JP2017033772A - Grounding device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a grounding device capable of easily obtaining desired ground resistance.SOLUTION: A grounding device is prepared with a magnitude of ground resistance that is adjusted in accordance with a shape of an external ground electrode 21 that encloses the surroundings of an internal ground electrode 20, a shape of the internal ground electrode 20 and resistivity of a filler 23 in the case a gap between the internal ground electrode 20 and the external ground electrode 21 is filled with the filler. The device is embedded in the ground in the vicinity of a place where the ground electrodes are required. An independent ground of an apparatus installed inside of a structure 11 is connected to the internal ground electrode 20 and the external ground electrode 21 is connected to a concatenation line 22 from a steel frame or reinforcement of the structure 11, thereby easily obtaining desired ground resistance. If an adjustment of the ground resistance is required after the grounding device is fitted, it can be easily performed by adjusting the resistivity of the filler.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a grounding device for grounding independently for each facility or equipment.

In general, grounding is used for the purpose of preventing electric shock to people, preventing fire due to electric leakage, preventing high voltage from entering the low-voltage circuit due to accidents in the interior of the transformer, and grounding the system at the neutral point of the transformer's low-voltage side. There are types of construction, such as Class A grounding, Class B grounding, Class C grounding, Class D grounding, and the like. Class A grounding work is applied to metal outer boxes and lightning arresters of high voltage equipment, and Class B grounding work is applied to the low voltage side of the transformer that transforms high voltage and low voltage. Class C grounding work is applied to metal outer boxes and metal tubes of low-voltage electric machinery and equipment exceeding 300V. Class D grounding work is applied to low-voltage electric machinery and equipment, metal outer boxes and metal pipes of 300V or less. Applied.
As a grounding method, there are an independent grounding method in which a grounding work is performed independently for each facility and equipment, and a common grounding method in which a plurality of grounding works are connected to a single grounding electrode. The independent grounding method requires a sufficient separation distance to eliminate the influence of the grounding electrodes, but in reality there are also site restrictions, so Class A grounding other than Class B grounding, Class C grounding As for D-type grounding, there is a case where it is connected to a steel frame or a reinforcing bar of a structure to be grounded in common (for example, see Patent Document 1).

  On the other hand, if Class B grounding is Class A grounding, Class C grounding, Class D grounding and common grounding, a large current corresponding to a short circuit current flows in the circuit at the time of ground fault, and protection coordination with other circuits cannot be achieved. For this reason, it is required to use an independent grounding system and to have a desired grounding resistance so that a weak grounding current can be reliably detected in the event of a grounding fault. For this purpose, the number, shape and length of the grounding rods of the independent grounding electrodes are adjusted to obtain a desired grounding resistance. In addition, there is a type in which a ground conductor is spirally wound around a ground rod to obtain a desired ground resistance (see Patent Document 2).

JP 2002-271964 A JP 2008-152927 A

  However, the grounding resistance is a grounding rod obtained from a preliminary study to ensure the desired value because the resistivity in the soil is unknown or not uniform, or because it is affected by nearby structures. The number, shape and length cannot be secured, and adjustment at the construction site is often required. In particular, when the resistivity in the soil is high, it takes a lot of labor to secure a desired resistance value.

  FIG. 4 is a configuration diagram of a conventional example showing an example of a grounding device for a structure. The structure 11 is, for example, a building. In FIG. 4, the structure 11 is a three-story building, and a part of the steel frame or the reinforcing bar (hereinafter referred to as a reinforcing bar 12) of the structure 11 is placed in the soil below the ground 13. The embedded rebar 12 is used as a common grounding electrode, and a grounding rod is embedded outside the structure 11 to form an independent grounding electrode 14.

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

  If a ground fault occurs at F1 in FIG. 4, the ground fault current is, as indicated by the arrow, ground fault point F1 → outer box of load 17c (class D grounding) → ground line 16c → structure 11 Rebar 12c → underground 18 → independent grounding electrode 14 → ground wire 16x → neutral point of transformer 15 (class B grounding) → low voltage winding of transformer 15 → power supply lines 19c1, 19c2 → route of ground fault point F1 It flows in. Therefore, when the independent ground electrode 14 must be provided outside the structure, the resistance varies depending on the earth resistivity of the soil 18 outside the structure 11 and the positional relationship between the structure 11 and the independent ground electrode 14. Therefore, the adjustment of the grounding resistance is also complicated.

