Method, device, use and system for gas density monitoring

Abstract

Density monitoring method for monitoring the gas density of a pollutant gas (10), comprising: a) Providing a closed reference volume (26) with a partition (28) movable between the reference volume (26) and the pollutant gas (10) to be monitored, b) Providing a reference gas (56) which has a global warming potential at least twice as low as that of the pollutant gas (10) in the reference volume (26) at a reference gas pressure increased compared to the filling pressure of the pollutant gas (10), c) Compensating for a force acting on the partition (28) due to the increased reference gas pressure in the reference volume (26) by means of a spring device (32), and d) Detecting a deflection of the partition (28) to monitor the gas density.

Description

[0001] The invention relates to a density monitoring method for monitoring the gas density of a harmful gas. Furthermore, the invention relates to a density monitor for monitoring the gas density of a harmful gas. Finally, the invention relates to an electrical system with a closed space, such as a housing, a container, or a tank, in which an insulating gas with environmentally harmful effects (harmful gas) is contained, and with a density monitor for monitoring the gas density of the insulating gas.

[0002] For the technological background, please refer to the following literature: [1] “Insulating gas density monitoring”, brochure of Trafag AG with the printing note “H70558a Trafag AG 11 / 2021” [2] DE 10 2010 055 249 B4 [3] DE 10 2013 115 007 B4 [4] DE 10 2016 123 588 A1 [5] WO 2019 / 192857 A1 [6] Wikipedia “Greenhouse potential”, downloaded on 20.01.2022 from https: / / de.wikipedia.org / wiki / Treibhauspotential [7] Novec Insulating Gases website 3M Germany, downloaded on 20 January 2022 from https: / / www.3mdeutschland.de / 3M / de_DE / novecde / anwendungen / isoliergas / [8] "Powering a sustainable future. 3M™ Novec™ Insulating Gases," a 3M brochure, downloaded on January 20, 2022, from https: / / multimedia.3m.com / mws / media / 14086000 / novec-insulating-gasesfor-power-generation.pdf [9] "sf6 replacement g3 flyer", brochure downloaded on 20.01.2022 from https: / / www.gegridsolutions.com / products / brochures / sf6-ersatz_g3-flyerger.pdf

[10] DE 102 32 823 A1

[11] DE 10 2017 104 919 A1

[12] DE 10 2019 126 134 A1

[13] DD 2 72 708 A1

[0003] Density monitors are devices, particularly measuring instruments, for monitoring the density of a gas to be monitored. As known from [1] to [5], density monitors are used in particular to monitor the density of a gas, for example, SF6, used as an insulator in gas-insulated high- and medium-voltage systems, such as high-voltage switchgear, converters, pipelines, switchgear, and transformers.

[0004] For this purpose, density monitors based on electronic measuring principles are known, for example, from

[10] . These are equipped with an electronic density sensor as the measuring transmitter. The sensor has a quartz oscillator arranged in the gas and provides a frequency signal proportional to the density of the gas as the measured value. The frequency signal is fed to an electronic evaluation unit. Further density monitors are known from

[11] to

[13] .

[0005] In contrast, density monitors based on mechanical measuring principles have become established on the market. Due to their mechanical measuring principle, they operate very reliably and require little maintenance, even over very long periods of time. In the simplest and most common case, a partition wall operating over a reference volume is connected to the measuring volume, with a partition wall movement caused by a change in gas density actuating a switch. For example, in the density monitors known from [1] to [5], a partition wall of a metal bellows is connected to a switch, so that a partition wall movement beyond a minimum travel triggers a switching operation.

[0006] The invention aims to make density monitoring more environmentally friendly using a mechanical measuring principle with reference volume.

[0007] To achieve this object, the invention provides a density monitoring method according to claim 1 as well as a density monitor and an electrical system according to the dependent claims.

[0008] Advantageous embodiments are the subject of the subclaims.

[0009] The invention provides, according to a first aspect thereof, a density monitoring method for monitoring the gas density of a harmful gas, comprising: a) Providing a closed reference volume with a partition wall arranged between the reference volume and the pollutant gas to be monitored, b) providing a reference gas which has a greenhouse potential that is at least two times lower than the pollutant gas, in the reference volume with a reference gas pressure that is higher than the pollutant gas pressure of the pollutant gas, c) compensating a force acting on the partition wall due to the increased reference gas pressure in the reference volume by means of a spring device, and d) Detecting a deflection of the partition to monitor the gas density.

