JP2008166104A - Grounding electrode, grounding electrode group, and reduction method of lightning surge voltage - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a grounding electrode capable of preventing a lightning damage due to lightning surge current by lowering further than a conventional one a grounding impedance of such as a building and various facility which is an object of lightning damage prevention. <P>SOLUTION: The grounding electrode 1 which flows lightning surge current I due to ground discharge 7 is constructed of a steel pipe 33 of which at least a part is embedded in the ground 15, a conductor 34 which is coaxially arranged in the steel pipe 33, and a filling material 40 which is filled between the steel pipe 33 and the conductor 34 and has conductivity. Thereby, the lightning surge current I flowing in the ground electrode 1 is shunted and its low frequency component I<SB>L</SB>flows in the conductor 34, and its high frequency component I<SB>H</SB>is made to flow in the steel pipe 33 and the filling material outside of the conductor 34. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a ground electrode, a ground electrode group, and a lightning surge voltage reduction method for preventing lightning damage by flowing a lightning surge current caused by a lightning strike to the ground.

  If a lightning surge current with high output flows through various facilities such as buildings, traffic lights, or trees due to a lightning strike, these will be destroyed. In the power transmission system, reverse flashing may occur and the power equipment may suffer lightning disasters. In recent years, electronic devices that are particularly vulnerable to electrical shocks have increased, and lightning damage has become a serious threat. In order to prevent such lightning damage, a conductor (usually also called a lightning rod, including a lightning rod, a lightning conductor, etc.) having a path through which a lightning surge current caused by a lightning strike flows to the ground side is used.

  In general, one end of the conductor is connected to a lightning arrester and is disposed on the top of a building or various facilities that are to be subjected to lightning damage so as to receive lightning strikes. The other end is connected to a ground electrode embedded in the ground. As a result, the lightning surge current is caused to flow in the order of the lightning conductor, the ground electrode, and the ground, and the damage is prevented by making a detour from the building or the like that is the object of lightning damage prevention. In the grounding work, for example, the grounding resistance (generally referred to as grounding impedance) in class A grounding is 10Ω or less. Usually, the ground impedance is represented by an equivalent circuit consisting of resistance, inductance, and capacitance. The resistance is mainly the contact resistance of the ground electrode with the ground as well as the ground resistance, the inductance is the inductance of the ground electrode, and the capacitance is the capacitance between the ground electrode and the ground. In the above-described equivalent circuit, the inductance and the resistance are configured in series connection, and the resistance and the capacitance are configured in parallel connection.

  In the ground impedance represented by this equivalent circuit, it should be noted that the voltage applied to the series circuit of the inductance and the resistance varies depending on the frequency component of the flowing current. That is, in the case of direct current, commercial frequency current of 50 Hz, and 60 Hz, most of the circuit voltage is a component added to the resistor. On the other hand, the frequency component of the current becomes wider, and the voltage of the inductance component becomes significant, and the circuit voltage becomes a value in which the resistance component and the inductance component are superimposed. Therefore, the reason why a high voltage corresponding to the resistance value or more is generated at the ground electrode when a lightning surge current flows through the ground electrode is due to this reason.

  The present invention is a technique for apparently reducing the above-described inductance. As a result, the potential increase of the ground electrode due to the lightning surge current can be suppressed. In the conventional grounding work, measures such as [1] further lowering the resistance or [2] lowering the grounding impedance are taken from the viewpoint of suppressing the potential increase of the grounding electrode against the lightning surge current. However, these constructions require very large costs and days. Further, the reduction in resistance in the above [1] does not necessarily lead to a reduction in ground impedance, and is not cost effective. In the above [2], there is a problem that this is also not cost effective, such as requiring additional construction and measurement many times until a desired value is obtained.

  Now, if the resistance is 10Ω, the inductance is 10 μH, and the lightning surge current is 100 kA and 100 kA / μs, the grounding impedance is 10 (Ω) × An increase in potential of 100 (kA) +100 (kA / μs) × 10 (μH) = 1000 (kV) +1000 (kV) = 2000 (kV) occurs. Reducing the inductance component voltage as much as possible is extremely effective in preventing dielectric breakdown of electrical equipment directly connected to the ground electrode or indirectly.

  If the potential rise of the ground electrode caused by a lightning surge current is large, the contact voltage and the stride voltage become high, and nearby residents and animals may get an electric shock, which is dangerous. In addition, when two ground electrodes are grounded close to each other, if the lightning surge current flows directly to the first, the electrical equipment connected to the ground electrode is also shunted by the lightning surge current. There are many disasters. This is one of the typical lightning disasters in home appliances.

  The present invention has been made in view of the above problems, and by reducing the ground impedance of a building or various equipment that is a target of lightning damage prevention, in particular, the above-described inductance lower than the value inherent to the conductor, the lightning surge current It is an object of the present invention to provide a ground electrode, a ground electrode group, and a lightning surge voltage reduction method capable of preventing lightning damage caused by the above and improving cost effectiveness.

  In order to solve the above problems, according to the present invention, a grounding electrode for flowing a lightning surge current caused by a lightning strike as well as a ground-fault current of a commercial frequency to the ground, at least a part of which is a tubular conductor embedded in the ground, An inner conductor coaxially disposed in the tubular conductor, and a conductive filler filled between the tubular conductor and the inner conductor, and a lightning surge current caused by the lightning strike is shunted, A ground electrode is provided, characterized in that a low frequency component flows mainly through the inner conductor and a high frequency component flows mainly through the tubular conductor and the filler.

  The present invention is a ground electrode having an effect of reducing the ground impedance. In particular, the ground electrode has a structure that reduces the inductance inherent to the ground electrode. Therefore, it has a function of suppressing an increase in ground voltage when a current flows not only against a ground fault current at a commercial frequency but also against a lightning surge current. In particular, while the work for reducing ground impedance is conventionally cut and try, the present invention is excellent in cost effectiveness including shortening the number of days because it requires only work to be provided on site. Moreover, since the inner conductor (center conductor) is electromagnetically shielded by the outer steel pipe as a tubular conductor in the ground electrode of the coaxial structure of the present invention, the ratio of the shunt surge is extremely small. The lightning disaster of electrical equipment is reduced by the effect of reducing the shunt current.

