 3-35 kV in the grounding slopes of the protective gaps, additional protective gaps should be installed at a height of at least 2,5 m from the ground. The recommended sizes of protective gaps are given in table. 4.2.9.

Table 4.2.9. Recommended sizes of main and additional protective gaps

4.2.148. In the switchgear of 35 kV and above, to which the overhead lines are connected, a RV or surge arrester must be installed.

Valve arresters or surge arresters should be selected taking into account the coordination of their protective characteristics with the insulation of the protected equipment, the correspondence of the highest operating voltage to the highest operating voltage of the network, taking into account higher harmonics and uneven distribution of voltage over the surface, as well as allowable voltage increases during the operation of backup relay protections in single-phase short to ground, with one-sided connection of the line or transient resonance at higher harmonics.

With increased distances from protective devices to protected equipment, in order to reduce the number of installed devices, RT or surge arresters with a lower level of remaining voltages than required by the conditions of insulation coordination can be used.

Distances along buses, including branches, from arresters to transformers and other equipment should be no more than those indicated in Table. 4.2.10 - 4.2.13 (see also 4.2.136). If the specified distances are exceeded, protective devices must be additionally installed on the busbars or linear connections.

Given in table. 4.2.10 - 4.2.13 the largest allowable distances to electrical equipment correspond to its insulation category "b" according to the state standard.

The largest allowable distances between the RV or surge arrester and the protected equipment are determined based on the number of lines and arresters included in the normal operation of the substation.

The number and location of installation of RV or surge arresters should be selected based on the electrical connection schemes adopted for the billing period, the number of overhead lines and transformers. In this case, the distances from the protected equipment to the RV or surge arrester must be within the permissible limits and at intermediate stages with a duration equal to the thunderstorm season or more. Emergency and repair work is not taken into account.

Table 4.2.10. The largest allowable distances from valve arresters to protected equipment 35-220 kV^{1), 2), 3), 4)}

1. Distances from RV to electrical equipment, except for power transformers, are not limited with the number of parallel operating overhead lines: at a voltage of 110 kV - 7 or more; for 150 kV - 6 or more; for 220 kV - 4 or more.

2. Permissible distances are determined to the nearest RV.

3. When using surge arresters instead of RV or when changing the test voltages of the protected equipment, the distance to power transformers or other electrical equipment is determined by the formula

L_opn =L_rv (U_Spanish - OR_opn)/(U_Spanish - OR_rv

where Lopn is the distance from the surge arrester to the protected equipment, m;

Lrv - distance from the arrester to the protected equipment, m;

Usp - test voltage of the protected equipment at full lightning impulse, kV;

Uopn, Urv - the remaining voltage on the surge arrester (RV) at a current of 5 kA - for voltage classes 110-220 kV; 10 kA - for voltage classes 330 kV and above.

4. If the cabled approach data differs, a linear interpolation of the allowable distance is allowed.

Table 4.2.11. The largest allowable distances from valve arresters to protected equipment 330 kV¹⁾

1. With different lengths of the protected approach, a linear interpolation of the value of the allowable distance is allowed.

* According to paragraph 3 of the notes to the table. 4.2.10.

** From RV installed at power transformers.

Table 4.2.12. The largest allowable distances from valve arresters to protected equipment 500 kV

* According to paragraph 3 of the notes to the table. 4.2.10. In the values ​​indicated by a fraction, the numerator is the allowable distance to the nearest RW (in a linear cell, on buses or at a reactor connection), the denominator is to a RW installed at the power transformer.

Table 4.2.13. The largest allowable distances from valve arresters to protected equipment 750 kV

* At a distance from the equipment installed at the input of the overhead line to the substation (communication capacitor, linear disconnector, etc.), to the point of connection of the overhead line to the busbar of the substation - no more than 45 m.

** The same, no more than 90 m.

*** When using surge arresters, including in switchgears with reduced air insulation gaps, or when changing test voltages, the allowable distances to power transformers (autotransformers) and shunt reactors and other electrical equipment are determined in accordance with paragraph 3 of the note to table. 4.2.10.

4.2.149. In the circuits of transformers and shunt reactors, RV or surge arresters must be installed without switching devices between them and the protected equipment.

Protective devices when the equipment is energized must be constantly switched on.

4.2.150. When connecting the transformer to the switchgear with a cable line of 110 kV and higher, a set of RV or surge arresters must be installed at the place where the cable is connected to the busbars of the switchgear with overhead lines. The grounding clamp РВ or surge arrester must be connected to the metal sheaths of the cable. In case of connection to the busbars of the switchgear of several cables directly connected to the transformers, one set of RV or arrester is installed on the busbars of the switchgear. The place of their installation should be chosen as close as possible to the places where the cables are connected.

