Insulating gas replacement method

Abstract

Provided is an insulating gas replacement method that can sufficiently achieve the effect of preventing global warming and that can efficiently execute replacement of insulating gas. This insulating gas replacement method comprises a recovery step (ST10), an encapsulation step (ST20), and an atmospheric pressure test step (ST30), and involves replacing a first insulating gas in a gas insulated switchgear (100) with a second insulating gas (20) having a global warming potential lower than that of the first insulating gas (10). In the recovery step, the first insulating gas is recovered from the interior space of a sealed tank (101). In the encapsulation step, the second insulating gas is introduced and encapsulated in the interior space of the sealed tank from which the first insulating gas has been recovered. In the atmospheric pressure test step, an atmospheric pressure test is executed on the gas insulated switchgear. The second insulating gas comprises at least one substance selected from oxygen, carbon dioxide, nitrogen, helium, neon, argon, xenon, and krypton. The recovery step, the encapsulation step, and the atmospheric pressure test step are each executed at a location where the gas insulated switchgear is installed.

Description

Insulation gas replacement method

[0001] An embodiment of the present invention relates to an insulation gas replacement method.

[0002] Gas-insulated switchgear is installed in electric power facilities such as substations and power plants. In gas-insulated switchgear, conductors are housed inside a sealed tank that is filled with insulating gas.

[0003] In gas-insulated switchgear, SF is used as the insulating gas in consideration of electrical performance (insulation performance, arc extinguishing performance). ６ Gases such as sulfur hexafluoride gas are used, but SF ６ SF gas is a greenhouse gas with a high global warming potential. ６ It has been proposed to replace the gas with, for example, a mixture of an organic fluorine compound and nitrogen.

[0004] Special Publication No. 2023-544971

[0005] However, the mixed gas of an organic fluorine compound and nitrogen has a global warming potential of more than 10 and not more than 2000, and therefore is not sufficiently effective in preventing global warming by reducing greenhouse gases.

[0006] On the other hand, naturally occurring gases such as air (gases consisting of at least one of oxygen, carbon dioxide, nitrogen, helium, neon, argon, xenon, and krypton) have a global warming potential of 1 or less. Therefore, when naturally occurring gases are used as insulating gases in gas-insulated switchgear, it is possible to obtain a sufficient effect of preventing global warming by reducing greenhouse gases.

[0007] However, naturally occurring gases such as air have low electrical performance (insulation performance, arc extinguishing performance). Therefore, when naturally occurring gases are sealed as insulating gases inside the sealed tank of an existing gas-insulated switchgear, the pressure of the naturally occurring gas sealed inside the sealed tank must be increased in order to obtain sufficient electrical performance of the gas-insulated switchgear. Therefore, in gas-insulated switchgears, SF ６When replacing gases with naturally occurring gases, it is necessary to verify that the strength of the sealed tank is sufficient under conditions where the pressure of the sealed naturally occurring gas is high, and to confirm that the gas-insulated switchgear meets the mechanical performance requirements.

[0008] The strength of the sealed tank is usually confirmed by stopping the operation of the gas-insulated switchgear and transporting the sealed tank from the installation site of the gas-insulated switchgear to, for example, a manufacturer's factory. Specifically, first, at the installation site of the gas-insulated switchgear, the insulating gas is recovered from inside the sealed tank, and then the sealed tank is disassembled. Then, the disassembled sealed tank is transported to a location where pressurization and measurement can be appropriately performed, such as a manufacturer's factory, to perform a pressure resistance test (e.g., a barometric pressure test) to confirm that the mechanical performance is satisfactory. Then, after the strength of the sealed tank is confirmed by the pressure resistance test, the sealed tank is transported to the original installation site, and the gas-insulated switchgear is reassembled. Then, at the original installation site, the insulating gas is sealed inside the sealed tank.

[0009] For these reasons, when replacing the insulating gas in gas-insulated switchgear with a naturally occurring gas with a low global warming potential, the gas-insulated switchgear must be disassembled, transported, pressure-tested, and reassembled to confirm that the sealed tank meets its mechanical performance requirements, resulting in increased labor costs. Furthermore, these operations require the power utility to shut down the gas-insulated switchgear for an extended period of time, potentially affecting the operation plan of the entire substation. As a result, it is not easy to efficiently replace the insulating gas, potentially hindering efforts to reduce greenhouse gas emissions.

[0010] Therefore, the problem that the present invention aims to solve is to provide an insulating gas replacement method that can fully achieve the effect of reducing greenhouse gases and can efficiently replace gases with naturally occurring gases.

[0011] The insulating gas replacement method of this embodiment includes a recovery process, a filling process, and a pressure test process, and involves replacing a first insulating gas with a second insulating gas having a lower global warming potential than the first insulating gas in a gas-insulated switchgear in which a first insulating gas is filled in the internal space of a sealed tank at a first standard pressure. In the recovery process, the first insulating gas is recovered from the internal space of the sealed tank. In the filling process, a second insulating gas is introduced into the internal space of the sealed tank from which the first insulating gas has been recovered in the recovery process, and the internal space is sealed so that the internal space is at a second standard pressure higher than the first standard pressure. In the pressure test process, a pressure test is performed on the gas-insulated switchgear under conditions in which the internal space of the sealed tank is at a pressure test pressure higher than the second standard pressure. The second insulating gas is a gas composed of at least one substance selected from the group consisting of oxygen, carbon dioxide, nitrogen, helium, neon, argon, xenon, and krypton, i.e., a naturally occurring gas such as air. The recovery process, the sealing process, and the pressure test process are each performed at the installation site where the gas-insulated switchgear is installed.

