JP6519083B2 - Grounding device - Google Patents

Description

  BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a grounding device for independently grounding equipment and equipment.

  In general, grounding is for the purpose of preventing electric shock to people etc., preventing fire due to leakage, preventing high voltage from entering the low voltage side due to a mixed accident inside the transformer, grounding the neutral point of the low voltage side of the transformer etc. The construction types include A-type grounding construction, B-type grounding construction, C-type grounding construction, and D-type grounding construction. The Class A grounding work is applied to a metal outer box for high-pressure equipment and a lightning arrester, and the Class B grounding work is applied to the low pressure side of a transformer that transforms high pressure and low pressure. Class C grounding work is applied to the metal outer box or metal tube of low voltage electric machine equipment exceeding 300 V, and Class D grounding work is applied to the low voltage electric machine equipment of 300 V or less, metal outer box and metal pipe etc. Applied.

  Grounding methods include an independent grounding method in which grounding works are performed independently for each facility or device, and a common grounding method in which a plurality of grounding works are connected to one grounding electrode and shared. In the independent grounding method, it is necessary to secure a sufficient separation distance to eliminate the mutual influence of the grounding electrodes, but there is actually a limitation on the site, so A grounding and C grounding are other than B grounding. As for D-type grounding, common ground may be connected to the steel frame or rebar of the structure. (See, for example, Patent Document 1).

  On the other hand, in order to reduce the lightning surge voltage that invades equipment and equipment, a surge protection device SPD (Surge Protective Device) (hereinafter simply referred to as SPD) is provided for each equipment and equipment, and lightning surge that invades equipment and equipment is While shunting to the ground (earth), the overvoltage applied to equipment and equipment is limited to a certain value.

Unexamined-Japanese-Patent No. 2002-271964

  However, if the steel frame and reinforcing bar of the structure are used as the common ground pole and the independent ground pole is provided outside the structure, when the lightning current flows into the steel frame and the reinforcing bar of the common ground pole, The voltage applied to the device may increase. This is because equipment and equipment connected to common ground are equipotential, but since the independent ground pole is provided outside the structure to which common ground is made, a potential difference occurs between the common ground pole and the independent ground pole. It is considered to be. Therefore, since SPD must be able to withstand large voltage and current applied to equipment and equipment when there is lightning current, SPD becomes larger.

  FIG. 6 is a configuration diagram of a conventional example showing an example of the grounding device in the case where the steel frame and the reinforcing bar of the structure are used as the common ground pole and the independent ground pole is provided outside the structure. The structure 11 is, for example, a building, and in FIG. 6, the structure 11 is a three-story building, and a part of the steel frame of the structure 11 and rebar (hereinafter referred to as rebar 12) is in the soil below the ground 13 The embedded reinforcing bar 12 is used as a common ground electrode, and a ground rod is embedded outside the structure 11 as an independent ground electrode 14.

  The neutral point of the transformer 15 installed inside the structure 11 is grounded to a B type and connected to the independent ground pole 14 outside the structure 11 by the ground wire 16x. Further, the outer box of the transformer 15 is A-type grounded and connected to the reinforcing bar 12y by the ground wire 16y. The outer box of the loads 17a, 17b, 17c is D-type grounded and connected to the reinforcing bars 12a, 12b, 12c by the ground wires 16a, 16b, 16c.

  Further, SPDs 20a1 and 20a2 for protecting the load 17a from lightning current are provided between the power supply lines 19a1 and 19a2 of the load 17a and the ground line 16a. Similarly, SPDs 20b1 and 20b2 for protecting load 17b from lightning current are provided between power supply lines 19b1 and 19b2 of load 17b and ground line 16b, and between power supply lines 19c1 and 19c2 of load 17c and ground line 16c. SPDs 20c1 and 20c2 are provided to protect the load 17c from lightning current.

  Now, it is assumed that there is a lightning strike at the top G of the structure 11 of FIG. Most of the lightning current that has flowed into the top of the head G branches from the top of the head G and flows to the shared ground electrode through the reinforcing bars 12z11, 12z12 to 12z41, 12z42 of the structure 11, as shown by the arrows.

