Patent Application
20240355538
This application claims the priority benefit of China application no. 202310450803.6, filed on Apr. 24, 2023. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.
The present invention relates to the technical field of insulating gases, and particularly relates to the formulation of an environment-friendly insulating gas mixture replacing SF6, as well as its application.
With the development of urban construction, the promotion and application of disaster-proof transformers has become increasingly important. Among all disaster-proof transformers, Gas-Insulated Transformers have the most potential for high-voltage and large-capacity. The increase in voltage levels and capacity means higher requirements for the insulation and thermal conductivity of the gas medium, making the search for high thermal conductivity insulating gases an urgent need.
SF6 gas is commonly used as an insulating gas in high-voltage electrical equipment due to its excellent insulation and arc extinguishing capabilities. However, it has a global warming potential (GWP) approximately 24,300 times higher than CO2 gas, making it a potent greenhouse gas. Therefore, it is crucial to find environment-friendly alternatives as insulation mediums to replace SF6. These alternatives should provide similar insulation performance to SF6 while minimizing any negative impact on the environment.
As a typical representative of fluorocarbon gases, C4F7N (Perfluoroisobutyronitrile) gas is a new type of environment-friendly insulating gas jointly released by ALSTON company and Minnesota Mining and Manufacturing (3M) company in 2014, and research shows that the insulation strength of C4F7N gas is about two times that of pure SF6 gas, while the global warming potential is about one-ninth of SF6 gas, making it a highly promising alternative to SF6 gas. However, the liquefaction temperature of C4F7N gas is high (the liquefaction temperature under atmospheric pressure is −4.7° C.), so it cannot be applied to outdoor gas-insulated power equipment alone, and it needs to be mixed with buffer gases with low liquefaction temperature. In practical engineering applications, CO2 gas is usually chosen as buffer gas. Numerous analyses and tests have shown that when the proportion of C4F7N by volume in the C4F7N/CO2 gas mixture is about 20%, the insulating property is comparable with SF6 gas, and the environmental protection performance is excellent, but the thermal conductivity is significantly improved.
Therefore, it is necessary to study the formulation of environment-friendly and thermally conductive insulation mixtures by mixing fluorocarbon gases.
In order to overcome the problems of the current technology, the present invention uses helium gas as a buffer medium for fluorocarbon gas to lower the GWP and liquefaction temperature of the insulating gas mixture and improve its thermal conductivity.
In order to realize the above purpose, the present invention provides the formulation of an insulating gas mixture replacing SF6, comprising a fluorocarbon gas and a helium gas, wherein the fluorocarbon gas can be perfluorocarbon gas or fluorocarbon-containing compound. The perfluorocarbon gases include Carbon Tetrafluoride (CF4), Hexafluoroethane (C2F6), Octafluoropropane (C3F8), Hexafluorobutadiene (C4F6), Octafluorocyclobutane (c-C4F8), Perfluorobutane (c-C4F10), etc. The fluorocarbon-containing compounds include Perfluorinated Ketones (represented by C5F10O and C6F12O), Perfluorinated Nitriles (represented by C4F7N), and Hydrofluorocarbons (HFCs), Trifluoromethyl Iodide (CF3I), Trifluoromethylsulfonyl Fluoride (CF3SO2F), etc.
Further, the proportion of helium gas by volume in the gas mixture is greater than or equal to 50% and less than or equal to 70%.
The present invention also provides steps for formulating the gas mixture, comprising filling a fluorocarbon gas and a helium gas into a vacuum-sealed container.
Further, the fluorocarbon gas is filled first followed by the helium gas.
Further before filling the fluorocarbon gas and the helium gas into the vacuum-sealed container, subjecting the vacuum-sealed container to an exclusion of tramp gases treatment.
Further, after charging the fluorocarbon gas and helium to obtain a gas mixture, in some cases it comprises increasing a pressure of the gas mixture.
This invention also presents the application of the insulating gas mixture mentioned above in disaster-proof transformers.
The present invention has the following advantageous effects compared to existing technologies:
Other features and advantages of the present invention will be explained in the subsequent description, and some of them may become apparent from the manual or be understood by carrying out the present invention. The purpose and other advantages of the present invention can be realized and obtained through the steps or test results indicated in the subsequent description and accompanying drawings.
The design principle of this invention resides in the fact that the Global Warming Potential (GWP) of fluorocarbon gases is generally high, while the GWP of helium gas is 0. Therefore, by controlling the proportion of helium gas and fluorocarbon gas by volume, the GWP of the insulating gas mixture can be reduced to below 2000. By adjusting the process parameters, the insulating gas mixture can achieve the same insulation performance as SF6 without changing the design, and meet the insulation performance requirements of Gas-Insulated Transformers. Additionally, due to the excellent thermal conductivity of helium gas, using the insulating gas mixture as the cooling medium for Gas-Insulated Transformers can effectively reduce the temperature of the transformer windings and further enhance the current-carrying capacity of the Gas-Insulated Transformer.
