JP2013012370A - Method for restricting spread of potential rise in ground electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a potential rise spread restriction method which makes it possible to restrict the spread of potential rise in a ground electrode at the falling of a thunderbolt, requiring less labor and cost than in conventional technology.SOLUTION: In a potential rise spread restriction method used to restrain a potential rise at a ground electrode on an induction side buried in the earth and having a lightning current flowing thereinto from spreading to a ground electrode on a non-induction side disposed around the ground electrode on the induction side, soil in a portion existing between the ground electrode on the induction side and the ground electrode on the non-induction side and separated from both ground electrodes is used as a soil improvement portion with relatively higher resistance than the earth existing in the vicinity. The soil improvement portion is formed, for example, in shape of the letter I, U or L or in shape of a cylinder in a plan view.

Description

  The present invention relates to a technique for suppressing an increase in potential generated during a lightning stroke from spreading around the ground electrode by improving the soil around the ground electrode. Here, “improvement of soil” means changing the resistivity of the soil relative to the resistivity of the surrounding earth by adjusting the composition and moisture content of the soil itself, as well as insulating materials in the ground. And changing the resistivity of the soil containing the insulating material to the resistivity of the surrounding earth.

  It is known that the lightning point potential rises during lightning strikes on steel towers and various electrical equipment, and this potential increase spreads to the surroundings and causes phenomena such as reverse flashing. Since there is a risk of destruction and damage, various measures have been taken conventionally.

  For example, in Patent Document 1, a plurality of ground wires are connected radially around a building, thereby reducing the surge inductance of the ground wires and reducing the current flowing through each ground wire to reduce the lightning point. A grounding system that suppresses the potential increase in the vicinity and increases the lightning current diverted to the entire grounding line to prevent a potential drop at a point away from the lightning strike, and equalizes the potential of the entire grounding system. The grounding structure is described.

Japanese Patent Laid-Open No. 9-27359, “Grounding Structure and Power Plant of Grounding System” (paragraphs [0025] to [0040], FIGS. 1 to 7 etc.)

  However, in the prior art described in Patent Document 1, a large number of ground wires are indispensable, and since the connection structure of these ground wires is complicated, a lot of labor and cost are required for grounding work. There was a problem.

  Therefore, a problem to be solved by the present invention is to provide a method capable of suppressing the increase in the potential of the ground electrode during a lightning strike to the surroundings with less labor and cost compared to the prior art.

In order to solve the above-described problem, the invention according to claim 1 is directed to the induced-side grounding in which the potential increase of the inducing-side grounding electrode embedded in the ground and through which the lightning current flows is disposed around the inducing-inducing side grounding electrode. In the potential rise ripple suppression method for suppressing the ripple to the electrode,
The resistance value of the soil at least between the induction-side ground electrode and the induced-side ground electrode and isolated from both ground electrodes is relative to the resistance value of the ground existing around the part. It is characterized by making the said part into the soil improvement part by making it high.

  The invention according to claim 2 is the ripple suppression method according to claim 1, wherein the soil improvement portion is substantially orthogonal to the ground surface between the induction-side ground electrode and the induced-side ground electrode. It is characterized in that it is composed of a substantially flat I-shaped soil buried.

  The invention according to claim 3 is the ripple suppression method according to claim 1, wherein the soil improvement part is a cylindrical soil embedded so as to surround the periphery of the induction-side ground electrode. It is characterized by becoming.

  According to a fourth aspect of the present invention, in the ripple suppression method according to the first aspect, the soil improvement portion has a side opposite to the induced-side ground electrode among the four surrounding surfaces centering on the induction-side grounded electrode. It is characterized by consisting of a substantially U-shaped flat surface arranged on three surfaces.

  The invention according to claim 5 is the ripple suppression method according to claim 1, wherein the soil improvement portion is located on the opposite side of the induced-side ground electrode among the four surrounding surfaces around the induction-side ground electrode. It is made of a substantially plane L-shaped soil disposed on two surfaces except one surface and one surface parallel to a line connecting the induction-side ground electrode and the induced-side ground electrode.

