JP2011034885A - Grounding structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To protect auxiliary facilities from lightning surge by equalizing grounding potential of the whole power equipment including the auxiliary facilities. <P>SOLUTION: Grounding resistance R5 of a camera control instrument 35 arranged in the periphery of a substation 10 is connected with a plurality of grounding wires 40A, 40B to a grounding net 20 of the substation 10. Thus, rise of the grounding potential of the camera control instrument 35 can be restrained when the lightning surge invades, and grounding potential of the whole substation 10 including the camera control instrument 35 can be equalized. Consequently, the auxiliary facilities located out of the grounding net 20, namely, the camera control instrument 35 can be protected from lightning surge U. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a grounding structure for an accessory facility provided around a power facility.

  As described in the following document 1, in a power facility such as a power generation / substation, a grounding network is provided to make the ground potential uniform.

JP 2008-66205 A

  However, there are cases where additional equipment such as a surveillance camera is added around the power equipment (outside the grounding network). In such a case, when the accessory equipment is grounded alone, when a lightning surge enters the power equipment, only the ground potential of the grounding network rises, and a potential difference is generated with respect to the ground potential of the accessory equipment. As a result, an overvoltage exceeding the withstand voltage is applied to the attached equipment and the equipment is broken.

  In order to avoid this, it is conceivable to connect the grounding resistance of the accessory equipment to the grounding network through a grounding wire so that the grounding potential of the entire power equipment including the accessory equipment is the same.

  However, if the ground resistance of the auxiliary equipment and the grounding network are simply connected by a single ground wire, the auxiliary equipment becomes the end of the line, and reflection occurs there. Therefore, when a lightning surge enters, a high lightning surge voltage is applied to the attached equipment, causing a potential difference between the ground potential of the attached equipment and the ground potential of the grounding network, and there is a risk that overvoltage is applied to the attached equipment. .

  The present invention has been completed based on the above-described circumstances, and an object thereof is to protect the auxiliary equipment from lightning surge by equalizing the ground potential of the entire power equipment including the auxiliary equipment.

  The present invention is characterized in that the grounding resistance of the accessory equipment provided around the power equipment is connected to the grounding network of the power equipment by a plurality of ground wires.

As an embodiment of the present invention, the following configuration is preferable.
・ Reduce the length of the ground wire. By doing in this way, it becomes possible to suppress the increase in the ground potential of the auxiliary equipment due to lightning surge, and the ground potential of the entire power equipment including the auxiliary equipment can be made uniform. In order to shorten the length of the grounding wire, for example, the grounding resistor of the accessory equipment and the grounding network may be connected with the shortest distance so that no extra length is generated in the grounding wire.

• Provide a resonance circuit consisting of a coil and a capacitor on the ground wire. By doing in this way, it becomes possible to extinguish a lightning surge by a resonance circuit, and the grounding potential of the whole electric power equipment including ancillary equipment can be equalized.

  According to the present invention, the grounding resistance of the accessory equipment is connected to the grounding network by a plurality of grounding wires. Therefore, the ground wire is connected in a ring shape and does not make a termination. From the above, even if a lightning surge propagates to the side of the auxiliary equipment through the ground line, reflection does not occur in the auxiliary equipment, and the ground potential of the auxiliary equipment does not increase as much as that of the grounding network. Therefore, the ground potential of the power equipment including the accessory equipment can be made uniform, and the accessory equipment outside the ground steel can be protected from lightning surge.

The figure which shows the grounding structure applied to Embodiment 1. The figure which shows having connected the camera control equipment to the grounding network with two grounding wires Diagram showing ground potential Diagram showing experimental circuit Diagram showing the waveform of the impulse applied to the experimental circuit The figure which shows transition of potential difference Vd when the number of grounding wires is one The figure which shows transition of the potential line Vd when two ground lines are used The figure which shows a circuit model when there is one grounding wire Diagram showing the circuit model when there are two ground wires A table summarizing the inductance of each ground wire Waveforms of impulses applied to the circuit models of FIGS. 8 and 9 The figure which shows transition of potential difference Vd when the number of grounding wires is one The figure which shows transition of potential difference Vd when there are two ground wires Waveforms of impulses applied to the circuit models of FIGS. 8 and 9 The figure which shows transition of potential difference Vd when the number of grounding wires is one The figure which shows transition of potential difference Vd when there are two ground wires The figure which shows the grounding structure applied to Embodiment 2. Diagram showing resonant circuit