With a cable length greater than twice the distance indicated in table. 4.2.10 - 4.2.13, RTS or surge arresters with the same remaining voltages as the protective device at the beginning of the cable, is installed at the transformer.

4.2.151. Unused windings of low and medium voltage of power transformers (autotransformers), as well as windings temporarily disconnected from the busbars of the switchgear during a thunderstorm period, must be connected in a star or delta and protected by an RV or surge arrester connected between the inputs of each phase and ground. Protection of unused low voltage windings, located first from the magnetic circuit, can be performed by grounding one of the vertices of the triangle, one of the phases or the star neutral, or by installing an RV or surge arrester of the appropriate voltage class on each phase.

Protection of unused windings is not required if a cable line with a length of at least 30 m, having a grounded sheath or armor, is permanently connected to them.

4.2.152. To protect the neutrals of the windings of 110-150 kV power transformers with insulation reduced relative to the insulation of the linear end of the winding and allowing operation with a grounded neutral, surge arresters should be installed to protect their insulation and withstand quasi-steady overvoltages for several hours in case of line phase failure.

In the neutral of the transformer, the insulation of which does not allow earthing, the installation of disconnectors is not allowed.

4.2.153. Switchgears 3-20 kV, to which overhead lines are connected, must be protected by RV or surge arresters installed on buses or at transformers. In justified cases, protective containers can be additionally installed. A valve arrester or surge arrester in the same cell as a voltage transformer must be connected upstream of its fuse.

When using overhead connection of transformers with 3-20 kV switchgear busbars, the distances from the RV and surge arrester to the protected equipment should not exceed 60 m for overhead lines on wooden supports and 90 m for overhead lines on metal supports.

When connecting transformers to buses with cables, the distances from the RV or arrester installed on the buses to the transformers are not limited.

Protection of the approaches of 3-20 kV overhead lines to the substation with lightning rods is not required under lightning protection conditions.

On the approaches of 3-20 kV overhead lines with wooden supports to the substation at a distance of 200-300 m from the substation, a set of protective devices (RT1) should be installed. On 3-20 kV overhead lines, which can be disconnected for a long time on one side during the thunderstorm season, protective devices (PT2) should be installed on the substation structure or on the end support of that end of the overhead line that can be disconnected for a long time. The distance from RT2 to the disconnected switch along the busbar should be no more than 10 m. With a transformer power of up to 0,63 MVA, it is allowed not to install tubular arresters on the approaches of 3-20 kV overhead lines with wooden supports.

If it is impossible to maintain the specified distances, as well as if there are voltage transformers at the disconnected end of the overhead line, instead of RT2, RV or arrester should be installed. The distance from the RV to the protected equipment should be no more than 10 m, for the arrester - increased in proportion to the difference between the test voltage of the voltage transformer and the remaining voltage of the arrester. When installing a RV or surge arrester at all inputs of overhead lines to the substation and their removal from substation equipment within the limits of permissible values ​​​​under the conditions of lightning protection, protective devices on the substation buses may not be installed. The grounding resistance of the arresters RT1 and RT2 should not exceed 10 ohms with a specific earth resistance up to 1000 ohm m and 15 ohms with a higher specific voltage.

At the approaches to substations of 3-20 kV overhead lines with metal and reinforced concrete supports, the installation of protective devices is not required. However, when using insulation reinforced by more than 3% on a 20-30 kV overhead line (for example, due to atmospheric pollution), an IP should be installed at a distance of 200-300 m from the substation and at its input.

Metal and reinforced concrete supports over 200-300 m of approach to the substation must be grounded with a resistance not exceeding those given in Table. 2.5.35.

Protection of 3-20 kV substations with low voltage up to 1 kV, connected to 3-20 kV overhead lines, must be carried out by RV or surge arresters installed on the high and low voltage side of the substation.

In the case of connecting a 3-20 kV overhead line to a substation using a cable insert, a set of RV or surge arresters must be installed at the point of connection of the cable to the overhead line. In this case, the grounding clamp of the arrester, the metal sheaths of the cable, as well as the body of the cable box must be connected to each other along the shortest path. The grounding clamp of the arrester must be connected to the grounding conductor by a separate descent. If the overhead line is made on wooden supports, a set of protective devices should be installed at a distance of 200-300 m from the end of the cable. If the length of the cable insert is more than 50 m, the installation of RV or arrester on the substation is not required. The resistance of the earthing device of the apparatus should be no more than the values ​​\u2.5.35b\uXNUMXbgiven in Table XNUMX.

