CN102983535A - A shielded line for improving ground field strength of DC transmission line - Google Patents

Abstract

The invention discloses a shielding circuit for improving ground field intensity of a direct-current transmission line, and belongs to the technical field of electromagnetic environment protection of a transmission line of an electric power system. The shielding circuit comprises a plurality of shielding wires, a shielding wire tower body for erecting the shielding wires, 1 layer of cross arms matched with the shielding wire tower body, and a plurality of suspension points for suspending shielding wire suspension parts, wherein the cross arms and the tower neck are provided with the suspension points; a plurality of shielding wire suspension points are arranged on the cross arm at equal intervals and used for suspending shielding wires in different arrangement modes. The central shaft of the shielding wire tower is 3m outside the straight line of the center of the transmission wire in relative horizontal position. The invention can control the electromagnetic environment parameters around the direct current transmission line on the basis of not changing the original transmission line construction scheme. The suppression of the ground synthetic field intensity is realized on the premise of not improving the radio interference, audible noise and corona loss, the construction cost of the tower can be greatly saved, and meanwhile, the transmission corridor is reduced, so that the extra-high voltage direct current transmission project is more economical and reasonable.

Description

A shielded line for improving ground field strength of DC transmission line

technical field

The invention belongs to the technical field of electromagnetic environment protection for power system transmission lines, and relates to a shielding line for improving the ground field strength of direct current transmission lines.

Background technique

The corona phenomenon of high-voltage transmission lines is a key technical issue that needs to be considered in engineering design, construction and operation. On the one hand, corona will cause power loss and increase the cost of power transmission. On the other hand, the radio interference, audible noise and space ion flow generated by corona will affect the electromagnetic environment around the transmission line. With the continuous development of the economy and the enhancement of people's environmental awareness, electromagnetic environmental problems have attracted more and more attention, especially in UHV DC projects, due to the increase in voltage levels, electromagnetic environmental problems have become more prominent.

At present, in the design of DC transmission lines, foreign empirical formulas such as EPRI and BPA are mainly used to optimize the selection of wires to improve the electromagnetic environment. This method often leads to a substantial increase in engineering investment. At the same time, it does not solve the problems of tight transmission corridors, difficulty in controlling the ground field strength under the line, and the improvement of the electromagnetic interference intensity of the line is not obvious.

Studies have shown that erecting shielded wires under DC lines can significantly reduce ground synthetic field strength without increasing radio interference and audible noise levels. The improvement of the above electromagnetic environment parameters will reduce the cost of the tower in the actual DC transmission project. At the same time, the cost of the shielded wire is low, and it can reduce the demolition of residential houses caused by the passing of the transmission corridor, and greatly reduce the overall investment of the transmission project. However, the effects of shielded wires on radio interference, audible noise, and ion currents are still lacking in research. At the same time, how to select the number of shielded wires, layout spacing, and layout height for UHV lines still needs a theoretical basis. Therefore, it is of great engineering value to propose a shielding line design method for improving the ground field strength under UHVDC transmission lines.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art, and propose a shielded line that improves the combined field strength of the ground under the UHVDC transmission line, so as to reduce the extreme value of the combined field strength on the ground, and at the same time prevent radio interference, It also has a suppression effect on electromagnetic environment parameters such as noise and ground ion current density.

A shielded line for improving the ground field strength of a direct current transmission line proposed by the present invention is characterized in that the shielded line includes a plurality of shielded wires, shielded wire poles and towers for erecting shielded wires, and shielded wire poles and towers are matched 1 layer of cross arm, with multiple suspension points for hanging shielded wire suspension parts on the cross arm; multiple shielded wire suspension points are set equidistantly on the cross arm, used to hang shielded wires in different arrangements. The relative horizontal position of the central axis of the shielded line pole tower is located 3m outside the center of the transmission line.

The shielded line can be made of steel-cored aluminum stranded wire, and the line type can be LGJ-50/8, LGJ-70/40, LGJ-120/25, LGJ-120/70, LGJ-240/40 or LGJ-300/ Any one of 70, the number of shielded wires is 1~3.

The tower body can be a cement tower or a simple steel tower; the height of the tower is 17 to 20m.

The collocation has 1 layer of cross arm, the total length of the cross arm is 6m, and 7 shielding wire suspension points are equidistantly distributed on the cross arm.