  In the ground electrode, the filler may contain one or more materials selected from the group consisting of a resistor, a dielectric, and a magnetic material.

  In the ground electrode, the tubular conductor and the inner conductor may be grounded after being terminated by a coaxial characteristic impedance.

  The ground electrode may be connected to a lightning arrester that sends a lightning surge current caused by a lightning strike to the ground side.

  The ground electrode may be formed in a coaxial shape integrated with the lightning arrester.

  The ground electrode may be connected to a grounding device that causes a ground fault current of a commercial frequency power facility or power facility to flow to the ground side.

  In the ground electrode, the tubular conductor may be embedded with the axial direction as a vertical direction.

  In the ground electrode, the tubular conductor may be embedded with the axial direction as a horizontal direction.

  In the ground electrode, the tubular conductor and the inner conductor may be connected to an equipotential bonding conductor.

  According to the present invention, there is provided a ground electrode group comprising a plurality of the ground electrodes.

  In addition, according to the present invention, there is provided a method for reducing a lightning surge voltage when a lightning surge current caused by a lightning strike flows to the ground, wherein the first current path is provided so that one end thereof is disposed in the ground. Providing a second current path whose impedance to the high frequency component of the lightning surge current is lower than that of the first current path, wherein the low frequency component of the lightning surge current mainly flows in the first current path, and the high frequency component is A method of reducing a lightning surge voltage, characterized in that the lightning surge voltage in the first current path is reduced by diverting the lightning surge current according to a frequency component so as to mainly flow in the second current path. Provided. Also, it functions as a conventional ground electrode in the same manner as in the past.

  In the lightning surge voltage reduction method, the first current path is configured by an inner conductor, and the second current path is coaxially disposed so as to cover an outer periphery of the inner conductor, and the tubular You may be comprised with the filler which has the electroconductivity with which it filled between the conductor and the said internal conductor.

  In the lightning surge voltage reducing method, the filler may contain one or more materials selected from the group consisting of a resistor, a dielectric, and a magnetic material.

  In the lightning surge voltage reducing method, an outer skin may be provided on the outer periphery of the coaxially arranged tubular conductor. As the outer skin, for example, concrete or the like can be used to take measures against corrosion of the steel pipe when buried.

  According to the present invention, it is possible to effectively suppress an increase in the potential of the ground electrode against a lightning surge current, and to realize a ground impedance that is much lower than that of the prior art. As a result, a lightning surge current can surely flow to the ground via the ground electrode, and an unexpected situation such as destruction of electronic equipment by flowing to the building side can be prevented. In addition, even if lightning surge current that has flowed to the ground flows to other facilities in the surrounding area, other adjacent grounding electrodes, surrounding people, etc. via the ground, the lightning surge voltage at the grounding electrode is very low. Because it is a value, the damage can be minimized and made safer.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the present specification and drawings, elements having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a configuration diagram showing an example in which the ground electrode 1 according to the first embodiment of the present invention is applied to a building 5 as a lightning damage prevention target. As shown in FIG. 1, on a roof of a building 5, a lightning arrester 10 as a lightning arrester is installed in a vertical direction as a lightning arrester that sends a lightning surge current caused by a lightning strike 7 to the ground side. A pull-down conducting wire 13 is connected to the lower end of the lightning arrester needle 10 so that the lightning surge current of the lightning 7 that has fallen to the upper end can flow through the conducting wire 13. The conducting wire 13 extends downward along the outer surface of the building 5, is introduced into the building 5 at a position lower than the ground 15, and is connected to a grounding portion 17 provided inside the building 5. The grounding portion 17 may be made of metal or the like disposed over the entire bottom portion in the building 5.

  As shown in FIG. 1, the ground portion 17 is connected to the ground electrode 1 and the equipotential bonding conductor 20. The potential equipotential bonding conductor 20 is connected to an electronic device 25 such as a personal computer or a metal pipe 26 such as a water pipe. In the present embodiment, the electronic device 25 is connected to an external power source 27. The equipotential bonding conductor 20 is, for example, a metal plate provided so as to hold the connected electronic device 25, the metal tube 26, and the like at an equipotential. Thereby, even if a lightning surge current due to the lightning strike 7 flows, a potential difference does not occur between the devices 25 and 26, so that lightning damage can be prevented.

  FIG. 2 is a vertical sectional view of the ground electrode 1. FIG. 3 is an enlarged cross-sectional view taken along the line XX of FIG. As shown in FIGS. 2 and 3, the ground electrode 1 has a configuration in which a bare conductor 34 is coaxially disposed inside an annular steel pipe 33 embedded in the ground 15 in the vertical direction. The steel pipe 33 as a tubular conductor is made of, for example, stainless steel or a corrosion-resistant steel pipe. The conductor 34 as an internal conductor is made of, for example, copper or the like, and is disposed in the steel pipe 33 from the upper end side to the lower end side along the axial direction. The upper end of the conductor 34 is disposed so as to slightly protrude outside the upper end of the steel pipe 33 and is connected to the grounding portion 17. In some cases, the conductor 34 is fixed at a central position in the steel pipe 33 by a plurality of insulating fixing devices 35 provided at predetermined intervals along the axial direction of the steel pipe 33.

  As shown in FIG. 3, a conductive filler 40 is filled between the steel pipe 33 and the conductor 34. In the present embodiment, as the filler 40, for example, cement in which the materials of the resistor 45, the dielectric 46, and the magnetic body 47 are mixed at a predetermined ratio is used. As the resistor 45, for example, metal fine powder (silver powder, copper powder, etc.) or graphite is used. As the dielectric 46, a material having a relatively high dielectric constant (for example, aluminum oxide, barium titanate, etc.) is used. Furthermore, as the magnetic body 47, for example, ferrite or the like is used. In addition, it is preferable that the cement as the filler 40 is reduced in weight, for example, by forming in a foamed shape.

  FIG. 4 is an enlarged perspective view of the ground electrode 1 in the vicinity of the ground 15. As shown in FIGS. 1, 2, and 4, the steel pipe 33 is embedded in the ground 15 substantially along the entire length in the axial direction, and its upper end protrudes from the ground 15. The matching unit 51 is configured to terminate the lower ends of the steel pipe 33 and the conductor 34 by a coaxial characteristic impedance formed by both of them (33, 34). In the present embodiment, a columnar concrete material is used as the matching unit 51, which is arranged in parallel and concentric with the steel pipe 33 in the axial direction.

