An environmentally friendly insulating mixed gas replacing SF6, its preparation method and application

Abstract

The present invention discloses an environmentally friendly insulating mixed gas that can replace SF6, as well as its preparation method and application. The environmentally friendly insulating mixed gas includes a carbon fluorine gas and He gas. The preparation method of the environmentally friendly insulating mixed gas that can replace SF6 includes filling a vacuum-evacuated sealed container with a carbon fluorine gas and He gas. Under the same inflation pressure, the insulating strength of the environmentally friendly insulating mixed gas of the present invention is close to that of SF6 gas, and the same insulating performance as SF6 can be obtained by slightly adjusting the inflation pressure. The insulating mixed gas of the present invention has good thermal conductivity. Compared with traditional SF6 gas, the insulating strength is equivalent, and the thermal conductivity can be improved by more than 20%. Compared with the SF6 alternative gas commonly used in engineering (C4F7N and CO2 mixed gas), the thermal conductivity can be improved by more than 16%. The environmentally friendly insulating mixed gas of the present invention can be used as an insulating and cooling medium for gas-insulated transformers, thereby increasing the capacity of gas-insulated transformers and having a wide range of application value.

Description

Technical Field

[0001] The present invention relates to the technical field of insulating gases, and in particular to an environmentally friendly insulating mixed gas replacing SF6, a preparation method thereof, and applications thereof. Background Art

[0002] With the development of urban construction, the promotion and application of disaster-resistant transformers has become an inevitable trend. Among all disaster-resistant transformers, gas-insulated transformers have the greatest potential for development towards high voltage and large capacity. The increase in voltage levels and capacity places higher demands on the insulation and thermal conductivity of the gas dielectric, making the search for highly thermally conductive insulating gases extremely urgent.

[0003] SF6 gas, with its excellent insulation and arc-extinguishing capabilities, is a common insulating gas used in high-voltage power equipment. However, SF6 has a global warming potential (GWP) approximately 24,300 times that of CO2, making it a potent greenhouse gas. Therefore, there is an urgent need to find a suitable environmentally friendly insulating medium to replace SF6 that offers similar insulation performance without negatively impacting the environment.

[0004] C4F7N, a representative of fluorocarbon gases, is a new environmentally friendly insulating gas launched by 3M in 2014. Studies have shown that C4F7N has a dielectric strength approximately twice that of pure SF6 and a global warming potential approximately one-ninth that of SF6, making it a promising alternative to SF6. However, due to its high liquefaction temperature (-4.7°C at atmospheric pressure), C4F7N cannot be used alone in outdoor gas-insulated power equipment. It must be mixed with a buffer gas with a lower liquefaction temperature. In practical engineering applications, CO2 is often used as a buffer gas. Numerous analyses and tests have shown that a C4F7N / CO2 mixture with a C4F7N content of approximately 20% exhibits comparable insulation performance to SF6 and excellent environmental performance, but exhibits no significant improvement in thermal conductivity.

[0005] Therefore, it is necessary to study the formation of environmentally friendly insulating mixed gases with good thermal conductivity by mixing with carbon and fluorine gases. Summary of the Invention

[0006] In order to overcome the problems existing in the prior art, the present invention uses He gas as a buffer medium for carbon-fluorine gases to reduce the liquefaction temperature of the environmentally friendly insulating mixed gas and improve its heat dissipation performance.

[0007] In order to achieve the above object, the present invention provides an environmentally friendly insulating mixed gas to replace SF6, including He gas and carbon fluorine gas, wherein the carbon fluorine gas includes: perfluorocarbon gas (C2F6, C3F8, c-C4F 10 etc.), perfluorinated ketone (C5F 10O and C6F 12 O, etc.), perfluorinated nitrile (C4F7N, etc.).

[0008] Furthermore, the proportion of He gas is less than or equal to 70%.

[0009] Furthermore, the proportion of He gas is less than or equal to 60%.

[0010] Furthermore, the proportion of He gas is greater than or equal to 50%.

[0011] The present invention also provides a method for preparing an environmentally friendly insulating mixed gas that can replace SF6, which comprises filling a vacuum sealed container with carbon fluorine gas and He gas.

[0012] Furthermore, the carbon fluorine gas is first filled in and then the He gas is filled in.