[0012] FIG. 1A is a diagram illustrating a gas-insulated switchgear 100 before replacement of the insulating gas in the first embodiment. FIG. 1B is a diagram illustrating a portion of the gas-insulated switchgear 100 before replacement of the insulating gas in the first embodiment. FIG. 1C is a flow diagram of an insulating gas replacement method in the first embodiment. FIG. 1D is a diagram illustrating a state of the gas-insulated switchgear 100 after the insulating gas replacement method in the first embodiment has been performed. FIG. 2A is a flow diagram of an insulating gas replacement method in the second embodiment. FIG. 2B is a diagram illustrating a state of the gas-insulated switchgear 100 after the insulating gas replacement method in the second embodiment has been performed. FIG. 3A is a flow diagram of an insulating gas replacement method in the third embodiment. FIG. 3B is a diagram illustrating a state of the gas-insulated switchgear 100 after the insulating gas replacement method in the third embodiment has been performed. FIG. 3C is a diagram showing the relationship between the pressure (P) in the internal space of the sealed tanks 101a, 101b, and 101c and the time (Time) when a system fault occurs in the third embodiment. FIG. 4A is a flow diagram of an insulation gas exchange method in a fourth embodiment. FIG. 4B is a diagram schematically showing the state of the gas-insulated switchgear 100 before the insulation gas exchange method is performed in the fourth embodiment. FIG. 4C is a diagram schematically showing the state of the gas-insulated switchgear 100 after the insulation gas exchange method is performed in the fourth embodiment. FIG. 5A is a flow diagram of an insulation gas exchange method in a fifth embodiment. FIG. 5B is a diagram schematically showing the state of the gas-insulated switchgear 100 after the insulation gas exchange method is performed in the fifth embodiment. FIG. 6A is a flow diagram of an insulation gas exchange method in a sixth embodiment. FIG. 6B is a diagram schematically showing the state of the gas-insulated switchgear 100 after the insulation gas exchange method is performed in the sixth embodiment. FIG. 7A is a flow diagram of an insulation gas exchange method in a seventh embodiment. Fig. 7B is a diagram schematically showing the state of the gas-insulated switchgear 100 after performing the insulation gas replacement method in the seventh embodiment. Fig. 8 is a flowchart of the insulation gas replacement method in the eighth embodiment. Fig. 9 is a flowchart of the insulation gas replacement method in a modified example 8-2 of the eighth embodiment.

[0013] First Embodiment [A] Configuration of Gas-Insulated Switchgear Before describing the insulating gas replacement method of this embodiment, an example of a gas-insulated switchgear before replacement of the insulating gas in the insulating gas replacement method will be described.

[0014] FIG. 1A is a diagram illustrating a gas-insulated switchgear 100 before replacement of insulating gas in the first embodiment.

[0015] As shown in FIG. 1A , a gas-insulated switchgear 100 includes a plurality of sealed tanks 101a, 101b, and 101c. The sealed tanks 101a, 101b, and 101c are, for example, cylindrical metal containers and are arranged side by side in the axial direction. The internal spaces of the sealed tanks 101a, 101b, and 101c are divided into gas compartments A1, A2, and A3 by insulating spacers 102. The insulating spacers 102 are made of an insulating material and support conductors 103 (first conductors) extending along the axial direction in the internal spaces of the sealed tanks 101a, 101b, and 101c. An insulating gas G10 (first insulating gas) is sealed in each of the gas compartments A1, A2, and A3. The insulating gas G10 may be, for example, SF ６ A gas is sealed in at a reference pressure (first reference pressure).

[0016] Of the multiple gas compartments A1, A2, and A3, gas compartment A1 has a conductor 103 provided as a bus 111a. In gas compartment A1, a lightning arrester 112a (first lightning arrester) is connected to the bus 111a. In gas compartment A1, an adsorption device 201a is installed in the sealed tank 101a. The adsorption device 201a is configured to adsorb moisture present in the internal space of the sealed tank 101a and components produced by decomposition of the insulating gas G10 in the internal space of the sealed tank 101a. In addition, in gas compartment A1, a gas valve V111a is installed outside the sealed tank 101a.

[0017] Of the multiple gas compartments A1, A2, and A3, gas compartment A2 is located adjacent to gas compartment A1. In gas compartment A2, a disconnector 111b connected to an operational earthing switch 112b and a high-speed earthing switch 113b is provided on the conductor 103. In gas compartment A2, an adsorption device 201b is installed in a sealed tank 101b. In addition, in gas compartment A2, a gas valve V111b is installed outside the sealed tank 101b.

[0018] Of the multiple gas compartments A1, A2, and A3, gas compartment A3 is located adjacent to gas compartment A2. In gas compartment A3, a gas circuit breaker 111c is provided on the conductor 103. In gas compartment A3, an adsorption device 201c is installed in a sealed tank 101c. In addition, in gas compartment A3, a gas valve V111c is installed outside the sealed tank 101c.

[0019] Fig. 1B is a diagram illustrating a part of the gas-insulated switchgear 100 before replacement of the insulating gas in the first embodiment. Fig. 1B illustrates details of the part where the sealed tank 101a and the sealed tank 101b are connected in the gas-insulated switchgear 100 shown in Fig. 1A. Although not shown, the part where the sealed tank 101b and the sealed tank 101c are connected is also similar.

[0020] 1B , in the gas-insulated switchgear 100, a flange F101a is provided at an end of the sealed tank 101a, and a flange F101b is provided at an end of the sealed tank 101b. The flange F101a of the sealed tank 101a and the flange F101b of the sealed tank 101b are ring-shaped plate bodies, and are fastened between them by a plurality of bolts BT1 (first bolts) via an insulating spacer 102. Although not shown, the plurality of bolts BT1 are attached at intervals so as to surround the outer peripheries of the sealed tanks 101a and 101b.

[0021] The insulating spacer 102 has an insulating portion 1021 and a metal flange portion 1022, which are integrally formed. In the insulating spacer 102, the insulating portion 1021 is coaxial with the sealed tanks 101a and 101b. The insulating portion 1021 has an opening formed in its center, and a contact 1031 is provided in the opening. In the insulating spacer 102, the metal flange portion 1022 is a ring-shaped plate body and is provided on the outer periphery of the insulating portion 1021. The metal flange portion 1022 is sandwiched between the flange F101a of the sealed tank 101a and the flange F101b of the sealed tank 101b.

[0022] The conductor 103 located inside the sealed tank 101a and the conductor 103 located inside the sealed tank 101b are electrically connected using a contact 1031. A slide contact 1032 is interposed between the conductor 103 located inside the sealed tank 101a and the contact 1031, and a slide contact 1032 is similarly interposed between the conductor 103 located inside the sealed tank 101b and the contact 1031.

[0023] The gas-insulated switchgear 100 is configured such that the internal spaces of the sealed tanks 101a and 101b are sealed by a seal member SL1 (first seal member). The seal member SL1 is, for example, an O-ring. In this example, the seal member SL1 is disposed between the flange F101a of the sealed tank 101a and the metal flange portion 1022 of the insulating spacer 102, and also between the flange F101b of the sealed tank 101b and the metal flange portion 1022 of the insulating spacer 102.

[0024] [B] Insulation Gas Replacement Method An insulation gas replacement method that is applied to the gas insulated switchgear 100 described above will be described.

[0025] Fig. 1C is a flow diagram of the insulation gas exchange method according to the first embodiment. Fig. 1D is a diagram schematically showing the state of the gas-insulated switchgear 100 after the insulation gas exchange method according to the first embodiment is performed.

[0026] In the insulating gas replacement method of this embodiment, the steps shown in FIG. 1C (recovery step (ST10), sealing step (ST20) (= introduction step (ST21), pressure adjustment step (ST22)), and air pressure test step (ST30)) are performed at the installation site where the gas-insulated switchgear 100 is installed.