  A lightning surge voltage reduction method according to the first embodiment of the present invention, which is performed by the ground electrode 1 configured as described above, will be described.

  As shown in FIG. 1, when lightning 7 is generated and lightning strikes the upper end of a lightning arrester 10 that is a lightning arrester, a lightning surge current I flows down from the lower end of the lightning arrester 10 to the conducting wire 13, and then from the conducting wire 13 to the ground electrode 1 flows. This lightning surge current I includes many frequency components. The lightning surge current I flowing to the ground electrode 1 flows from the upper end side to the lower end side along the axial direction of the conductor 34 of the ground electrode 1 in FIG. Around the conductor 34, a steel pipe 33 coaxially disposed so as to cover the outer periphery of the conductor 34 is arranged, and between the conductor 34 and the steel pipe 33, a conductive filler 40 is filled. Therefore, the lightning surge current I attenuates when flowing through the conductor 34. This phenomenon will be described below with reference to the circuit diagram shown in FIG.

  FIG. 5 shows a ground electrode according to the first embodiment of the present invention constituted by the steel pipe 33, the conductor 34 and the filler 40 when the lightning surge current I passed from the upper end side of the conductor 34 flows to the ground side. FIG. 4 is a circuit diagram showing an equivalent circuit per unit length. In FIG. 5, L is the inductance of the conductor 34, R is the resistance of the conductor 34, and C is the capacitance between the conductor 34 and the steel pipe 33. G is a conductance caused by the filler 40 containing the resistor 45, the dielectric 46, and the magnetic body 47.

When lightning surge current I flows through the conductor 34, as shown in FIG. 5, the current I _H mainly high-frequency components of the lightning surge current I, the outside of the filling material 40 and steel pipe 33 of the conductor 34 (i.e. , It tends to flow from point A1 to point B2 in FIG. Therefore, lightning surge current flowing through the conductor 34 is I _L composed mainly of low frequency components obtained by subtracting the I _H from lightning surge current I. Thus, the grounding electrode 1 according to the first embodiment of the present invention, the lightning surge current I lightning 7 and the low-frequency components I _L, it is diverted to the high frequency component I _H, the low-frequency components I _L is predominantly the conductors 34 of the first current path flows, the high frequency component I _H is configured, primarily through the steel pipe 33 and filler 40 as the second current path.

The approximate lightning surge voltage V _L generated when the attenuated lightning surge current I (that is, the low frequency component I _L of the lightning surge current I) flows through the conductor 34 is V _L = L × dI _L / dt. The lightning surge voltage V _L is a lightning surge voltage V _{L + H} = L × {d (I _L that is generated when a lightning surge current I (= I _L + I _H ) flows through the conductor 34 as in a conventionally known ground electrode. + I _H ) / dt}.

On the other hand, when the high-frequency component I _H of the lightning surge current I flows through the steel pipe 33 and the filler 40 outside the conductor 34, resistance heating is mainly performed by the resistor 35, the dielectric 36 and the magnetic substance 37 contained in the filler 40. , Dielectric heating, and induction heating occur, and part of the energy is consumed.

A low frequency component I _L lightning surge current I flowing through the conductor 34, mainly in the high-frequency component I _H of the lightning surge current I flowing through the filler 40 and the steel pipe 33, earth flows to the lower side along the axial direction When reaching a position lower than 15, as shown in FIG. 4, it flows out to the ground 15 through the matching unit 51, and a part thereof flows out to the ground 15 from a portion in contact with the steel pipe 33.

According to the above embodiment, the ground electrode 1 is configured as a coaxial cable in which the conductor 34 is arranged at the center of the steel pipe 33, and the conductive filler 40 is filled between the steel pipe 33 and the conductor 34. it allows diverted when lightning surge current I flows through the conductor 34, the low-frequency components I _L flows mainly conductor 34 as a first current path, and the periphery of the high frequency component I _H mainly conductor 34 The second current path provided can be made to flow. As a result, the amount of current flowing through the conductor 34 can be reduced and the lightning surge voltage (L × di / dt) generated in the conductor 34 can be reduced as compared with the case of a conventionally known ground electrode in which almost all the lightning surge current I flows through the conductor 34. Therefore, it is possible to reduce the ground impedance to a value lower than the conventional value. As a result, the diversion amount flowing to the building side is reduced, and as a result, the situation such as destruction of electrically connected electronic devices is reduced.

  Further, by reducing the lightning surge voltage caused by the ground electrode 1 as described above, the lightning surge current passed through the ground 15 via the ground electrode 1 minimizes the damage to surrounding buildings and people. It becomes possible. Hereinafter, the effect is demonstrated using the example shown in FIG.6 and FIG.7.

  In the example shown in FIG. 6A, another building 55 exists near the building 5 provided with the ground electrode 1. As shown in FIG. 6A, the other building 55 includes an electronic device 65 and the like connected to an external power source 67, for example. The other building 55 is grounded by a conventionally known ground electrode 61 embedded in the ground 15. The ground electrode 61 is connected to the electronic device 65 through the conductive wire 60. FIG. 6B shows a lightning surge in the ground 15 when a lightning surge current I flows from the ground electrode 1 to the ground 15 when a lightning 7 falls on the building 5 shown in FIG. It is the graph which showed the value of the voltage with the position in the ground 15. In FIG. 6B, the vertical axis represents the value of the lightning surge voltage, and the horizontal axis represents the position (namely, distance) on the ground 15. The positional relationship in the horizontal direction in FIG. 6A corresponds to the distance indicated by the horizontal axis in FIG. When the building 5 shown in FIG. 6A includes a conventionally known ground electrode instead of the ground electrode 1, the relationship between the lightning surge voltage and the distance is as shown by the dotted line in FIG. 6B. .

