A device and method for reducing the resultant electric field under an electric power transmission line

Abstract

This invention discloses a device and method for reducing the composite electric field of DC transmission lines. The transmission line has sub-conductors, and the device includes a smooth metal accessory. The smooth metal accessory is a cylindrical structure with an opening on the side and is coaxially wrapped around the outside of the sub-conductor. By adding a smooth metal accessory to the conductor, this invention reduces the surface roughness of the conductor, thereby increasing the critical corona initiation field strength of the conductor. Ultimately, it can effectively reduce the composite electric field of DC transmission lines at ground level, filling the technical gap where the composite electric field of DC transmission lines at ground level is difficult to control from the conductor itself.

Description

Technical Field

[0001] This invention relates to the field of power grid environmental protection, and in particular to an apparatus and method for reducing the DC composite electric field under transmission lines. Background Technology

[0002] To meet the requirements of large-scale, long-distance, high-capacity, and low-loss power transmission, ultra-high-voltage AC transmission projects have developed rapidly in China. With the increase in transmission lines and the growing strain on transmission corridors, high-voltage transmission lines are increasingly approaching villages, urban residential areas, and other areas where people live, work, and frequently engage in activities. Simultaneously, due to increased public awareness of self-protection, the impact of high-voltage transmission lines on residents' health has become a widespread concern, leading to electromagnetic environment disputes and complaints. To control the electric field level at environmentally sensitive points near transmission lines, electromagnetic environment prediction is typically used in the early stages of line construction. Adjusting parameters such as the transmission line's wiring type and distance from the ground to control the power frequency electric field is difficult. Adjusting the line itself to meet relevant control standards is challenging, necessitating alternative control methods. Currently, the main method is to add shielding wires or shielding nets beneath the line. However, existing shielding measures are difficult to implement in practical projects due to significant building modifications and maintenance difficulties. Summary of the Invention

[0003] This invention provides an apparatus and method for reducing the DC composite electric field under transmission lines, which can reduce the DC composite electric field under transmission lines.

[0004] An embodiment of the present invention provides a device for reducing the DC composite electric field under a transmission line. The transmission line has a sub-conductor. The device includes a smooth metal accessory, which is a cylindrical structure with an opening on the side and is coaxially wrapped around the outside of the sub-conductor.

[0005] In some embodiments, the smooth metal attachment includes a first smooth metal attachment and a second smooth metal attachment. The first smooth metal attachment is coaxially wrapped around the outside of the sub-conductor, and the second smooth metal attachment is coaxially wrapped around the outside of the first smooth metal attachment. The opening of the second smooth metal attachment is offset from the opening of the first smooth metal attachment in the circumferential direction of the sub-conductor.

[0006] In some embodiments, a plurality of first smooth metal attachments are arranged along the length direction of the sub-conductor, the openings of each first smooth metal attachment are located on the same straight line, and two adjacent first smooth metal attachments are in contact with each other; a plurality of second smooth metal attachments are arranged along the length direction of the sub-conductor, the openings of each second smooth metal attachment are located on the same straight line, and two adjacent second smooth metal attachments are in contact with each other.

[0007] In some embodiments, the inner diameter D of the cylindrical structure is equal to the diameter of the sub-conductor, the radial thickness d is 0.15~0.2mm, the axial length L is 10~15cm, and the width c of the opening is πD / 4.

[0008] In some embodiments, the smooth metal attachment is a semi-austenitic material with an elastic modulus of 200 GPa and a hardness greater than or equal to 400 HB.

