JP6842008B2 - High withstand voltage evaluation method for high withstand voltage cable, high withstand voltage cable, and insulated lightning protection system - Google Patents

Description

The present invention is a method for evaluating the withstand voltage of a high withstand voltage cable used in an insulated lightning protection system in which a lightning receiving portion that receives a lightning strike and a pulling lead wire that allows a lightning current to flow to a ground electrode are insulated from a building. And related to insulated lightning protection systems.

In the highly electronic society of recent years, an extremely static electromagnetic environment is desired in buildings such as data centers, large-scale simulation facilities, hospitals equipped with operating rooms, and research facilities. When a lightning strike occurs on such a building, an overvoltage is induced in the electric / electronic equipment in the building due to the influence of the lightning current, which causes a failure or malfunction of the electric / electronic equipment.

As a method of suppressing the influence of lightning strikes on a building, a lightning receiving part (lightning rod, ridge-raising conductor, etc.) of the lightning protection system and a pull-down lead wire that allows lightning current received by the lightning receiving part to flow to the grounding electrode of the earth are used as the building structure. An insulated, so-called separate lightning protection system (hereinafter referred to as an insulated lightning protection system) may be adopted.

As an insulated lightning protection system, an insulated pipe with a plurality of lightning rod-shaped insulators integrally attached to the lightning rod support tube is used, an insulated wire is passed through the insulated pipe support tube, and the insulated wire is passed through the tip of the insulated pipe support tube. , The lightning rod, the insulated wire, and the wall lightning rod support tube are mechanically connected from the two-piece mounting bracket, and the lightning rod and the insulated wire are electrically connected. (For example, see Patent Document 1).

In addition, a lightning rod is laid on the roof of the building insulated from the building, and a lightning rod consisting of one or more shielded power cables or a high-frequency coaxial cable for power is connected in advance between the lightning rod and the ground electrode. When a lightning rod is pulled down from the top of the building through a lightning cable through the metal pipeline that passes through the inside of the building and a lightning rod is guided by the lightning rod, the induced current that flows in the opposite direction to the lightning current that flows through the lightning rod flows through the metal pipeline. As a result, the generation of the external magnetic field of the lightning rod due to the lightning rod is suppressed, the lightning current is passed through the ground through a specific path at the time of a lightning rod, and the electromagnetic field due to the induced lightning is not generated inside the building (for example, Patent Documents). 2).

Japanese Unexamined Patent Publication No. 11-40390 Japanese Unexamined Patent Publication No. 2011-288920

However, in such an insulated lightning rod, the withstand voltage performance of the high withstand voltage cable used for the pull-down lead wire could not be easily evaluated. Conventionally, the withstand voltage of a high withstand voltage cable has been evaluated by the voltage drop due to the inductance of the cable conductor of the high withstand voltage cable. That is, it was evaluated by the product of the inductance L of the cable conductor and the wave front steepness di / dt of the lightning current. There are two types of lightning strikes (hereinafter referred to as subsequent lightning strikes), and in the case of subsequent lightning strikes, the wave front steepness di / dt of the lightning current is calculated to be 10 times that of the first lightning strike, so the lightning overvoltage for the subsequent lightning strike is realistic. It was not fully evaluated because it was not a value.

JIS Z9290-1 (2014) "Lightning Protection Part 1 General Principles" defines lightning protection levels and lightning current parameters according to those levels. The standard lightning protection level is IV, and the current parameter of the first lightning strike at this time is a current peak value of 100 kA (wave head length 10 μs / wave tail length 350 μs), and a wave head steepness (wave height value / wave head length) of 100 kA /. 10 μs = 10 kA / μs. In the subsequent lightning stroke, the current crest value is 25 kA (wave crest length 0.25 μs / crest length 100 μs), and the crest steepness (crest value / crest length) is 25 kA / 0.25 μs = 100 kA / μs. Thus, in the case of a subsequent lightning strike, the wave front steepness di / dt of the lightning current is calculated to be 10 times that of the first lightning strike.

The first lightning strike is characterized by a large amount of discharge charge and a large amount of lightning energy, while the subsequent lightning strike is a lightning strike following the first lightning strike, and lightning strikes accompanied by subsequent lightning strikes account for 60 to 70%. Is said to be. This subsequent lightning strike is characterized by a large crest steepness as described above. Specifically, the wave front steepness of the first lightning stroke is 10 kA / μs, whereas that of the subsequent lightning stroke is 100 kA / μs. The larger the crest steepness, the larger the lightning overvoltage caused by the inductance L. Thus, the lightning overvoltage for subsequent lightning strikes has not been fully evaluated because it is not a realistic value.

Therefore, in order to strictly evaluate the lightning overvoltage, advanced analysis techniques such as electromagnetic field analysis and transient analysis were used. Although it is possible to evaluate lightning overvoltage by electromagnetic field analysis, since electromagnetic field analysis has to deal with a small circuit space (for example, several millimeters) in a large space (for example, an area of 100 m square), a computer The amount of calculation is enormous and unrealistic. In addition, there is a general-purpose transient phenomenon analysis method, but this method requires the construction of an equivalent circuit and requires sufficient knowledge and a high level of calculation skill, so it cannot be handled by general designers.