As shown in FIG. 6 (b), when a conventionally known ground electrode is used, the initial value of the lightning surge current voltage (lightning surge voltage) when flowing to the ground 15 is U _E0 , but infinite. When the ground electrode 1 of the present invention is used with the far-point potential set to zero, the value of the lightning surge voltage that flows to the ground 15 is greatly reduced, and the initial value of the lightning surge voltage immediately after flowing to the ground 15 Is U _E1 . Generally, the lightning surge voltage gradually attenuates as it travels to a position (distance) farther away from the point where the light is passed to the ground 15, but when a conventionally known ground electrode is used for the building 5, The lightning surge voltage at the point D of the adjacent ground electrode 61 still has a very high value U _D0 , and the electronic device 65 is damaged by this high voltage. On the other hand, when the ground electrode 1 according to the present invention is used, the lightning surge voltage at the point D of the adjacent ground electrode 61 becomes a sufficiently low value _UD1 , and damage to the electronic device 65 is avoided. As described above, according to the present invention, it is possible to reduce or harm the damage caused by the lightning surge voltage on the adjacent ground electrode 61.

On the other hand, when the conventionally known ground electrode 61 is used as the ground electrode of the building 5 instead of the ground electrode 1 of the present invention, as shown by a dotted line in FIG. Although the initial value of the current voltage (lightning surge voltage) is U _E0 , if the ground electrode 1 of the present invention is used as the adjacent ground electrode, the ground electrode 15 is in direct contact with the ground electrode 15 as conventionally known. Since the steel pipe portion 33 serves as an electromagnetic shield for the central conductor 34 because the steel pipe portion 33 is not the conductor but the central conductor 34, intrusion of lightning surge current into the central conductor 34 is suppressed. . Further, since the current of the low frequency component selectively flows through the center conductor 34 due to its property, the current surge voltage is greatly reduced.

  Next, it will be described with reference to FIG. 7 that the damage to the surrounding people is minimized. In the example shown in FIG. 7A, a pedestrian 70 walking near the building 5 provided with the ground electrode 1 is shown. FIG. 7B shows a lightning surge voltage in the ground 15 when the lightning surge current I flows from the ground electrode 1 to the ground 15 when the lightning 7 falls on the building 5 shown in FIG. It is the graph which showed the value of with the position in the earth 15. In FIG. 7B, the vertical axis represents the value of the lightning surge voltage, and the horizontal axis represents the position (that is, the distance) on the ground 15. The positional relationship in the horizontal direction in FIG. 7A corresponds to the distance indicated by the horizontal axis in FIG. When the building 5 shown in FIG. 7A includes a conventionally known ground electrode instead of the ground electrode 1, the relationship between the lightning surge voltage and the distance is as shown by the dotted line in FIG. 7B. Become.

As shown in FIGS. 7A and 7B, when a conventionally known ground electrode is used, the initial value of the lightning surge current voltage (lightning surge voltage) when flowing to the ground 15 is U _E0. On the other hand, when the ground electrode 1 of the present invention is used, the value of the lightning surge voltage flowing to the ground 15 is greatly reduced, and the initial value of the lightning surge voltage immediately after flowing to the ground 15 is U _E1. It has become. Thus, the lightning surge voltage gradient (solid line in FIG. 7B) when the ground electrode 1 of the present invention is used is the lightning surge voltage gradient (FIG. 7B) when the conventionally known ground electrode is used. ) Dotted line)).

As shown in FIG. 7 (a), since both feet of the pedestrian 70 are in contact with the ground 15 at different positions L1 and L2, a lightning surge current flowing from the contact electrode 1 to the ground 15 is generated by the pedestrian 70. When the current flows to the ground 15 immediately below, a lightning surge voltage (referred to as a stride voltage) corresponding to the potential difference between both feet is applied to the pedestrian 70. However, when the ground electrode 1 of the present invention is used, the gradient of the lightning surge voltage is moderated as described above, so that the potential difference between the position L1 of one foot and the position L2 of the other foot. It is reduced to a significantly lower value of the potential difference U _S0 when using a U _S1, the conventional ground electrode. Thus, according to the present invention, even when a lightning surge current flows through the pedestrian 70, the damage can be effectively reduced.

  In the above-described example, the electric shock due to the lightning surge current of the pedestrian 70 has been described. However, as shown in FIG. 7A, the contact person 71 is in direct contact with the building 5 by using the ground electrode 1 of the present invention. The electric shock damage can be effectively reduced or made harmless.

For example, as shown by a dotted line in FIG. 7B, when a conventionally known ground electrode is used, a lightning surge voltage (referred to as a contact voltage) received when the contact person 71 receives an electric shock is This is a potential difference U _T0 between the position W and the position L0 of the contact person 71, which is significantly larger than the potential difference U _{S0 received} by the pedestrian 70 described above. However, when the ground electrode 1 of the present invention is used, as shown by the solid line in FIG. 7B, the lightning surge voltage is sufficiently reduced and the degree of attenuation is moderate, so that the contact person 71 is electrocuted. potential difference U _T1 applied when is in a very low value. As described above, according to the present invention, even when a lightning surge current flows, it is possible to effectively reduce the electric shock damage of the contact person 71.

  Furthermore, as described above, the ground electrode 1 having a coaxial structure can basically greatly reduce the inductance component of the conventional ground electrode, thereby reducing the value of the ground impedance. Among the ground impedances, there is an advantage that the value of the reactance component does not depend on a normal soil environment (for example, resistivity) in which the ground electrode 1 is installed. Further, when the ground electrode 1 is installed in the building 5 or the like that is the object of lightning damage prevention, the manufactured ground electrode 1 is transported to the site where the installation location (for example, the building 5 or the like) is located, and the hole is formed along the vertical direction. After excavation, the ground electrode 1 can be inserted and fixed in this hole, and the construction can be facilitated.

  Furthermore, since the ground electrode 1 has a coaxial structure as described above, the steel pipe 33 of the ground electrode 1 can shield current from outside and protect the conductor 34. Thereby, the situation where the induced lightning surge current flows into the conductor 34 from the ground 15 can be prevented. Further, for example, when another ground electrode is provided adjacent to the ground electrode 1, the lightning surge current flowing from the other adjacent ground electrode to the ground 15 flows into the center conductor 34 of the ground electrode 1. The amount can be reduced.