[0010] According to a further aspect, the invention provides a density monitor for monitoring a gas density of a harmful gas, comprising: a measuring volume, a connection for connecting the measuring volume to a room containing the harmful gas, a closed reference volume filled with a reference gas different from the pollutant gas to be monitored, which has a global warming potential GWP<100, where GWP is the CO2 equivalent based on 100 years according to IPCC AR5, wherein the reference gas is filled with an excess pressure compared to the pressure in the measuring volume during normal operation of the density monitor, a partition wall that separates the reference volume from the measurement volume, a partition wall deflection detection device for detecting a deflection of the partition wall, and a spring device for elastically exerting a force on the partition to compensate for the overpressure in the reference volume.

[0011] In preferred embodiments, a density monitor is used to monitor a gas density of a harmful gas, wherein the density monitor comprises a measuring volume, a connection for connecting the measuring volume to a space containing the harmful gas, a closed reference volume, a partition wall that separates the reference volume from the measuring volume and a partition wall deflection detection device for detecting a deflection of the partition wall and at least one spring device for elastically exerting a force on the partition wall, wherein the reference volume contains a reference gas different from the pollutant gas to be monitored, which has a global warming potential GWP<100, where GWP is the CO2 equivalent based on 100 years according to IPCC AR5, with a reference gas pressure that is greater than a pollutant gas pressure in the measuring volume, wherein a force acting on the partition wall due to the increased reference gas pressure in the reference volume is compensated by means of the spring device.

[0012] According to a further aspect, the invention provides an electrical system comprising a space filled with an insulating gas as the harmful gas and a density monitor which is connected to the space for monitoring the gas density of the harmful gas, wherein the density monitor has a measuring volume which is connected to the space, a closed reference volume which is filled with a reference gas which is different from the harmful gas to be monitored, which reference gas has a global warming potential GWP<100, where GWP refers to the CO2 equivalent based on 100 years according to IPCC AR5, and has an overpressure compared to the harmful gas pressure prevailing in the space, a partition wall which separates the reference volume from the measuring volume, a partition wall deflection detection device for detecting a deflection of the partition wall, and at least one spring device for elastically exerting a force on the partition wall in order to compensate for the overpressure in the reference volume.

[0013] A preferred embodiment of at least one of the aspects of the invention comprises: b1) Providing a gas with a GWP<100, preferably GWP<20, particularly preferably GWP>2, where GWP denotes the CO2 equivalent based on 100 years according to IPCC AR5, as reference gas in the reference volume.

[0014] A preferred embodiment of at least one of the aspects of the invention comprises: b2) Providing a gas from the group comprising air, N2, O2, noble gases, Ar, Kr, He, CO2 and mixtures of the aforementioned gases with each other or with another gas as a reference gas in the reference volume.

[0015] A preferred embodiment of at least one of the aspects of the invention comprises: Providing the reference gas with a reference gas pressure that is 2.5-45% higher than the harmful gas pressure in the reference volume.

[0016] A preferred embodiment of at least one of the aspects of the invention comprises: c1) Applying a first spring force of the spring device to the partition wall acting in the direction of the reference volume to compensate for the force caused by the increased reference gas pressure.

[0017] For example, the spring device comprises a first spring for exerting the first spring force. The first spring is preferably designed as a first compression spring, which acts on the harmful gas side of the partition and urges it toward the reference volume.

[0018] A preferred embodiment of at least one of the aspects of the invention comprises: c2) Applying a second spring force to the partition wall in the direction of the harmful gas to extend the monitorable gas density range.

[0019] For example, the spring device comprises a second spring for exerting the second spring force. The second spring is preferably designed as a second compression spring acting on the partition wall from the reference volume side.

[0020] A preferred embodiment of at least one of the aspects of the invention comprises: Adjusting the first spring force depending on the harmful gas pressure and / or the reference gas pressure. In particular, the preferred embodiment of the invention comprises selecting the spring constant of the first spring depending on the harmful gas pressure and / or the reference gas pressure.

[0021] A preferred embodiment of at least one of the aspects of the invention comprises: Adjusting the second spring force according to a desired gas density value or gas density range for at least one switching point or switching range. In particular, the second aspect comprises selecting the spring constants of the first and / or second spring according to a desired gas density value or gas density range for at least one switching point or switching range.

[0022] A preferred embodiment of at least one of the aspects of the invention comprises: Selection of a preload of at least one spring of the spring device according to a gas density value or gas density range desired for at least one switching point or one switching range.

[0023] A preferred embodiment of at least one of the aspects of the invention comprises: Limiting the effectiveness of at least one spring of the spring device to a partial area of ​​the deflection path of the partition wall.

[0024] A preferred embodiment of at least one of the aspects of the invention comprises: Limiting the effectiveness of the first spring to a range below a specified gas density threshold.

[0025] According to a preferred embodiment of at least one of the aspects of the invention, a metal bellows is or is provided for separating the reference volume from a measuring volume containing the harmful gas, wherein the partition wall is formed on the metal bellows.