[0009] An embodiment of the present invention provides a method for reducing the DC composite electric field under a transmission line using the above-described apparatus, wherein there are buildings under the transmission line, and the method includes the following steps: Based on the parameters of the power transmission line and the distance between the building and the power transmission line, a finite element calculation model of the building's electric field is established. Based on the finite element calculation model of the building's electric field, the electric field strength E at the building is calculated when the installation length X of the smooth metal fitting on the transmission line takes different values. The relationship formula between the electric field strength E at the building and the installation length X of the smooth metal fitting on the transmission line is obtained. The electric field strength E0 at the building when the transmission line does not corrode is obtained. The installation length X of the smooth metal fitting on the transmission line when the difference ∆E between E and E0 is within a set range is obtained as the optimal installation length of the smooth metal fitting on the transmission line. Install the smooth metal fitting according to the optimal installation length of the smooth metal fitting on the transmission line.

[0010] In some embodiments, obtaining the relationship formula between the electric field strength E at the building and the installation length X of the smooth metal fitting on the transmission line includes: plotting the relationship curve between the electric field strength E at the building and the installation length X of the smooth metal fitting on the transmission line when the installation length X of the smooth metal fitting on the transmission line takes different values, and obtaining the relationship formula (1) between the electric field strength E at the building and the installation length X of the smooth metal fitting on the transmission line using an exponential fitting method. Equation (1) can be found in [reference needed]. Figure 6 In the formula, a and b are both exponential fitting parameters.

[0011] In some embodiments, obtaining the installation length X of the smooth metal accessory on the transmission line when the difference ∆E between E and E0 is within a set range includes: obtaining the installation length X of the smooth metal accessory on the transmission line when ∆E is less than or equal to 0.5.

[0012] In some embodiments, installing smooth metal accessories according to the optimal installation length of the smooth metal accessories on the transmission line includes: obtaining the number N of smooth metal accessories to be installed using formula (2) based on the optimal installation length of the smooth metal accessories on the transmission line, where formula (2) is shown in [reference needed]. Figure 7In the formula, L is the axial length of the smooth metal fitting, and n is the number of conductor splits in the transmission line. Install the smooth metal accessories according to the number N of smooth metal accessories to be installed.

[0013] In some embodiments, installing smooth metal accessories includes: coaxially wrapping a plurality of first smooth metal accessories around the outside of a sub-conductor, with the openings of each first smooth metal accessory aligned on the same straight line, the first smooth metal accessories arranged along the length of the sub-conductor, and two adjacent first smooth metal accessories in contact; and coaxially wrapping a plurality of second smooth metal accessories around the outside of the first smooth metal accessories, with the openings of each second smooth metal accessory aligned on the same straight line, the openings of each second smooth metal accessory being offset from the openings of each first smooth metal accessory in the circumferential direction of the sub-conductor, the second smooth metal accessories arranged along the length of the sub-conductor, and two adjacent second smooth metal accessories in contact.

[0014] According to an embodiment of the present invention, a device for reducing the DC composite electric field beneath a transmission line is provided. The transmission line has sub-conductors, and the device includes a smooth metal attachment. The smooth metal attachment is a cylindrical structure with an opening on its side and is coaxially wrapped around the outside of the sub-conductor. By adding a smooth metal attachment to the conductor, the present invention reduces the surface roughness of the conductor, thereby increasing the critical corona initiation field strength of the conductor. Ultimately, it can effectively reduce the ground-based DC composite electric field, filling the technical gap where the ground-based DC composite electric field of existing ultra-high voltage DC lines is difficult to control from the conductor itself. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1-2 This is a schematic diagram of the structure of the smooth metal accessory in an embodiment of the present invention; Figure 3 This is a schematic diagram showing the locations of buildings and power transmission lines in an embodiment of the present invention; Figure 4 This is a flowchart illustrating the process of the smooth metal accessory in an embodiment of the present invention; Figure 5 The curve showing the relationship between the electric field strength E at the building and the installation length X of the smooth metal fitting on the transmission line; Figure 6 For example, Equation (1); Figure 7For example, Equation (2); Figure 8 Equation (3) is given. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0018] See Figure 1 This invention provides an apparatus for reducing the combined DC electric field beneath a power transmission line. The transmission line can be an ultra-high voltage (UHV) transmission line. The transmission line has a sub-conductor 2, which can be a steel-cored aluminum stranded wire. The apparatus includes a smooth metal attachment 1, which is a cylindrical structure with an opening 11 on its side, and is coaxially wrapped around the outside of the sub-conductor 2.