  As a second embodiment of the present invention, as shown in FIG. 8, a plurality of ground electrodes 1 having different characteristic impedances may be connected to each other to form a ground electrode group 2. FIG. 8 is a cross-sectional view showing a vertical cross section of a ground electrode group 2 having three ground electrodes 1 as an example. In the example of the ground electrode group 2 shown in FIG. 8, all three ground electrodes 1 are embedded in the ground 15 at substantially equal intervals with each other with the tube axis direction of the steel pipe 33 as a tubular conductor set in the vertical direction. As shown in FIG. 8, the conductors 34 of the three ground electrodes 1 are connected to each other outside the steel pipes 33 to become one. The conductors 34 joined together in this way are connected to the lightning arrester 10 provided at the upper part of the building 5 via, for example, the grounding part 17 shown in FIG.

  According to the second embodiment of the present invention, since the plurality of ground electrodes 1 are used, each ground electrode 1 can be made smaller than the conventional one. Thereby, conveyance and construction of each ground electrode 1 are greatly facilitated. Note that the second embodiment also has the same effect as the first embodiment.

  As a third embodiment of the present invention, as shown in FIG. 9, when a plurality of ground electrodes 1 having different characteristic impedances are installed, the tube axis direction may be horizontal and embedded in the ground 15. FIG. 9 is a cross-sectional view showing a horizontal cross section of a ground electrode group 2 having four ground electrodes 1 as an example. In the example of the ground electrode group 2 shown in FIG. 9, the four ground electrodes 1 are all arranged in the same horizontal plane with the tube axis direction of the steel pipe 33 as a tubular conductor being the horizontal direction. The four ground electrodes 1 are radially arranged so that the tube axis directions thereof are perpendicular to each other. Each ground electrode 1 is arranged with the end portion on the side where the conductor 34 as an internal conductor extends outside the steel pipe 33 facing the center of radiation. In the third embodiment of the present invention, a hollow space 80 is provided at the center of the radial ground electrode group 2, and the conductors 34 of the four ground electrodes 1 are connected to each other in the space 80. It is connected. The conductors 34 joined together in this way are extended upward along the vertical direction, and are connected to a lightning arrester 10 provided at the upper part of the building 5 via, for example, the grounding part 17 shown in FIG. .

  According to the third embodiment of the present invention, by arranging the tube axis direction of the steel pipe 33 of the ground electrode 1 horizontally, holes formed in, for example, the ground 15 when the ground electrode 1 is embedded have the same depth. Its construction is facilitated, such as better. Further, when a plurality of ground electrodes 1 are connected to form the ground electrode group 2, the ends of the ground electrodes 1 on the side where the lightning surge current flows can be arranged away from each other, It becomes possible to reduce the influence. Note that the third embodiment has the same effect as that of the first embodiment.

  As a fourth embodiment of the present invention, as shown in FIG. 10, the lightning arrester 10 and the ground electrode 1 for flowing a lightning surge current due to a lightning strike 7 to the ground side may be formed in an integrated coaxial shape. FIG. 10 is a vertical sectional view of an upright lightning rod 85 as an example in which the lightning arrester 10 and the ground electrode 1 are formed in an integrated coaxial shape. In the example shown in FIG. 10, the lightning rod 85 is erected independently, and has a protruding needle 86 at the upper end. Note that the lightning arrester and the ground electrode may be integrated and provided in an existing facility or the like. For example, if this configuration is used by connecting to the overhead ground wire of the power transmission line and connecting the upper end of the ground electrode to the overhead ground wire, an increase in the lightning surge voltage of the overhead ground wire can be reduced.

  According to the fourth embodiment of the present invention, since the lightning surge current due to the lightning strike 7 flows through the coaxial lightning arrester 10 before reaching the ground electrode 1, the potential increase of the lightning surge current is more effectively suppressed. The ground impedance can be greatly reduced. Further, in all routes (that is, a route flowing in the atmosphere above the ground 15 and a route in the ground 15) until the lightning surge current flows from the lightning arrester 10 to the ground 15 through the matching device 51. The occurrence of discharge such as flashover due to lightning surge current can be prevented. Furthermore, it is possible to prevent a current from flowing into this path from the outside. Note that the fourth embodiment has the same effect as that of the first embodiment.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, this invention is not limited to the example which concerns. It is obvious for those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea described in the claims, and of course, the technical scope of the present invention is also possible. It is understood that it belongs to.

  In the embodiment described above, the case where the steel pipe 33 made of, for example, stainless steel or a corrosion-resistant steel pipe is used as the tubular conductor has been described, but a tubular conductor formed of other materials may be used.

  In the above-described embodiment, the case where cement in which all of the resistor 45, the dielectric 46, and the magnetic body 47 are mixed at a predetermined ratio has been described as the filler 40. Any material having electrical conductivity may be used. Further, the filler 40 may contain one or more materials selected from the group consisting of the resistor 45, the dielectric 46, and the magnetic body 47. Furthermore, materials other than the resistor 45, the dielectric 46, and the magnetic body 47 may be included.

  In the embodiment described above, the case where the resistor 45 is a metal fine powder (silver powder, copper powder, or the like) or graphite has been described, but other materials may be used as the resistor 45.

  In the embodiment described above, the case where the dielectric 46 is aluminum oxide or barium titanate has been described. However, other materials may be used as the dielectric 46.

  In the above-described embodiment, the case where the magnetic body 47 is ferrite has been described, but a material other than these may be used as the magnetic body 47.

  In the embodiment described above, a case has been described in which a cylindrical concrete material arranged axially parallel to and concentric with the steel pipe 33 is used as the matching unit 51. However, the matching unit 51 uses impedance matching. Any material and shape may be used.

  In the above-described embodiment, the case where the ground electrode 1 of the present invention is used alone has been described. However, for example, it may be used in combination with a conventionally known ground electrode such as a mesh ground electrode. There is an effect of reducing the ground impedance.

  In the above-described embodiment, the case where the ground electrode group 2 has three or four ground electrodes 1 has been described, but an arbitrary number of ground electrodes 1 may be included. Further, the plurality of ground electrodes 1 included in the ground electrode group 2 may have any arrangement configuration.

  In the above-described embodiment (fourth embodiment), the case where the lightning arrester 10 and the ground electrode 1 are formed in an integral coaxial shape has been described, but the coaxial lightning arrester 10 and the coaxial grounding are described. For example, a bellows-shaped coaxial or non-coaxial intermediate portion may be provided between the electrode 1 and the lightning arrester 10 and the ground electrode 1 may be connected via the intermediate portion.