For these reasons, it is difficult to easily select a high withstand voltage cable with appropriate withstand voltage performance, and as a result, a high withstand voltage cable that cannot withstand lightning strikes is adopted, or the withstand voltage margin is overestimated. In some cases, a pressure resistant cable was used.

An object of the present invention is to provide a high withstand voltage evaluation method for a high withstand voltage cable, a high withstand voltage cable, and an insulated lightning protection system that can easily and accurately evaluate the withstand voltage of the high withstand voltage cable.

In the method for evaluating the withstand voltage of a high withstand voltage cable according to the invention of claim 1, the lightning overvoltage Vcs applied to the light receiving portion side of the high withstand voltage cable in which the cable conductor and the shield conductor are commonly grounded is the following equation (1) and (1). It is characterized in that it is calculated by the equation 2) and it is evaluated that the withstand voltage of the high withstand voltage cable is a withstand voltage that can withstand a lightning strike.

When 2D / v0 <tr, Vcs = Ist · Z0 · 2D / v0… (1)
When 2D / v0 ≧ tr, Vcs = Imax · Z0… (2)
However, D: high withstand voltage cable length, v0: lightning current propagation speed, tr: lightning current rise time, Ist: lightning current crest steepness, Z0: characteristics between the cable conductor and shield conductor of the high withstand voltage cable. Impedance, Imax: Peak value of lightning current.

The high withstand voltage cable according to the invention of claim 2 is a high withstand voltage cable that satisfies the withstand voltage of the high withstand voltage cable evaluated in claim 1 or the withstand voltage that is expected to have a margin in the evaluated withstand voltage.

The insulated lightning protection system using the high-voltage cable according to the invention of claim 3 has a lightning receiving portion that receives a lightning strike and a pull-down lead wire that allows a lightning current received by the lightning receiving portion to flow to a grounding electrode of the earth. In an insulated lightning protection system that is insulated from the above, the high withstand voltage cable according to claim 2 is used as the pull-down lead wire.

According to the invention of claim 1, the cable length D of the high withstand voltage cable in which the cable conductor and the shield conductor are commonly grounded , the propagation speed of the lightning current v0, the rise time tr of the lightning current, the wave front steepness Ist of the lightning current, When the characteristic impedance Z0 between the cable conductor and the shield conductor of the high withstand voltage cable and the peak value Imax of the lightning current are set, the lightning overvoltage Vcs applied to the light receiving part side of the high withstand voltage cable in response to a lightning strike is 2D / v0 < When tr, it is calculated by Vcs = Ist ・ Z0 ・ 2D / v0, and when 2D / v0 ≧ tr, it is calculated by Vcs = Imax ・ Z0, and the withstand voltage of the high withstand voltage cable is the withstand voltage that can withstand lightning. Therefore, it is possible to easily and accurately evaluate the lightning overvoltage applied to the light receiving portion side of the high withstand voltage cable.

According to the invention of claim 2, the high withstand voltage cable satisfying the lightning overvoltage applied to the lightning receiving portion side of the high withstand voltage cable evaluated in claim 1 or the withstand voltage expected to be marginal to the evaluated lightning overvoltage. It is possible to obtain an appropriate high withstand voltage cable that can withstand lightning strikes without excessively expecting the withstand voltage margin.

According to the invention of claim 3, it is an insulated lightning protection system in which a lightning receiving part that receives a lightning strike and a pulling lead wire that causes a lightning current received by the lightning receiving part to flow to a grounding electrode of the earth are insulated from the building. Since the high withstand voltage cable according to claim 2 is used as the pull-down lead wire, an appropriate insulated lightning protection system capable of withstanding lightning strikes can be constructed.

The waveform diagram which shows an example of the waveform of the lightning current I (t) flowing into the lightning receiving part side of a high withstand voltage cable. The waveform diagram which shows an example of the waveform of the lightning overvoltage Vcs (t) applied to the lightning receiving part side of a high withstand voltage cable. The image figure of the traveling wave and the reflected wave of the lightning overvoltage Vcs (t) applied to the lightning receiving part side of a high withstand voltage cable. When the reflected wave voltage V2 (t) reflected by the lightning receiving part of the high withstand voltage cable is t <tr (when the lightning overvoltage does not rise to the peak value Imax · Z0), the lightning receiving part of the high withstand voltage cable The voltage waveform diagram of the lightning overvoltage Vcs (t) of. Lightning reception of the high withstand voltage cable when the reflected wave voltage V2 (t) reflected by the lightning receiving part of the high withstand voltage cable is t ≧ tr (after the lightning overvoltage reaches the peak value Imax · Z0). The voltage waveform diagram of the lightning overvoltage Vcs (t) of the part. The cross-sectional view which shows an example of the high withstand voltage cable used for the analysis model of the withstand voltage of a high withstand voltage cable. The circuit diagram which shows an example of the experimental circuit used for the analysis model of the withstand voltage of a high withstand voltage cable. The graph of the analysis result of the lightning overvoltage of the first lightning strike and the subsequent lightning stroke with the high withstand voltage cable length D as a parameter when the grounding electrode is individually grounded for the high withstand voltage cable having the specifications of Table 1. The graph of the analysis result of the lightning overvoltage of the first lightning strike and the subsequent lightning stroke with the high withstand voltage cable length D as a parameter when the grounding electrode is commonly grounded for the high withstand voltage cable having the specifications of Table 1. The flowchart which shows an example of the process of the withstand voltage evaluation method of the high withstand voltage cable which concerns on embodiment of this invention.