<Embodiment 1>
1. Overall Description Embodiment 1 of the present invention will be described with reference to the accompanying drawings. This embodiment illustrates a substation 10 as an example of the power equipment of the present invention, and FIG. 1 shows a configuration diagram of the substation 10. The substation 10 includes an electrical device 11 such as a transformer, a management building 13, trusses 15 </ b> A to 15 </ b> C that support a lead-in wire 17 branched from an overhead line. Below these substations 10 (under the ground), a grounding network 20 is embedded corresponding to the construction range of the substation 10.

  The grounding network 20 is connected to each other by a grounding wire in which a plurality of grounding resistors R are stretched in a net shape, and has a size that covers almost the entire construction range of the substation 10. The electrical equipment 11, the management building 13, trusses 15A to 15C and the like are grounded to the grounding network 20, and the overhead ground wire 8 of the power transmission tower 5 is also grounded.

  A surrounding fence 21 is provided around the substation 10. This surrounding fence 21 partitions the substation 10 from the periphery. A camera 30 and a camera control device 35 that controls the camera 30 are provided in an area partitioned by the surrounding fence 21. A power line 25 is drawn between the camera control device 35 and the power supply device 13A of the building 13, and the camera control device 35 is configured to be supplied with power from the power supply device 13A of the building 13.

  The camera 30 and the camera control device 35 are out of the range of the grounding network 20, and the grounding resistance R5 of the camera control device 35 is installed at a place away from the grounding network 20. This is because the camera 30 is added after the construction of the substation 10.

  A lightning arrester 36 is connected to the camera control device 35 in parallel. This lightning arrester 36 is for limiting the voltage so that, when a voltage higher than the withstand voltage (about 10 kV) is applied to the camera control device 35, the lightning arrester 36 becomes conductive and an overvoltage higher than the withstand voltage is not applied to the camera control device 35.

  In this embodiment, as shown in FIG. 2, the ground resistance R5 of the camera control device 35 and the ground network 20 are connected by two ground wires (specifically, CV cables) 40A and 40B. Yes. By adopting such a ground structure, the ground potential of the entire substation 10 including the camera control device 35 can be made uniform. Hereinafter, the reason will be specifically described by taking a case where a lightning strike occurs on the steel tower 5 around the substation and a lightning surge U enters the power plant 10 through the overhead ground wire 8 as an example.

  When the lightning surge U propagates to the grounding network 20 through the overhead ground wire 8, the grounding potential (voltage between the grounds) of the grounding network 20 is raised to “V1” as shown in FIG. Further, the lightning surge U propagated to the grounding network 20 propagates to the camera 30 side through the grounding wires 40A and 40B. Here, since the two ground wires 40A and 40B are connected in a ring shape, the camera control device 35 does not end the line. Therefore, it is possible to suppress reflection of the lightning surge U that propagates in the camera control device 35.

  From the above, the ground potential “V2” of the camera control device 35 does not rise as much as the ground potential “V1” of the ground network 20. Therefore, the ground potential of the entire substation 10 including the camera control device 35 can be made uniform, and the potential difference Vd between the ground potential “V2” and the ground potential “V1” can be reduced.

  Moreover, it is preferable to set the lengths of the ground wires 40A and 40B as short as possible. This is because it is considered that the effect of suppressing reflection can be increased as the distance of the ground wire is shorter. The camera control device 35 can be protected from the lightning surge U by determining the lengths of the ground wire 40A and the ground wire 40B so that the potential difference Vd is less than the withstand voltage of the lightning arrester 36.

  This is because when an overvoltage exceeding the withstand voltage is applied to the camera control device 35, the lightning arrester 36 is activated to suppress the voltage applied to the camera control device 35 below the withstand voltage. However, if such an overvoltage is repeatedly applied, the lightning arrester 36 will not operate and eventually the camera control device 35 will be destroyed.

  In this embodiment, the lengths of the ground lines 40A and 40B are determined so that the potential difference Vd is less than the withstand voltage “10 kV” of the lightning arrester 36 by performing a simulation using a circuit model to be described later.