  In the above-described embodiment, the case where the ground electrode 1 exerts an effect on the lightning surge current caused by the lightning strike 7 has been described. However, the ground electrode 1 is used when, for example, the electric device 25 illustrated in FIG. However, it is possible to exhibit the same effect as the lightning surge current against the commercial frequency leakage current.

  In the above-described embodiment, the case where the ground electrode 1 is directly embedded in the ground 15 has been described. However, an outer skin such as cement may be provided on the outer periphery of the ground electrode 1. By providing the outer skin on the outer periphery of the steel pipe 33 in this way, it is possible to take measures against corrosion of the steel pipe 33 when the ground electrode 1 is embedded.

  In general, the main frequency component of the lightning surge current is considered to be 10 KHz to 1 MHz, and by performing a trial calculation that applies a general transmission equation to the ground electrode 1 according to the embodiment of the present invention shown in FIG. The effectiveness is verified from the analysis by the sinusoidal steady current method.

  As described above, the ground electrode 1 according to the present invention can be regarded as an equivalent circuit of the lossy line shown in FIG. 5, and therefore, a trial calculation is performed by applying a known general formula below. In the equivalent circuit of the lossy line shown in FIG. 5, when the resistance R and the conductance G are set to 0, it corresponds to the equivalent circuit of the lossless line.

In general, as shown in FIG. 11, the coaxial cable 95 in which the outer diameter of the inner conductor 91 is a and the inner diameter of the outer conductor 92 is b is such that the inner conductor 91 and the outer conductor 92 are air-insulated. When a current of frequency f (Hz) is passed, inductance L (μH / m), capacitance C (pF / m) and resistance R (Ω / m) per unit length of the coaxial cable 95, and It is known that the impedance Z ₀ (Ω) can be obtained by the following formulas (1) to (4).
L = 0.2 × ln (b / a) (1)
C = (55.6 × ε _S ) / {ln (b / a)} (2)
R = {4.15 × 10 ⁻⁸ × (a + b) × √f} / (a × b) (3)
Z ₀ = 60 × ln (b / a) (4)
In the above equation (2), ε _S is a dielectric constant.

11 is filled with polyethylene instead of air between the inner conductor 91 and the outer conductor 92 of the coaxial cable 95 shown in FIG. 11, and a current of frequency f = 3 × 10 ⁹ (Hz) is passed through the coaxial cable 95. It is known that the conductance G (S / m) of the coaxial cable 95 is obtained by the following equation (5).
G = (7.35 × 10 ⁻¹⁰ ) / {ln (b / a)} (5)

However, in the present invention, the conductivity of the filler 40 between the conductor 34 of the ground electrode 1 and the steel pipe 33 is dominant, so the conductance G of the ground electrode 1 is the conductivity σ (S / M) is suitably obtained by the following formula (6).
G = (σ × 2π) / {ln (b / a)} (6)

  Table 1 shows the calculation based on the above equation (6) for the case where substances having various electrical conductivity σ (S / m) are used as the filler 40 (containing the resistor 45, the dielectric 46 and the magnetic body 47). Each value of the conductance G (S / m) of the ground electrode 1 is shown. In Table 1, the outer diameter of the inner conductor 91 is a = 10 (mm), and the inner diameter of the outer conductor 92 is b = 1000 (mm).

Now, in the equivalent circuit shown in FIG. 5, γ represented by the following formula (7) is generally called a propagation coefficient.
γ = √ {(R + jωL) × (G + jωC)} (7)
Note that ω (rad / s) is an angular frequency of the current flowing through the equivalent circuit, and ω = 2πf. here,
γ = α + jβ (8)
And α, β are set, the ratio of the voltage component of the inner conductor 91 to the outer conductor 92 when the current flows through the equivalent circuit shown in FIG. It has been.
| {V (x) / v (x + l)} | = e ^αl (9)
However, assuming that the current flows through the equivalent circuit from position x to position (x + l) by l (m), the voltage component value at position x is v (x), and the voltage component value at position (x + l) is v (x + l). ). Thereby, the attenuation rate D (dB) is obtained by the following formula (10).
D = 20 × log ₁₀ e ^αl
= (Αl) × 20 × log ₁₀ e
= 8.686 × (αl) (10)

  Accordingly, the values of L, C, R and G obtained from the above equations (1) to (3) and (6) are substituted into the above equation (7), the value of the propagation coefficient γ is calculated, When the value of α is calculated using Expression (8), the attenuation factor D (dB) of the voltage component of the lightning surge current flowing through the conductor 34 of the ground electrode 1 can be obtained from the above Expression (10). In the above equation (10), the voltage component is targeted, but the same applies to the current decay rate.

The trial calculation here assumes that the outer diameter of the conductor 34 of the ground electrode 1 shown in FIG. 2 is 10 (mm) and the inner diameter of the steel pipe 33 is 1000 (mm). Therefore, by applying a = 10 and b = 1000 to the above equations (1) and (2), the inductance L and the capacitance C of the ground electrode 1 are L = 1 (μH / m), C = 12 (pF / M). Further, referring to Table 1, the conductance G values that are optimal for the trial calculation are set to G = 0.01, 0.1, 1.0, 10.0 (S / m) (that is, conductivity σ = 0.00733). , 0.0733, 0.733, 7.33 (S / m)). FIG. 12 shows the unit length when lightning surge currents of three types of frequencies f = 10 ⁴ , 10 ⁵ , 10 ⁶ (Hz) flow through the conductor 34 of the ground electrode 1 for each of these four types of conductance G. The result of each trial calculation of the per-thickness attenuation rate D (dB) is shown.

  As shown in FIG. 12, the attenuation factor D (dB) of the lightning surge current flowing through the conductor 34 increases as the value of the conductance G (that is, the conductivity σ) increases (within a range in which the conductance of the metal is not extremely large). It can be seen that it increases. Accordingly, when the ground electrode 1 is configured as a coaxial cable as in the present invention and the electrical conductivity σ is increased so that the filler 40 has the resistor 45, the lightning surge current flowing through the conductor 34 is relatively increased. It can be seen that there is an effect of being attenuated and diverted by the outside of the conductor 34 (ie, the filler 40 and the steel pipe 33).