Lightning protection of 3-20 kV conductors is carried out as lightning protection of overhead lines of the corresponding voltage class.

4.2.154. Cable inserts 35-220 kV with a length of less than 1,5 km must be protected on both sides by protective devices. Cables 35-110 kV are protected by group III RVS or RT, and 220 kV cables are protected by group II RVS or corresponding surge arresters. With a cable length of 1,5 km or more on overhead lines with metal and reinforced concrete supports, the installation of arresters or limiters at the ends of the cable is not required.

4.2.155. Protection of 35-110 kV substations with transformers up to 40 MB A connected to branches with a length less than the required length of the protected approach (see tables 4.2.8 and 4.2.10) from existing overhead lines without a cable, it is allowed to perform according to a simplified scheme (Fig. . 4.2.18), including:

• valve arresters; are installed on the substation at a distance from the power transformer of no more than 10 m when using group III RW and no more than 15 m when using group II RW. In this case, the distance from the RV to the rest of the equipment should not exceed 50 and 75 m, respectively. The distance to the limiters is determined in the same way as it was indicated earlier in Table. 4.2.10 - 4.2.13;
• cable lightning rods for approach to the substation along the entire length of the branch; with a branch length of less than 150 m, it should be additionally protected with catenary or rod lightning rods along one span of the operating overhead line on both sides of the branch;
• sets of protective devices RT1, RT2 with a grounding resistance of not more than 10 Ohm, installed on wooden supports: RT2 - on the first support with a cable from the side of the overhead line or at the border of the area protected by lightning rods; RT1 - on an unprotected section of the overhead line at a distance of 150-200 m from RT2.

With a run length of more than 500 m, the installation of a set of tubular arresters РТ1 is not required.

Protection of substations, where the distances between the RV and the transformer exceed 10 m, is carried out in accordance with the requirements given in 4.2.148.

Simplified protection of the substation, in accordance with the above requirements, is also allowed to be performed in the case of connecting the substation to the existing overhead lines using short approaches (Fig. 4.2.19). In this case, the transformers must be protected by group II RV or by the corresponding surge arresters.

Simplified protection of substations connected to newly constructed overhead lines is not allowed.

Rice. 4.2.18. Lightning surge protection schemes for substations connected to overhead lines with branches up to 150 and more than 150 m long

Rice. 4.2.19. Protection schemes against lightning surges of substations connected to overhead lines with the help of entries up to 150 and more than 150 m long

4.2.156. In areas with an earth resistivity of 1000 Ohm m or more, the grounding resistance of the arresters RT1 and RT2 35-110 kV, installed to protect the substation, which are connected to the existing overhead lines on branches or using short calls, should be no more than 30 Ohm. In this case, the grounding conductor RT2 must be connected to the grounding device of the substation.

4.2.157. Switching devices installed on poles of overhead lines up to 110 kV, which are not protected by a cable along the entire length, as a rule, must be protected by protective devices installed on the same poles on the consumer side. If the switching device is normally open, the arresters must be mounted on the same support on each energized side.

When installing switching devices at a distance of up to 25 m along the length of the overhead line from the place where the line is connected to the substation or distribution point, installation of protective devices on a support is usually not required. If the switching devices are normally turned off during the thunderstorm season, then protective devices must be installed on the support from the side of the overhead line.

On overhead lines with voltage up to 20 kV with reinforced concrete and metal supports, it is allowed not to install protective devices to protect switching devices that have insulation of the same class as overhead lines.

Installation of switching devices within the limits of the overhead line approaches protected by the cable, which are indicated in 4.2.155, 4.2.162 and the distances according to Table. 4.2.10 is allowed on the first support from the side of the line, as well as on the following approach supports, provided that their insulation strength is equal.

The resistance of the grounding devices of the apparatus must meet the requirements given in 2.5.129.

4.2.158. A branch from an overhead line, carried out on metal and reinforced concrete supports, must be protected by a cable along its entire length, if it is connected to an overhead line protected by a cable along its entire length. When making branches on wooden supports, a set of protective devices must be installed at the place of their connection to the overhead line.

4.2.159. To protect the sectioning points of 3-10 kV, protective devices must be installed - one set on the end support of each supply overhead line with wooden supports. In this case, the grounding descents of protective devices should be connected to the grounding device of the switching point.

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

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