  In addition, it cannot be overemphasized that the shape of a soil improvement part and a structure are not limited to what was described in Claims 2-5 mentioned above, In short, it is between an induction | guidance | derivation side ground electrode and a to-be-induced side ground electrode. Any shape and structure may be used as long as the resistance value of the soil existing and isolated from both ground electrodes is relatively higher than the resistance value of the ground existing around the portion.

According to the present invention, it is possible to prevent the ground potential of various electrical devices and communication devices existing around the induction-side ground electrode, which is a lightning strike point, from rising, and to prevent destruction or damage of these devices due to reverse flashing or the like. Can be prevented.
Further, since the work of connecting a large number of ground wires to each other as in the prior art is not required, labor and cost can be reduced.

It is a figure which shows the analysis space used in order to analyze the vertical ground electrode and the electric potential rise in the circumference | surroundings, (a) is a perspective view, (b) is a top view, (c) is a front view. It is a figure which shows the injection current waveform used for the analysis. It is the figure which showed the shape of the soil improvement part, (a-1)-(e-1) is a front view of Case1-5, (a-2)-(e-2) is a top view of Case1-5. is there. It is a figure which shows the electric potential change of the ground electrode in Case0. It is a figure which shows the electric potential change of the ground electrode in Case0 and Case1. It is a figure which shows the electric potential change of the ground electrode in Case0 and Case2. It is a figure which shows the electric potential change of the ground electrode in Case0 and Case3. It is a figure which shows the electrical potential change of the ground electrode in Case0 and Case4. It is a figure which shows the electric potential change of the ground electrode in Case0 and Case5. It is the figure which showed the shape of the soil improvement part in Case5, (e-1) is a front view, (e-2) is a top view. It is a figure which shows the electrical potential change of the ground electrodes 21 and 22 at the time of changing the resistivity of a soil improvement part in Case5. In Case 5, the steady increase in potential of the ground electrode 21 (FIG. 12A), the steady increase in potential of the ground electrode 22 (FIG. 12C), and the ground electrode when the resistivity of the soil improvement portion is changed. It is a figure which shows the electric potential rise peak value of 22 (FIG.12 (b)). It is a figure which shows the electrical potential change of the ground electrodes 21 and 22 at the time of changing the depth of a soil improvement part in Case5. In Case 5, the steady increase in potential of the ground electrode 21 (FIG. 14 (a)), the steady increase in potential of the ground electrode 22 (FIG. 14 (c)), and the ground electrode when the depth of the soil improvement portion is changed. It is a figure which shows the electric potential rise peak value of 22 (FIG.14 (b)). It is a figure which shows the electrical potential change of the ground electrodes 21 and 22 at the time of changing the thickness of a soil improvement part in Case5. In Case 5, the steady increase in potential of the ground electrode 21 (FIG. 16A), the steady increase in potential of the ground electrode 22 (FIG. 16C), and the ground electrode when the thickness of the soil improvement portion is changed. It is a figure which shows the electric potential rise peak value of 22 (FIG.16 (b)). It is a figure which shows the electrical potential change of the ground electrodes 21 and 22 at the time of changing the width | variety of a soil improvement part in Case5. In Case 5, when the width of the soil improvement part is changed, the potential increase steady value of the ground electrode 21 (FIG. 18A), the potential increase steady value of the ground electrode 22 (FIG. 18C), and the ground electrode 22 are increased. It is a figure which shows the electric potential rise peak value (FIG.18 (b)).

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, FIG. 1 is a diagram showing an analysis space used for analyzing the ground electrode and its surrounding potential rise during a lightning stroke, (a) is a perspective view, (b) is a plan view, and (c) is a plan view. It is a front view.
In FIG. 1, the step size of the analysis space 10 is Δs = 0.25 m in all the x, y, and z directions, and the size of the analysis space 10 is x direction: 76 m, y direction: 74 m, z direction: 27. It was 5 m. The six boundary surfaces surrounding the analysis space 10 simulate open spaces using Liao's secondary absorption boundary conditions. Here, the secondary absorption boundary condition of Liao is described in, for example, p. Of “Electromagnetic field and antenna analysis by FDTD method” by Jun Uno (published on March 20, 1998, Corona). 72-p. 80.
The ground structure is assumed to be filled from the bottom of the analysis space 10 to a height of 14.5 m with a material having ρ = 100 Ωm and a relative dielectric constant ε _r = 10. In FIG. 1C, 11 indicates the virtual ground surface.