Hereinafter, the background to the present invention will be described. By conducting experiments and numerical analysis, and repeatedly analyzing and examining the waveforms of the obtained lightning current and lightning overvoltage, the inventors use the calculation formulas represented by the following formulas (1) and (2). The maximum value of the lightning overvoltage (withstand voltage required between the cable conductor and shield conductor of the high withstand voltage cable) applied to the light receiving part side of the high withstand voltage cable where the cable conductor and shield conductor are commonly grounded can be calculated. I found.

The grounding method for high-voltage cables includes common grounding in which the cable conductor and shield conductor of the high-voltage cable are commonly grounded using the same grounding electrode, and the cable conductor and shield conductor are individually grounded using different grounding electrodes. There is an individual grounding, and the common grounding itself is a general grounding method when using a high withstand voltage cable, but the inventors of the present invention can use the common grounding as the grounding method for the high withstand voltage cable. It was found that it can be applied.

First, the calculation formula will be described. Now, the lightning overvoltage applied to the light receiving part side of the high withstand voltage cable is Vcs [kV], the cable length is D [m], the lightning current rise time tr [s], the peak value of the lightning current is Imax [A], The wave front steepness Ist [kA / μs] of the lightning current, the relative dielectric constant of the insulator between the cable conductor and the shield conductor is εr, the light velocity in vacuum is C0 [m / s], and the cable conductor and the shield conductor Propagation speed v0 [m / s] between, outer diameter (radius) of cable conductor is r [m], outer diameter (radius) of shield conductor is R [m], characteristic impedance between cable conductor and shield conductor Is Z0 [Ω].
<Calculation formula>
When 2D / v0 <tr: Vcs = Ist ・ Z0 ・ 2D / v0… (1)
When 2D / v0 ≧ tr: Vcs = Imax · Z0… (2)
The other relational expressions are as follows.

v0 = C0 / √εr… (3)
Z0 = 60ln (R / r) / √εr… (4)
Ist = Imax / tr ... (5)
As can be seen from equations (1) to (5), the physical specifications of the high withstand voltage cable (shield conductor outer diameter dimension R, cable conductor outer diameter dimension r, relative permittivity εr of insulator, high withstand voltage cable). If the length D) and the target lightning current parameter (peak value Imax, rise time tr) are known, it is possible to calculate the lightning overvoltage (maximum value of the lightning overvoltage) required for the high withstand voltage cable. Therefore, the lightning overvoltage applied to the high withstand voltage cable can be easily evaluated.

Next, in the calculation formulas expressed by equations (1) and (2), a lightning overvoltage applied to the lightning receiving portion side of the high withstand voltage cable (required between the cable conductor and the shield conductor of the high withstand voltage cable). Explain that the withstand voltage) can be calculated.

First, the lightning current I (t) can be expressed by the following equations (6) and (7). However, the timing of the lightning strike is t = 0.

When t <tr: I (t) = Ist · t… (6)
When t ≧ tr: I (t) = Imax ... (7)
That is, as shown in FIG. 1, when the lightning current does not rise to the peak value Imax (when t <tr), the lightning current I (t) is represented by the equation (6), and the lightning current reaches the peak value Imax. After reaching (when t ≧ tr), the lightning current I (t) is expressed by Eq. (7).

FIG. 1 is a waveform diagram showing an example of the waveform of the lightning current I (t) flowing into the lightning receiving portion side of the high withstand voltage cable. The lightning current increases at the crest steepness Ist from the point of lightning strike (t = 0) to the point of peak value Imax (t = tr), reaches the peak value Imax at the time point (t = tr), and thereafter. The lightning current is constant at the peak value Imax.

The lightning overvoltage Vcs (t) applied to the lightning receiving portion side of the high withstand voltage cable (lightning overvoltage Vcs (t) generated between the cable conductor and the shield conductor) is the lightning current represented by equations (6) and (7). It is obtained by multiplying I (t) by the characteristic impedance Z0 of the high withstand voltage cable, and is represented by the following equations (8) and (9).