[0027] As a result, the insulating gas G10 (first insulating gas) sealed in the internal space of the sealed tanks 101a, 101b, and 101c before the insulating gas replacement method is performed (see Figure 1A) is replaced with insulating gas G20 (second insulating gas) as shown in Figure 1D.

[0028] Here, the insulating gas G20 is a gas (naturally occurring gas) that has a lower global warming potential than the insulating gas G10, which is SF6 gas or the like, and is made of at least one substance selected from the group consisting of oxygen, carbon dioxide, nitrogen, helium, neon, argon, xenon, and krypton. In other words, the insulating gas G20 may be a single gas of any of the above substances, or may be a mixed gas such as air containing oxygen, carbon dioxide, nitrogen, or the like.

[0029] The details of each step ST10, ST20 (=ST21, ST22), and ST30 in the insulation gas replacement method of this embodiment will be described below.

[0030] [B-1] ST10 When performing the insulation gas exchange method in this embodiment, first, as shown in FIG. 1C, SF ６ The insulating gas G10, which is a gas or the like, is recovered (recovery step ST10).

[0031] Here, insulating gas G10 sealed in the internal space of sealed tanks 101a, 101b, and 101c at reference pressure P10 (first reference pressure) is recovered to the outside via gas valves V111a, V111b, and V111c (see FIG. 1A).

[0032] [B-2] ST21 Next, as shown in FIG. 1C, an insulating gas G20, which is a naturally occurring gas, is introduced (introduction step (S21)).

[0033] Here, SF ６An insulating gas G20, which is a naturally occurring gas, is introduced into the internal spaces of the sealed tanks 101a, 101b, and 101c into which an insulating gas G10, such as a gas, has been collected, via gas valves V111a, V111b, and V111c. The naturally occurring insulating gas G20 is introduced so that the pressure in the internal spaces reaches an atmospheric pressure test pressure P30 for performing an atmospheric pressure test in the next process. In other words, the naturally occurring insulating gas G20 is introduced as the gas for the atmospheric pressure test.

[0034] The atmospheric test pressure P30 is a pressure higher than the reference pressure P20 (second reference pressure) preset for the gas-insulated switchgear 100 after the insulating gas has been replaced with the naturally occurring insulating gas G20. For example, the atmospheric test pressure P30 is 1.25 times the maximum operating pressure, which is higher than the reference pressure P20 (second reference pressure).

[0035] The insulating gas G20 (natural gas) after replacement is the same as the insulating gas G10 (SF ６ The electrical performance (insulation performance, arc extinguishing performance) of the gas-insulated switchgear 100 after replacement with the insulating gas G20 is lower than that of the gas-insulated switchgear 100 before replacement. Therefore, the reference pressure P20 (second reference pressure) set for the gas-insulated switchgear 100 after replacement with the insulating gas G20 is higher than the reference pressure P10 (first reference pressure) set for the gas-insulated switchgear 100 before replacement.

[0036] [B-3] ST30 Next, as shown in FIG. 1C, a pressure test is carried out (pressure test step (ST30)).

[0037] The atmospheric pressure test is performed under the condition that the internal space of the sealed tanks 101a, 101b, and 101c is at an atmospheric pressure test pressure P30. By performing the atmospheric pressure test, it is confirmed whether or not damage such as deformation has occurred in the gas-insulated switchgear 100.

[0038] [B-4] ST22 Next, as shown in FIG. 1C, the pressure of the internal space into which insulating gas G20, which is a naturally occurring gas, has been introduced in sealed tanks 101a, 101b, and 101c is adjusted (pressure adjustment step (S22)).

[0039] Here, for example, gas valves V111a, V111b, and V111c are used to adjust the pressure in the internal spaces of the sealed tanks 101a, 101b, and 101c to a reference pressure P20, and then the internal spaces are sealed.

[0040] [C] Summary As described above, in this embodiment, the SF ６ In a gas-insulated switchgear 100 filled with an insulating gas G10 such as a gas, the insulating gas G10 is replaced with an insulating gas G20 having a lower global warming potential than the insulating gas G10. The insulating gas G20 is a gas (naturally occurring gas) made of at least one substance selected from oxygen, carbon dioxide, nitrogen, helium, neon, argon, xenon, and krypton, and has a global warming potential of 1 or less. Therefore, in this embodiment, it is possible to sufficiently obtain the effect of preventing global warming by reducing greenhouse gases.

[0041] As already mentioned, the insulating gas G20, which is a naturally occurring gas, is SF ６ However, in this embodiment, SF ６ Since the insulating gas G20, which is a naturally occurring gas, is sealed in the internal space at a reference pressure P20 (second reference pressure) higher than the reference pressure P10 (first reference pressure) at which the insulating gas G10, such as a gas, is sealed, it is possible to obtain sufficient electrical performance of the gas-insulated switchgear 100. In addition, in this embodiment, an air pressure test is performed at an air pressure test pressure P30 higher than the reference pressure P20 (second reference pressure). The air pressure test is performed to check whether or not damage such as deformation has occurred in the gas-insulated switchgear 100, and if the test confirms that there are no problems, the mechanical performance of the gas-insulated switchgear 100 can be guaranteed.

[0042] In the insulation gas replacement method of this embodiment, each process (recovery process (ST10), charging process (ST20) (= introduction process (ST21), pressure adjustment process (ST22)), and air pressure test process (ST30)) is performed at the installation site where the gas-insulated switchgear 100 is installed. Therefore, in this embodiment, no transportation work is required when replacing the insulation gas. As a result, work such as disassembly, transportation, and reassembly can be omitted, and the period during which the gas-insulated switchgear 100 is out of operation can be shortened, thereby suppressing an increase in work costs associated with replacing the insulation gas. Therefore, in this embodiment, the replacement of the insulation gas can be performed efficiently.

[0043] Second Embodiment [A] Insulation Gas Exchange Method Fig. 2A is a flow diagram of an insulation gas exchange method according to a second embodiment. Fig. 2B is a diagram schematically illustrating a state of the gas-insulated switchgear 100 after the insulation gas exchange method has been performed according to the second embodiment.

[0044] As shown in Figures 2A and 2B, this embodiment includes a step of replacing an existing bolt BT1 (first bolt; see Figure 1A) with another bolt BT2 (second bolt) (bolt replacement step (ST41)). Except for this point and related points, this embodiment is the same as the first embodiment (see Figures 1B and 1C). Therefore, explanations of overlapping points will be omitted as appropriate.

[0045] In this embodiment, as shown in FIG. 2A, the step of replacing the bolt BT1 with another bolt BT2 (bolt replacement step (ST41)) is performed by SF ６ This is performed at the installation site after a process of recovering insulating gas G10 (recovery process ST10).

[0046] Here, a bolt having a higher tensile strength than the existing bolt BT1 is used as the bolt BT2.