Inside the analysis space 10, two vertical ground electrodes 21 and 22 are arranged, and a current injection line 23 is connected to one of the ground electrodes 21. A thin wire conductor model having a radius of 5.75 mm is used for the ground electrodes 21 and 22 and the current injection line 23.
One ground electrode (induction-side ground electrode) 21 is for injecting a lightning current from a current source (not shown) (with an internal resistance of 500Ω) through a current injection line 23, and the other ground The electrode (induced-side ground electrode) 22 is an electrode for measuring a potential increase value when a lightning current is injected into the ground electrode 21. Here, the potential increase value of the ground electrodes 21 and 22 is the integration of the electric field on the ground plane from the absorption boundary surface 12 (see FIGS. 1B and 1C) to each measurement point (the ground electrodes 21 and 22). The value is measured using a voltage probe 24 (see FIG. 1 (a)).

Under the above analysis conditions, a current is injected assuming that the ground electrode 21 is a lightning strike point such as a steel tower, and a resistivity ρ = 10 kΩm and a relative dielectric constant ε _r = 10 around the ground electrode 21 as described later. The potentials and potential rise values appearing on the ground electrodes 21 and 22 when the shape of the soil (hereinafter, a part of the soil having the above-described resistivity and relative permittivity is referred to as a soil improvement part) were varied. .
FIG. 2 shows the waveform of the current injected into the ground electrode 21, which represents the wavefront length of a general return lightning stroke, which has a wavefront length of about 1.0 μs and a peak wave value of 1.0 A. It is.
For the calculation of the potential rise value, an FDTD method (Finite-Difference Time-Domain Method), which is a kind of numerical electromagnetic field analysis, was used. This FDTD method is a well-known numerical electromagnetic analysis method described in Chapter 1 of the above-mentioned document “Electromagnetic field and antenna analysis by FDTD method”.

  Next, Fig.3 (a)-(e) divides and shows the shape of a soil improvement part in five cases (Case1-5). In each figure, the left figure is a front view around the ground electrodes 21 and 22, the right figure is a plan view, (a-1) is a front view of Case 1, and (a-2) is a plan view of Case 1. Similarly, (b-1) and (b-2) are Case 2, (c-1) and (c-2) are Case 3, (d-1) and (d-2) are Case 4, (E-1) and (e-2) indicate Case 5, respectively. In these drawings, reference numerals 31 to 35 denote soil improvement portions, respectively.

The inventor injects the current with the ground electrode 21 as a lightning strike point (induction side) for the Cases 1 to 5 having the soil improvement portions 31 to 35 having various shapes shown in FIG. By observing how the potential of the electrode 21 spills over the ground electrode 22 (induced side), the inventors studied diligently about the shape of the soil improvement portion where the potential increase at the ground electrode 22 is most suppressed.
As described above, the resistivity ρ of the soil improvement part is sufficiently larger than the resistivity of the surrounding ground so that ρ = 10 kΩm, and the relative dielectric constant is ε _r = 10. The resistivity and relative dielectric constant of these soil improvement parts can be easily realized by adjusting the composition of the soil and the amount of water contained therein.