  In FIG. 3, as a comparative example, the ground potential “V3” of the camera control device 35 when the ground resistance R5 of the camera control device 35 and the ground network 20 are connected by only one ground line 40A. It is shown. As shown in FIG. 3, the ground potential “V3” when connected by only one ground line 40A is significantly higher than the ground potential “V1”. This is because if the number of ground lines is one, the ground resistance R5 of the camera control device 35 becomes the end of the line, so that reflection is large (reflection coefficient is large) and the ground potential of the camera control device 35 is increased. It is.

  FIG. 3 shows a ground potential V4 of the camera control device 35 when the camera control device 35 is single-grounded (no ground wire) by the ground resistor R5 as a comparative example. In the case of single grounding, the ground potential V4 does not increase, but the potential difference Vd of the ground network 20 with respect to the ground potential “V1” is also increased. As described above, in the case of using one grounding wire or in the case of single grounding, the grounding potential cannot be made uniform and a grounding structure that is vulnerable to the lightning surge U is obtained.

2. Experiment Next, the surge test will be described. Reference numeral 50 shown in FIG. 4 is an impulse generator, which generates an impulse that assumes a lightning surge (an impulse having a waveform similar to that of a lightning surge).

  In this experiment, as shown in FIG. 4, the impulse generator 50 generates the impulse shown in FIG. 5 and applies it to the truss 15 </ b> A that is commonly grounded to the grounding network 20.

  The ground potential of the camera control device 35 and the grounding network 20 are respectively set when the ground wire is only “40A” and when the ground wire is “40A” and “40B”. The voltmeter 60 measures the potential difference Vd of the ground potential (specifically, the ground potential of the truss 15B).

  In this experiment, a CV cable is used for the grounding wire, the grounding wire 40A has an inductance L per unit length of 6.3 μH / m, and the grounding wire 40B is used per unit length. An inductance L having a size of 1.0 μH / m was used. The length of the ground line 40A is about 90 m, and the length of the ground line 40B is about 15 m.

  As a result of the above-described surge test, the potential difference Vd when the ground line is set to one of “40 A” is about 52 V at the maximum as shown in FIG. 6, whereas the ground lines are “40 A” and “40 B”. ", The potential difference Vd is about 21 V as shown in FIG. Thus, it has been proved by experiments that the potential difference Vd can be made smaller when two ground wires are used.

3. Simulation Next, simulation using a circuit model will be described. The circuit model in FIG. 8 is a simulation of the circuit in which the camera control device 35 and the ground network 20 are connected to one ground line 40A in the experimental model shown in FIG. The circuit model in FIG. 9 is a simulation of a circuit in which the camera control device 35 and the grounding network 20 are connected by two grounding wires 40A and 40B.

  8 and 9, the node (A) indicates the truss 15A, the node (B) indicates the truss 15B, and the node (C) indicates the camera control device 35. That is, R1 is the ground resistance of the truss 15A, R3 is the ground resistance of the truss 15B, and R5 is the ground resistance of the camera control device 35.

  “Lab” is the inductance of the grounding network 20 connecting the truss A and the truss B, “Lca” is the inductance of the grounding wire 40A connecting the truss A and the camera control device 35, and “Lbc” is the camera control device 35. This is the inductance of the ground wire 40B connecting the truss B.

  8 is applied to both the circuit model shown in FIG. 8 and the circuit model shown in FIG. 9 by applying the impulse of FIG. 11 assuming the lightning surge U (the impulse having the same waveform and voltage as the lightning surge). A simulation for measuring the potential difference Vd between (B) and the node (C) is performed by a computer (not shown) while changing the specifications (circuit constants) shown in FIG.

  In the circuit model of FIG. 8 (pattern with one ground line), the potential difference Vd between the node (B) and the node (C) is “36 kV” as shown in FIG.

  On the other hand, in the circuit model of FIG. 9 (pattern of two ground lines), the potential difference Vd between the node (B) and the node (C) can be remarkably reduced compared to the pattern of one ground line, and the ground potential can be reduced. The result that it can be made uniform was obtained.