The suspension point of the shielded wire can be in the form of a metal hoop, and the connection between the shielded wire and the tower is directly connected to the suspension point through a clamping tube and a U-shaped ring, or the shielded wire is connected through a clamping tube and a U-shaped ring at the end to the monolithic insulator and then to the suspension point.

The grounding of the shielded wire can be directly connected to the pole tower at the hanging point of the metal hoop, and grounded through the pole tower; or directly connected to the vertical grounding body through the step-by-step down conductor. The ground resistance range is 30Ω~50Ω.

The shielded wire can be a single one, suspended at the suspension point in the center of the cross arm; the height of the suspension point is 19m, the sag is 7m, the minimum height to the ground is 12m, and the average height is 15.33m.

The shielded wires may be three shielded wires suspended on the hanging points at the head, middle and end of the cross arm, and the height of the hanging points is 16m.

Features and beneficial effects of the present invention are as follows:

1. The shielded line proposed by the present invention can control the electromagnetic environment parameters around the DC transmission line without changing the original construction scheme of the transmission line. Under the premise of not increasing radio interference, audible noise and corona loss, the suppression of ground synthetic field strength can be achieved, and the suppression effect can reach up to 55%.

2. The shielding line proposed by the present invention can optimize the tower design scheme of the direct current transmission project by suppressing the electromagnetic environment parameters, and greatly save the construction cost of the tower.

3. The transmission corridor with reduced shielded lines proposed by the present invention will greatly reduce the demolition cost caused by the lines passing through residential buildings, making the UHV DC transmission project more economical and reasonable.

Description of drawings

FIG. 1 is a schematic structural diagram of Embodiment 1 of a shielded circuit of the present invention.

Fig. 2 is a schematic structural diagram of Embodiment 2 of the shielded circuit of the present invention.

Specific implementation method

The shielded line proposed by the present invention for improving the ground field strength of a direct current transmission line is described in detail below with reference to the accompanying drawings and embodiments.

The shielded line structure proposed by the present invention for improving the ground field strength of DC transmission lines is shown in Figure 1, including a plurality of shielded wires (not shown in the figure), a shielded wire tower body 1 for erecting shielded wires, shielded The cross arm 2 matched with the pole tower body, and the cross arm and the tower neck are provided with multiple suspension points for suspending shielded wire suspension parts;

The shielding wire selected in the present invention adopts steel-cored aluminum stranded wire, and the number of shielding wires may be 1 to 3. The line type can be any one of LGJ-50/8, LGJ-70/40, LGJ-120/25, LGJ-120/70, LGJ-240/40 or LGJ-300/70.

The shielding wire tower of the present invention can adopt cement pole tower or simple steel pole tower. The tower is 17 to 20m high. Equipped with 1 layer of cross arm, the total length of the cross arm is 6m, and 7 shielding wire suspension points are set equidistantly on the cross arm, which are used to suspend shielding wires in different arrangements. The relative horizontal position of the central axis of the shielded wire tower is 3m outside the center of the transmission wire (ie, the pole wire). The relative horizontal position of the shielded wire and the pole conductor, the average height of the shielded wire to the ground, and the relative position between multiple shielded wires are related to the number of shielded wires and the resulting ground synthetic field strength. Click Layout. Two grounding methods can also be used for shielding wire grounding: 1) Connect directly to the tower at the hanging point of the metal hoop, and ground through the tower. 2) It is directly connected to the vertical grounding body through the step-by-step down-conductor. The ground resistance range is 30Ω~50Ω.

The shielded wire hanger is in the form of a metal hoop, and two specific structures can be used to connect the shielded wire to the tower: 1) The shielded wire hanger composed of a clamping tube and a U-shaped ring directly connects the shielded wire to the suspension point 2) The shielded wire suspension is composed of a clamping tube, a U-shaped ring and a single-piece insulator arranged at the end of the shielded wire. Connect the clamping tube and the U-shaped ring at the end of the shielded wire to the single-piece insulator, and then connect to the suspension point . The two different connection methods depend on the grounding form.

The specific implementation of each part of the embodiments of the present invention is described as follows:

Example 1

This embodiment adopts the above-mentioned shielded line structure, as shown in Figure 1; the voltage applied to the polar wires is ±800kV, the total length of the shielded wires is 300m, and the center span is 400m.