  An object of the present invention is to provide a grounding device capable of easily obtaining a desired grounding resistance.

  The grounding device of the present invention is connected to an internal grounding pole that is independently grounded for equipment installed inside the structure and a connecting wire from a steel frame or a reinforcing bar of the structure and surrounds the periphery of the internal grounding pole. An external grounding electrode and a filler for adjusting a grounding resistance filled between the internal grounding electrode and the external grounding electrode are provided.

  According to the present invention, the grounding resistance of this device is provided with an external grounding electrode that surrounds the periphery of the internal grounding electrode, and the external grounding electrode constitutes a structure having a sufficiently low resistance value with respect to the required grounding resistance value. Since it is connected with a connecting wire from the steel frame or reinforcing bar, the grounding resistance from infinity to the external grounding electrode can be ignored. The size of the grounding resistance of the grounding device shall be determined by adjusting the resistivity of the filler filled between the internal grounding electrode and the external grounding electrode, and adjusting the radius and length of the internal grounding electrode and the external grounding electrode. Can do. Thereby, the magnitude of the ground resistance value and the shape of the ground electrode can be planned in advance, and a desired ground resistance can be easily obtained. In addition, when it is necessary to adjust the grounding resistance after attaching the grounding device, it can be easily performed by adjusting the resistivity of the filler.

The lineblock diagram showing an example of the grounding device concerning the embodiment of the present invention. The block diagram of an example of the ground pole part of the grounding device which concerns on embodiment of this invention. Explanatory drawing of the grounding pole part in the case of calculating | requiring the resistance of the grounding apparatus which concerns on embodiment of this invention in consideration of the influence of a structure by electromagnetic field analysis. The block diagram of the prior art example which shows an example of the grounding apparatus of a structure.

  Embodiments of the present invention will be described below. FIG. 1 is a configuration diagram showing an example of a grounding device according to an embodiment of the present invention. In the embodiment of the present invention, in place of the grounding rod of the independent grounding pole 14 in the conventional example shown in FIG. 4, an independently grounded internal having a dimension set to have a desired resistance value in advance. The grounding electrode 20 is composed of an external grounding electrode 21 that surrounds the internal grounding electrode 20, and the external grounding electrode 21 is connected to a common ground by a connecting line 22, and between the internal grounding electrode 20 and the external grounding electrode 21. Is filled with a filler 23. Since other configurations are the same as those in FIG. 4, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  In FIG. 1, an internal grounding electrode 20 is a grounding electrode that independently grounds a device installed inside the structure 11, and is provided outside the structure 11. In FIG. 1, the internal grounding electrode 20 is formed in a rod shape, and the device installed inside the structure 11 is a transformer 15, and the neutral point of the class B grounded transformer 15 is represented by a grounding wire 16 x. 11 is connected to the external grounding electrode 20 outside.

  The external ground electrode 21 is provided so as to surround the internal ground electrode 20. In FIG. 1, the external grounding electrode 21 is formed in a cylindrical shape, and a rod-shaped internal grounding electrode 20 is housed in the cylinder and the side surface of the internal grounding electrode 20 is surrounded. Further, the external grounding electrode 21 is connected to the reinforcing bar 12 of the structure 11 in which the equipment installed inside the structure 11 is commonly grounded by a connecting wire 22. Thereby, the external grounding electrode 21 is maintained at the same potential as the reinforcing bar 12 of the structure 11 that is commonly grounded.

  Furthermore, a filling material 23 having a resistivity set in advance so as to have a desired resistance value is filled between the internal ground electrode 20 and the external ground electrode 21, that is, in the cylinder of the external ground electrode 21. Yes.

  Assuming that a ground fault has occurred at F1 in FIG. 1, the ground fault current is the ground fault point F1 → the outer box of the load 17c (class D grounding) → the ground line 16c → the structure 11 as indicated by the arrow. Rebar 12c → connecting wire 22 → external grounding electrode 21 → filling material 23 → internal grounding electrode 20 → grounding wire 16x → neutral point of transformer 15 (class B grounding) → low voltage winding of transformer 15 → power supply line 19c1 , 19c2 → flows along the ground fault point F1. The ground fault current flows from the reinforcing bar 12c of the structure 11 to the external grounding electrode 21 through the soil 18 in addition to the connecting wire 22, but the resistance of the connecting wire 22 is smaller than the resistance of the soil 18; Most of the ground fault current flows through the connecting line 22.