  On the other hand, several% of the lightning current flowing into the crown portion G flows from the crown portion G → rebar 12a of the structure 11 → ground wire 16a → SPD 20a1 and 20a2 → power supply lines 19a1 and 19a2 of the load 17a. Then, the power supply lines 19c1 and 19c2 of the load 17c are shunted to the transformer 15 side and the load 17c side. The lightning strike current shunted to the transformer 15 flows from the low voltage winding of the transformer 15 to the neutral point of the transformer 15 (type B ground) to the ground wire 16 x to the independent ground pole 14. Further, the lightning strike current branched to the load 17c side flows from the SPDs 20c1 and 20c2 of the load 17c → the grounding wire 16c → the rebar 12c of the structure 11 and flows to the common grounding electrode.

  FIG. 7 is a graph showing an example of the lightning current Ig, the SPD both-end voltage Vs, and the SPD current Is when a lightning strike occurs on the top G of the structure 11 of FIG. The SPD both-ends voltage Vs appearing in the SPDs 20a1 and 20a2 of the load 17a is a voltage between the ground line 16a and the power supply lines 19a1 and 19a2 of the load 17a. In this case, the voltage Vs across the SPD is suppressed to the SPD limit voltage VL, and the waveform of the SPD current Is flowing through the SPDs 20a1 and 20a2 is similar to the lightning current Ig. The processing energy of the SPDs 20a1 and 20a2 installed in the load 17a is an integral of a value obtained by multiplying the SPD limit voltage VL of the SPDs 20a1 and 20a2 by the SPD current Is.

  Here, in the case where the reinforcing bar 12 of the structure 11 is used as a common ground pole and the independent ground pole 14 is provided outside the structure, if there is a lightning strike on the structure 11, the electric potential of the common ground pole is increased by the lightning strike. The potentials of the common ground electrode and the independent ground electrode 14 do not become equal. The SPD both-end voltage Vs is a voltage between the ground line 16a and the power supply lines 19a1 and 19a2 of the load 17a, and as described above, at the time of lightning strike, part of the lightning strike current Ig in the SPDs 20a1 and 20a2 is B of the transformer 15. It flows for a long time in a waveform similar to a lightning strike current waveform to the independent ground pole 14 via the seed ground. Therefore, when the independent ground electrode 14 is provided outside the structure, the energy which the SPDs 20a1 and 20a2 have to process for the lightning current becomes large, and the SPDs 20a1 and 20a2 become large.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a grounding device capable of reducing the energy processed by the SPD even when the independent ground pole is provided outside the structure, and achieving the miniaturization of the SPD. .

The grounding device of the present invention is a grounding device in which a steel frame or a reinforcing bar of a structure is used as a common ground pole and an independent ground pole is provided outside the structure, wherein the independent ground pole is an apparatus of the device installed inside the structure. Among them, the internal ground pole connected to the ground wire of the equipment to be independently grounded and embedded at a predetermined depth from the ground outside the structure and connected to the connection line from the steel frame or rebar of the structure And an external ground pole which is surrounded by the internal ground pole and buried at a predetermined depth from the ground and is independently grounded and maintained at the same potential as the common ground pole even when the potential is increased by a lightning strike current , Even when the potential increases due to the lightning current of the structure, the external ground pole is maintained at the same potential as the common ground pole, whereby the lightning current flowing to the internal ground pole surrounded by the external ground pole is reduced. To Ground apparatus according to symptoms.

  According to the present invention, an external ground pole surrounding the periphery of the independently grounded internal ground pole is provided outside the structure, and the external ground pole is connected to the joint line from the commonly grounded steel frame or rebar for common ground Therefore, the generated voltage and the duration time of the SPD insertion point can be reduced, and the conduction current and the conduction time of the SPD can be shortened. Therefore, the energy processed by the SPD can be reduced, and miniaturization of the SPD can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS The block diagram which shows an example of the earthing | grounding apparatus which concerns on embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS The block diagram of an example of the ground pole part of the earthing | grounding apparatus which concerns on embodiment of this invention. Explanatory drawing of the grounding pole part in the case of calculating | requiring the voltage of the SPD insertion location by the grounding pole which surrounded the internal grounding pole by the external grounding pole, and a single internal grounding pole by electromagnetic field analysis. FIG. 4 is a waveform chart of the lightning current and the voltage at the SPD insertion point with and without the external ground pole shown in FIG. 3. The graph which shows an example of the lightning strike current Ig in case a lightning strike was carried out to the crown part G of the structure of FIG. 1, the SPD both-ends voltage Vs, and the SPD electric current Is. The block diagram of the conventional example which provides the steel frame of a structure and rebar as a common ground pole, provides an independent ground pole in the exterior of a structure, and shows an example of a grounding device. FIG. 7 is a graph showing an example of a lightning strike current Ig, an SPD both-end voltage Vs, and an SPD current Is when a lightning strike occurs on the top G of the structure of FIG. 6.