[0013] Furthermore, before filling the carbon fluorine gas and He gas, the vacuum sealed container is subjected to a process of removing impurity gases.

[0014] Furthermore, after the carbon fluorine gas and He gas are filled and mixed to obtain the mixed gas, the process also includes increasing the pressure of the mixed gas.

[0015] Furthermore, the proportion of He gas in the mixed gas is greater than or equal to 50%.

[0016] The present invention also provides the application of the above-mentioned environmentally friendly insulating mixed gas that replaces SF6, which is applied in disaster-proof transformers.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) The environmentally friendly insulating mixed gas of the present invention has a lower GWP value than SF6 gas;

[0019] (2) Under the same inflation pressure, the insulation strength of the environmentally friendly insulating mixed gas of the present invention is close to that of SF6 gas. When applied to the insulating medium of a gas-insulated transformer, the insulation performance equivalent to that of SF6 can be obtained by slightly adjusting the inflation pressure;

[0020] (3) The environmentally friendly insulating mixed gas of the present invention has good thermal conductivity. Compared with traditional SF6 gas, its insulation strength is equivalent and its thermal conductivity can be improved by more than 20%. Compared with the SF6 alternative gas commonly used in engineering (C4F7N and CO2 mixed gas), its thermal conductivity can be improved by more than 16%.

[0021] (4) The environmentally friendly insulating mixed gas of the present invention can be used as the insulating and cooling medium of the gas-insulated transformer, thereby improving the heat dissipation capacity of the transformer and alleviating the greenhouse effect caused by SF6 gas leakage. It is expected to further increase the capacity of the gas-insulated transformer and has a wide range of application value in the field of electrical equipment.

[0022] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the steps or test results indicated in the description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 The test curves and fitting curves of the power frequency discharge test results of the environmentally friendly insulating mixed gas replacing SF6 and SF6 gas prepared in Examples 2 to 6 of the present invention are shown;

[0025] Figure 2 The temperature rise curve and temperature drop curve of the transformer winding of the environmentally friendly insulating mixed gas replacing SF6, 18% C4F7N / CO2 mixed gas and SF6 gas prepared in Example 1 of the present invention are shown. DETAILED DESCRIPTION

[0026] The design concept of the present invention is that: the GWP of He gas is 0, and by regulating He gas and carbon fluorine gas in a reasonable proportion, the GWP of the environmentally friendly insulating mixed gas can be reduced to below 2000 after mixing; the environmentally friendly insulating mixed gas can achieve the same insulation performance as SF6 by adjusting the process parameters, and meet the insulation performance requirements of the gas insulated transformer without changing the design; at the same time, based on the good thermal conductivity of He gas, the environmentally friendly insulating mixed gas is used as the cooling medium inside the gas insulated transformer, which can effectively reduce the transformer winding temperature and further improve the current capacity of the gas insulated transformer.

[0027] To this end, the present invention provides an environmentally friendly insulating mixed gas to replace SF6, including carbon fluorine gas and He gas.

[0028] In one embodiment of the present invention, the proportion of He gas is less than or equal to 70%. Preferably, when the proportion of He gas is equal to 70%, the insulation strength of the environmentally friendly insulating mixed gas replacing SF6 reaches 80% of the insulation strength of SF6 at the same gas pressure.

[0029] In one embodiment of the present invention, the proportion of He gas is less than or equal to 60%. Preferably, when the proportion of He gas is equal to 60%, the environmentally friendly insulating mixed gas that replaces SF6 can directly replace SF6 gas to meet the insulation design requirements of the gas transformer.

[0030] Existing disaster-resistant gas transformers use SF6 gas as an insulating and heat dissipating medium. In some embodiments of the present invention, the proportion of He gas is set at 60-70%, while the proportion of fluorocarbon gas is 30-40%. This ratio allows technicians to better implement the present invention without changing the existing transformer parameters.

[0031] In a preferred embodiment of the present invention, the He gas content is greater than or equal to 50%. Extensive testing and data simulation have shown that when the He gas content is less than 50%, the thermal conductivity of the environmentally friendly insulating gas mixture replacing SF6 is significantly reduced, the liquefaction temperature increases, and the mixture fails to meet the design standards for gas transformers.