When t <tr: Vcs (t) = Z0 ・ Ist ・ t… (8)
When t ≧ tr: Vcs (t) = Imax · Z0… (9)
FIG. 2 is a waveform diagram showing an example of the waveform of the lightning overvoltage Vcs (t) applied to the lightning receiving portion side of the high withstand voltage cable. Similar to the lightning current I (t) flowing into the lightning receiving portion side of the high withstand voltage cable shown in FIG. 1, the lightning overvoltage Vcs (t) applied to the lightning receiving portion side of the high withstand voltage cable is the time when the lightning strikes (t = 0). ) To the peak value Imax ・ Z0 (t = tr), it increases with the slope of Z0 ・ Ist, and at the time point (t = tr), it becomes the peak value Imax ・ Z0, and after that, the peak value Imax ・ Z0 It becomes constant.

Next, consider the reflection of the lightning overvoltage Vcs (t) applied to the lightning receiving portion side of the high withstand voltage cable. FIG. 3 is an image diagram of a traveling wave and a reflected wave of a lightning overvoltage Vcs (t) applied to the lightning receiving portion side of the high withstand voltage cable. When there is a lightning strike, a lightning overvoltage Vcs (t) is induced in the lightning receiving portion 12 of the high withstand voltage cable 11. Now, let V be the maximum value of the lightning overvoltage Vcs (t).

As shown in FIG. 3, the lightning overvoltage Vcs (t) travels as a traveling wave from the light receiving portion 12 of the high withstand voltage cable 11 through the cable conductor toward the ground electrode 13 (T1), and D / v0 from the lightning strike. After the lapse of time, the ground (grounding electrode 13) is reached (T2).

Since the grounding of the high withstand voltage cable 11 is a common ground and the cable conductor of the high withstand voltage cable 11 and the shield conductor are connected on the grounding electrode 13 side, the lightning overvoltage Vcs (t) is reflected by the grounding electrode 13. Then, the reflected wave voltage V1 (t) having the opposite polarity travels toward the light receiving portion 12 side of the high withstand voltage cable 11 (T3). That is, the absolute value of the magnitude of the opposite polarity reflected wave voltage V1 (t) is the same as the lightning overvoltage Vcs (t), but since it has the opposite polarity, it is in the negative direction of the opposite polarity reflected wave voltage V1 (t). The magnitude is -V.

Then, the reflected wave voltage V1 (t) having the opposite polarity reaches the lightning receiving portion 12 of the high withstand voltage cable 11 after a time of 2D / v0 elapses after the lightning strike (T4). In the lightning receiving portion 12 of the high withstand voltage cable 11, since the cable conductor and the shield conductor are not connected and are open, the polarity of the voltage is reflected here without being inverted. Therefore, the reflected wave voltage V2 (t) reflected by the lightning receiving portion 12 of the high withstand voltage cable 11 becomes twice as large (-2V) as the reflected wave voltage V1 (t) of the opposite polarity, and the ground electrode is again grounded. It will proceed toward the 13th side. In this case, the voltage obtained by adding the reflected wave voltage V2 to the lightning overvoltage Vcs (t) travels toward the grounding electrode 13 side (T5).

Here, the reflected wave voltage V2 (t) reflected by the lightning receiving portion 12 of the high withstand voltage cable 11 is represented by the following equations (10) and (11).

When t <2D / v0:
V2 (t) = 0 ... (10)
When t ≧ 2D / v0:
V2 (t) = -2, Z0, Ist, (t-2D / v0) ... (11)
That is, when t <2D / v0, the reflected wave voltage V2 (t) reflected by the lightning receiving portion 12 of the high withstand voltage cable 11 does not exist, so it is 0 as shown in equation (10), and t = 2D / v0. Only then is it reflected by the lightning receiving unit 12 to generate the reflected wave voltage V2 (t) shown in Eq. (11).

Therefore, the lightning overvoltage Vcs (t) of the lightning receiving portion of the high withstand voltage cable 11 when the reflected wave voltage V2 (t) reflected by the lightning receiving portion 12 is also taken into consideration is the right side of the equations (8) and (9). It is shown by Eqs. (12) and (13) in which the reflected wave voltage V2 (t) is added to.

When t <tr: Vcs (t) = Z0 · Ist · t-V2 (t) ... (12)
When t ≧ tr: Vcs (t) = Imax · Z0-V2 (t)… (13)

FIG. 4 shows the height when the reflected wave voltage V2 (t) reflected by the lightning receiving portion 12 of the high withstand voltage cable 11 is t <tr (when the lightning overvoltage does not rise to the peak values Imax · Z0). It is a voltage waveform diagram of the lightning overvoltage Vcs (t) of the lightning receiving part of a pressure-resistant cable 11. That is, when t <tr, t = 2D / v0, when t = 2D / v0, Vcs (t) becomes the maximum value, and after t = 2D / v0, it decreases. In this case, it is represented by the following equation (14) obtained by substituting the equation (11) into the equation (12).

Vcs (t) = Z0 ・ Ist ・ t-2 ・ Z0 ・ Ist ・ (t-2D / v0)… (14)
In this equation (14), the maximum value of Vcs (t) is Z0 · Ist · 2D / v0 when t = 2D / v0, and the calculation formula (Vcs = Ist · Z0.2D) shown in the formula (1). / V0).