[0026] Preferably, the reference gas is selected from the group comprising air, N2, O2, noble gases, Ar, Kr, He, CO2 and mixtures of the aforementioned gases with one another or with another gas.

[0027] In a preferred embodiment of at least one of the aspects of the invention, a first spring acting on the partition wall in the direction of the reference volume is or will be provided to compensate for the force caused by excess pressure and a second spring acting on the partition wall in the direction of the harmful gas to expand the monitorable range of the gas density.

[0028] Preferably, the density monitor according to the invention or an advantageous embodiment thereof is designed to carry out the method according to the invention or an advantageous embodiment thereof. Preferably, the method according to the invention or an advantageous embodiment thereof is carried out with a density monitor according to the invention or an advantageous embodiment thereof.

[0029] Preferably, the method according to the invention or an advantageous embodiment thereof is carried out on an electrical system of the invention or an advantageous embodiment thereof.

[0030] Features or steps disclosed for one of the aspects of the invention - method, device, system - or advantageous embodiments thereof may also be provided in one of the other aspects of the invention or advantageous embodiments thereof.

[0031] Advantageous embodiments of the invention relate to density monitors with gases with a low greenhouse effect, in particular density monitors with green or climate-neutral gases, as well as uses thereof, such as density monitoring methods to be carried out therewith. Preferred embodiments of the invention relate to mechanically operating density monitors without SF6, which are designed to monitor the density of SF6.

[0032] In particular, a density monitor based on the reference chamber principle (mechanical measuring principle) is provided. The density monitor is preferably used to monitor gas density in high-voltage switchgear (gas-insulated switchgear, outdoor switchgear, dead tanks) to prevent damaging arcs and ensure the safety of the systems over long periods of time (e.g., 30 years). A temperature-compensated pressure switch is a special design example of a density monitor. Temperature compensation is achieved, in particular, via a reference volume thermally connected to the gas to be monitored.

[0033] As is also known from [1] to [5], a density monitor or a temperature-compensated pressure switch of this type measures against a reference volume. In previously known density monitors of this type, the reference volume must be filled gas-tight with the same gas to be measured as the gas to be monitored at approximately the same pressure as the system pressure. Thus, known density monitors of this type must be filled with greenhouse gases such as SF6, some of which are harmful to the environment. To date, the same insulation gas used by the system manufacturer has to be used to ensure sufficient temperature compensation. The gas space (system gas) and the reference volume are separated from each other by a metal bellows, for example. A density and pressure difference between the gas spaces leads to a mechanical lift of the metal bellows. This gas (SF6) is a greenhouse gas with a very high GWP (>10,000) and is subject to increasingly strict environmental regulations, see reference [6].The gas behavior and the function of the density monitor are described in detail in the reference [1], to which reference is made for further details.

[0034] According to preferred embodiments, the density monitor is a purely mechanical density monitor, typically supplied with two to four switching points (e.g., switching point 1 = alarm 640 kPa, switching point 2 = refill procedure required 620 kPa, and switching point 3 = emergency shutdown 600 kPa). The switching point thresholds are located on so-called isochore values ​​so that a pure temperature effect does not lead to a false alarm. The optimal filling pressure in the reference volume for previously known density monitors in this example would be 620 kPa; the errors for the other two switching points would be a few kPa for a temperature range of -25°C and 50°C.

[0035] The reference gas chamber principle requires the filling of the internal reference volume with the identical system gas for good temperature compensation (for example, outdoor use between -60°C and +60°C is possible). Traditionally, SF6, CF4 with N2, and mixtures thereof are used in high-voltage technology for liquefaction purposes. For several years, less environmentally harmful substitute gases have also been available on the market, which already cause significantly lower GWP, see references [7] to [9]. Nevertheless, many systems worldwide continue to be filled with SF6, as do the reference chamber systems of the density monitors used. Furthermore, the substitute gases that must be filled into the reference chamber of existing density monitors based on the reference volume principle still have a relatively high global warming potential.

[0036] Preferred embodiments of the invention use any less climate-damaging or, more preferably, climate-neutral gases (i.e., gases without a greenhouse effect) such as N2, Kr, or Ar as fill gases for the reference chamber. To achieve the same isochore (specified in kPa / °C) as SF6 (or another greenhouse gas used as an insulating gas), overfilling is performed.

[0037] In particular, a filling pressure approximately 3-40% higher is used to simulate the required filling pressures between 1 and 12 bar for SF6, for example. The reference gas (e.g., a climate-neutral gas, i.e., a non-greenhouse gas) is therefore preferably filled at a pressure between 1.5 and 20 bar.