  Hereinafter, embodiments of the present invention will be described. FIG. 1 is a block diagram showing an example of a grounding device according to an embodiment of the present invention. According to the embodiment of the present invention, in contrast to the conventional example shown in FIG. 6, the internal grounding pole 22 which is independently grounded instead of the grounding bar of the independent grounding pole 14 and the external grounding pole surrounding the periphery of the internal grounding pole 22. The external ground pole 23 is connected to the common ground by a connecting line 24. Since the other configuration is the same as that of FIG. 6, the same reference numerals are given to the same elements, and duplicate explanations will be omitted.

  In FIG. 1, the internal ground electrode 22 is a ground electrode for independently grounding a device installed inside the structure 11, and is provided outside the structure 11. In FIG. 1, the internal ground electrode 22 is in the form of a rod, but may be plate-like, cylindrical or the like. The device installed inside the structure 11 is a transformer 15, in which the neutral point of the B-type grounded transformer 15 is connected to the internal ground pole 22 outside the structure 11 by the ground wire 16x. Is shown.

  The external ground pole 23 is provided to surround the inner ground pole 22. In FIG. 1, the external ground electrode 23 is formed in a cylindrical shape, and a rod-like internal ground electrode 22 is accommodated in the cylinder to surround the side surface of the internal ground electrode 22. Further, the external ground pole 23 is connected to the reinforcing bar 12 of the structure 11 by a connecting line 24. As a result, the external ground electrode 23 is maintained at the same potential as the rebar 12 of the structure 11 that is commonly grounded. In FIG. 1, the external ground electrode 23 is formed in a cylindrical shape, but may be a spherical or polygonal cylinder instead of the cylindrical shape.

  Now, it is assumed that there is a lightning strike at the top G of the structure 11 of FIG. Most of the lightning current that has flowed into the top of the head G branches from the top of the head G and flows to the shared ground electrode through the reinforcing bars 12z11, 12z12 to 12z41, 12z42 of the structure 11, as shown by the arrows. In addition, a part of the current flowing to the reinforcing bar 12 c flows and disperses to the external ground pole 23 through the connecting line 24.

  On the other hand, several% of the lightning current flowing into the crown portion G flows from the crown portion G → rebar 12a of the structure 11 → ground wire 16a → SPD 20a1 and 20a2 → power supply lines 19a1 and 19a2 of the load 17a. Then, the power supply lines 19c1 and 19c2 of the load 17c are shunted to the transformer 15 side and the load 17c side. The lightning strike current shunted to the transformer 15 flows from the low voltage winding of the transformer 15 to the neutral point of the transformer 15 (type B ground) to the ground wire 16 x to the internal ground pole 22.

  Further, the lightning strike current branched to the load 17c side flows from the SPDs 20c1 and 20c2 of the load 17c → the grounding wire 16c → the rebar 12c of the structure 11 and flows to the common grounding electrode. In addition, lightning current flows from the rebar 12c of the structure 11 through the connecting line 24 to the external ground pole 23.

  Since the external ground pole 23 is connected to the rebar 12c of the structure 11 with common ground by the connecting line 24, the external ground pole 23 is maintained at the same potential as the rebar 12c of the structure 11 with common earth. That is, even if the potential of the common ground electrode rises due to a lightning strike, the potential of the external ground electrode 23 also rises in the same manner as the potential of the common ground electrode. Therefore, the lightning strike current flowing to the internal ground pole 22 surrounded by the external ground pole 23 becomes small, and the conduction time becomes short, so that the SPD can be miniaturized.

  In the above description, the case where the internal grounding electrode 22 independently grounds the apparatus to which the B ground is connected has been described. However, instead of the B ground, the A ground, the C ground, and the D ground equipment are independent. It may be the case of grounding.

  Next, the reduction of the voltage Vs0 at the SPD insertion point by the grounding device according to the embodiment of the present invention will be described. FIG. 2 is a configuration diagram of an example of a ground pole portion of the grounding device according to the embodiment of the present invention. As shown in FIG. 2, the lengths of the internal ground electrode 22 and the external ground electrode 23 are l, and the internal ground electrode 22 and the external ground electrode 23 are embedded at a position of the embedded depth t from the ground 13. Further, it is assumed that the radius of the rod-like inner ground electrode 22 is a, and the radius of the outer ground electrode 23 is b.