[0047] [B] Summary In the gas-insulated switchgear 100 of this embodiment, SF ６The insulating gas G20, which is a naturally occurring gas, is sealed in the internal space at a reference pressure P20 (second reference pressure) higher than the reference pressure P10 (first reference pressure) at which the insulating gas G10 is sealed. However, in this embodiment, the existing bolts BT1 are replaced with bolts BT2 having a higher tensile strength than the existing bolts BT1. Therefore, in this embodiment, the mechanical performance of the gas-insulated switchgear 100 can be ensured.

[0048] [C] Modifications In the above embodiment, the step of replacing the bolt BT1 with another bolt BT2 (bolt replacement step (ST41)) is performed by SF ６ Although this is performed after the step of recovering the insulating gas G10 (recovery step ST10), it may also be performed before the step of recovering the insulating gas G10 (recovery step ST10). In this case, the bolt BT1 is replaced with another bolt BT2 one by one to ensure the connection state between the multiple sealed tanks 101a, 101b, 101c.

[0049] <Third embodiment> [A] Insulation gas replacement method Fig. 3A is a flow diagram of an insulation gas replacement method according to a third embodiment. Fig. 3B is a diagram schematically showing a state of the gas-insulated switchgear 100 after the insulation gas replacement method according to the third embodiment is performed.

[0050] As shown in Figures 3A and 3B, this embodiment includes a process (pressure relief device installation process (ST42)) of installing pressure relief devices 201ax, 201bx, and 201cx in place of the existing adsorption devices 201a, 201b, and 201c (see Figure 1A). Except for this point and related points, this embodiment is similar to the first embodiment (see Figures 1A and 1C). Therefore, explanations of overlapping matters will be omitted as appropriate.

[0051] In this embodiment, as shown in FIG. 3A, the step of installing the pressure relief devices 201ax, 201bx, and 201cx (pressure relief device installation step (ST42)) is performed by SF ６ This is performed at the installation site after a process of recovering insulating gas G10 (recovery process ST10).

[0052] Here, the pressure relief devices 201ax, 201bx, 201cx are configured to maintain the pressure in the internal spaces of the sealed tanks 101a, 101b, 101c at or below the pressure relief pressure PR when the internal spaces of the sealed tanks 101a, 101b, 101c reach a pressure relief pressure PR that is lower than the burst pressure PT at which the sealed tanks 101a, 101b, 101c burst and the burst pressure PS at which the insulating spacer 102 bursts. Specifically, the pressure relief devices 201ax, 201bx, 201cx are configured to connect the internal spaces of the sealed tanks 101a, 101b, 101c to the outside when the internal spaces of the sealed tanks 101a, 101b, 101c reach the pressure relief pressure PR.

[0053] In addition, the pressure relief devices 201ax, 201bx, and 201cx of this embodiment are configured to have an adsorption function to adsorb moisture present in the internal space of the sealed tank 101a and components produced by the decomposition of the insulating gas G20 in the internal space of the sealed tank 101a.

[0054] [B] Summary The functions and effects of this embodiment will be described.

[0055] FIG. 3C is a diagram showing the relationship between the pressure (P) in the internal space of the sealed tanks 101a, 101b, and 101c and the time (Time) when a system accident occurs in the third embodiment.

[0056] As shown in Fig. 3, when a system fault occurs, the pressure P in the internal space increases over time due to arc discharge that occurs in the internal space. ６ The insulating gas G10, such as a natural gas, is replaced with the insulating gas G20, which is a naturally occurring gas. The heat capacity of the insulating gas G20, which is a naturally occurring gas, is SF ６This is two to four times the heat capacity of the insulating gas G10, which is a gas, etc. Therefore, unlike the case of this embodiment, if the pressure relief devices 201ax, 201bx, and 201cx are not installed, the pressure P in the internal space will rise as shown by the dashed lines in Figure 3, and may reach the burst pressure PT at which the sealed tanks 101a, 101b, and 101c will be destroyed and the burst pressure PS at which the insulating spacer 102 will be destroyed, during the time period before the fault clearance time TJ, causing a breakdown.

[0057] However, in the present embodiment, pressure relief devices 201ax, 201bx, and 201cx are installed. Therefore, when the internal space reaches pressure relief pressure PR, the pressure relief devices 201ax, 201bx, and 201cx connect the internal space of the sealed tanks 101a, 101b, and 101c to the outside, and the pressure P in the internal space drops. As a result, in the present embodiment, the pressure P in the internal space does not reach the burst pressure PT at which the sealed tanks 101a, 101b, and 101c are destroyed or the burst pressure PS at which the insulating spacer 102 is destroyed during the time period before the fault clearance time TJ. Therefore, in the present embodiment, it is possible to effectively prevent the destruction of the sealed tanks 101a, 101b, 101c, etc.

[0058] In addition, SF ６ In a gas-insulated switchgear in which insulating gas G10, such as a gas, is sealed, the atmospheric release of greenhouse gases is generally not permitted. Therefore, the mechanical strength of the sealed tank 101 is set to prevent the insulating gas G10 from being released into the atmosphere in the event of a system fault, and instead a pressure relief device is not provided. In contrast, when replacing the insulating gas G10 with insulating gas G20, which is a naturally occurring gas, the naturally occurring gas does not qualify as a greenhouse gas and can be released into the atmosphere. Therefore, in this embodiment, pressure relief devices 201ax, 201bx, and 201cx are provided in the sealed tanks 101a, 101b, and 101c to reduce the internal pressure, thereby preventing deformation and destruction of the sealed tanks 101a, 101b, and 101c and the insulating spacer 102.

[0059] [C] Modifications In the above embodiment, the existing adsorption devices 201a, 201b, and 201c (see FIG. 1A) are replaced with other pressure relief devices 201ax, 201bx, and 201cx, but this is not limiting. The pressure relief devices 201ax, 201bx, and 201cx may be installed in other parts of the sealed tanks 101a, 101b, and 101c, such as handholes and manholes.

[0060] Fourth Embodiment [A] Insulation Gas Replacement Method FIG. 4A is a flow diagram of an insulation gas replacement method according to a fourth embodiment.

[0061] Fig. 4B is a diagram schematically showing the state of the gas-insulated switchgear 100 before the insulation gas replacement method is performed in the fourth embodiment. In contrast, Fig. 4C is a diagram schematically showing the state of the gas-insulated switchgear 100 after the insulation gas replacement method is performed in the fourth embodiment.

[0062] As shown in Figures 4A, 4B, and 4C, this embodiment includes a step of installing a reinforcing structure 500 in the sealed tanks 101d and 101e (reinforcing structure installation step (ST43)). Except for this point and related points, this embodiment is the same as the first embodiment (see Figures 1B and 1C). Therefore, explanations of overlapping points will be omitted as appropriate.