In addition, as shown in FIG. 12, when G = 0.01 (S / m) (that is, conductivity σ = 0.733 (S / m)), the attenuation factor D has a frequency f = 10 ^4. Lightning surge current at (Hz) is D = 0.2 (dB), Lightning surge current at frequency f = 10 ⁵ (Hz) is D = 0.5 (dB), Lightning surge at frequency f = 10 ⁶ (Hz) It can be seen that the current is D = 1.5 (dB). This indicates that, among the lightning surge currents flowing through the conductor 34, a high-frequency component having a higher frequency is attenuated and is diverted by the outside of the conductor 34 (that is, the filler 40 and the steel pipe 33).

FIG. 13 shows three types of frequencies f = 10 ⁴ , 10 ⁵ , 10 for each of five types of conductance G obtained by adding the value of G = 0 (σ = 0) to the above four types of conductance G. ⁶ shows the results of trial calculations of the characteristic impedance Z ₀ of the ground electrode 1 when a lightning surge current of ⁶ (Hz) flows through the conductor 34 using the above equation (4). This corresponds to the resistance of the matching device.

FIG. 13 is a graph giving a guide to the matching impedance of the present invention. In the case of lossless (G = 0 (σ = 0)), the characteristic impedance Z ₀ is 288.7 (Ω) as shown in FIG. It is well known that the characteristic impedance is constant without depending on the frequency when there is no loss in this way, and this means that the matching resistance is 288.7 (Ω) when there is no loss. Means that the voltage-current characteristic is consumed at the end without being disturbed. On the other hand, in the case of loss, the characteristic impedance differs depending on the value of conductance G (that is, dielectric constant σ) shown in FIG. 13 and depends on the frequency. This is the matching impedance. As shown in FIG. 13, the impedance Z ₀ of the ground electrode 1 is such that the value of the impedance Z ₀ of the ground electrode 1 is lossless as the value of the conductance G (ie, conductivity σ) increases (G = 0 ( σ = 0)) is lower than 288.7 (Ω), and a guideline for matching impedance is obtained.

  Next, when the ground electrode 1 according to the embodiment of the present invention is used, it is estimated how much the value of the lightning surge voltage can be reduced as compared with the case where the conventionally known ground electrode is used. Try. In this trial calculation, it is assumed that the ground electrode of the present invention is a coaxial cable in which the outer diameter of the conductor 34 of the ground electrode 1 shown in FIG. 2 is 10 (mm) and the inner diameter of the steel pipe 33 is 1000 (mm). That is, in FIG. 11, a = 10 and b = 1000. On the other hand, it is assumed that a conventionally known ground electrode is a cable that does not have a steel pipe and has a conductor with an outer diameter of 10 (mm) exposed. Assuming that the atmospheric region where the lightning surge current flows is handled by the coaxial model, assuming that the outer radius is 50 (m), a = 10 and b = 50000 in FIG.

  As for the ground electrode 1 of the present invention and the conventionally known ground electrode assumed as described above, a current having a frequency of 1 (MHz) and a magnitude of 20 (kA) has a length of 5 m in the axial direction of the cable. ) Specifically, each lightning surge voltage when flowing through the distance is calculated. As described above, the conductance L of the ground electrode 1 of the present invention is obtained as L = 1 (μH / m) from the above equation (1). Similarly, when the conductance L of a conventionally known ground electrode is obtained from the above equation (1), L = 1.7 (μH / m), which is about twice as large.

First, assuming that all current flows through the conductor, the lightning surge voltage v can be calculated from the following equation (11) as a voltage generated between the cables.
v = j × ω × L × I (11)
That is, in the case of the ground electrode 1 of the present invention, the lightning surge voltage v is v = 2π × 1 × 10 ⁶ × 1 × 10 ⁻⁶ × 20 × 10 ³ ≈600 (kV). On the other hand, in the case of a conventionally known ground electrode, the value of the conductance L is about 1.7 times, so that the lightning surge voltage v is also 1.7 times, that is, v≈1020 (kv). Very high value.

  Furthermore, in the ground electrode 1 of the present invention, when G = 1.0 (S / m), as shown in FIG. 12, the lightning surge voltage has a damping rate D = 15 (per unit length due to the shunt effect). Therefore, when the lightning surge current flows 5 (m) along the axial direction, the attenuation rate becomes D = 5 × 15 = 75 (dB). Since 75 (dB) corresponds to 1/1000 or less, the lightning surge voltage v when the ground electrode 1 of the present invention is used is assumed to be 1000 (600 (kV)) assuming that the frequency is 1 (MHz). It is theoretically calculated that it is suppressed to a very small value of 1 / min, that is, v≈1 (kv).

  Note that the lightning surge voltage described above corresponds to the lightning surge voltage generated at the outlet end of the ground electrode 1. Therefore, since this value is low, the influence on the surroundings of the lightning surge voltage can be made very small, and the contact voltage and the stride voltage can be reduced to effectively reduce the electric shock accident disaster. .

  INDUSTRIAL APPLICABILITY The present invention is particularly useful for a ground electrode that flows a lightning surge current caused by a lightning strike to the ground and prevents lightning damage. For example, ground electrodes such as distribution poles of wiring systems in the power system field, ground electrodes such as overhead wire support columns in the electric railway field, ground electrodes such as road lighting columns and traffic signal columns in the road field, mobile communication in the information communication field It is very useful for ground electrodes for base pole antennas, ground electrodes for surveillance cameras, and ground electrodes for various manufacturing factories and storage facilities in the engineering field.