  Now, the grounding device of condition 1 shown in Table 1 is prepared. That is, it was set as a = 0.014 m, b = 0.3 m, l = 2.0 m, t = 0.8 m.

図３は、内部接地極２２を外部接地極２３で包囲した接地極及び単独の内部接地極２２によるＳＰＤ挿入箇所の電圧Ｖｓ０を電磁界解析のうちＦＤＴＤ（Finite-difference time-domain method）法：有限差分時間領域法による電磁界解析（以下、単に電磁界解析という）により求める場合の接地極部分の説明図であり、図３（ａ）は内部接地極２２を外部接地極２３で包囲した接地極によるＳＰＤ挿入箇所の電圧Ｖｓ０を電磁界解析により求める場合の説明図、図３（ｂ）は単独の内部接地極２２によるＳＰＤ挿入箇所の電圧Ｖｓ０を電磁界解析により求める場合の説明図である。

FIG. 3 shows the FDTD (Finite-difference time-domain method) method in the electromagnetic field analysis of the voltage Vs0 at the SPD insertion point by the ground electrode in which the internal ground electrode 22 is surrounded by the external ground electrode 23 and the single internal ground electrode 22: FIG. 3A is an explanatory view of a ground electrode portion in the case of obtaining by electromagnetic field analysis by the finite difference time domain method (hereinafter simply referred to as electromagnetic field analysis), and FIG. Explanatory drawing in the case of calculating | requiring the voltage Vs0 of the SPD insertion location by an electrode by electromagnetic field analysis, FIG.3 (b) is explanatory drawing in the case of calculating | requiring voltage Vs0 of the SPD insertion location by the single internal grounding electrode 22 by electromagnetic field analysis .

  As shown in FIG. 3 (a), a connecting wire 24 from the reinforcing bar 12 of the structure 11 is provided on the external ground pole 23 with respect to the ground pole in which the internal ground pole 22 is surrounded by the external ground pole 23. A lightning strike current (100 kA, 10/350 μs) simulating a lightning strike is applied to the top of the head G, and the current flowing through the connecting line 24 and the voltage between the internal ground pole 22 and the external ground pole 23 (voltage Vs0 at the SPD insertion point) ) Was obtained by electromagnetic field analysis in the shape of the grounding device of condition 1. The voltage Vs0 at the SPD insertion point is a voltage between the ground line 16a where the lightning strikes and the power supply lines 19a1 and 19a2 of the load 17a. In this case, the ground resistivity ρ of the location where the internal ground pole 22 and the external ground pole 23 of the grounding device of condition 1 are installed is 100 Ωm, and the distance d between the rebar 12 and the internal ground pole 22 is 5 m.

  Similarly, as shown in FIG. 3B, a lightning strike current (100 kV, 10/350 μs) simulating a lightning strike is poured into the top portion G of the structure 11 with respect to a single internal ground pole 22 to The voltage between the rebar and the internal ground electrode 22 (voltage Vs0 at the SPD insertion point) was determined by electromagnetic field analysis in the shape of the grounding device under condition 1 (with no external ground electrode).

  Fig. 4 is a waveform diagram of the lightning current and the voltage at the SPD insertion point with and without the external ground electrode shown in Fig. 3, and Fig. 4 (a) is a waveform diagram of the lightning current Ig. 4 (b) is a waveform diagram of the voltage Vs01 at the SPD insertion point in the presence of the external ground pole shown in FIG. 3 (a), and FIG. 4 (c) is the absence of the external ground pole shown in FIG. It is a wave form diagram of voltage Vs02 of the SPD insertion part in the case.

  The maximum value Vs0m1 of the voltage Vs01 at the SPD insertion point in the presence of the external ground pole is about 1.75 [kV], as can be seen from FIG. 4B, and the SPD insertion point at the absence of the external ground pole. The maximum value Vs0m2 of the voltage Vs02 is approximately 21.7 [kV], as can be seen from FIG. 4 (c).

  In addition, when the voltage Vs0 at the SPD insertion point exceeds the SPD limit voltage VL, the limit voltage generation time T1 when the SPD limit voltage VL is 1 kV is as shown in FIG. As can be seen from b), it is about 7 μsec, and the limited voltage generation time T2 without the external ground electrode is 20 μsec or more as can be seen from FIG. 4 (c). Table 2 summarizes these values.