FIG. 5 shows a case where the reflected wave voltage V2 (t) reflected by the lightning receiving portion 12 of the high withstand voltage cable 11 occurs when t ≧ tr (after the lightning overvoltage reaches the peak values Imax · Z0). It is a voltage waveform diagram of the lightning overvoltage Vcs (t) of the lightning receiving part of a high withstand voltage cable 11. That is, when t ≧ tr, t = 2D / v0, and from the time point (t = tr) to the time point (t = 2D / v0), Vcs (t) has a peak value of Imax · Z0. It decreases after t = 2D / v0. That is, in this case, it is represented by the following equation (15) obtained by substituting the equation (11) into the equation (13).

Vcs (t) = Imax, Z0-2, Z0, Ist, (t-2D / v0) ... (15)
In the formula (15), the maximum value of Vcs (t) is the peak value Imax · Z0 from the time point (t = tr) to the time point (t = 2D / v0), and the calculation formula shown in the formula (2). (Vcs = Imax · Z0).

In the above explanation, it is assumed that the traveling wave of the lightning overvoltage is totally reflected on the lightning receiving portion 12 side and the ground side (grounding electrode 13 side) of the high withstand voltage cable 11, but even if it is not totally reflected, it has the opposite polarity. Since the reflected wave is determined when it reaches the lightning receiving portion, the maximum value of the lightning overvoltage can be calculated by the equations (1) and (2). In this way, if the specifications such as the waveform of the lightning current and the length of the high withstand voltage cable are known, the withstand voltage specifications required for the high withstand voltage cable can be easily determined.

Next, the validity of equations (1) and (2) will be described. In order to examine the analysis model of the high withstand voltage cable, we decided to investigate the lightning overvoltage generated in the high withstand voltage cable by impulse experiment. FIG. 6 is a cross-sectional view showing an example of the high withstand voltage cable used for the analysis model of the withstand voltage of the high withstand voltage cable. The high withstand voltage cable 11 has a cylindrical cable conductor 15 around a cylindrical insulator 14a in the core portion, and a cylindrical insulator 14b is provided on the outside of the cable conductor 15 via a semiconductive layer 16a. Further, a shield conductor 17 is provided on the outside of the cylindrical insulator 14b via a semi-conductive layer 16b, and the outside of the shield conductor 17 is covered with the insulator 14c. In this case, the relative permittivity of the insulator 14b between the cable conductor 15 and the shield conductor 17 is εr.

FIG. 7 is a circuit diagram showing an example of an experimental circuit used for the analysis model of the withstand voltage of the high withstand voltage cable 11. The voltage waveform of the lightning overvoltage is input from the impulse device 18 to the lightning receiving side of the high withstand voltage cable 11 having the high withstand voltage cable length D, and the grounding resistance R is connected to the common ground and individual ground by the changeover switch 19 on the grounding electrode side. I tried to switch with.

The analysis model of the high withstand voltage cable 11 was created by using the instantaneous value analysis program XTAP (Central Research Institute of Electric Power Industry). The specifications of the high withstand voltage cable 11 were reflected by using the analysis model in the program XTLC that can analyze the distributed constant lines included in XTAP. Table 1 shows the specifications (parameters) of the high withstand voltage cable 11 used in the analysis model.

そして、高耐圧ケーブル長Ｄを変化させて雷過電圧の解析をした。図８及び図９に雷過電圧の解析結果を示す。図８は、表１の諸元を有する高耐圧ケーブルについて接地極を個別接地をした場合の高耐圧ケーブル長Ｄをパラメータとした第一雷撃及び後続雷撃の雷過電圧の解析結果のグラフであり、図８（ａ）は第一雷撃を印加したときの高耐圧ケーブルのケーブル導体とシールド導体との間に生じる雷過電圧Ｖのグラフ、図８（ｂ）は後続雷撃を印加したときの高耐圧ケーブルのケーブル導体とシールド導体との間に生じる雷過電圧Ｖのグラフである。接地抵抗Ｒは１００Ω、第一雷撃は電流波高値１００ｋＡ（波頭長１０μｓ／波尾長３５０μｓ）、後続雷撃は電流波高値２５ｋＡ（波頭長０．２５μｓ／波尾長１００μｓ）、高耐圧ケーブル長Ｄは、１０ｍ、２０ｍ、５０ｍ、１００ｍの場合を示している。

Then, the lightning overvoltage was analyzed by changing the high withstand voltage cable length D. 8 and 9 show the analysis results of the lightning overvoltage. FIG. 8 is a graph of the analysis results of the lightning overvoltage of the first lightning strike and the subsequent lightning strike with the high withstand voltage cable length D as a parameter when the grounding electrode is individually grounded for the high withstand voltage cable having the specifications shown in Table 1. FIG. 8 (a) is a graph of the lightning overvoltage V generated between the cable conductor and the shield conductor of the high withstand voltage cable when the first lightning strike is applied, and FIG. 8 (b) is the high withstand voltage cable when the subsequent lightning strike is applied. It is a graph of the lightning overvoltage V generated between the cable conductor and the shield conductor of. The ground resistance R is 100Ω, the first lightning stroke has a current wave height of 100 kA (wave crest length 10 μs / wave tail length 350 μs), the subsequent lightning stroke has a current wave height of 25 kA (wave crest length 0.25 μs / wave tail length 100 μs), and the high withstand voltage cable length D is. The cases of 10 m, 20 m, 50 m, and 100 m are shown.