  Since the external grounding electrode 21 is connected to the reinforcing bar 12c of the common-grounded structure 11 by the connecting wire 22, the external grounding electrode 21 is maintained at the same potential as the reinforcing bar 12c of the common-grounded structure 11. Therefore, since there is no influence of a nearby structure and it is not necessary to consider the resistance of the soil 18, the internal grounding electrode and the external grounding having dimensions set in advance so as to obtain a desired resistance value. A desired grounding resistance can be easily obtained simply by attaching a grounding device made of a pole and a filler. In addition, even when the ground resistance value needs to be changed after the grounding device is attached, a desired grounding resistance can be easily obtained simply by adjusting the resistivity of the filler.

  In the above description, the internal grounding electrode 20 has been described with respect to the case where the B-grounded device is independently grounded, but instead of the B-type grounding, the A-grounding, the C-grounding, and the D-grounded device are independent. It may be a case of grounding. Moreover, although the case where the grounding device comprised by the internal grounding electrode 20 and the external grounding electrode 21 was provided in the exterior of the structure 11 was shown, you may make it provide in the structure 11 inside.

  Next, the grounding resistance of 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 ground device according to the embodiment of the present invention. As shown in FIG. 2, the lengths of the internal ground electrode 20 and the external ground electrode 21 are assumed to be l, and the internal ground electrode 20 and the external ground electrode 21 are embedded at the embedded depth t from the ground 13. Further, it is assumed that the radius of the rod-shaped internal ground electrode 20 is a, and the radius of the external ground electrode 21 is b. It is assumed that the resistivity of the filler 23 is ρ.

  Now, four kinds of grounding devices shown in Table 1 are prepared. That is, grounding devices of Condition 1, Condition 2, Condition 3, and Condition 4 were prepared. The earth resistivity ρe at the location where the internal grounding electrode 20 and the external grounding electrode 21 of the grounding devices of conditions 1, 2, 3, and 4 are installed is 100 Ωm. The resistivity ρ of condition 1 and condition 2 is 100 Ωm, which is the same as the ground resistivity ρe. In conditions 3 and 4, the resistivity ρ of the filler is 50 Ωm and 80 Ωm to compare with 100 Ωm in conditions 1 and 2. It was.

条件１、条件２、条件３及び条件４の接地装置の内部接地極２０と外部接地極２１との間の抵抗は（１）式で示す算出式から求められる。

The resistance between the internal grounding electrode 20 and the external grounding electrode 21 of the grounding device of Condition 1, Condition 2, Condition 3 and Condition 4 is obtained from the calculation formula shown by Formula (1).

R = (ρ / 2πl) · ln (b / a) (1)
Equation (1) represents the resistance value when a single grounding device in which the external grounding electrode 21 surrounding the internal grounding electrode 20 is formed into a cylindrical shape is used as an independent grounding electrode without considering the influence of the nearby structure 11. It is a formula.

  On the other hand, in the embodiment of the present invention, the external grounding electrode 21 of the grounding device and the reinforcing bar 12c of the structure 11 are connected by the connecting wire 22, and the internal grounding electrode 20 and the grounding wire 16x are connected. The resistance value of the grounding device in consideration of the influence of the structure 11 in consideration of these conditions is calculated using the FDTD (Finite-difference time-domain method) method (electromagnetic field analysis by the finite difference time domain method (hereinafter referred to as the finite difference time domain method)). It was simply obtained by electromagnetic field analysis)).

  FIG. 3 is an explanatory diagram of the grounding electrode portion when the resistance of the grounding device is obtained by considering the influence of the structure 11 by electromagnetic field analysis. FIG. FIG. 3B is an explanatory diagram in the case where the voltage between the grounding electrode 20 and the structure 11 is obtained by electromagnetic field analysis and the resistance value of the grounding device is obtained. FIG. It is explanatory drawing in the case of calculating | requiring the voltage between these by an electromagnetic field analysis, and calculating | requiring the grounding resistance value of a grounding apparatus.