Case 1 in FIGS. 3A-1 and 3A-2 is an example in which a rectangular parallelepiped soil extending in the vertical direction with the ground electrode 21 as the center is used as the soil improvement portion 31, FIGS. Case 2 of -2) is an example in which the soil improvement part 32 is a square cylindrical (planar square) soil whose inner surface is at a distance of 0.75 m from the ground electrode 21 with the ground electrode 21 as the center, FIG. Case 3 in 1) and (c-2) is an example in which the soil improvement part 33 is made of a three-plane planar soil excluding one surface on the ground electrode 22 side among the four surrounding surfaces surrounding the ground electrode 21, FIG. Case 4 of (d-1) and (d-2) is an example in which the soil improvement part 34 is a planar L-shaped soil excluding one surface parallel to the line connecting the ground electrodes 21 and 22 in Case 3, FIG. -1), Case 5 of (e-2) is one side of the ground electrode 22 side with a distance of 0.75 m from the ground electrode 21 ( The soil surface I-shaped) is an example of a soil improvement unit 35.
The length of each part of the soil improvement parts 31-35 is as showing in FIG. 3, and the distance between the ground electrodes 21 and 22 is 2 m. In addition, the length L in the figure is changed to three types as shown in Table 1 (case 1 is 0.25 m, 1 m, and 1.75 m, and cases 2 to 5 are 0.25 m, 0.5 m, and 1 m). Measured.
Case 0 in Table 1 is a case where soil improvement is not performed around the ground electrode 21 (between the ground electrodes 21 and 22), and is a comparison object of Cases 1 to 5.

  FIG. 4 is a diagram illustrating the calculation result of the potential change of the ground electrodes 21 and 22 for Case0. When the soil improvement part was not provided between the ground electrodes 21 and 22, a capacitive potential increase with a steady value of 30 V appeared at the ground electrode 21 on the induction side. This potential rise spread to the surroundings, and an inductive potential rise with a peak value of 7V and a steady value of 6V appeared at the ground electrode 22 on the induced side.

FIG. 5 is a diagram illustrating calculation results of potential changes of the ground electrodes 21 and 22 in Case 0 and Case 1 (FIGS. 3A-1 and 3A-2).
According to these waveforms, when the soil improvement of Case 1 is performed, the ground resistance of the ground electrode 21 increases depending on the size of the soil improvement portion 31, so that the potential increase value is increased on the induction side. . Further, the potential increase value was not reduced at the ground electrode 22. That is, the potential increase was larger than the result of Case 0 on both the induction side and the induced side, and good results were not obtained.

FIG. 6 is a diagram showing calculation results of potential changes of the ground electrodes 21 and 22 in Case 0 and Case 2 (FIGS. 3B-1 and 3B-2).
According to these waveforms, when the soil improvement of Case 2 is performed, the ground resistance of the ground electrode 21 on the induction side is increased depending on the size of the soil improvement portion 32 as in the case of Case 1. However, since the shape of the soil improvement part 32 of Case 2 is cylindrical and the soil is not improved immediately in the vicinity of the ground electrode 21, the amount of increase in ground resistance was not as great as in Case 1. In addition, the increase in potential of the ground electrode 22 on the induced side was reduced as the size of the soil improvement unit 32 was increased.
From the above results, when the ground electrode 22 that does not want to propagate the potential rise is disposed so as to surround the ground electrode 21 on the induction side, the ground electrode 21 is surrounded by the cylindrical soil improvement unit 32 as in Case 2. This method is considered effective. However, since the potential of the ground electrode 21 on the induction side is slightly higher than that in the case where soil improvement is not performed, it is necessary to strengthen lightning protection measures on the induction side.

7, FIG. 8, and FIG. 9 respectively show Case 0 and Case 3 (FIG. 3 (c-1), (c-2)), Case 0 and Case 4 (FIG. 3 (d-1), (d-2)), It is a figure which shows the calculation result of the electric potential change of the ground electrodes 21 and 22 in Case0 and Case5 (FIG. 3 (e-1), (e-2)).
From these waveforms, as the scale of the soil improvement parts 33 to 35 becomes smaller, such as Case 3 (U-shaped) → Case 4 (L-shaped) → Case 5 (I-shaped), the potential increase at the ground electrode 21 on the induction side is suppressed. Has been. This is simply because the grounding resistance of the ground electrode 21 changes (becomes smaller) depending on the scale of the soil improvement portions 33 to 35. In addition, the potential increase reduction effect of the ground electrode 22 on the induced side was almost the same in Cases 3 to 5.
Specifically, in Cases 3 to 5, the potential rise at the ground electrode 21 on the induction side is about 5 to 55%, but the potential rise at the ground electrode 22 on the induced side is about 25 to 60% as a steady value. It was revealed that the wave height was reduced by about 15 to 30%. For these Case 3 (U-shaped), Case 4 (L-shaped), and Case 5 (I-shaped), the ground electrode 22 on the induced side around the ground electrode 21 on the induction side (in other words, around the lightning strike point) And the number and arrangement of electrical devices that are desired to suppress the spread of potential rise).