In FIG. 8A when the first lightning strike is applied, the curve C1 is a graph of the lightning overvoltage V when the high withstand voltage cable length D is 10 m, and the curve C2 is the lightning overvoltage V when the high withstand voltage cable length D is 20 m. The graph, curve C3 is a graph of lightning overvoltage V when the high withstand voltage cable length D is 50 m , and curve C4 is a graph of lightning overvoltage V when the high withstand voltage cable length D is 100 m. As can be seen from FIG. 8A, in the case of the first lightning strike, the peak value of the lightning overvoltage V generated between the cable conductor and the shield conductor of the high withstand voltage cable is 10,000 kV, and the high withstand voltage cable length. The shorter D, the shorter the time to reach the peak value.

On the other hand, in FIG. 8B when the subsequent lightning strike is applied, the curve C11 is a graph of the lightning overvoltage V when the high withstand voltage cable length D is 10 m, and the curve C12 is the lightning overvoltage when the high withstand voltage cable length D is 20 m. The graph of V, the curve C13 is a graph of the lightning overvoltage V when the high withstand voltage cable length D is 50 m , and the curve C14 is a graph of the lightning overvoltage V when the high withstand voltage cable length D is 100 m. As can be seen from FIG. 8B, in the case of a subsequent lightning strike, the peak value of the lightning overvoltage V generated between the cable conductor and the shield conductor of the high withstand voltage cable is 2,500 kV, and in the case of the first lightning strike. However, as in the case of the first lightning strike, the shorter the high withstand voltage cable length D, the shorter the time to reach the peak value.

In the case of individual grounding, it can be seen that the lightning overvoltage V of the first lightning stroke and the subsequent lightning stroke is approximately the product of the peak value of the current flowing through the cable conductor and the grounding resistance R. That is, it can be seen that the overvoltage due to the ground resistance R is dominant over the overvoltage due to the impedance of the high withstand voltage cable. In actual construction, since there is potential interference between the two grounding electrodes, it is assumed that the lightning overvoltage will be smaller than this analysis result.

Next, FIG. 9 is a graph of the analysis results of the lightning overvoltage of the first lightning strike and the subsequent lightning strike with the high withstand voltage cable length D as a parameter when the grounding electrode is commonly grounded for the high withstand voltage cable having the specifications shown in Table 1. 9 (a) is a graph of the lightning overvoltage V generated between the cable conductor and the shield conductor of the high withstand voltage cable when the first lightning strike is applied, and FIG. 9 (b) is the graph when the subsequent lightning strike is applied. It is a graph of the lightning overvoltage V generated between the cable conductor and the shield conductor of a high withstand voltage cable. As in the case of individual grounding, the ground resistance R is 100Ω, the first lightning strike has a current crest length of 100 kA (wave crest length 10 μs / crest length 350 μs), and the subsequent lightning strike has a current crest length of 25 kA (wave crest length 0.25 μs / crest length 100 μs). The high withstand voltage cable length D shows the cases of 10 m, 20 m, 50 m, and 100 m.

In FIG. 9A, the curve C1 is a graph when the high withstand voltage cable length D is 10 m, the curve C2 is a graph when the high withstand voltage cable length D is 20 m, and the curve C3 is a graph when the high withstand voltage cable length D is 50 m . The graph and the curve C4 are graphs when the high withstand voltage cable length D is 100 m. As can be seen from FIG. 9A, in the case of the first lightning strike, the peak value of the lightning overvoltage increases in proportion to the high withstand voltage cable length D, but even when the high withstand voltage cable length D is 100 m. The peak value of the lightning overvoltage is about 200 kV, which is sufficiently smaller than that in the case of individual grounding.

Furthermore, the inventors also paid attention to the waveform shown in FIG. 9 (a). As mentioned above, conventionally, the lightning overvoltage in the first direct lightning strike has been evaluated by Ldi / dt. Looking at FIG. 9A, the lightning overvoltage oscillates with the passage of time. Such vibration cannot be explained simply by the inductance of Ldi / dt or the high withstand voltage cable. Therefore, the inventors thought that such a lightning overvoltage would occur due to the reflection of the lightning current and voltage even in the first lightning strike. That is, it can be explained that the waveform of the lightning overvoltage vibrates due to repeated reflections of the lightning current and voltage. Then, it was found that the maximum value of the lightning overvoltage is determined by the relationship between the time when the reflected wave reaches the lightning receiving portion side of the high withstand voltage cable and the rising time of the lightning current. From the above consideration, it was found that the high withstand voltage cable lightning overvoltage can be evaluated by the equation (1).