[0032] In a preferred embodiment of the present invention, by increasing the pressure of the environmentally friendly insulating gas mixture replacing SF6 to 1.2 times the pressure of SF6 gas under equivalent conditions, the insulation strength of the environmentally friendly insulating gas mixture replacing SF6 can be increased to be comparable to that of SF6 at the lowest carbon-fluorine gas content (30%). Therefore, without increasing the carbon-fluorine gas content, simple gas pressure adjustment can meet the insulation design requirements of gas transformers.

[0033] In one embodiment of the present invention, at an absolute pressure of 0.3 MPa, when the proportion of fluorocarbon gases in the environmentally friendly insulating mixed gas that replaces SF6 is 40%, the heat dissipation performance of the environmentally friendly insulating mixed gas that replaces SF6 is better than that of fluorocarbon and CO2 mixed gas (fluorocarbon gases account for 18%) and SF6 gas.

[0034] In one embodiment of the present invention, the fluorocarbon gas may be a perfluorocarbon, a perfluoroketone, or a perfluoronitrile gas.

[0035] In a preferred embodiment of the present invention, the fluorocarbon gas is selected as C4F7N gas.

[0036] The present invention also provides a method for preparing an environmentally friendly insulating mixed gas that can replace SF6, which comprises filling a vacuum sealed container with carbon fluorine gas and He gas.

[0037] In one embodiment of the present invention, to better utilize the prepared environmentally friendly insulating mixed gas substitute for SF6, the sealed container is a transformer that meets the required airtightness. The sealed container can also be a gas tank or other container, but must meet airtightness requirements and a certain compressive strength.

[0038] In one embodiment of the present invention, prior to filling the fluorocarbon gas and He gas, the evacuated sealed container is subjected to a gas removal treatment to remove impurities. Alternatively, the transformer cavity and piping can be subjected to multiple gas scrubbing treatments using CO2 gas to remove other gas impurities within the cavity and piping.

[0039] In one embodiment of the present invention, the carbon fluorine gas is first filled in and then the He gas is filled in.

[0040] In a preferred embodiment of the present invention, after the carbon fluorine gas and He gas are charged and mixed to obtain the mixed gas, the process further includes increasing the pressure of the mixed gas.

[0041] The present invention also provides the use of the above-mentioned environmentally friendly insulating mixed gas that replaces SF6 in gas-insulated transformers, which is used in disaster-proof transformers.

[0042] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0043] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the specific embodiments of the present invention and the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0044] Example 1

[0045] A method for preparing an environmentally friendly insulating mixed gas that replaces SF6 comprises the following steps:

[0046] (1) Vacuum the transformer that meets the airtightness requirements, and continue to vacuum for 10 minutes after the gauge pressure drops to -0.1 MPa (absolute pressure 0 MPa);

[0047] (2) Use CO2 gas to wash the transformer cavity and pipeline three times to remove other gas impurities in the transformer cavity and pipeline;

[0048] (3) After washing, the transformer cavity is evacuated for 60 minutes. First, C4F7N gas with a low saturated vapor pressure and a proportion of 40% is filled until the gauge pressure reaches 0.02Mpa (absolute pressure 0.12MPa). Let it stand for 5 minutes and wait for the reading to stabilize. At this time, the valve connected to the transformer cavity is closed, the pipeline is evacuated, and then He gas with a proportion of 60% is filled into the cavity until the gauge pressure reaches 0.2MPa (absolute pressure 0.3MPa). Let it stand for 5 minutes and wait for the reading to stabilize. The environmentally friendly insulating mixed gas that replaces SF6 is prepared. It should be noted that absolute pressure is the pressure directly acting on the surface of a container or object; the absolute pressure value takes absolute vacuum as the starting point and is the pressure relative to zero pressure. Gauge pressure refers to the part of the total absolute pressure that exceeds the surrounding atmospheric pressure (one atmosphere is 0.1MPa). In this step, a gauge pressure of 0.2MPa is equivalent to an absolute pressure of 0.3MPa.

[0049] Example 2 to Example 6

[0050] The preparation method of the environmentally friendly insulating mixed gas that replaces SF6 is basically the same as that in the embodiment, except that it is prepared according to the ratio of C4F7N gas to He gas in Table 1.