  Further, even when the number of ground lines is two, the potential difference Vd shows a different value when the specifications shown in FIG. 10 are changed, and the potential difference Vd tends to decrease as the length of the ground lines 40A and 40B decreases. It was understood that

  In the simulation using the circuit model of FIG. 9, the ground line 40A is handled as an existing one, and the length of the ground line 40A and the inductance per unit length are fixed. Specifically, the length was “90 m” and the inductance per unit length was “6.3 μH / m”.

  Then, the length and the inductance per unit length were determined by adjusting the length of the ground line 40B and the inductance per unit length so that the potential difference Vd was less than “10 kV” which is the withstand voltage of the lightning arrester.

  As a result, as shown in the table of FIG. 10, if the length of the ground wire 40B is set to “15 m” and the inductance per unit length is set to “1.0 μH / m”, the node (B) as shown in FIG. And the node (C) potential difference Vd can be suppressed to “6 kV”, which is about 60% of the withstand voltage, and it has been confirmed that a grounding structure resistant to lightning surge U can be achieved.

  The relationship between the potential difference Vd and the inductance per unit length of the ground wire can be considered as follows. That is, in order to reduce the potential difference Vd, it is preferable to reduce the inductance per unit length. However, for example, if the inductance value per unit length between two ground wires is different, the degree of reflection changes accordingly, so how to set the inductance per unit length depends on the other ground wires. It is necessary to determine in consideration of the inductance value per unit length.

  Further, when a simulation was performed in which the impulse having the waveform shown in FIG. 14 was applied to the circuit model shown in FIG. 8, the potential difference Vd became the waveform shown in FIG. Further, when a simulation was performed in which the impulse having the waveform shown in FIG. 14 was applied to the circuit model shown in FIG. 9, the potential difference Vd became the waveform shown in FIG. The simulation result is almost the same as the data obtained by the surge experiment, and the validity of the circuit models of FIGS. 8 and 9 can be confirmed.

<Embodiment 2>
Next, Embodiment 2 will be described with reference to FIGS. The resonance circuit 70 is added to one or both of the ground lines 40A and 40B with respect to the configuration of the first embodiment.

  As shown in FIG. 18, the resonance circuit 70 is a parallel resonance circuit in which a coil L and a capacitor C are connected in parallel, and the resonance frequency is set to the lightning surge U frequency. In this way, the lightning surge U can be extinguished by the resonance circuit 70, so that the potential difference Vd can be reduced and the ground potential can be made uniform.

  In this embodiment, the grounding resistor R5 of the camera control device 35 and the grounding network 20 are connected by the two grounding wires 40A and 40B.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention.
(1) In the first and second embodiments, the substation 10 is illustrated as an example of the power facility. However, the power facility is not limited to the substation 10 and may be a power plant, a switching station, or the like. Good.
(2) In the first and second embodiments, the camera control device 35 is illustrated as an example of the peripheral equipment. However, the peripheral equipment is not limited to the equipment related to the camera 30, and the mercury lamp and lighting control thereof are performed. It may be a control device or the like.

  (3) In the first and second embodiments, the number of ground lines is two. However, the number of ground lines is not limited to two, and may be two or more.

  (4) In the second embodiment, the resonant circuit 70 is attached to the ground lines 40A and 40B. However, of the ground lines 40A and 40B, a variable inductance may be provided on the ground line. This is because the increase in the ground potential with respect to the lightning surge U is also affected by the soil where the power equipment is built, and an error from the calculation on the desk tends to occur. Therefore, if a variable inductance is provided, such an error can be adjusted.

10 ... Substation (corresponding to "electric power equipment" of the present invention)
DESCRIPTION OF SYMBOLS 11 ... Transformer 13 ... Management building 15 ... Truss 20 ... Grounding network 25 ... Power supply line 30 ... Camera 35 ... Camera control apparatus (equivalent to "peripheral apparatus" of this invention)
36 ... Arrester R5 ... Ground resistance 40A ... Ground wire 40B ... Ground wire

Claims (3)

A grounding structure for connecting a grounding resistance of an accessory facility provided around a power facility to a grounding network of the power facility by a plurality of ground wires. The grounding structure according to claim 1, wherein a length of the grounding wire is shortened. The ground structure according to claim 1, wherein a resonance circuit including a coil and a capacitor is provided on the ground line.

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