To this end, the present invention provides the formulation of an insulating gas mixture replacing SF6, comprising a fluorocarbon gas and a helium gas.
In the preferred embodiments of the present invention, the fluorocarbon gas is selected as C4F7N gas.
In one preferred embodiment of this invention, the proportion of helium gas by volume is equal to 60%. In this case, the insulating gas mixture, which replaces SF6, can directly meet the insulation design requirements of gas transformers.
In another preferred embodiment of this invention, the proportion of helium gas by volume is equal to 70%. In this case, the insulation strength of the insulating gas mixture reaches only 80% of the insulation strength of SF6 under the same gas pressure. However, the insulation strength of the insulating gas mixture can still be increased to be equivalent to the insulation strength of SF6 by increasing the pressure of the gas mixture to 1.2 times the pressure of SF6 at the same state. Therefore, without raising the proportion of Fluorocarbon gas, it is possible to meet the design requirements of gas transformer insulation by simple adjustment of air pressure.
Some embodiments of this invention set the proportion of helium gas by volume to be 60-70%, and the proportion of fluorocarbon gas by volume to be 30-40%. Such a ratio setting facilitates the technician to better implement the embodiment of the present invention without changing the parameters of the existing transformer.
In the preferred embodiments of the present invention, the proportion of helium gas by volume is greater than or equal to 50%. Through numerous experiments and data simulations, it shows that when the proportion of helium gas by volume is less than 50%, the thermal conductivity of the insulating gas mixture significantly decreases and the liquefaction temperature increases, which does not meet the design standards of gas-insulation transformers.
In one embodiment of the present invention, at an absolute pressure of 0.3 MPa, when the proportion of the fluorocarbon gas by volume is 40%, the thermal conductivity of the gas mixture is superior to that of SF6 gas and 18% C4F7N/82% He gas mixture.
The present invention also provides the methods for formulating the insulating gas mixture replacing SF6, which comprises filling a fluorocarbon gas and a helium gas into a vacuum-sealed container.
In one embodiment of the present invention, in order to have a better application of the prepared insulating gas mixture, the airtight container is selected as a transformer, and the airtightness of the transformer is qualified. Of course, the airtight container can also be selected as a gas tank or other containers, but it needs to meet the requirements of airtightness and a certain compressive strength.
In one embodiment of the present invention, the filling of the fluorocarbon gas and helium gas is further preceded by subjecting the vacuum-sealed container to an exclusion of tramp gases treatment. As an optional method, CO2 gas can be used for gas washing treatments of the transformer's chamber and pipes to remove other tramp gases present in the chamber and pipes.
In one embodiment of the present invention, the fluorocarbon gas is filled first followed by helium gas.
In one embodiment of the present invention, after filling the fluorocarbon gas and the helium gas in the vacuum-sealed container to form a gas mixture, it also comprises increasing the pressure of the gas mixture.
The present invention also provides the application of the above-mentioned insulating gas mixture: applying it in disaster-proof transformers.
Neither the endpoints of the ranges nor any of the values disclosed in the present invention are limited to that precise range or value, and these ranges or values should be understood as including values that are close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of different ranges and individual point values, as well as individual point values, can be combined to obtain one or more new numerical ranges. These numerical ranges should be considered specifically disclosed in this invention.
The technical solutions in the embodiments of the present invention will be described clearly and completely in the following in connection with specific embodiments of the present invention and the accompanying figures of the specification. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by a person of ordinary skill in the art without making creative labor are within the scope of protection of the present invention.
A method for formulating an insulating gas mixture as a substitute for SF6 includes the following steps:
The steps for formulating the insulating gas mixture replacing SF6 is basically the same as that of Embodiment 1, with the difference being that the mixture is prepared according to the proportions of C4F7N gas and helium gas by volume specified in Table 1.