[0051] Table 1 Ratio of C4F7N gas to He

[0052] <![CDATA[Percentage of C4F7N gas (%)]]> He gas proportion (%) Example 2 5 95 Example 3 15 85 Example 4 25 75 Example 5 50 50 Example 6 75 25 Example 7 30 70 Example 8 35 65

[0053] Test Case

[0054] In order to study the insulation performance of the environmentally friendly insulating mixed gas prepared by the present invention as a substitute for SF6, a power frequency breakdown test was conducted on it and compared with SF6 gas. The absolute pressure of the test was between 0.1 and 0.2 MPa (the common pressure range of gas transformers), the test electrodes were ball-to-ball electrodes with a spacing of 2.5 mm, and the electric field non-uniformity was 1.21. The specific power frequency discharge test process of the gas gap was carried out in accordance with the IEC60243-1:2013 and GB / T 16927.1-2011 "Appendix A.1.3 Class III Continuous Discharge Test" method. The results are as follows Figure 1 shown.

[0055] Under the condition of absolute pressure of 0.1-0.2 MPa, the power frequency discharge test results of the environmentally friendly insulating mixed gas replacing SF6 prepared in Examples 2-6 are as follows: Figure 1 As shown by the solid line in Figure 1Analysis shows that when the absolute pressure varies between 0.1 and 0.2 MPa, the dielectric strength of SF6 gas is between that of the environmentally friendly insulating mixed gas with a C4F7N ratio of 25% (Example 4) and a C4F7N ratio of 50% (Example 5), and the power frequency discharge voltage of Examples 2 to 6 varies approximately linearly with the change in pressure. Linear fitting is performed on the curves of the power frequency discharge voltage of Examples 2 to 6 as they vary with pressure, and the curves of the power frequency discharge voltage of Examples 2 to 6 as they vary with pressure when the absolute pressure varies between 0.2 and 0.3 MPa are obtained, as shown in FIG. Figure 1 The dotted part is shown.

[0056] Based on the power frequency discharge tests of Examples 2 to 6, the power frequency insulation strength of the environmentally friendly insulating mixed gas replacing SF6 of Examples 1 and Examples 7 to 8 when the absolute gas pressure is 0.1 MPa, 0.2 MPa, and 0.3 MPa can be calculated by linear fitting. The results are shown in Table 2.

[0057] Table 2 Calculation results of Example 1 and Examples 7-8 when the absolute pressure is 0.1 MPa, 0.2 MPa, and 0.3 MPa

[0058]

[0059] From the analysis of the calculated results in Table 2, it can be concluded that when the absolute gas pressure is 0.1 MPa, 0.2 MPa, and 0.3 MPa, the power frequency insulation strength of the environmentally friendly insulating mixed gas replacing SF6 in Example 1 and Examples 7-8 can reach more than 80% of the insulation strength of SF6 gas; by increasing the mixed gas pressure to 1.2 times the SF6 gas pressure under the same conditions, the same insulation performance as SF6 gas can be achieved, meeting the insulation design requirements of gas transformers.

[0060] In order to study the thermal conductivity of the environmentally friendly insulating mixed gas that replaces SF6 prepared by the present invention, a transformer short-circuit temperature rise test was carried out, and the test was carried out in accordance with Section 11.5.1 of the standard GB / T 1094.15-2020 Power Transformer Part 15: Gas-filled Power Transformer. The test transformer has a rated input voltage of 200V, a rated capacity of 15kVA, and a maximum output voltage of 50kV. The specific test process is as follows: at an absolute pressure of 0.3MPa, SF6 gas, 18% C4F7N / CO2 mixed gas (C4F7N gas accounts for 18%, CO2 gas accounts for 82%) and 40% C4F7N / He mixed gas (C4F7N gas accounts for 40%, He gas accounts for 60%, i.e., Example 1) are respectively filled into the test transformer to carry out a transformer short-circuit temperature rise test. During the test, the low-voltage end is connected to the current riser, the input current is 20A, the high-voltage end is short-circuited, the temperature rise time is about 5 hours, and the current riser input is disconnected when the transformer temperature reaches a stable value. During the entire temperature rise test, the average steady-state temperature rise curve of the transformer winding is as follows: Figure 2 As shown in the figure (the average steady-state temperature rise of the transformer winding refers to the difference between the average steady-state temperature of the transformer winding and the ambient temperature), the cooling process (downward curve) is the actual measured value of the test, and the heating process (upward curve) is the predicted value of the thermal circuit model of the gas-insulated transformer.