  In FIG. 3A, in the circuit in which the injection line 24 is connected to the internal grounding electrode 20 and the external grounding electrode 21 and the reinforcing bar 12c of the structure 11 are connected by the connecting wire 22, the grounding in consideration of the influence of the structure 11 is considered. The resistance value of the device is obtained. A simulated current flowing at the time of occurrence of a ground fault is caused to flow from the injection line 24 in FIG. 3A, and the voltage between the injection line 24 (internal grounding electrode 20) and the structure 11 (reinforcing bar 12c) is calculated by electromagnetic field analysis. The resistance value of the grounding device was obtained. Thereby, it is possible to calculate the resistance value of the grounding device assuming B-type grounding in consideration of the influence of the structure 11.

  Similarly in FIG. 3 (b), in the same circuit as in FIG. 3 (a), a simulated current flowing from the injection line 24 at the time of the occurrence of the ground fault is caused to flow away from the injection line 24 (internal grounding electrode 20). The voltage between the reference point 25 was calculated by electromagnetic field analysis, and the ground resistance value of the grounding device was obtained. Thereby, the grounding resistance value of the grounding device which assumed the B class grounding which considered the influence of the structure 11 seen from infinity can be calculated.

  Table 2 shows the resistance value obtained from the equation (1) and the resistance value obtained by the electromagnetic field analysis of FIGS. 3 (a) and 3 (b).

表２において、条件１、条件２、条件３、条件４の（１）式の算出式から求めた抵抗値と、電磁界解析から求めた抵抗値とは、それぞれの条件において近い値になっていることがわかる。（１）式の算出式と図３の電磁界解析から求めた抵抗値の差は、外部接地極２１が構造物１１の鉄筋１２ｃに接続されているためと考えられるが、接地装置の抵抗値は（１）式で近似できることが分かる。

In Table 2, the resistance value obtained from the calculation formula (1) of Condition 1, Condition 2, Condition 3, and Condition 4 and the resistance value obtained from the electromagnetic field analysis are close to each other. I understand that. The difference between the calculated value of the equation (1) and the resistance value obtained from the electromagnetic field analysis of FIG. 3 is considered that the external grounding electrode 21 is connected to the reinforcing bar 12c of the structure 11, but the resistance value of the grounding device Can be approximated by equation (1).

  In Table 2, from the condition 1 and the condition 2 in which the radius b of the external ground electrode 21 and the length l of the ground electrode are changed, any resistance value can be obtained by changing the radius b of the external ground electrode and the length l of the ground electrode. It can be seen that can be secured.

  In Table 2, by changing the resistivity ρ of the filler 23 from Condition 1 (Condition 2), Condition 3, and Condition 4 in which the resistivity ρ of the filler 23 is changed, an arbitrary resistance value can be secured. Recognize.

  In addition, the grounding resistance value as an independent grounding electrode obtained by electromagnetic analysis in conditions 1, 2, 3, and 4 is also the grounding resistance value obtained from the calculation formula (1) and the resistance value obtained from electromagnetic field analysis. The close values in the respective conditions indicate that the value as the independent grounding pole can be obtained by using the grounding device of the embodiment of the present invention connected to the connecting wire 22 from the steel frame or the reinforcing bar of the structure 11. It will be secured.

  As described above, according to the embodiment of the present invention, the external grounding electrode 21 surrounding the internal grounding electrode 20 that is independently grounded is provided outside the structure 11, and the external grounding electrode 20 is commonly grounded. Since it is connected to the connecting wire 22 from the steel frame or the reinforcing bar and is held at the common ground potential, the voltage V between the internal ground electrode 20 of the grounding device and the structure 11 due to the ground fault current can be reduced. The ground resistance can be adjusted only by adjusting the resistivity ρ of the filler 23 filled between the internal ground electrode 20 and the external ground electrode 21. This makes it possible to easily obtain a desired ground resistance that can reliably detect a ground fault current.

  As mentioned above, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 11 ... Structure, 12 ... Reinforcing bar, 13 ... Ground, 14 ... Independent earthing pole, 15 ... Transformer, 16 ... Grounding wire, 17 ... Load, 18 ... Underground, 19 ... Power line, 20 ... Internal earthing pole, 21 ... external ground electrode, 22 ... connecting line, 23 ... filler, 24 ... injection line, 25 ... reference point at infinity

Claims (1)

An internal grounding pole that is independently grounded for equipment installed inside the structure;
An external grounding electrode connected to a connecting line from a steel frame or a reinforcing bar of the structure and surrounding the inner grounding electrode;
A filler filled between the internal ground electrode and the external ground electrode for adjusting the ground resistance;
A grounding device comprising:

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