[0019] The smooth metal accessory 1 includes a first smooth metal accessory 12 and a second smooth metal accessory 13. The first smooth metal accessory 12 is coaxially wrapped around the outside of the sub-conductor 2, and the second smooth metal accessory 13 is coaxially wrapped around the outside of the first smooth metal accessory 12. The opening 11 of the second smooth metal accessory 13 and the opening 11 of the first smooth metal accessory 12 are offset in the circumferential direction of the sub-conductor 2.

[0020] Multiple first smooth metal attachments 12 are arranged along the length of the sub-conductor 2, with the openings 11 of each first smooth metal attachment 12 located on the same straight line, and adjacent first smooth metal attachments 12 are in close contact (i.e., without gaps, in tight contact). Multiple second smooth metal attachments 13 are arranged along the length of the sub-conductor 2, with the openings 11 of each second smooth metal attachment 13 located on the same straight line, and adjacent second smooth metal attachments 13 are in close contact (i.e., without gaps, in tight contact).

[0021] The inner diameter D of the cylindrical structure is equal to the diameter of the sub-conductor 2. The radial thickness d is between 0.15 and 0.2 mm, such as 0.15 mm, 0.18 mm, or 0.2 mm. The axial length L is between 10 and 15 cm, such as 10 cm, 12 cm, or 15 cm. The width c of the opening 11 is πD / 4.

[0022] The smooth metal accessory 1 is made of semi-austenitic material with an elastic modulus of 200 GPa and a hardness greater than or equal to 400HB.

[0023] An embodiment of the present invention provides a method for reducing the composite electric field of a DC transmission line using the above-described apparatus. The transmission line is situated beneath a building. The method includes the following steps: (1) Based on the parameters of the transmission line and the distance between the building and the transmission line, a finite element calculation model of the building's electric field is established.

[0024] In the above steps, refer to Figure 2 The parameters of a transmission line include the height H of the transmission line, the phase spacing a, the height m of the building, and the distance b of the building from the center of the transmission line.

[0025] (2) Based on the finite element calculation model of the building's electric field, calculate the electric field strength E at the building when the installation length X of the smooth metal accessory 1 on the transmission line takes different values, obtain the relationship formula between the electric field strength E at the building and the installation length X of the smooth metal accessory 1 on the transmission line, obtain the electric field strength E0 at the building when the transmission line does not corona, obtain the installation length X of the smooth metal accessory 1 on the transmission line when the difference ∆E between E and E0 is within the set range, and take it as the optimal installation length of the smooth metal accessory 1 on the transmission line.

[0026] In the above steps, when calculating the electric field strength E at the building when the installation length X of the smooth metal accessory 1 on the transmission line takes different values, X can take values ​​such as 5m, 10m, 20m, 50m and 100m.

[0027] See Figure 4 To obtain the relationship between the electric field strength E at the building and the installation length X of the smooth metal accessory 1 on the transmission line, the following steps are taken: Based on the electric field strength E at the building when the installation length X of the smooth metal accessory 1 on the transmission line takes different values, the relationship curve between the electric field strength E at the building and the installation length X of the smooth metal accessory 1 on the transmission line is plotted. The relationship formula (1) between the electric field strength E at the building and the installation length X of the smooth metal accessory 1 on the transmission line is obtained by using the exponential fitting method. Equation (1) can be found in [reference needed]. Figure 6 In the formula, a and b are both exponential fitting parameters. It should be noted that E0 is an exponential fitting parameter, which is also the electric field strength at the building when the transmission line does not corona.