[0063] 4B , in the gas-insulated switchgear 100 before the insulation gas replacement method is performed, the bellows 300 is interposed between the plurality of sealed tanks 101 d, 101 e. The bellows 300 is configured to expand and contract in the axial direction in response to displacement of the sealed tanks 101 d, 101 e in the axial direction due to thermal expansion, etc.

[0064] The sealed tanks 101d and 101e are fixed to the foundation FN via legs 400. The sealed tanks 101d and 101e have insulating spacers 102 attached to both ends, and are filled with insulating gas G10. In this state, a gas pressure thrust F2 (bellows cross-sectional area × gas pressure) is generated in the insulating spacers 102 on both sides of the sealed tanks 101d and 101e. The gas pressure thrust F2 is received and balanced by the sealed tanks 101d and 101e, so no external force is normally generated. Meanwhile, a gas pressure thrust F1 acts on the insulating spacer 102 adjacent to the bellows 300. However, because the bellows 300, unlike the sealed tank 101d, has spring properties, it expands and contracts to balance the gas pressure thrust F1, and the gas pressure thrust F1 is applied to the insulating spacer 102 located near the bellows 300. Therefore, a gas pressure thrust F1 is applied to the sealed tanks 101d and 101e, and is applied to the foundation FN via the legs 400 that connect the sealed tanks 101d and 101e to the foundation FN. Normally, when installing a gas-insulated switchgear, the foundation FN is designed to be able to withstand the gas pressure thrust F1 (bellows cross-sectional area × P10 (first reference gas pressure)).

[0065] 4A and 4C , in this embodiment, a reinforcing structure 500 is installed in the sealed tanks 101 d and 101 e by performing an insulation gas exchange method. The installation of the reinforcing structure 500 is performed at the installation site of the gas-insulated switchgear 100, similar to the other processes.

[0066] 4C , the reinforcing frame 500 includes a frame main body 501 and a frame support portion 502. In the reinforcing frame 500, the frame support portion 502 is provided for each of the plurality of sealed tanks 101d, 101e. The frame main body 501 extends along the axial direction of the plurality of sealed tanks 101d, 101e, and is supported by each of the plurality of sealed tanks 101d, 101e via the frame support portion 502 so as to face the plurality of sealed tanks 101d, 101e and the bellows 300 with a gap therebetween in the radial direction.

[0067] [B] Summary The functions and effects of this embodiment will be described.

[0068] As shown in Figure 4B, a load is applied to the foundation FN on which the frame 400 supporting the multiple sealed tanks 101d and 101e is installed, due to a gas pressure thrust F1 caused by the pressure of the insulating gas G10 sealed in the internal space of the sealed tanks 101d and 101e.

[0069] In this embodiment, SF ６ When replacing the insulating gas G10 such as gas with the insulating gas G20 which is a naturally occurring gas, SF ６ An insulating gas G20, which is a naturally occurring gas, is sealed in the internal space at a reference pressure P20 (second reference pressure) higher than a reference pressure P10 (first reference pressure) for sealing the insulating gas G10 such as gas.

[0070] The gas pressure thrust F1 generated after the gas is replaced with the insulating gas G20, which is a naturally occurring gas, is a value obtained by multiplying the cross-sectional area of ​​the bellows 300 by the reference pressure P20 (second reference pressure). ６ The gas pressure thrust F1 generated before replacement when insulating gas G10 such as gas is sealed is a value obtained by multiplying the reference pressure P10 by the cross-sectional area of ​​the bellows 300. As described above, the reference pressure P20 after replacement is higher than the reference pressure P10 before replacement, so a greater load is applied to the foundation FN after the insulating gas replacement. As a result, it may be difficult to adequately support the multiple sealed tanks 101d and 101e on the foundation FN in terms of mechanical strength.

[0071] However, in this embodiment, a reinforcing frame 500 is installed on the sealed tanks 101d, 101e. Therefore, at least a part of the gas pressure thrust F1 acting on the tanks 101d, 101e, a gas pressure thrust F3, is applied to the reinforcing frame 500, but because the reinforcing frame 500 connects the tanks 101d, 101e, the forces are balanced. Therefore, in this embodiment, the gas pressure thrust F4 applied to the replaced foundation FN is smaller than the gas pressure thrust F1 before replacement (F4 = F1 - F3, that is, F4 < F1).

[0072] Fifth Embodiment [A] Insulation Gas Exchange Method Fig. 5A is a flow diagram of an insulation gas exchange method according to a fifth embodiment. Fig. 5B is a diagram schematically illustrating a state of the gas-insulated switchgear 100 after the insulation gas exchange method has been performed according to the fifth embodiment.

[0073] As shown in Figures 5A and 5B, this embodiment includes a step of replacing an existing seal member SL1 (first seal member; see Figure 1A) with another seal member SL2 (second seal member) (seal member replacing step (ST44)). Except for this point and related points, this embodiment is the same as the first embodiment (see Figures 1B and 1C). Therefore, explanations of overlapping points will be omitted as appropriate.

[0074] In this embodiment, as shown in FIG. 5A, the step of replacing the seal member SL1 with another seal member SL2 (seal member replacing step (ST44)) is performed by SF ６ This is performed at the installation site after a process of recovering insulating gas G10 (recovery process ST10).

[0075] Here, a sealing material that has better sealing performance against the insulating gas G20 after replacement than the existing sealing member SL1 is used as the sealing member SL2. For example, the sealing member SL2 is made of fluororubber and is selected in consideration of its sealing performance against the insulating gas G20 after replacement.

[0076] [B] Summary In the gas-insulated switchgear 100 of this embodiment, SF ６ The insulating gas G20, which is a naturally occurring gas, is sealed in the internal space at a reference pressure P20 (second reference pressure) higher than a reference pressure P10 (first reference pressure) at which the insulating gas G10, such as a gas, is sealed. However, in this embodiment, the existing sealing member SL1 is replaced with a sealing member SL2, which has better sealing performance against the insulating gas G20 after replacement than the existing sealing member SL1. Therefore, in this embodiment, the sealing performance of the gas-insulated switchgear 100 can be ensured.

[0077] In particular, when the existing seal member SL1 is an O-ring made of ethylene propylene rubber, the insulating gas G20 after replacement is CO ２ When the gas contains CO ２ Compared to other naturally occurring gases, CO ２Therefore, it becomes difficult to maintain the gas pressure or gas concentration required for the insulation performance of the gas-insulated switchgear 100. However, by using an O-ring made of fluororubber as the replacement seal member SL2, it is possible to selectively permeate CO ２ It is possible to effectively prevent the permeation of

[0078] Sixth Embodiment [A] Insulation Gas Exchange Method Fig. 6A is a flow diagram of an insulation gas exchange method according to a sixth embodiment. Fig. 6B is a diagram schematically illustrating a state of the gas-insulated switchgear 100 after the insulation gas exchange method has been performed according to the sixth embodiment.