[0038] In a preferred embodiment, gases that are widely and inexpensively available on the market, such as industrial air, N2, Ar, or even CO2, are used as the reference gas. Although CO2 is known as a greenhouse gas, with its GWP of 1, it is far more climate-friendly than the system gases to be monitored. Other noble gases are also possible or can be added. For example, the reference chamber can be filled and welded to ensure a gas-tight seal under a protective gas atmosphere that already corresponds to the atmosphere that will later be present in the reference chamber.

[0039] Preferably, the density monitor has a filling opening for filling the reference volume and / or for changing the composition or pressure of the reference pressure.

[0040] In order to achieve comparable accuracies and switching point distances of the density monitor as with previous mechanical density monitors with reference volume principle, it is preferable to partially compensate for the higher force of the gas pressure spring.

[0041] In preferred embodiments of the invention, at least two additional springs are used in the construction to compensate for this force effect.

[0042] A first spring serves to compensate for the force of the reference chamber. The first spring exerts a first elastic force on the partition wall in the direction of the reference volume, either directly or indirectly. For example, if designed as a compression spring, the first spring acts on the partition wall from the corrosive gas side, e.g., from the side of the measurement volume.

[0043] The first spring is preferably selected depending on the pressure and has spring constants, for example, between 15 and 140 N / mm at 1 and 12 bar filling pressure.

[0044] A second spring exerts a second elastic force on the partition wall in the opposite direction to the first elastic force. In particular, the second spring exerts a second elastic force on the partition wall, directly or indirectly, toward the corrosive gas. The second spring—if designed as a compression spring—is housed, for example, in the reference volume and acts on the partition wall from the reference volume side.

[0045] The second spring preferably has a spring constant of approximately 20-30 N / mm. The second spring serves as the reference chamber for range extension. This allows, for example, widely spaced switching points or an extended display range to be achieved.

[0046] By selecting or adjusting the different spring constants of the first and second spring, their preload and / or their effective travel, the density monitor can be adapted to prevailing pressures, desired switching points or display ranges and the corrosive gas.

[0047] For adjusting the effective path, at least one stop can be provided, for example, which limits the effect of at least one of the springs to one or more specific areas of the deflection path of the partition wall.

[0048] Preferred embodiments of the invention provide a temperature-compensated density monitor without the use of an environmentally harmful gas («green gas» density monitor).

[0049] Preferably, a density monitor for high and medium voltage switchgear with green gas (e.g. nitrogen, argon, helium...) with temperature compensation is provided.

[0050] Adjusting the isochore gradient to the customer gas—plant gas, insulation gas, or harmful gas—is preferably achieved by overfilling the reference chamber with green gas. This additional force from the gas spring can then be compensated for by spring force.

[0051] Preferred embodiments use a noble gas as the reference gas. For example, argon gas (green gas) allows the reference chamber to be sealed without additional components such as expanders or spheres and under pressure (argon gas).

[0052] In a preferred embodiment, the force compensation by a spring device or at least one spring thereof is limited to a portion of the measuring range. For example, the first spring is only effective for the low-pressure range. Preferably, the first spring is only used up to the lowest switching alarm; this arrangement achieves a more precise switching point, since the spring is no longer used at the switching points.

[0053] In preferred embodiments, different pressure ranges can be realized through the interaction of spring forces and the reference force—i.e., the force due to the reference gas pressure in the reference volume. Depending on the desired pressure range, the spring forces as well as the preload of the first and second spring elements can be designed accordingly.

[0054] The spring device can be constructed in different ways. For example, it can be designed as a spring arrangement with at least one or preferably several springs. A "spring" is understood to be an elastically deformable machine element for exerting a spring force. A spring can be formed by one spring element or several spring elements acting in parallel and / or in series. Examples of springs or spring elements that can be used include coil springs, gas springs, rubber springs, elastomer blocks, leaf springs, torsion springs, spiral springs, spring washers, conical springs, etc. Metallic springs, in particular coil compression springs, are preferred.

[0055] Examples of implementation are explained in more detail below using the attached drawing. It shows: Fig. 1 shows a section through a measuring sensor of a density monitor according to an embodiment of the invention; Fig.2 shows a section through a lower part of a density monitor connected to an electrical system according to a further embodiment of the invention; Fig. 3 a section through the upper part of the density monitor of Fig. 2.

[0056] The figures show different embodiments of a density monitor 14 to be connected to an electrical system 12 filled with harmful gas 10, wherein Fig. 1 a sensor 16 of the density monitor 14 according to an embodiment to illustrate the functional principle, Fig. 2 the connection of the sensor 16 of the density monitor according to a further embodiment to the system 12, and Fig. 3 shows an embodiment of a switching and / or display part 18 of the density monitor 14 that can be connected to the measuring sensor 16 according to one of the embodiments.