[0028] Obtaining the installation length X of the smooth metal accessory 1 on the transmission line when the difference ∆E between E and E0 is within a set range includes: obtaining the installation length X of the smooth metal accessory 1 on the transmission line when ∆E is less than or equal to 0.5. In other words, the installation length X of the smooth metal accessory 1 on the transmission line is obtained when the absolute value ∆E of the difference between E and E0 is less than or equal to 0.5.

[0029] (3) Install the smooth metal accessory 1 according to the optimal installation length of the smooth metal accessory 1 on the transmission line.

[0030] The above steps involve installing the smooth metal accessory 1 according to its optimal installation length on the transmission line, including the following process: 1) Based on the optimal installation length of the smooth metal accessory 1 on the transmission line, the installation quantity N of the smooth metal accessory 1 is obtained using formula (2). Formula (2) is shown in [reference needed]. Figure 7 In the formula, L is the axial length of the smooth metal accessory 1, and n is the number of conductor splits in the transmission line.

[0031] 2) Install smooth metal accessory 1 according to the number N of smooth metal accessory 1 to be installed.

[0032] See Figure 3 Installing the smooth metal accessory 1 includes the following process: 1) Multiple first smooth metal attachments 12 are coaxially wrapped around the outside of the sub-conductor 2, and the openings 11 of each first smooth metal attachment 12 are located on the same straight line. Each first smooth metal attachment 12 is arranged along the length of the sub-conductor 2, and two adjacent first smooth metal attachments 12 are in close contact (that is, without gaps, in tight contact).

[0033] 2) Multiple second smooth metal attachments 13 are coaxially wrapped around the outside of the first smooth metal attachment 12, and the openings 11 of each second smooth metal attachment 13 are located on the same straight line. The openings 11 of each second smooth metal attachment 13 and the openings 11 of each first smooth metal attachment 12 are staggered in the circumferential direction of the sub-conductor 2. Each second smooth metal attachment 13 is arranged along the length direction of the sub-conductor 2, and two adjacent second smooth metal attachments 13 are in close contact (that is, without gaps, in tight contact).

[0034] The following detailed description is provided with reference to specific embodiments: When the transmission line is 18m high, the phase spacing is 22, and the distance between the building and the center of the transmission line is 9m, the electric field strength E at the building location is calculated as a function of the installation length X of the smooth metal attachment 1 on the transmission line, as shown below. Figure 4 As shown, for Figure 4 By fitting the curves in the figure, the relationship between the electric field strength E at the building and the installation length X of the smooth metal attachment 1 on the transmission line is obtained by formula (3). Formula (3) can be found in [reference needed]. Figure 8 It can be seen that when the installation length of the smooth metal accessory 1 on the transmission line reaches 60m, the electric field strength at the building is basically close to the nominal field level of 12kV / m. The electric field strength is reduced by about 52% compared with 25kV / m without the smooth metal accessory 1, which meets the electric field control limit requirements.

[0035] This invention reduces the surface roughness of the conductor by adding a smooth metal accessory 1, thereby increasing the critical corona initiation field strength of the conductor and ultimately effectively reducing the ground DC composite electric field. This fills the technical gap in controlling the ground DC composite electric field of existing UHVDC lines, which is difficult to control from the conductor itself.

[0036] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A device for reducing the combined DC electric field beneath a transmission line, the transmission line having sub-conductors, characterized in that, The device includes a smooth metal attachment, which is a cylindrical structure with an opening on the side, and the smooth metal attachment is coaxially wrapped around the outside of the sub-conductor.

2. The apparatus as claimed in claim 1, characterized in that, The smooth metal accessory includes a first smooth metal accessory and a second smooth metal accessory. The first smooth metal accessory is coaxially wrapped around the outside of the sub-conductor, and the second smooth metal accessory is coaxially wrapped around the outside of the first smooth metal accessory. The opening of the second smooth metal accessory is offset from the opening of the first smooth metal accessory in the circumferential direction of the sub-conductor.