On the other hand, in FIG. 9B, the curve C11 is a graph when the high withstand voltage cable length D is 10 m, the curve C12 is a graph when the high withstand voltage cable length D is 20 m, and the curve C13 is a graph when the high withstand voltage cable length D is 50 m . The graph at the time, the curve C14 is a graph when the high withstand voltage cable length D is 100 m.

In the case of a subsequent lightning strike, the peak value of the lightning overvoltage is higher than the high withstand voltage cable length D until the high withstand voltage cable length D is 20 m, but when the high withstand voltage cable length D is 50 m or 100 m, lightning strikes. The peak value of overvoltage reaches a plateau at about 450 kV. It can be seen that with common grounding, the withstand voltage can be suppressed to a low level without consideration for grounding resistance as with individual grounding.

Here, if the lightning overvoltage applied to the high withstand voltage cable depends on the inductance of the high withstand voltage cable, it is conceivable that a lightning overvoltage proportional to the length of the high withstand voltage cable will be generated. As you can see, the peak value of lightning overvoltage has peaked even if the high-voltage cable is long. In this way, the lightning overvoltage leveled off because the reflected wave arrived after the lightning voltage rose to its peak value.

From the consideration of FIGS. 9A and 9B, the inventors have found that the peak value of the lightning overvoltage appears due to the reflection of the lightning current. The maximum value of the lightning overvoltage is determined by the relationship between the time when the reflected wave reaches the lightning receiving part side of the high withstand voltage cable and the rising time of the lightning current, that is, it can be evaluated by the equations (1) and (2). The inventors found out.

As described above, in the case of individual grounding, as shown in FIG. 8, since the lightning overvoltage is extremely large and it can be judged that individual grounding is not realistic in selecting a high withstand voltage cable, common grounding is adopted in the present invention.

Next, regarding the validity of the equations (1) and (2), the withstand voltage obtained by the equations (1) and (2) is compared with the analysis result obtained by the analysis.

The comparison conditions are eight combinations of two lightning current parameters (first lightning strike and subsequent lightning strike) and four high-voltage cable lengths D (10 m, 20 m, 50 m, 100 m). The specifications of the high withstand voltage cable are as shown in Table 1.

The following values can be obtained from the specifications of the high withstand voltage cable shown in Table 1 and the equations (3) and (4). The propagation speed v0 between the cable conductor and the shield conductor of the high withstand voltage cable is determined by Eq. (3).
v0 = 1.73 × 108 [m / s]… (16)
The characteristic impedance Z0 of the high withstand voltage cable is determined by Eq. (4).
Z0 = 17.8 [Ω]… (17)
Further, the following values can be obtained from the lightning current parameters (first lightning strike: current wave height value 100 kA (wave head length 10 μs / wave tail length 350 μs), subsequent lightning strike: 25 kA (wave head length 0.25 μs / wave tail length 100 μs)).

At the time of the first lightning strike: Ist = 10 [kA / μs]… (18)
At the time of subsequent lightning strike: Ist = 100 [kA / μs]… (19)
The calculated value of the lightning overvoltage obtained by substituting these equations (16) to (19) into the equations (1) and (2) and the lightning overvoltage of the analysis result obtained from the graph of the analysis result shown in FIG. The values of are shown in Table 2.

表２から分かるように、（１）式及び（２）式の計算式から求めた雷過電圧の計算値と解析結果から求めた雷過電圧の値との誤差は、最大で５．３％であることから、実用的に問題のない精度で評価が可能であることが分かる。

As can be seen from Table 2, the error between the calculated value of the lightning overvoltage obtained from the formulas (1) and (2) and the value of the lightning overvoltage obtained from the analysis result is 5.3% at the maximum. From this, it can be seen that the evaluation can be performed with an accuracy that does not cause any practical problems.

Next, FIG. 10 is a flowchart showing an example of the process of the withstand voltage evaluation method of the high withstand voltage cable according to the embodiment of the present invention. First, the high withstand voltage cable length D, the lightning current propagation speed v0, the lightning current rise time tr, the characteristic impedance Z0 between the cable conductor and the shield conductor of the high withstand voltage cable, and the lightning current peak value Imax are acquired (S1). ).

The high withstand voltage cable length D is obtained from the specifications of the high withstand voltage cable, the propagation speed v0 of the lightning current is obtained from the above equation (3), and the characteristic impedance Z0 between the cable conductor and the shield conductor of the high withstand voltage cable is Obtained from the above equation (4). Further, the peak value Imax of the lightning current is obtained from the current parameter of the first lightning strike and the current parameter of the subsequent lightning strike. That is, the peak value Imax of the lightning current of the first lightning strike is the current peak value of 100 kA as described above, and the peak value Imax of the lightning current of the subsequent lightning strike is the current peak value of 25 kA. The rise time tr of the lightning current is obtained from the above equation (5). The crest steepness Ist of the lightning current of the first lightning strike can be obtained by (peak value / crest length) as described above. The crest steepness Ist of the first lightning stroke is a crest value of 100 kV and the crest length is 10 μs, so (100 kA / 10 μs) = 10 kA / μs. Since the crest steepness Ist of the subsequent lightning strike has a crest value of 25 kA and the crest length is 0.25 μs, (25 kA / 0.25 μs) = 100 kA / μs.