[0079] As shown in Figures 6A and 6B, this embodiment includes a step (conductor replacement step (ST45)) of replacing the existing conductor 103 (first conductor; see Figure 1A) with another conductor 103X (second conductor). Except for this point and related points, this embodiment is the same as the first embodiment (see Figures 1B and 1C). Therefore, explanations of overlapping points will be omitted as appropriate.

[0080] In this embodiment, as shown in FIG. 6A, the step of replacing the conductor 103 (first conductor; see FIG. 1A) with another conductor 103X (second conductor) (conductor replacing step (ST45)) is carried out by SF ６ This is performed at the installation site after a process of recovering insulating gas G10 (recovery process ST10).

[0081] Here, the conductor 103X (second conductor) is a conductor that has at least one of an electric field alleviation function that alleviates the electric field on the surface in the internal space more than the conductor 103 and a heat dissipation function that is higher than the conductor 103.

[0082] For example, the conductor 103X is a coated conductor in which a coating layer 1034 is applied to the surface of the conductor body 1030. The coating layer 1034 is formed of an insulating resin such as epoxy resin. Because the conductor 103X is a coated conductor, the conductor surface is smooth, improving discharge characteristics, and heat radiation is efficiently generated, thereby suppressing temperature increases. Note that the outer surface of the contact 1031 may also be coated.

[0083] [B] Summary In the gas-insulated switchgear 100 of this embodiment, SF ６ In this embodiment, the insulating gas G10, such as a gas, is replaced with the insulating gas G20, which is a naturally occurring gas. As described above, the insulating gas G20, which is a naturally occurring gas, is sealed in the internal space at a reference pressure P20 (second reference pressure) higher than the reference pressure P10 (first reference pressure) at which the insulating gas G10 is sealed, thereby improving the electrical performance of the gas-insulated switchgear 100. In this embodiment, the existing conductor 103 is replaced with the conductor 103X, which has at least one of an electric field alleviation function that alleviates the electric field more than the conductor 103 and a heat dissipation function that is higher than the conductor 103. Therefore, in this embodiment, it is possible to more effectively prevent the occurrence of areas with insufficient electrical performance or insufficient temperature rise suppression performance due to the replacement of the insulating gas, thereby ensuring the performance of the gas-insulated switchgear 100.

[0084] [C] Modifications In the above embodiment, the conductor 103X (second conductor) is described as being replaced with a painted conductor to provide a conductor having at least one of an electric field relaxation function and a heat dissipation function superior to that of the conductor 103. However, this is not limited to this. The conductor 103X (second conductor) may be replaced with a conductor whose shape has been modified to improve the electric field relaxation function or a conductor with high conductivity (e.g., a copper conductor). Furthermore, the contact 1031 may be replaced with a conductor whose shape has been modified to improve the electric field relaxation function or a conductor with high conductivity. Furthermore, the slide contact 1032 may be replaced with a conductor with higher conductivity.

[0085] Seventh Embodiment [A] Insulation Gas Exchange Method Fig. 7A is a flow diagram of an insulation gas exchange method according to a seventh embodiment. Fig. 7B is a diagram schematically illustrating a state of the gas-insulated switchgear 100 after the insulation gas exchange method according to the seventh embodiment is performed.

[0086] As shown in Figures 7A and 7B, this embodiment includes a process (arrestor replacement process (ST46)) of replacing the existing lightning arrester 112a (first lightning arrester; see Figure 1A) with another lightning arrester 112ax (second lightning arrester). Except for this point and related points, this embodiment is the same as the first embodiment (see Figures 1B and 1C). Therefore, explanations of overlapping points will be omitted as appropriate.

[0087] In this embodiment, as shown in FIG. 7A, the step of replacing the lightning arrester 112a (see FIG. 1A) with another lightning arrester 112ax (lightning arrester replacement step (ST46)) is performed by SF ６ This is performed at the installation site after a process of recovering insulating gas G10 (recovery process ST10).

[0088] Here, the lightning arrester 112ax is a lightning arrester that has improved electrical characteristics by flattening the voltage-current characteristics and increasing the short-term energy tolerance compared to the lightning arrester 112a, and has a reduced operating voltage.

[0089] [B] Summary In the gas-insulated switchgear 100 of this embodiment, SF ６ The insulating gas G10, such as a natural gas, is replaced with an insulating gas G20, which is a naturally occurring gas. Correspondingly, in this embodiment, the existing lightning arrester 112a is replaced with a lightning arrester 112ax (second lightning arrester) having a lower operating voltage than the existing lightning arrester 112a. By using a lightning arrester with a lower operating voltage, the insulation design of the gas-insulated switchgear 100 can be relaxed. Therefore, in this embodiment, the insulation design of the gas-insulated switchgear 100 can be rationalized.

[0090] Eighth Embodiment [A] Insulation Gas Replacement Method FIG. 8 is a flow diagram of an insulation gas replacement method according to an eighth embodiment.

[0091] As shown in FIG. 8, this embodiment includes a step of performing a leak test (leak test step (ST31)). Except for this point and related points, this embodiment is the same as the first embodiment (see FIG. 1C). Therefore, explanations of overlapping points will be omitted as appropriate.

[0092] [A-1] ST10 When performing the insulating gas exchange method in this embodiment, first, as shown in FIG. ６ The insulating gas G10, which is a gas or the like, is recovered (recovery step ST10).

[0093] [A-2] ST21a Next, as shown in FIG. 8, an insulating gas G20, which is a naturally occurring gas, is introduced (introduction step (ST21a)).

[0094] Here, an insulating gas G20 other than the insulating gas G20 used as the leak test gas in the leak test described later is introduced into the internal space of the sealed tanks 101a, 101b, and 101c as the air pressure test gas. When the naturally occurring gas used as the leak test gas in the leak test described later is helium gas, the air pressure test gas is a naturally occurring gas other than the leak test gas (e.g., air). The introduction of the insulating gas G20 as the air pressure test gas is performed so that the pressure in the internal space becomes an air pressure test pressure P30 for performing the air pressure test in the next process.

[0095] [A-3] ST30 Next, as shown in FIG. 8, a pressure test is carried out (pressure test step (ST30)).

[0096] The air pressure test is carried out in the same manner as in the above embodiment, and it is confirmed whether or not any damage such as deformation has occurred in the gas-insulated switchgear 100 .

[0097] [A-4] ST50 Next, as shown in FIG. 8, the insulating gas G20 introduced as the gas for the atmospheric pressure test is recovered (gas recovery step for the atmospheric pressure test (ST50)).