3. The apparatus as described in claim 2, characterized in that, A plurality of first smooth metal attachments are arranged along the length direction of the sub-conductor, with the openings of each first smooth metal attachment located on the same straight line, and two adjacent first smooth metal attachments in contact with each other; a plurality of second smooth metal attachments are arranged along the length direction of the sub-conductor, with the openings of each second smooth metal attachment located on the same straight line, and two adjacent second smooth metal attachments in contact with each other.

4. The apparatus as claimed in claim 1, characterized in that, The inner diameter D of the cylindrical structure is equal to the diameter of the sub-conductor, the radial thickness d is 0.15~0.2mm, the axial length L is 10~15cm, and the width c of the opening is πD / 4.

5. The apparatus as claimed in claim 1, characterized in that, The smooth metal accessory is made of semi-austenitic material with an elastic modulus of 200 GPa and a hardness greater than or equal to 400 HB.

6. A method for reducing the DC composite electric field beneath a transmission line using the apparatus of any one of claims 1-5, wherein there is a building beneath the transmission line, characterized in that, The method includes the following steps: Based on the parameters of the power transmission line and the distance between the building and the power transmission line, a finite element calculation model of the building's electric field is established. Based on the finite element calculation model of the building's electric field, the electric field strength E at the building is calculated when the installation length X of the smooth metal accessory on the transmission line takes different values. The relationship formula between the electric field strength E at the building and the installation length X of the smooth metal accessory on the transmission line is obtained. The electric field strength E0 at the building when the transmission line does not corrode is obtained. The installation length X of the smooth metal accessory on the transmission line when the difference ∆E between E and E0 is within a set range is obtained as the optimal installation length of the smooth metal accessory on the transmission line. Install the smooth metal accessory according to the optimal installation length of the smooth metal accessory on the power transmission line.

7. The method as described in claim 6, characterized in that, The formula for obtaining the relationship between the electric field strength E at the building and the installation length X of the smooth metal accessory on the transmission line includes: drawing the relationship curve between the electric field strength E at the building and the installation length X of the smooth metal accessory on the transmission line when the installation length X of the smooth metal accessory on the transmission line takes different values, and obtaining the formula for the relationship between the electric field strength E at the building and the installation length X of the smooth metal accessory on the transmission line using the exponential fitting method (1). （1）； In the formula, a and b are both exponential fitting parameters.

8. The method as described in claim 6, characterized in that, Obtaining the installation length X of the smooth metal accessory on the transmission line when the difference ∆E between E and E0 is within a set range includes: obtaining the installation length X of the smooth metal accessory on the transmission line when ∆E is less than or equal to 0.

5.

9. The method as described in claim 6, characterized in that, Installing the smooth metal accessory according to the optimal installation length of the smooth metal accessory on the transmission line includes: obtaining the installation quantity N of the smooth metal accessory according to the optimal installation length of the smooth metal accessory on the transmission line and using formula (2); （2）； In the formula, L is the axial length of the smooth metal accessory, and n is the number of conductor splits in the transmission line; Install the smooth metal accessories according to the number N of smooth metal accessories to be installed.

10. The method as described in claim 6, characterized in that, Installing the smooth metal attachments includes: coaxially wrapping a plurality of first smooth metal attachments around the outside of the sub-conductor, with the openings of each first smooth metal attachment aligned on the same straight line, each first smooth metal attachment arranged along the length of the sub-conductor, and two adjacent first smooth metal attachments in contact; and coaxially wrapping a plurality of second smooth metal attachments around the outside of the first smooth metal attachments, with the openings of each second smooth metal attachment aligned on the same straight line, the openings of each second smooth metal attachment offset from the openings of each first smooth metal attachment in the circumferential direction of the sub-conductor, each second smooth metal attachment arranged along the length of the sub-conductor, and two adjacent second smooth metal attachments in contact.

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