Next, it is determined whether or not 2D / v0 <tr (S2). When 2D / v0 <tr is satisfied, it means that the lightning current has not risen to the peak value Imax. At this time, Vcs = Ist · Z0.2D / v0, and the cable conductor and the shield conductor are commonly grounded. The withstand voltage of the high withstand voltage cable is evaluated (S3). That is, it is the above-mentioned equation (1), and is the voltage when the lightning overvoltage Vcs applied to the lightning receiving portion side of the high withstand voltage cable when t = 2D / v0 in FIG. 4 is the maximum value.

On the other hand, in the determination of step S2, when 2D / v0 <tr, that is, when 2D / v0 ≧ tr, it is the state after the lightning current has risen to the peak value Imax, and in this case, Vcs = Imax. At Z0, the withstand voltage of the high withstand voltage cable in which the cable conductor and the shield conductor are commonly grounded is evaluated (S4). That is, it is the above-mentioned equation (2), and is the voltage when the lightning overvoltage Vcs applied to the lightning receiving portion side of the high withstand voltage cable when t = 2D / v0 in FIG. 5 is the maximum value.

According to the embodiment of the present invention, attention is paid to the fact that the waveform of the lightning overvoltage is vibrating and that the peak value of the lightning overvoltage reaches a plateau even if the high withstand voltage cable is long, and the lightning applied to the high withstand voltage cable is applied. It was found that the overvoltage does not depend on the inductance of the high withstand voltage cable, but the peak value of the lightning overvoltage appears due to the reflection of the lightning current. As a result, the physical specifications of the high withstand voltage cable (shield conductor outer diameter dimension R, cable conductor outer diameter dimension r, relative permittivity εr of insulator, high withstand voltage cable length D) and the target lightning current If the parameters (peak value Imax, rise time tr) are known, it is possible to calculate the lightning overvoltage (maximum value of the lightning overvoltage) required for the high withstand voltage cable. I was able to get it. Therefore, the lightning overvoltage applied to the high withstand voltage cable can be easily and accurately evaluated.

In addition, by adopting a high withstand voltage that satisfies the lightning overvoltage applied to the lightning receiving part side of the evaluated high withstand voltage cable or the withstand voltage that is expected to have a margin for the evaluated lightning overvoltage, the withstand voltage margin is excessively increased. It can be an appropriate high-voltage cable that can withstand lightning strikes without being over-predicted.

Furthermore, the lightning receiving part that receives lightning strikes and the insulated lightning protection system that insulates the lightning current received by the lightning receiving part from the grounding electrode of the earth to the grounding electrode of the earth are evaluated as a pulling wire. By using the high withstand voltage cable, it is possible to construct an appropriate insulated lightning protection system that can withstand lightning strikes.

Although the embodiment of the present invention has been described above, this embodiment is presented as an example and is not intended to limit the scope of the invention. These novel embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. This embodiment and its modifications are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

11 ... High withstand voltage cable, 12 ... Lightning receiving part, 13 ... Ground electrode, 14 ... Insulator, 15 ... Cable conductor, 16 ... Semi-conductive layer, 17 ... Shield conductor, 18 ... Impulse device, 19 ... Changeover switch

Claims (3)

The lightning overvoltage Vcs applied to the lightning receiving part side of the high withstand voltage cable in which the cable conductor and the shield conductor are commonly grounded is calculated by the following equations (1) and (2), and the withstand voltage of the high withstand voltage cable becomes a lightning strike. A method for evaluating the withstand voltage of a high withstand voltage cable, which is characterized by evaluating that the withstand voltage can be withstood.
When 2D / v0 <tr, Vcs = Ist · Z0 · 2D / v0… (1)
When 2D / v0 ≧ tr, Vcs = Imax · Z0… (2)
However, D: high withstand voltage cable length, v0: lightning current propagation speed, tr: lightning current rise time, Ist: lightning current crest steepness, Z0: characteristics between the cable conductor and shield conductor of the high withstand voltage cable. Impedance, Imax: Peak value of lightning current. A high withstand voltage cable characterized by satisfying the withstand voltage of the high withstand voltage cable evaluated in claim 1 or the withstand voltage expected to be marginal in the evaluated withstand voltage. The reduction lead wire is described in claim 2 in an insulated lightning protection system in which a lightning receiving portion that receives a lightning strike and a pulling wire that allows a lightning current received by the lightning receiving portion to flow to a grounding electrode of the earth are insulated from a building. Insulated lightning protection system characterized by using the high withstand voltage cable of.

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