[0098] Here, insulating gas G20, which is a gas for pressure testing, is collected from the internal spaces of the sealed tanks 101a, 101b, and 101c.

[0099] [A-5] ST21b Next, as shown in FIG. 8, an insulating gas G20, which is a naturally occurring gas, is introduced (introduction step (S21b)).

[0100] In this embodiment, for example, He gas from the insulating gas G20, which is a naturally occurring gas, is introduced as a leak test gas for conducting a leak test in the next step (ST31). Here, the insulating gas G20 is introduced so that the pressure in the internal space becomes a leak test pressure for conducting the leak test in the next step (ST31). The leak test pressure is a reference pressure P20 (second reference pressure) of the insulating gas G20 that is finally sealed in the internal space in the insulating gas replacement method of this embodiment.

[0101] [A-6] ST31 Next, as shown in FIG. 8, a leak test is carried out (leak test step (ST31)).

[0102] The leak test is a test for confirming that the amount of leakage of the insulating gas G20 introduced as a leak test gas from the internal space of the sealed tanks 101 a, 101 b, and 101 c to the outside is equal to or less than a specified value. Here, the leak test is performed at the installation site of the gas-insulated switchgear 100, for example, outside the sealed tanks 101 a, 101 b, and 101 c, using a detector that detects a component of the insulating gas G20 (e.g., He), similar to other processes.

[0103] [A-7] ST51 Next, as shown in FIG. 8, the insulating gas G20 introduced as the gas for leak testing is recovered (leak test gas recovery step (ST51)).

[0104] Here, insulating gas G20, which is a gas for leak testing, is collected from the internal spaces of the sealed tanks 101a, 101b, and 101c.

[0105] [A-8] ST21c Next, as shown in FIG. 8, an insulating gas G20, which is a naturally occurring gas, is introduced (introduction step (S21c)).

[0106] Here, an insulating gas G20 other than the insulating gas G20 used as the leak test gas in the leak test is introduced into the internal space of the sealed tanks 101a, 101b, and 101c. If the naturally occurring gas used as the leak test gas in the leak test is helium gas, a naturally occurring gas other than helium gas (e.g., air) is introduced. The insulating gas G20 is introduced so that the pressure in the internal space becomes the reference pressure P20.

[0107] [B] Summary As described above, in this embodiment, the leak test is performed at the installation site of the gas-insulated switchgear 100. Therefore, disassembly, transportation, and reassembly are not required, which suppresses increases in work costs that arise from performing the leak test and shortens the period during which the gas-insulated switchgear is out of operation, thereby enabling efficient replacement of the insulating gas.

[0108] In this embodiment, the leak test is performed after the recovery step (ST10) is performed, with a detector detecting the amount of gas leaked from the internal space, in a state where insulating gas G20 (second insulating gas) is sealed in the internal space as a leak test gas so that the internal space is at reference pressure P20 (second reference pressure). Then, the air pressure test is performed after the leak test is performed, with insulating gas G20 (second insulating gas) sealed in the internal space as a air pressure test gas so that the internal space is at air pressure test pressure P30. Therefore, in this embodiment, the leak test and air pressure test can be performed efficiently.

[0109] In this embodiment, the insulating gas G20 (second insulating gas) used as the leak test gas is, for example, He gas. Since the amount of He gas contained in the atmosphere is extremely small, He gas leaked into the atmosphere can be easily detected using a detector. Therefore, the leak test can be performed accurately.

[0110] [C] Modifications [C-1] Modification 8-1 In the above embodiment, the insulating gas G20 used as the gas for leak testing is different from the insulating gas G20 finally sealed in the internal space, but this is not limited to this. The insulating gas G20 used as the gas for leak testing and the insulating gas G20 finally sealed in the internal space may be the same. In this case, the above-mentioned leak test gas recovery step (ST50) does not need to be performed.

[0111] [C-2] Modification 8-2 FIG. 9 is a flowchart of an insulating gas replacement method in Modification 8-2 of the eighth embodiment.

[0112] As shown in FIG. 9, this modification includes a step of performing a leak test (a leak test step (ST31)) as in the above embodiment (see FIG. 8). However, in this modification, SF ６ This modification differs from the eighth embodiment in that a leak test is performed using an insulating gas G10 such as a gas as the leak test gas. Except for this and related points, this modification is the same as the eighth embodiment. Therefore, explanations of overlapping points will be omitted as appropriate.

[0113] [C-2-1] ST60 When performing the insulating gas replacement method in this modified example, first, as shown in FIG. ６ An insulating gas G10 such as a gas is introduced (introduction step (S60)).

[0114] In this modification, SF ６ An insulating gas G10 such as a gas is introduced as a pressure test gas for performing a pressure test in the next step (ST30). Here, the insulating gas G10 is introduced so that the pressure in the internal space becomes a pressure test pressure P30.

[0115] [C-2-2] ST30 Next, as shown in FIG. 9, a pressure test is performed (pressure test step (ST30)).

[0116] The air pressure test is carried out in the same manner as in the above-described modified example, and it is confirmed whether or not any damage such as deformation has occurred in the gas-insulated switchgear 100 .

[0117] [C-2-3] ST61 Next, as shown in FIG. 9, the pressure in the internal space into which the insulating gas G10 has been introduced is adjusted (pressure adjusting step (S61)).

[0118] The pressure is adjusted in the same manner as in the above-described modified example, and the pressure in the internal space is adjusted to the reference pressure P20, which is the leak test pressure.

[0119] [C-2-4] ST31 Next, as shown in FIG. 9, a leak test is carried out (leak test step (ST31)).

[0120] In this modification, the leak test uses the insulating gas G10 as the leak test gas, and checks whether the insulating gas G10, which is the leak test gas, leaks from the internal space of the sealed tanks 101a, 101b, and 101c to the outside. Here, the leak test is performed by, for example, detecting the component (SF) of the insulating gas G10 outside the sealed tanks 101a, 101b, and 101c. ６ ) is used to detect the fault at the installation site of the gas-insulated switchgear 100, similar to the other processes.

[0121] [C-2-5] ST10 Next, as shown in FIG. ６ The insulating gas G10, which is a gas or the like, is recovered (recovery step ST10).

[0122] [C-2-6] ST20 Next, as shown in FIG. 9, insulating gas G20, which is a naturally occurring gas, is enclosed (enclosing step (ST20)).

[0123] Here, SF ６ An insulating gas G20, which is a naturally occurring gas, is introduced into the internal space of each of the sealed tanks 101a, 101b, and 101c into which an insulating gas G10, such as a gas, has been collected. The insulating gas G20, which is a naturally occurring gas, is introduced so that the internal space reaches a reference pressure P20, and the internal space is sealed.