The shielded wire tower body of this embodiment adopts cement pole 11; the shielded wire adopted is a single shielded wire of LGJ-70/40 type (not shown in the figure), and is suspended on the central hanging point 13 of the cross arm 12 (Fig. The 7 circles on the middle crossarm are the hanging points); this setting produces the best suppression effect on the synthetic field strength on the ground. The shielded wire tower is erected on the side of the positive polarity wire. The height of the tower is 20m, and the nominal height is 19m; the height of the suspension point is 19m, the sag is 7m, the minimum height to the ground is 12m, and the average height is 15.33m. The shielding wire is directly connected to the tower at the hanging point of the metal hoop, and the suspension is composed of a clamping tube and a U-shaped ring, and is grounded through the tower.

Example 2

The applied voltage of the pole wire, the total length of the shielding wire, and the center span are 400m with the embodiment 1. The shielded wire pole tower body of this embodiment adopts a steel pole tower 21, as shown in Figure 2; the shielded wires used are 3 shielded wires of the LGJ-300/70 model, and the three shielded wires are suspended on the head end hanging point of the cross arm 22 23. On the middle hanging point 24 and the end hanging point 25 (the 7 circles on the cross arm in the figure are the hanging points). This setting produces the best effect of suppressing the synthetic field strength on the ground. The shielded wire tower is erected on the side of the negative wire, the tower is 17m high, and the name is 16m high. Taking the negative wire as a reference, the relative horizontal positions of the three shielded wires are the center of the negative wire, 3m outside, and 6m outside. The height of the suspension point is 16m, the sag is 7m, the minimum height to the ground is 9m, and the average height is 12.33m. The shielded wire is directly connected to the vertical grounding body through the step-by-step down-lead. The suspension is composed of a clamping tube, a U-shaped ring and a single-piece insulator. Connect the clamping tube and the U-shaped ring at the end of the shielded wire to the single-piece insulator. Then connect to the suspension point, the grounding resistance is selected as 40Ω.

Claims (8)

1. shielded line that is used for improving DC power transmission line ground field intensity, it is characterized in that, this shielded line comprises many shielding conductors, is used for setting up the shielding conductor shaft tower tower body of shielding conductor, 1 layer of cross-arm of shielding conductor shaft tower body collocation, a plurality of hitch points for hanging the shielding conductor suspender that cross-arm is provided with; A plurality of shielding conductor hitch points equidistantly are set on the cross-arm, are used for hanging the shielding conductor of different arrangements.Shielding conductor shaft tower central shaft relative level position is the outer 3m of place, transmission pressure center straight line.

2. shielded line as claimed in claim 1 is characterized in that, described shielded line adopts steel reinforced aluminium conductor, line style can be LGJ-50/8, LGJ-70/40, any one among LGJ-120/25, LGJ-120/70, LGJ-240/40 or the LGJ-300/70, shielding conductor radical are 1～3.

3. shielded line as claimed in claim 1 is characterized in that, described shaft tower tower body is cement shaft tower or Simple steel shaft tower; Shaft tower high 17 is to 20m.

4. shielded line as claimed in claim 1 is characterized in that, described cross-arm overall length is 6m, equidistant 7 shielding conductor hitch points that distribute on the cross-arm.

5. shielded line as claimed in claim 1, it is characterized in that, described shielding conductor hitch point adopts metal anchor ear form, be connected between shielding conductor and shaft tower and adopt shielding conductor directly to be connected to hitch point by clamp pipe and U-loop, or shielding conductor is connected to monolithic insulator by end clips spool and U-loop, is connected to hitch point again.

6. shielded line as claimed in claim 1 is characterized in that, the employing of described shielding conductor ground connection directly is connected with shaft tower at metal anchor ear hitch point place, passes through tower grounding; Or directly be connected with Grounding Grids by downlead step by step.The earth resistance scope is at 30 Ω ~ 50 Ω.

7. shielded line as claimed in claim 4 is characterized in that, described shaft tower height is 20m, exhales to claim highly to be 19m; Shielding conductor is single, hangs on the cross-arm central point; The hitch point height is 19m, sag 7m, and minimum is 12m to ground level, average height is 15.33m.

8. shielded line as claimed in claim 4 is characterized in that, described shaft tower height is 17m, exhales to claim highly to be 16m; Shielding conductor be three shielding conductors hang on cross-arm head end, centre and terminal hanging point on.

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