[0057] The electrical installation 12 is, in particular, a gas-insulated high- or medium-voltage installation, such as a high- or medium-voltage switchgear, a high- or medium-voltage transformer, a high- or medium-voltage pipeline, a high- or medium-voltage switching device, or a transformer. For gas insulation, a chamber 24 of the electrical installation 12 is filled with an insulating gas. Such insulating gases are greenhouse gases with a high global warming potential (GWP) and are therefore harmful gases that are harmful to the climate. For example, the harmful gas 10 used as the insulating gas in the installation 12 is one of the gases SF6, CF4 with N2, a mixture thereof, or an SF6 substitute gas, as explained in more detail in the references [7] to [9]. The pressure under which the harmful gas 10 is in the chamber 24 is referred to below as the harmful gas pressure. This pressure (e.g., SF6 pressure) is specified as a predetermined filling pressure on the installation side.

[0058] The density monitor 14 is used to monitor the gas density of the harmful gas 10. It has the measuring sensor 16 designed as a sensor for the system gas.

[0059] According to the embodiments shown in the figures, the density monitor 14 has a measuring volume 20, a connection 22 for connecting the measuring volume 20 to the space 24 of the electrical system 12 containing the harmful gas 10, a closed reference volume 26, a movable or deflectable partition 28 which separates the reference volume 26 from the measuring volume 20, a partition deflection detection device 30 for detecting a deflection 31 of the partition 28 and a spring device 32.

[0060] The connection 22 is designed as a pressure connection for the pressure- and fluid-tight connection of the measuring volume 20 to the chamber 24 of the system 12. At least one gas passage 23 leading to the system 12 is formed in the connection 22. In the illustrated embodiment, the connection 22 has several gas passages 23.

[0061] To form the measurement volume 20 and the reference volume 26, in preferred embodiments, the interior of a housing 34 of the measuring sensor 16 is divided into several chambers by means of at least one metal bellows 36. A measurement chamber 38 communicating with the connection 22 forms the measurement volume 20. A reference chamber 40 for forming the reference volume 26 is separated from this by the metal bellows 36 or one of several metal bellows 36a. The partition wall 28 is formed on this metal bellows 36, 36a. For example, the partition wall 28 is formed by a bellows base 42 of this metal bellows 36, 36a.

[0062] In the illustrated embodiment, the reference chamber 40 is formed between several metal bellows 36a, 36i. An outer metal bellows 36a with the partition 28 separates the reference chamber 40 from the measuring volume 20. An inner metal bellows 36i separates the reference chamber 40 from the switching and display part 18.

[0063] The partition deflection detection device 30 detects a movement or deflection 31 of the partition 28 caused by a change in the noxious gas pressure relative to the pressure in the reference volume 26. Because the reference volume 26 is in thermal communication with the measurement volume 20 and thus also with the noxious gas 10, temperature compensation occurs. Thus, using the reference chamber principle, as explained in detail in reference [1], the gas density can be detected via the deflection 31 of the partition.

[0064] The partition wall deflection detection device 30 has a transmission element 44 for transmitting the deflection of the partition wall 28 to switching or display elements 46a-46d, 48 of the switching and / or display part 18. A switching rod 49 connected to the partition wall 28 for joint movement serves as the transmission element 44, for example. The switching rod 49 has a pressure plunger 50 and a crossbar 52 with arms 54a-54d of different lengths. This allows different (e.g., a first to fourth) switching elements 46a-46d to be switched at different positions of the deflection of the partition wall 28—and thus at different gas density values ​​(switching points), for example to emit different alarms or shutdown signals. Furthermore, the pressure plunger 50 can drive a customer-specific display 48.

[0065] An upper stop 66 is arranged on the switching rod 49 to limit movement of the partition 28 in case of excessive pressures in the measuring volume.

[0066] While in the density monitors from references [1] to [5] a reference chamber is filled with the same gas and at the same pressure as in the system 12, the reference volume 26 in the embodiments of the invention is filled with a reference gas 56 that differs from the pollutant gas 10 and has a significantly lower global warming potential than the pollutant gas 10. For example, the GWP of the reference gas 34 is more than a factor of two lower than the GWP of the pollutant gas 10 to be monitored.

[0067] As reference gases, gases with a GWP of <100, preferably GWP of <20, and particularly preferably GWP of <2 are used. Particularly preferred are widely available, inexpensive gases such as industrial air or compressed air, N2, O2, Ar, or even CO2, whereby CO2, with a global warming potential of GWP=1, is still significantly more climate-friendly than any insulating gas. In other embodiments, noble gases such as Ar, Kr, and He are used. Especially when shielding gases such as Ar and Kr are used, the reference chamber 40 can be sealed gas-tight during filling by welding.

[0068] As known from [1], the gas density is measured along isochores.

