RU2288529C1 - Grounding connection for supporting structures of overhead power transmission lines - Google Patents

Abstract

FIELD: power engineering; erection of transmission lines and grounding of their supporting structures.

SUBSTANCE: proposed grounding connection whose ground electrode is made in the form of cylindrical helical spiral with its diameter equal to that of supporting structure foundation pit is specially designed to reduce labor consumption for mounting and wiring grounding connection as well as to minimize earth excavation and welding operations and to enhance performance characteristics; ground electrode is installed in foundation pit together with supporting structure. Ground electrode turns are distributed throughout foundation pit depth in inverse proportion to resistivity of soil layers in pit and not uniformly. Turns are held in ground electrode by means of locks. Ground electrode is integrated with reinforced-concrete supporting structure hardware by welding in common grounding connection. Such arrangement affords standard resistance of grounding connection without additional earth excavation work and use of progressive operations in erection of power transmission lines.

EFFECT: reduced labor consumption for grounding connection installation, earth excavation, and welding operations; enhanced performance characteristics.

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Description

The invention relates to the electric power industry, in particular to the construction of power lines, grounding poles, metal structures, lightning rods.

Known grounding devices for grounding the supports of overhead power lines and other elements of electrical installations located in small areas. The most widespread are grounding devices made of horizontal or vertical electrodes, or in various combinations of vertical and horizontal electrodes, combined into a single structure (for example: according to a typical project series 3.407-83 “Grounding devices of VL 0.4 supports; 6-10; 20 and 35 kV ”, Moscow: Selenergoproekt, 1971).

The disadvantage of such grounding devices is the high complexity of their installation, including excavation and welding. Typical structures occupy large areas of land.

Known grounding device, as SU No. 1791882, MKI H 01 R 4/66, Bull. No. 4 dated 01/30/93, containing a horizontal electrode located in the trench and made in plan in the form of a symmetrical broken line consisting of straight segments located at right angles to each other.

The disadvantage of this device is that it slightly reduces the amount of earthwork and does not contribute to equalizing the potential at the support.

Known grounding device for A.S. SU No. 1363352, MKI 01 R 4/66, Bull. No. 48 dated 12.30.87 (adopted as a prototype), containing an annular electrode buried in the ground, and an electric vertical electrode connected to it.

The disadvantage of the grounding device is that it involves the execution of an annular trench around the support for laying the ring electrode, and the recommended depth of the trench, equal to the ratio of its depth to the radius of the electrode as 0.25 to 0.30, does not take into account the heterogeneity of the soil resistivity in depth.

The technical solution to the problem is to reduce the complexity of work during the installation of grounding devices, reduce the volume of earthwork and welding, reduce the resistance of grounding devices and touch voltage to the support in cases of leakage currents to the ground or lightning discharges.

This problem is solved by the fact that in the grounding device for overhead power transmission towers containing an annular ground electrode, buried in the ground, and a vertical electrode connected to it, the ground electrode is in the form of a cylindrical spiral spiral with a varying number of turns in depth, inversely proportional to the resistivity of the soil layers in the pit, and with a diameter of turns equal to the diameter of the pit drilled in the ground to install the support of the overhead power line, while the ground electrode is equipped with a latch E regulating the magnitude of the step between the windings and their locking position when backfilling the excavation ground.

The invention is illustrated in the drawing, where figure 1 shows the grounding device for the support of overhead power lines - a General view, and figure 2 is a view along section aa.

A device for grounding the support 1 of an overhead power transmission line consists of an earthing switch 2 connected to a vertical electrode 3 and placed in the pit 4. The earthing switch 2 is equipped with clamps 5 that regulate the step 6 between the individual turns and fixing their position when filling the pit 4 with earth.

The metal reinforcement 7 of the support 1 using the electrode 3 of the welded joint 8 is connected to the ground electrode 2.

The grounding device is mounted and operates as follows.

On the track of the power transmission line under construction, at the point of placement of the support 1, using a drilling and crane mechanism, a pit 4 is drilled, the diameter of which is much larger than the diameter of the support 1. Earthing switch 2, made in factory conditions from round steel, with a diameter of at least 10 mm, and delivered to the object is stretched in the form of a cylindrical spiral, lengthwise the depth of the pit 4. Between the formed turns of the ground electrode 2, the value of step 6 is set so that the number of turns falling on each layer of the earth is reversed but in proportion to the resistivity of this layer, i.e. the lower the electrical resistivity of the earth layer, the more rings of the ground electrode should be located in it and the smaller is the step 6 between the turns. This ensures that the current flows to the ground optimally, providing the least resistance to the entire grounding device.

The position of the grounding coils in the device is fixed with the help of clips 5 made of perforated strip with folding shelves. The assembled grounding device is lowered into the pit 4. On the axis of the grounding device, a support 1 with an electrode 3 is installed, which is connected to the reinforcement 3 of the reinforced concrete support 1. The electrode 3 is connected to the ground electrode 2 using a welding connection 8 and forms a general, electrically connected, design of the grounding device. The support 1 and ground electrode 2 installed in the pit 4 are filled with earth, the clamps 5 during filling keep the coils of the ground electrode 2 from offset, keeping the steps 6 set by the project.

It is known that the resistance to spreading of the current of the ground electrode in the form of a round of round steel, with an average depth of its location in the ground equal to or greater than the radius of the ring, is determined by the formula (1):

where R is the resistance of the ground electrode to current spreading, Ohm;

D is the diameter of a single turn of the ground electrode system, m;

d is the diameter of the steel of which the ground electrode is made, m;

h is the average depth of the coil, equal to the distance from the surface of the earth to the coil, m;

ρ - resistivity of the earth, Ohm · m.

An analysis of formula (1) shows that the resistance of the ground electrode R varies inversely with the diameter of the ring D and its depth h. In addition, it should be borne in mind that the current spreading from the ground electrode occurs unevenly, to a much greater extent, the current flows from the end of the ground electrode. This is taken into account in formula (1) in that the diameter of the ring and the depth of laying are additionally included in the formula under the logarithm sign. The resistance of the grounding device is directly proportional to ρ and, in turn, varies with depth h according to the law of variation of ρ. If ρ decreases, then the proportion of the electric current flowing down from the part of the ground electrode located in the layer with a lower resistivity increases proportionally.

Thus, if the grounding device is made of grounding conductors with several ring turns equal to the diameter of the pit for supporting the power line, and connect them together in the form of a cylindrical helical spiral so that most of them are located in the lower layer of the earth with the lowest resistivity, then a decrease in the overall resistance of the grounding device will be achieved and the distribution of potential on the earth's surface will be improved.

This design allows us to provide the standard value of the resistance of the grounding device of the support without performing labor-intensive excavation work, to organize in-line technology for the construction of the line with fewer construction mechanisms and less labor costs, to improve the technical and economic performance of the grounding device. Especially effective is the proposed grounding device in those cases where the supports are installed in the soil with high corrosivity to concrete and reinforcement, when the underground part of the support is protected by an insulating coating.

Claims (1)

A grounding device for overhead power transmission towers, comprising an annular ground electrode system buried in the ground and a vertical electrode connected to it, characterized in that the ground electrode has the shape of a cylindrical helical spiral with a varying number of turns in depth, inversely proportional to the resistivity of the soil layers in the pit, and the diameter of the turns equal to the diameter of the pit drilled in the ground to install the support of the overhead power line, while the ground electrode is equipped with clamps regulating E step size between the coils and their locking position when backfilling the excavation ground.

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