[0124] As described above, in this modification, similarly to the eighth embodiment, the leak test is performed at the installation site of the gas-insulated switchgear 100. Therefore, transportation work and the like are not required, which suppresses increases in costs and enables efficient replacement of the insulating gas.

[0125] In this modification, the atmospheric pressure test is performed by SF ６ Before recovering the insulating gas G10, the insulating gas G10 is sealed in the internal space so that the internal space is at the atmospheric pressure test pressure P30. The leak test is then carried out after the atmospheric pressure test is carried out. ６ Before recovering the insulating gas G10, the internal space filled with the insulating gas G10 is adjusted to a reference pressure P20 (leak test pressure), thereby enabling the leak test and the air pressure test to be carried out efficiently in this modified example.

[0126] In the leak test of this modified example, SF ６ Insulating gas G10, such as SF gas, is used as the gas for leak testing. ６ The insulating gas G10, which is a gas such as SF, does not normally exist in the atmosphere. ６ The detector can be used to easily detect leakage of the insulating gas G10 into the atmosphere, making it possible to accurately carry out a leak test.

[0127] <Others> Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the inventions and their equivalents as defined in the claims.

[0128] 100: gas insulated switchgear, 101a: sealed tank, 101b: sealed tank, 101c: sealed tank, 101d: sealed tank, 101e: sealed tank, 102: insulating spacer, 103: conductor, 103X: conductor, 111a: busbar, 111b: disconnector, 111c: gas circuit breaker, 112a: lightning arrester, 112ax: lightning arrester, 112b: work earthing switch, 112c: high-speed earthing switch, 201a: suction device, 201ax: pressure relief device, 201b: suction device, 201bx: pressure relief device, 201c: suction device, 201cx: pressure relief device, 300: bellows, 400: frame, 500: reinforcing frame, 501: frame body, 502: frame support part, 1021: insulating part, 1022: metal flange part, 1030: conductor body, 1031: contact, 1032: slide contact, 1034: paint layer, F101a: flange, F101b: flange, FN: foundation, G10: insulating gas, G20: insulating gas, T1: bolt BT1, T2: bolt BT2, V111a: gas valve, V111b: gas valve, V111c: gas valve

Claims

1. An insulating gas replacement method for a gas-insulated switchgear in which a first insulating gas is sealed in the internal space of a sealed tank at a first standard pressure, for replacing the first insulating gas with a second insulating gas having a lower global warming potential than the first insulating gas, comprising: a recovery step of recovering the first insulating gas from the internal space of the sealed tank; a filling step of introducing the second insulating gas into the internal space of the sealed tank from which the first insulating gas has been recovered in the recovery step and sealing the internal space so that the internal space has a second standard pressure higher than the first standard pressure; and a pressure test step of performing a pressure test on the gas-insulated switchgear under the condition that the internal space of the sealed tank has a pressure test pressure higher than the second standard pressure, wherein the second insulating gas is a gas consisting of at least one substance selected from oxygen, carbon dioxide, nitrogen, helium, neon, argon, xenon, and krypton, and the recovery step, filling step, and pressure test step are each performed at the installation site where the gas-insulated switchgear is installed. Insulation gas replacement method.

2. The insulating gas replacement method of claim 1, wherein the filling process comprises an introduction process of introducing the second insulating gas into the internal space, and a pressure adjustment process of adjusting the pressure of the internal space into which the second insulating gas has been introduced in the introduction process, wherein the introduction process introduces the second insulating gas so that the pressure in the internal space becomes the atmospheric pressure test pressure, the atmospheric pressure test process is carried out after the introduction process is carried out, and the pressure adjustment process is carried out after the atmospheric pressure test process is carried out.

3. The insulation gas replacement method according to claim 1, wherein the sealed tank is fastened using first bolts at the installation site, and the insulation gas replacement method includes a bolt replacement step of replacing the first bolts with second bolts having a higher tensile strength than the first bolts, and the bolt replacement step is performed at the installation site.

4. An insulating gas exchange method according to claim 1, further comprising a pressure relief device installation step of installing a pressure relief device in the sealed tank, wherein the pressure relief device is configured to maintain the pressure in the internal space of the sealed tank at or below the pressure relief pressure by communicating the internal space of the sealed tank with the outside of the sealed tank when the internal space of the sealed tank reaches a pressure relief pressure lower than a burst pressure at which components constituting the sealed tank are broken, and the pressure relief device installation step is carried out at the installation site.

5. The insulation gas exchange method according to claim 1, further comprising a reinforcing frame installation step of installing a reinforcing frame in the sealed tank, wherein the reinforcing frame installation step is carried out at the installation site.

6. The insulating gas exchange method according to claim 1, wherein the internal space of the sealed tank of the gas-insulated switchgear is sealed by a first sealing member at the installation location, and the insulating gas exchange method includes a sealing member exchange step of replacing the first sealing member with a second sealing member that has better sealing performance against the second insulating gas than the first sealing member, and the sealing member exchange step is carried out at the installation location.

7. The insulating gas exchange method according to claim 1, wherein, at the installation location, the sealed tank accommodates a first conductor in the internal space, and the insulating gas exchange method includes a conductor exchange step of exchanging the first conductor with a second conductor having at least one of an electric field alleviation function that alleviates the electric field in the internal space more than the first conductor and a heat dissipation function higher than the first conductor, and the conductor exchange step is performed at the installation location.

8. The insulating gas replacement method according to claim 1, wherein a first lightning arrester is installed in the sealed tank at the installation site, and the insulating gas replacement method includes a lightning arrester replacement step of replacing the first lightning arrester with a second lightning arrester having a lower operating voltage than the first lightning arrester, and the lightning arrester replacement step is performed at the installation site.

9. The insulating gas replacement method according to claim 1, further comprising a leak test process of performing a leak test on the sealed tank under conditions in which the pressure in the internal space is adjusted to the second reference pressure, wherein the leak test process is performed at an installation site where the gas-insulated switchgear is installed.

10. The insulating gas replacement method described in claim 9, wherein in the leak test process, the leak test is carried out using a detector that detects components that have leaked from the internal space after the recovery process is carried out, with the second insulating gas sealed in the internal space as a leak test gas so that the internal space becomes the second reference pressure, and in the air pressure test process, the air pressure test is carried out before the leak test process is carried out, with the second insulating gas sealed in the internal space as an air pressure test gas so that the internal space becomes the air pressure test pressure.

11. The insulating gas replacement method described in claim 9, wherein in the air pressure test step, the air pressure test is performed before the recovery step, with the first insulating gas sealed in the internal space so that the internal space is at the air pressure test pressure, and in the leak test step, the leak test is performed after the air pressure test step, with the internal space sealed with the first insulating gas adjusted to the second reference pressure, using a detector that detects components that have leaked from the internal space.

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