[0069] To align the isochore gradients of the reference gas and the pollutant gas to be monitored, the reference gas 56 is filled into the reference chamber 40 at an overpressure compared to the specified system filling pressure (pollutant gas filling pressure). The overpressure is, for example, 2.5%–45%. Thus, the reference gas pressure is 2.5%–45%, preferably 3% to 40%, higher than the pollutant gas pressure. Example values ​​for different system filling pressures of SF6 as the monitored gas and N2 with 5% He as the reference gas are shown in Table 1. Table 1 SF6 filling pressure kPa N2 filling pressure including 5% helium kPa Isochore gradient in kPa / °C 100 103 0.35 200 211 0.72 300 324 1.11 400 442 1.52 500 567 1.96 600 699 2.41 700 839 2.90 800 981 3.42 900 1135 3.96 1000 1296 4.54 1100 1466 5.15

[0070] In one possible embodiment, during the manufacture of the density monitor 14, the reference chamber 40 is preferably prefabricated as a separate unit filled by gas-tight connection of the inner and outer metal bellows 36a, 36i and then installed in the housing 34. In the Fig. 1 and Fig.In the embodiments shown in Figure 2, the reference chamber 40 is formed by an inner bellows 40i, the bellows base 42, an outer bellows 40a, and a flange cover 62, which is part of the housing 34 of the measuring sensor 16 (also called the sensor system). The bellows 40a, 40i are designed as metal bellows 36a, 36i and are connected to the flange cover 62 in a fluid-tight manner by their edges shown above in the figures. A filling hole 62 is provided on the flange cover for filling the reference chamber 40. The density monitor thus has a filling device for filling the reference chamber 40 and / or for exchanging the reference gas or for changing the reference gas pressure. The reference gas pressure can thus be adapted to a change in the filling pressure in the system 12, so that the overpressure in the reference chamber 40 can be adjusted relative to the filling pressure in the system 12.

[0071] The spring device 32 is provided to compensate for at least some effects that occur due to the use of the climate-friendly reference gas in the reference chamber instead of the pollutant gas to be monitored for temperature compensation.

[0072] Due to the reference gas pressure being higher than the harmful gas pressure, the gas spring formed by the filled metal bellows 36 exerts a greater force than in conventional density monitors. The spring device 32 is designed specifically to compensate for this force due to the excess pressure.

[0073] In the illustrated embodiments, the spring device 32 comprises a first spring 58 for exerting a first spring force on the partition 28 in the direction of the reference gas. The first spring force serves to compensate for the force acting on the partition 29 due to the overpressure in the reference volume 26.

[0074] The first spring 58 is selected depending on the filling pressure and, in a design according to the measuring sensor 16 as shown in the figures with the typical dimensions resulting from [1] and the reference gas according to Table 1, has, for example, a spring constant with a value between 15 N / mm at 1 bar filling pressure and 140 N / mm at 12 bar filling pressure. The first spring 58 serves to compensate the force of the reference chamber. In general, the spring constant is selected depending on the respective measuring sensor, in particular the area of ​​the partition wall or other pressurized surfaces. Suitable values ​​can easily be found using simple tests based on the given example and the explanations given in [1].

[0075] In the illustrated embodiment, the first spring 58 is designed as a compression spring, arranged on the contact side of the separating membrane 28, i.e., for example, in the measuring volume 20, and exerts the first spring force on the side of the partition 28 facing the contact 12 or the measuring volume 20. A spring guide 68 for guiding the first spring 58 is attached to the partition 28, for example, in the form of a pin-shaped projection projecting from the bellows base 42. The free end of the projection of the spring guide 68 serves as a lower stop 70 for limiting the movement of the partition 28 toward the measuring volume 20.

[0076] Furthermore, the spring device 32 has a second spring 60 for exerting a second spring force on the partition 28 in the direction of the measuring volume 20 or the harmful gas 10. The second spring 60 can be used to expand the measuring range. In the exemplary embodiments described here with the reference gas and the filling values ​​from Table 1 and the typical dimensions from reference [1], the second spring 60 has a spring constant of approximately 20-30 N / mm. The second spring 60 serves the reference chamber 40 for range extension; thus, for example, widely spaced switching points or an extended display range can be created.

[0077] In the illustrated embodiment, the second spring 60 is also designed as a compression spring and is arranged on the side of the partition wall 28 facing the reference chamber 40 in the reference chamber 40 and serves to set the switching point(s) or display range.

[0078] By selecting and / or adjusting spring constants and possible preloads of the springs 58, 60 of the spring device 32, the measuring sensor 16 can be adjusted to predetermined pressures, measuring ranges and switching points or switching ranges.

[0079] Furthermore, the effective path of at least one of the springs, e.g. the first spring 58, can be limited by means of at least one stop (not shown).