Table 2 (three significant figures) shows the potential of the grounding electrode 21 on the induction side in Cases 1 to 5, the potential of the grounding electrode 22 on the induced side, and the grounding electrode on the induction side with respect to Case 0 of Cases 1 to 5 21 is a summary of the increase rate of the potential 21 and the decrease rate of the potential increase of the ground electrode 22 on the induced side.

Next, the results of examining the scale and effect of the I-shaped soil improvement part 35 shown as Case 5 among various soil improvement parts will be described below.
FIG. 10 is a diagram illustrating the shape of the soil improvement unit 35 in Case 5, in which (e-1) is a front view and (e-2) is a plan view. Here, the influence on the potential increase when the resistivity and the size (depth, thickness, width) of the soil improvement part 35 were changed was examined.
In FIG. 10, the depth h = 2 m, the thickness L ₁ = 0.5 m, the width L ₂ = 1.0 m, and the resistivity ρ = 10 kΩm as a reference, and the resistivity ρ is in the range of 1 to 10 kΩm. And the depth h was changed within a range of 0.5 to 3.5 m, the thickness L ₁ was changed to 0.25 to 1.0 m, and the width L ₂ was changed within a range of 0.5 to 4.0 m. .
The waveform of the current injected into the ground electrode 21 is the same as that shown in FIG. 2, and is a step wave current having a wavefront length of about 1.0 μs and a peak value of 1.0 A.

  FIG. 11 is a diagram illustrating a calculation result of a potential change of the ground electrodes 21 and 22 when the resistivity ρ of the soil improvement unit 35 is changed. Further, FIG. 12 shows a steady increase in potential of the ground electrode 21 (FIG. 12A) and a steady increase in potential of the ground electrode 22 (FIG. 12C) when the resistivity of the soil improvement unit 35 is changed. And the calculation result of the electric potential rise peak value of the ground electrode 22 is shown. Note that the case of ρ = 100 Ωm has the same resistivity as the ground around the soil improvement unit 35, and can be regarded as a case where the soil is not improved.

As is clear from FIGS. 11 and 12, the resistivity of the soil improvement unit 35 does not greatly affect the potential increase value of the ground electrode 21 on the induction side. On the other hand, the potential increase value of the ground electrode 22 on the induced side can be reduced as the resistivity of the soil improvement unit 35 is increased.
From FIG. 12, the potential increase reduction effect of the ground electrode 22 is saturated at the resistivity ρ = 5 to 10 kΩm of the soil improvement unit 35. However, this is the result when the resistivity of the surrounding ground is ρ = 100 Ωm.

Next, FIG. 13 is the case of changing the depth h [m] of soil improvement unit 35, FIG. 15 is the case of changing the thickness _L 1 [m], 17 changing the width _L 2 [m] The calculation results of the potential change of the ground electrodes 21 and 22 in the case of the above are shown.
14 shows a case where the depth h [m] of the soil improvement part 35 is changed, FIG. 16 shows a case where the thickness L ₁ [m] is changed, and FIG. 18 shows a case where the width L ₂ [m] is changed. In this case, the potential rise steady value of the ground electrode 21 ((a) in each figure), the potential rise steady value of the ground electrode 22 ((c) in each figure), and the potential rise peak value of the ground electrode 22 (each (B) of the figure is shown.