It is a block diagram which shows an example at the time of applying the ground electrode 1 which concerns on the 1st Embodiment of this invention to the building 5 as the object of lightning damage prevention. 2 is a vertical sectional view of the ground electrode 1. FIG. It is XX arrow expanded sectional view of FIG. FIG. 3 is an enlarged perspective view of the ground electrode 1 in the vicinity of the ground 15. The unit length of the ground electrode 1 according to the first embodiment of the present invention constituted by the steel pipe 33, the conductor 34, and the filler 40 when the lightning surge current I flowing from the upper end side of the conductor 34 flows to the ground side. It is the circuit diagram which showed the equivalent circuit of a hit. It is a figure explaining the influence which the ground electrode 1 which concerns on embodiment of this invention has on the surrounding building 55, Fig.6 (a) demonstrates the positional relationship of the ground electrode 1 and the building 55 around it. It is explanatory drawing. FIG. 6B shows the relationship between the lightning surge voltage value (vertical axis) when the lightning surge current I flows from the ground electrode 1 to the ground 15 and the position (horizontal axis) from the flow point. It is a graph. FIG. 7A is a diagram for explaining the influence of the ground electrode 1 according to the embodiment of the present invention on the surrounding humans 70 and 71, and FIG. 7A shows the humans 70 and 71 around the contact electrode 1 and the ground electrode 1. It is explanatory drawing explaining the positional relationship of these. FIG. 7B shows the relationship between the lightning surge voltage value (vertical axis) when the lightning surge current I flows from the ground electrode 1 to the ground 15 and the position (horizontal axis) from the flow point. It is a graph. It is sectional drawing of the perpendicular direction of the ground electrode group 2 which has multiple ground electrodes 1 based on the 2nd Embodiment of this invention. FIG. 6 is a horizontal cross-sectional view of a ground electrode group 2 having four ground electrodes 1 each having a horizontal tube axis direction according to a third embodiment of the present invention. It is a block diagram which shows the structure of the ground electrode 1 formed in the coaxial shape integrated with the lightning arrester 10 which sends the lightning surge current by the lightning strike 7 to the ground side based on the 4th Embodiment of this invention. 3 is a schematic perspective view of a coaxial cable 95. FIG. For each of the four types of conductance G, the results of trial calculation of the attenuation rate D (dB) per unit length when currents of three types of frequencies f flow through the conductor 34 are shown. Three values f = 10 ⁴ , 10 ⁵ , 10 ⁶ (Hz) for each value of five types of conductance G obtained by adding a value of G = 0 (σ = 0) to each value of four types of conductance G 6 shows the results of trial calculation of the characteristic impedance Z ₀ of the ground electrode 1 when the AC current flows through the conductor 34 using the above equation (4).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ground electrode 2 Ground electrode group 5 Building 7 Lightning strike 10 Lightning arrester 13, 60 Conductor 15 Ground 17 Grounding part 20 Equipotential bonding conductor 25, 65 Electronic equipment 26 Metal pipe 33 Steel pipe 34 Conductor 35 Fixing device 40 Filler 45 Conductor 46 Dielectric material 47 Magnetic material 51 Matching device 55 Other building 67 External power supply 70 Pedestrian 71 Contact person 80 Space 85 Standing type lightning rod 86 Projection needle 91 Internal conductor 92 External conductor 95 Coaxial cable A1, A2, B1, B2 Equivalent circuit point a outer diameter b inner diameter C capacitance D position of other building 55 G conductance
I Lightning surge current (overall)
Of the low frequency current component I position of the high-frequency current component L inductance L0 contacts 71 _H lightning surge currents L1, L2 origin position O coordinates of the pedestrian's foot R resistor U _D0 conventional ground electrode I _L lightning surge current The value of the lightning surge voltage at point D in the case U _D1 The value of the lightning surge voltage at point D in the case of the ground electrode of the present invention U _E0 The initial value of the lightning surge voltage in the case of a conventionally known ground electrode U _E1 Grounding of the present invention Initial value of lightning surge voltage in the case of electrodes U _{S0 Step} voltage in the case of a conventionally known ground electrode U _{S1 Step} voltage in the case of the ground electrode of the present invention U _T0 Contact voltage in the case of a conventionally known ground electrode U _{T1 Present} invention Contact voltage in case of ground electrode W Wall position XX Section line

Claims (13)

A ground electrode that sends lightning surge current from lightning to the ground.
A tubular conductor at least partially embedded in the ground;
An inner conductor coaxially disposed within the tubular conductor;
A filler filled between the tubular conductor and the inner conductor and having conductivity for a high-frequency component;
A ground electrode, wherein a lightning surge current caused by a lightning strike is shunted, a low-frequency component mainly flows through the inner conductor, and a high-frequency component mainly flows through the tubular conductor and the filler. The ground electrode according to claim 1, wherein the filler contains one or more materials selected from the group consisting of a resistor, a dielectric, and a magnetic material. The ground electrode according to claim 1 or 2, wherein the tubular conductor and the inner conductor are grounded after being terminated by a characteristic impedance of a coaxial system. The grounding electrode according to any one of claims 1 to 3, wherein the grounding electrode is connected to a lightning arrester that sends a lightning surge current caused by a lightning strike to the ground side. The ground electrode according to claim 4, wherein the ground electrode is formed in a coaxial shape integrated with the lightning arrester. The ground electrode according to any one of claims 1 to 5, wherein the tubular conductor is embedded with the axial direction being a vertical direction. The ground electrode according to any one of claims 1 to 6, wherein the tubular conductor is embedded with an axial direction as a horizontal direction. The ground electrode according to claim 1, wherein the tubular conductor and the inner conductor are connected to an equipotential bonding conductor. A ground electrode group comprising a plurality of ground electrodes according to claim 1. A method of reducing lightning surge voltage when a lightning surge current caused by lightning strikes the ground,
Providing a first current path such that one end thereof is disposed in the ground, and providing a second current path having an impedance to a high frequency component of the lightning surge current lower than that of the first current path;
The lightning surge current is shunted according to the frequency component so that the low frequency component of the lightning surge current mainly flows in the first current path and the high frequency component mainly flows in the second current path. A method for reducing lightning surge voltage, comprising reducing lightning surge voltage in a current path. The first current path is composed of an inner conductor,
The second current path is composed of a tubular conductor arranged coaxially so as to cover the outer periphery of the inner conductor, and a conductive filler filled between the tubular conductor and the inner conductor. The lightning surge voltage reducing method according to claim 10, wherein the lightning surge voltage is reduced. The method for reducing lightning surge voltage according to claim 11, wherein the filler contains one or more materials selected from the group consisting of a resistor, a dielectric, and a magnetic material. The method of reducing lightning surge voltage according to claim 11 or 12, wherein an outer skin is provided on an outer periphery of the coaxially arranged tubular conductor.

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