In order to investigate the insulating properties of the insulating gas mixture in this invention, it was subjected to electrical discharge test at an AC voltage of 50 Hz, and the test results were compared with those of SF6 gas. The absolute air pressure of the test ranged from 0.1 to 0.2 MPa (common air pressure range for gas transformers). The test electrode was a ball-ball electrode with a pitch of 2.5 mm, and the electric field non-uniformity was 1.21. The procedure for performing AC electrical discharge tests on specific gas gaps follows the guidelines outlined in IEC 60243-1:2013 “Electric strength of insulating materials-Test methods-Part 1: Tests at power frequencies”. The results are shown in
Under the condition of absolute air pressure of 0.1 to 0.2 MPa, the results of the electrical discharge test of the insulating gas mixture prepared in Embodiment 2 to 6 are shown in the solid line portion in
Based on the discharge tests of Embodiment 2 to 6, the insulation strength of the insulating gas mixture of Embodiment 1 and Embodiment 7-8 can be extrapolated by linear fitting when the absolute air pressures are 0.1 MPa, 0.2 MPa, 0.3 MPa, and the results are shown in Table 2.
From the analysis of the extrapolation results in Table 2, it can be concluded that the insulation strength of the insulating gas mixture of Embodiment 1 and Embodiment 7-8 can reach more than 80% of the insulation strength of SF6 gas when the absolute gas pressure is 0.1 MPa, 0.2 MPa and 0.3 MPa. By elevating the pressure of the gas mixture to 1.2 times the pressure of the SF6 gas in the same state, the same insulating strength as that of the SF6 gas can be achieved, which meets the design requirements for the insulation of the Gas-Insulated Transformers.
In order to study the thermal conductivity of the insulating gas mixture prepared as a substitute for SF6 gas in this invention, it was subjected to a transformer short-circuit temperature rise test, which was carried out in accordance with IEC 60076-15:2015 “Power transformers-Part 15: Gas-filled power transformers “. The rated input voltage of the test transformer is 200V, the rated input current is 20 A, and the maximum output voltage of the test-transformer is 50 kV. The specific experimental procedure comprises filling the test transformer with SF6 gas, 18% C4F7N/82% CO2 gas mixture, and 40% C4F7N/60% He gas mixture (Embodiment 1) under the absolute pressure of 0.3 MPa to carry out the transformer short-circuit temperature rise test. During the test, the low-voltage input of the test transformer is connected to the high-current-output transformer, the input current is 20 A and the high-voltage output end is short-circuited. The temperature rise duration is around 5 hours, and the low-voltage input of the test-transformer is disconnected when the transformer temperature reaches a stable value. The temperature rise curve and cooling curve of the windings during the whole test are shown in
According to the results in Table 3, under the same test conditions, the test transformer using the insulating gas mixture (with a 40% proportion of C4F7N gas and a 60% proportion of helium gas by volume, with insulation strength equivalent to SF6 gas) prepared Embodiment 1 has a more than 20% lower average steady-state temperature rise of the transformer winding than the SF6 gas-filled transformer with the same gas pressure, and has a more than 16% lower average steady-state temperature rise of the transformer winding than the 18% C4F7N/82% CO2 gas-filled transformer.
Furthermore, in Embodiment 5 of the present invention, the proportion of helium gas by volume is equal to 50%, at which point the results of the transformer short-circuit temperature rise test show that the average steady state temperature rise of Implementation Embodiment 5 is increased relative to Embodiment 1, but the overall performance is still better than that of SF6 gas at the same gas pressure. Therefore, in order to maintain the thermal conductivity of the insulating gas mixture replacing SF6, the proportion of helium gas by volume should be greater than or equal to 50%.
In summary, the present invention introduced the formulation of an insulating gas mixture to replace SF6 by using helium gas as a buffer medium for the C4F7N gas in order to lower the GWP and liquefaction temperature, and improve the thermal conductivity. When the C4F7N gas accounts for 30% by volume of the mixture, the insulation performance of the gas mixture can reach 80% of SF6 gas. Furthermore, by adjusting the pressure, the insulation performance can be equivalent to SF6 gas. When the C4F7N gas accounts for 40% by volume of the mixture, it can directly replace SF6 gas to meet the insulation design requirements of Gas-Insulated Transformers. When the C4F7N gas accounts for 40% by volume of the mixture, the thermal conductivity of the gas mixture is superior to that of SF6 gas and 18% C4F7N/82% CO2 gas mixture at an absolute pressure of 0.3 MPa. The insulating gas mixture of the present invention can be used as the insulation and cooling medium of Gas-Insulated Transformers to improve the current-carrying capacity of the transformers and mitigate the greenhouse effect caused by SF6 gas leakage. It has wide application value in the field of electrical equipment.
Finally, it should be noted that the above description is only the preferred embodiments of the present invention and is not intended to limit the scope of the invention. Although detailed descriptions of the embodiments have been provided, those skilled in the art can still modify the technical solutions described in the embodiments or make equivalent replacements for some technical features described therein. Any modifications, equivalent substitution, improvement, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202310450803.6 | Apr 2023 | CN | national |