According to these FIG. 13 to FIG. 18, the larger the shape of the soil improvement portion 35 is, the larger the potential increase value of the induction side, that is, the ground electrode 21 is. It is clear that the potential rise can be effectively reduced.
Similar to the resistivity of the soil improvement part 35, there are also saturation characteristics when the depth and width are changed. In this condition, the depth h = 3 m and the width L ₂ = 4.0 m, respectively. Saturation started at about. Respect thickness L ₁ has not been confirmed saturation characteristic, which is (in the current model 2m) distance between the ground electrodes 21 and 22 are for narrow, electrode spacing in the longer condition, thickness It is considered that the saturation characteristic of L ₁ appears similarly to the depth h and the width L ₂ .

As described above, according to this embodiment, the lightning strike to the ground electrode 21 can be achieved by changing the resistivity and size (depth, thickness, width) of the soil improvement portion between the ground electrodes 21 and 22. It is possible to suppress the potential increase that sometimes occurs from spreading to the ground electrode 22 side.
In other words, depending on the number and arrangement of the ground electrode 21 on the induction side and the ground electrode 22 on the induced side that is not desired to spread the potential rise, the cylindrical, U-shaped, L-shaped, and I-shaped soil improvement portions 32 to 35 are arranged. By properly using, it is possible to effectively reduce the potential increase on the induced side while suppressing the potential increase on the induction side during a lightning strike.
Thereby, it is possible to prevent the ground potential of various electric devices and communication devices existing around the lightning strike point from rising, and to prevent destruction and damage of the device due to reverse flashlight or the like.
In addition, since the effect of suppressing the potential rise varies depending on the resistivity and size (depth, thickness, width) of the soil improvement part, the size, shape, number, and positional relationship of the ground electrode, In doing so, it is desirable to conduct a design analysis in consideration of cost effectiveness by conducting an analytical study in advance.

In each of the above-described embodiments, it is assumed that the soil improvement portion is formed of homogeneous high-resistance soil. However, for example, a flat or granular, powdered rubber or other insulating material is embedded in the soil, and this insulation is performed. The entire soil of the part including the material can also be used as the soil improvement part.
In each embodiment, the resistivity of the soil improvement part is higher than the resistivity of the surrounding ground, but the resistivity of the soil improvement part is relatively high by lowering the resistivity of the surrounding earth. It may be made to become.

10: Analysis space 11: Virtual ground surface 12: Absorption boundary surface 21: Vertical ground electrode (induction-side ground electrode)
22: Vertical ground electrode (guided ground electrode)
23: Current injection line 24: Voltage probe

Claims (5)

A potential rise ripple suppression method for suppressing a rise in potential of an induction side ground electrode embedded in the ground and through which a lightning current flows propagates to an induced side ground electrode arranged around the induction side ground electrode In
The resistance value of the soil at least between the induction-side ground electrode and the induced-side ground electrode and isolated from both ground electrodes is relative to the resistance value of the ground existing around the part. A method for suppressing the spread of the potential increase in the ground electrode, wherein the portion is made a soil improvement portion by increasing the height of the ground electrode. In the ripple suppression method according to claim 1,
In the ground electrode, wherein the soil improvement portion is made of a substantially I-shaped flat surface embedded so as to be substantially orthogonal to the ground surface between the induction-side ground electrode and the induced-side ground electrode. A method for suppressing the spread of potential rise. In the ripple suppression method according to claim 1,
The method for suppressing the spread of a potential increase in a ground electrode, wherein the soil improvement part is made of cylindrical soil embedded so as to surround the periphery of the induction-side ground electrode. In the ripple suppression method according to claim 1,
The soil improvement part is composed of a substantially U-shaped flat surface disposed on three sides of the surrounding four sides except the opposite side of the induced side ground electrode with the origin side ground electrode as a center. A method for suppressing the spread of potential rise in the ground electrode. In the ripple suppression method according to claim 1,
The soil improvement part connects the induction-side ground electrode and the induced-side ground electrode with one of the surrounding four sides around the induction-side ground electrode and the opposite side of the induced-side ground electrode. A method for suppressing the spread of a potential increase in a ground electrode, characterized by comprising a substantially L-shaped flat surface disposed in two directions except one side parallel to a line.

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