[0080] In one example, the first spring 58 acts only for the low-pressure range. The first spring is only active up to the lowest switching alarm, for example, and then strikes the stop that is stationary relative to the housing 34, so that the partition 28 moves free of the first spring force in the remaining operating range. This arrangement achieves a more precise, higher switching point, since the first spring is no longer active at the other switching points.

[0081] With the density monitor 14, a density monitoring method for monitoring the gas density of the harmful gas 10 can be carried out, comprising the steps: a) Providing a closed reference volume 26 with a partition wall 28 arranged between the reference volume 26 and the harmful gas 10 to be monitored, b) providing a reference gas 56, which has a greenhouse potential that is at least two times lower than that of the noxious gas 10, in the reference volume 26 with a reference gas pressure that is higher than the filling pressure of the noxious gas 10, c) compensating a force acting on the partition wall 28 due to the increased reference gas pressure in the reference volume 26 by means of at least one spring device 32, and d) Detecting a deflection of the partition wall 28 to monitor the gas density.

[0082] Further embodiments of the method, the density monitor 14, its uses, and the system 12 result from the application of the measures explained here for filling a reference volume 26 with a more climate-friendly reference gas 56 and compensating for disadvantages caused by the deviation between the reference gas 56 and the pollutant gas 10 to be monitored by increasing the pressure in the reference chamber 40 and compensating for forces by the spring device 32 on the density monitors operating with reference volumes, which are described and shown in references [1] to [5]. Therefore, for further possible features of embodiments of the density monitor 14 according to the invention and their uses, reference is expressly made to references [1] to [5].

[0083] With preferred embodiments of the density monitoring method, even a highly climate-damaging greenhouse gas such as SF6 can be mechanically and temperature-compensatedly monitored for its gas density, without requiring such a climate-damaging gas for the manufacture and operation of the density monitor 14. In addition to the environmental benefits resulting from the use of climate-friendly gases as the reference gas, the costs for the manufacture, transport, assembly, and installation of the density monitor 14 can also be significantly reduced, since the safety measures otherwise required for harmful gases can be eliminated and much more cost-effective gases can be used as reference gases.

[0084] Any disadvantages with regard to the accuracy and the usual spread of switching points or displays are remedied by means of a spring device 32 which preferably operates purely mechanically with simple springs.

[0085] According to some embodiments not shown in detail, the spring device 32 can have an adjustment device for changing at least one force parameter of the spring device 32. For example, the spring device 32 has a preload adjustment device for adjusting a preload of at least one of the springs 58, 60, such as in particular the second spring 60. This allows, in particular, the display range and at least one or some of the switching points or their distance (with respect to the gas density) to be adjusted.

[0086] In order to monitor a gas density of a greenhouse gas in a more climate-friendly and cost-effective manner, a density monitoring method for monitoring the gas density of a harmful gas (10) is proposed, comprising: a) providing a closed reference volume (26) with a partition wall (28) movably arranged between the reference volume (26) and the harmful gas (10) to be monitored, b) providing a reference gas (56) which has a greenhouse potential that is at least two times lower than the harmful gas (10) in the reference volume (26) with a reference gas pressure that is higher than the filling pressure of the harmful gas (10), c) compensating a force acting on the partition wall (28) due to the increased reference gas pressure in the reference volume (26) by means of a spring device (32), and d) detecting a deflection of the partition wall (28) to monitor the gas density.

[0087] Furthermore, a gas density monitor (14), its use in such a method and an electrical system (12) provided therewith are proposed. List of reference symbols: 10 Harmful gas 12 electrical system 14 density monitors 16 sensors 18 Switching and / or display part 20 measuring volumes 22 connection 23 Gas feedthrough to the system 24 Room (gas room of the electrical system) 26 Reference volumes 28 Partition wall 30 Partition deflection detection device 31 deflection 32 Spring device 34 Sensor housing 36 metal bellows 36a outer metal bellows 36i inner metal bellows 38 measuring chamber 40 reference chamber 40a Bellows outside (reference chamber) 40i bellows inside (reference chamber) 42 Bellows bottom (partition wall - reference chamber) 44 Transmission element 46a first switching element 46b second switching element 46c third switching element 46d fourth switching element 48 ad 49 shift rod 50 pressure tappets 52 Crossbar 54a first boom 54b second boom 54c third boom 54d fourth boom 56 Reference gas 58 first spring 60 second spring 62 flange cover 64 Filling opening (reference chamber) 66 upper stop 68 Lead 70 lower stop