図３（ａ）に示した外部接地極有りの本発明の実施形態の場合は、図３（ｂ）に示した外部接地極無しの従来例の場合に比較し、ＳＰＤ挿入箇所の最大電圧Ｖｓ０m１は、１．７５ｋＶであり、外部接地極無しの場合のＳＰＤ挿入箇所の最大電圧Ｖｓ０mが大幅に小さくなっていることが分かる。また、ＳＰＤの制限電圧発生時間Ｔ１は７μsecでありＳＰＤの制限電圧発生時間Ｔが大幅に短縮していることが分かる。

In the case of the embodiment of the present invention with the external ground pole shown in FIG. 3A, the maximum voltage Vs0m1 at the SPD insertion point is compared with the conventional example without the external ground pole shown in FIG. Is 1.75 kV, and it can be seen that the maximum voltage Vs0m at the SPD insertion point when there is no external ground electrode is significantly reduced. Further, it can be seen that the limit voltage generation time T1 of the SPD is 7 μsec, and the limit voltage generation time T of the SPD is significantly shortened.

  As described above, when the external ground pole 23 is provided on the internal ground pole 22, the maximum voltage Vs0m at the SPD insertion point is significantly greater in the presence of the lightning current than in the case where the external ground pole 23 is not provided. Smaller. From this, when the SPD is inserted into the SPD insertion point, when the external ground electrode 23 is provided on the internal ground electrode 22, the current flow of the SPD becomes significantly smaller than in the case where the external ground electrode 23 is not provided. In addition, the limit voltage generation time T of the SPD is also significantly reduced.

  FIG. 5 is a graph showing an example of the lightning current Ig, the SPD both-end voltage Vs, and the SPD current Is in the case where there is a lightning strike at the top G of the structure 11 of FIG. Now, assuming that there is the same lightning strike as in the case of FIG. 7, the lightning strike current Ig is the same as in the case of FIG. The magnitude of the voltage Vs across the SPD that appears in the SPDs 20a1 and 20a2 of the load 17a is the same as in FIG. 7, but the time of occurrence of the limiting voltage is significantly shorter unlike in the case of FIG. In addition, since the SPD conduction current and conduction time decrease, the energy processed by the SPD (an integral value of the SPD limit voltage VL multiplied by the current Is flowing through the SPD) decreases, so the SPD 20 can be miniaturized. It can be done.

  This is because the external ground pole 23 is connected to the steel frame 12 which is the common ground via the connecting wire 24, the external ground pole 23 has the same potential as the common ground potential, and part of the lightning current Ig is the external ground pole 23 It is thought that it is for spreading to a distant place via.

  According to the embodiment of the present invention, the external ground pole 23 surrounding the periphery of the internal ground pole 22 which is independently grounded to the outside of the structure 11 is provided, and the external ground pole 23 is a connection from the common earthed steel frame or rebar. It is connected to the line 24 and held at the common ground potential. Therefore, since the external ground pole 23 has the same potential as the common ground potential, and part of the lightning current Ig is diffused to the distant via the external ground pole 23, the voltage at the SPD insertion point is Thus, the SPD limiting voltage generation time can be shortened, and the energy processed by the SPD 20 can be reduced. Thereby, the miniaturization of the SPD 20 can be achieved.

  While the embodiments of the present invention have been described above, the embodiments are presented as examples and are not intended to limit the scope of the invention. This novel embodiment can be implemented in other various forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. This embodiment and its modifications are included in the scope and the gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 11 ... Structure, 12 ... Rebar, 13 ... Ground, 14 ... Independent ground pole, 15 ... Transformer, 16 ... Ground wire, 17 ... Load, 19 ... Power wire, 20a1-20c2 ... SPD, 22 ... Internal ground pole, 23: External ground pole, 24: Connected line

Claims (1)

In a grounding device in which a steel frame or a reinforcing bar of a structure is used as a common ground pole and an independent ground pole is provided outside the structure, the independent ground pole is
An internal grounding electrode is independently grounded embedded therein to be connected to a ground line of the equipment to be independent ground of equipment installed is outside of a predetermined from the ground depth of the structure of the structure,
The common ground pole is connected to the connecting line from the steel frame or rebar of the structure, surrounds the inner ground pole, is buried at a predetermined depth from the ground, and is independently grounded and the potential increases due to lightning current. And an external ground pole maintained at the same potential .
Even when the potential increases due to the lightning current of the structure, the external ground pole is maintained at the same potential as the common ground pole, whereby the lightning current flowing to the internal ground pole surrounded by the external ground pole is reduced. A grounding device characterized by

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