[0061] Under an absolute pressure of 0.3 MPa, the input current at the low-voltage end of the gas-insulated transformer is 20 A, and the high-voltage end is short-circuited for 5.2 hours. The average steady-state temperature rise of the gas-insulated transformer winding is shown in Table 3.

[0062] Table 3 Average steady-state temperature rise of gas-insulated transformer windings

[0063] Filling gas type <![CDATA[40%C4F7N / He]]> <![CDATA[SF6]]> <![CDATA[18%C4F7N / CO2 <!-- 5 -->]]> Average steady-state temperature rise 37.01℃ 49.33℃ 44.41℃

[0064] From the results in Table 3, it can be seen that under the same test conditions, the test transformer is filled with the environmentally friendly insulating mixed gas (C4F7N gas accounts for 40% and He gas accounts for 60% instead of SF6) prepared in Example 1. Under this condition, the insulation strength is equivalent to that of SF6 gas. The average steady-state temperature rise of the transformer winding is reduced by more than 20% compared with the transformer filled with SF6 gas at the same pressure, and is reduced by more than 16% compared with the transformer filled with 18% C4F7N / CO2 mixed gas.

[0065] Furthermore, in Example 5 of the present invention, the He gas content is equal to 50%. The transformer short-circuit temperature rise test results show that while the average steady-state temperature rise of Example 5 is slightly higher than that of Example 1, the overall performance is still superior to that of SF6 gas at the same pressure. Therefore, to maintain the thermal conductivity of the environmentally friendly insulating mixed gas substitute for SF6, the He gas content should be greater than or equal to 50%.

[0066] In summary, the present invention uses He gas as a buffer medium for C4F7N gas to reduce the liquefaction temperature of the environmentally friendly insulating mixed gas and improve heat dissipation performance, thereby preparing an environmentally friendly insulating mixed gas that replaces SF6. When the C4F7N gas ratio is 30%, the environmentally friendly insulating mixed gas prepared by the present invention can achieve an insulation performance of up to 80% of that of SF6 gas, and can further achieve the same insulation performance as SF6 gas by adjusting the pressure. When the C4F7N gas ratio is 40%, it can directly replace SF6 gas to meet the insulation design requirements of gas transformers. When the C4F7N gas ratio in the environmentally friendly insulating mixed gas prepared by the present invention is 40%, the heat dissipation performance is better than that of a C4F7N and CO2 mixed gas (C4F7N gas ratio is 18%) and SF6 gas at an absolute pressure of 0.3 MPa. The environmentally friendly insulating mixed gas of the present invention can be used as an insulation and cooling medium for gas-insulated transformers, improving the heat dissipation capacity of the transformer while mitigating the greenhouse effect caused by SF6 gas leakage. It is expected to further increase the capacity of gas-insulated transformers and has wide application value in the field of electrical equipment.

[0067] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An environmentally friendly insulating mixed gas that replaces SF6, characterized in that: It is composed of carbon-fluorine gas and He gas, wherein the He gas accounts for 60% to 70% and the carbon-fluorine gas accounts for 30% to 40%, and the carbon-fluorine gas is selected as C4F7N gas; The thermal conductivity of the mixed gas is increased by 20% or more compared to SF6; The insulation strength of the environmentally friendly insulating mixed gas is equivalent to that of SF6 after the mixed gas pressure is increased.

2. A method for preparing an environmentally friendly insulating mixed gas to replace SF6, characterized in that: The method includes filling a vacuum sealed container with carbon fluorine gas and He gas; The He gas accounts for 60% to 70%, and the carbon-fluorine gas accounts for 30% to 40%. The carbon-fluorine gas is selected as C4F7N gas. The thermal conductivity of the mixed gas is increased by 20% or more than that of SF6.

3. The preparation method according to claim 2, characterized in that Fill with fluorocarbon gas first and then fill with He gas.

4. The preparation method according to claim 2, characterized in that Before filling the carbon fluorine gas and He gas, the vacuum sealed container is subjected to a treatment to remove impurity gases.

5. Use of the environmentally friendly insulating mixed gas as claimed in claim 1 as an alternative to SF6 in disaster-proof transformers.

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