Claims

[1] Density monitoring method for monitoring the gas density of a harmful gas (10), comprising: a) providing a closed reference volume (26) with a partition wall (28) movably arranged between the reference volume (26) and the harmful gas (10) to be monitored, b) providing a reference gas (56) which has a greenhouse potential that is at least two times lower than the harmful gas (10) in the reference volume (26) with a reference gas pressure that is higher than the filling pressure of the harmful gas (10), c) compensating a force acting on the partition wall (28) due to the increased reference gas pressure in the reference volume (26) by means of a spring device (32), and d) detecting a deflection of the partition wall (28) to monitor the gas density. [2] Density monitoring method according to claim 1, characterized by that step b) includes at least one of the steps: (b1) providing a gas with a GWP<100 as a reference gas (56), where GWP is the CO2 equivalent based on 100 years according to IPCC AR5; b2) providing a gas from the group comprising air, N2, O2, noble gases, Ar, Kr, He, CO2, a mixture of at least two of the aforementioned gases with one another and a mixture formed from one or more of the aforementioned gases with an admixture of a further gas as a reference gas (56). [3] Density monitoring method according to one of the preceding claims, characterized by , that step b) contains: Providing the reference gas (56) with a reference gas pressure that is 2.5-45% higher than the filling pressure of the harmful gas (10). [4] Density monitoring method according to one of the preceding claims, comprising the steps: c1) applying a first spring force of the spring device (32) to the partition wall (28) acting in the direction of the reference volume (26) to compensate for the force caused by the increased reference gas pressure and c2) applying a second spring force to the partition wall (28) acting in the direction of the harmful gas to extend the monitorable range of the gas density. [5] Density monitoring method according to claim 4, characterized by at least one of the steps: 5.1 Selection of the first spring force depending on the filling pressure of the harmful gas (10) and / or the reference gas pressure; 5.2 Selecting a spring constant of a first spring (58) of the spring device (32) which exerts the first spring force, depending on the filling pressure of the harmful gas (10) and / or the reference gas pressure; 5.3 Adjusting the second spring force according to a gas density value or gas density range desired for at least one switching point or one switching range; 5.4 Selection of the spring constants of a first spring (58) of the spring device (32) exerting the first spring force and / or a second spring (60) of the spring device (32) exerting the second spring force in accordance with a gas density value or gas density range desired for at least one switching point or one display range, 5.5 Selecting a preload of at least one spring (58, 60) of the spring device (32) according to a gas density value or gas density range desired for at least one switching point or one display or switching range, 5.6 Limiting the effectiveness of at least one spring (58, 60) of the spring device (32) to a partial area of ​​the deflection path of the partition wall (28); 5.7 Limiting the effectiveness of a first spring (58) of the spring device (32) exerting the first spring force to a range below a predetermined gas density threshold. [6] Density monitoring method according to one of the preceding claims, characterized by in that in step a) a metal bellows (36a, 36) is provided for separating the reference volume (26) from a measuring volume (20) containing the harmful gas (10), wherein the partition wall (28) is formed on the metal bellows (36a, 36). [7] Density monitor (14) for monitoring a gas density of a harmful gas (10), comprising: a measuring volume (20), a connection (22) for connecting the measuring volume (20) to a space (24) containing the harmful gas (10), a closed reference volume (26) filled with a reference gas (56) different from the pollutant gas (10) to be monitored, which has a global warming potential GWP<100, where GWP denotes the CO2 equivalent based on 100 years according to IPCC AR5, where the reference gas (56) is filled with an overpressure compared to a standard pressure of the pollutant gas (10) or a filling pressure of the pollutant gas (10) during normal operation of the density monitor (14), a partition wall (28) separating the reference volume (26) from the measuring volume (20), a partition wall deflection detection device (30) for detecting a deflection of the partition wall (28), and a spring device (32) for elastically exerting a force on the partition wall (28) in order to compensate for the excess pressure in the reference volume (26). [8] Density monitor (14) according to claim 7, characterized bythat the reference gas (56) is selected from the group comprising air, N2, O2, noble gases, Ar, Kr, He, CO2, a mixture of at least two of the aforementioned gases with one another and a mixture which is essentially formed from one or more of the aforementioned gases with an admixture of another gas. [9] Density monitor (14) according to one of claims 7 or 8, characterized by that the spring device (32) has a first spring (58) acting on the partition wall (28) in the direction of the reference volume (26) for compensating the force caused by excess pressure and a second spring (60) acting on the partition wall (28) in the direction of the measuring volume (20) for expanding the monitorable range of the gas density. [10] Use of a density monitor according to one of claims 7 to 9 for carrying out the method according to one of claims 1 to 6. [11] Electrical system (12) comprising a space (24) filled with a harmful gas (10) as insulating gas at a predetermined filling pressure and a density monitor (14) according to one of claims 7 to 9, which is connected to the space (24) for monitoring the gas density of the harmful gas (10). [12] Electrical system (12) according to claim 14, characterized by that the reference gas pressure in the reference volume (26) is 2.5-45% higher than the filling pressure.

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